Listeriosis

FEMS Microbiol Lett, 1997 Mar 15, 148(2), 189 - 95
Listeria monocytogenes infection of HeLa cells results in listeriolysin O-mediated transient activation of the Raf-MEK-MAP kinase pathway; Weiglein I et al.; In this study we investigated the effect of Listeria monocytogenes infection on the activation of the Raf-MEK-MAP kinase pathway in eukaryotic host cells . HeLa cell infection with L . monocytogenes EGD resulted in a rapid, but transient, phosphorylation of the MAP kinases erk-1 and erk-2, a transient phosphorylation of the MAP kinase kinase MEK-1, and a transient activation of the MAP kinase kinase kinase Raf . In parallel to the transient phosphorylation of the MAP kinases, we detected induced expression of the MAP kinase phosphatase MKP-1 . Additionally we present evidence that listeriolysin O is the inducing agent for activation of the Raf-MEK-MAP kinase pathway.

J Exp Med, 1997 Mar 3, 185(5), 921 - 31
Crucial role of interferon consensus sequence binding protein, but neither of interferon regulatory factor 1 nor of nitric oxide synthesis for protection against murine listeriosis; Fehr T et al.; Listeria monocytogenes is widely used as a model to study immune responses against intracellular bacteria . It has been shown that neutrophils and macrophages play an important role to restrict bacterial replication in the early phase of primary infection in mice, and that the cytokines interferon-gamma (IFN-gamma) and tumor necrosis factor-alpha (TNF-alpha) are essential for protection . However, the involved signaling pathways and effector mechanisms are still poorly understood . This study investigated mouse strains deficient for the IFN-dependent transcription factors interferon consensus sequence binding protein (ICSBP), interferon regulatory factor (IRF) 1 or 2 for their capacity to eliminate Listeria in vivo and in vitro and for production of inducible reactive nitrogen intermediates (RNI) or reactive oxygen intermediates (ROI) in macrophages . ICSBP-/- and to a lesser degree also IRF2-/- mice were highly susceptible to Listeria infection . This correlated with impaired elimination of Listeria from infected peritoneal macrophage (PEM) cultures stimulated with IFN-gamma in vitro; in addition these cultures showed reduced and delayed oxidative burst upon IFN-gamma stimulation, whereas nitric oxide production was normal . In contrast, mice deficient for IRF1 were not able to produce nitric oxide, but they efficiently controlled Listeria in vivo and in vitro . These results indicate that (a) the ICSBP/IRF2 complex is essential for IFN-gamma-mediated protection against Listeria and that (b) ROI together with additional still unknown effector mechanisms may be responsible for the anti-Listeria activity of macrophages, whereas IRF1-induced RNI are not limiting.

Int J Food Microbiol, 1997 Mar 3, 34(3), 319 - 27
Differences in pathogenicity for chick embryos and growth kinetics at 37 degrees C between clinical and meat isolates of Listeria monocytogenes previously stored at 4 degrees C; Avery SM et al.; Fifteen clinical strains of Listeria monocytogenes (eight strains of serogroup 4 and seven strains of serogroup 1) and 15 meat isolates (all serogroup 1) were stored with no growth in phosphate-buffered saline (pH 7.0) at 4 degrees C for 4 weeks . Pathogenicity for 14 day old chick embryos and growth kinetics in brain heart infusion (BHI) broth at 37 degrees C of the strains were determined before and after storage . Although no differences in pathogenicity between clinical and meat strains were found when tested as fresh cultures significant differences became apparent after cold storage . Firstly, the pathogenicity of clinical strains was not affected by storage, whereas the average mortality of embryos inoculated with meat strains decreased from 98.7 to 68.0% . Secondly, clinical strains subcultured at 37 degrees C had a significantly shorter average lag phase than meat strains after cold storage . The results of this study indicate that strains that caused human listeriosis have a higher resistance to the effects of unfavourable storage conditions than meat strains with respect to pathogenicity and lag phase duration at body temperature.

Int J Food Microbiol, 1997 Mar 3, 34(3), 221 - 32
Predictive modelling of growth of Listeria monocytogenes . The effects on growth of NaCl, pH, storage temperature and NaNO2; McClure PJ et al.; The effect of NaCl concentration (5.0 115.0 g/l) . pH value (4.0-7.2), temperature (1-35 degrees C) and NaNO2 concentration (0 200 mg/l) on the growth responses of Listeria monocytogenes, in laboratory medium was investigated . The growth curves generated within this matrix of conditions were fitted using the function of Baranyi and Roberts (1994) and the growth responses modelled using a quadratic polynomial to produce response surfaces . Growth curves could then be regenerated for any set of conditions within the experimental matrix and values predicted for the growth rate, doubling time, lag time and time to 1000-fold increase . The model was validated using data from published literature and was found to give realistic predictions for doubling times in foods, including meat and meat products, milk, dairy products and vegetables . Predictions from this model (Baranyi and Roberts . 1994) compared favourably with those from the models of Buchanan and Phillips (1990), Murphy et al . (1996) and the Food MicroModel.

Curr Biol, 1997 Mar 1, 7(3), R164 - 7
Cell motility: complex dynamics at the leading edge; Machesky LM; The intracellular pathogen Listeria monocytogenes is a useful model for general actin-based cell motility, because it recruits host actin and associated proteins for movement . Recent data have shown that these associated proteins include the Ena/VASP family of proteins and the actin-related proteins Arp2 and Arp3.

Vaccine, 1997 Mar, 15(4), 433 - 40
Influenza-specific immunity induced by recombinant Listeria monocytogenes vaccines; Ikonomidis G et al.; In this study, we evaluate two Listeria monocytogenes strains that express influenza nucleoprotein (NP) sequences for their ability to protect against challenge with influenza-virus . The construction of one strain, which expresses only the Kd restricted NP epitope (NP 147-155), is described in this study; the other strain, which expresses the full NP sequence in the form of a fusion protein, has been described previously . The ability of the two strains to present the Kd restricted NP epitope in vitro and induce NP-specific CTL in vivo is also described . Mice immunized by the intravenous route with either strain cleared a subsequent (3 weeks post-immunization) influenza virus infection more rapidly as indicated by reduced virus titers in the lungs 5 days after challenge . Efficacy of both recombinant L . monocytogenes strains as vaccines in this system was equivalent and equal to that of recombinant vaccinia expressing NP.

Vaccine, 1997 Mar, 15(4), 395 - 401
Effective adjuvants for the induction of antigen-specific delayed-type hypersensitivity; Baldridge JR et al.; Vaccines utilizing poorly immunogenic subunit antigens are dependent upon adjuvants to drive the appropriate T cell responses . In an effort to determine the ability of several adjuvants to promote cell-mediated immunity (CMI), we assessed delayed-type hypersensitivity (DTH) in mice inoculated with heat-killed Listeria monocytogenes (HKLM) vaccines . The vaccines were formulated as oil-in-water emulsions containing one or more of the following bacterial-derived immunostimulators: MPL immunostimulant, a monophosphoryl lipid A preparation, synthetic trehalose dicorynomycolate (TDCM) and Mycobacterium phlei cell wall skeleton (CWS) . Oil-in-water emulsions containing HKLM without adjuvants did not induce DTH responsiveness in mice . The incorporation of TDCM, or MPL plus TDCM and/or CWS to the formulation enabled the HKLM vaccine to stimulate CMI characterized by DTH responsiveness . Following antigen challenge the resulting increases in footpad thickness ranged from 15-20% and were comparable to the DTH driven by complete Freund's adjuvant . Adjuvants composed of MPL/TDCM and MPL/TDCM/CWS induced responses equivalent to those measured in mice immunized with viable L . monocytogenes, and the responses remained at these levels for at least 2 months . Furthermore, in vivo depletion of CD4+ T cells, but not CD8+ T cells, abrogated the induction and expression of DTH, indicating that the response is mediated by CD4+ T cells.

J Med Microbiol, 1997 Mar, 46(3), 239 - 50
Neutrophils and tumour necrosis factor-alpha are important for controlling early gastrointestinal stages of experimental murine listeriosis; Conlan JW; The present study examined the need for neutrophils and tumour necrosis factor-alpha (TNF alpha) for early defence against gut infection with the enteroinvasive, facultative intracellular bacterial pathogen, Listeria monocytogenes . Mice were treated with a neutrophil-depleting monoclonal antibody (MAb) or a MAb directed against TNF alpha, and the consequences of these treatments on the course of orally initiated infection with the pathogen were monitored . By day 3, orally initiated L . monocytogenes infection in mice treated with either MAb was severely exacerbated to the extent that up to 5000-fold more listeriae were recovered from the walls of the stomach, small intestine, caecum or large intestine of treated mice than from controls . Systemic infection resulting from the ingestion of L . monocytogenes was also severely enhanced in mice treated with these MAbs . Therefore, the results showed that neutrophils and TNF alpha have a critical role in the early defence against enteroinvasive L . monocytogenes infection initiated by a natural (in this case the oral) route, as well as in the control of subsequent systemic infection.

J Cell Sci, 1997 Mar, 110 ( Pt 6), 731 - 43
Internalized Listeria monocytogenes modulates intracellular trafficking and delays maturation of the phagosome; Alvarez-Dominguez C et al.; Previous studies have shown that early phagosome-endosome fusion events following phagocytosis of Listeria monocytogenes are modulated by the live organism . In the present study, we have characterized more fully the intracellular pathway of dead and live Listeria phagosomes . To examine access of endosomal and lysosomal markers to phagosomes containing live and dead Listeria, quantitative electron microscopy was carried out with intact cells using internalized BSA-gold as a marker to quantify transfer of solute from endosomal and lysosomal compartments to phagosomes . To monitor the protein composition of phagosomal membranes and to quantify transfer of HRP from endosomes and lysosomes to phagosomes, highly enriched phagosomes containing live and dead Listeria were isolated . Enriched phagosomal membranes were used for western blotting experiments with endosomal and lysosomal markers . In this study, we used a listeriolysin-deficient mutant, Listeria(hly-), that is retained within the phagosome following phagocytosis . Western blotting experiments indicate that early endosomal markers (mannose receptor, transferrin receptor) and key fusion factors necessary for early events (NSF, alpha/beta-SNAP) but not late endosomal markers (cation dependent mannose 6-phosphate receptor) or lysosomal proteins (cathepsin D or lamp-1) accumulate on the live-Listeria phagosomal membranes . On the contrary, phagosomes containing dead-Listeria are readily accessible by both endocytic and lysosomal markers . Studies with radiolabeled dead- and live-Listeria(hly-) indicate that, following phagocytosis, degradation of the live microorganism is substantially delayed . These findings indicate that dead-Listeria containing phagosomes rapidly mature to a phagolysosomal stage whereas live-Listeria(hly-) prevents maturation, in part, by avoiding fusion with lysosomes . The data suggest that by delaying phagosome maturation and subsequent degradation, Listeria prolongs survival inside the phagosome/endosome assuring bacterial viability as a prelude to escape into the cytoplasm.

Lett Appl Microbiol, 1997 Mar, 24(3), 166 - 8
Nucleotide sequence analysis of two virulence-associated genes in Listeria monocytogenes serotype 1/2b and comparison with the same genes in other serotypes important in human disease; Vines A et al.; The nucleotide sequences of the hly and plcA genes (encoding listeriolysin, a thiol-activated cytolysin and a non-specific phospholipase C, respectively) were determined for two strains of Listeria monocytogenes serotype 1/2b . The deduced amino acid sequences for listeriolysin were identical for the two strains and identical to that of listeriolysin from serotype 4b . The two serotype 1/2b strains differed in one amino acid (histidine vs asparagine) in the deduced amino acid sequence for phosopholipase C.

Mol Microbiol, 1997 Mar, 23(5), 1075 - 85
Carbon-source regulation of virulence gene expression in Listeria monocytogenes; Milenbachs AA et al.; All known virulence genes of Listeria monocytogenes are under positive regulation by the transcription factor PrfA . Previous work employing the L . monocytogenes strain NCTC7973 suggested that the disaccharide cellobiose might serve as a specific "signature molecule' which functions to prevent activation of the PrfA-controlled regulon in a soil environment . We have examined three other L . monocytogenes strains, 10403S, LO28 and EGD, all commonly regarded as wild-type isolates, and find that NCTC7973 is anomalous with respect to the effect of carbohydrates on the expression of PrfA-controlled gene expression . In the case of 10403S, LO28 and EGD, several other readily metabolized mono- and disaccharides are as effective as cellobiose in repressing expression of the PrfA-controlled gene hly, indicating that the cellobiose effect is not specific, and suggesting that NCTC7973 may be a partially deregulated variant . Moreover, concentrations of cellobiose and other sugars required for repression of hly expression (> 1 mM) were found to significantly enhance growth of L . monocytogenes cultures, suggesting that the repression phenomenon probably results from a metabolic effect of sugar utilization rather than a signal-sensing response . Thus the previously reported cellobiose effect may reflect an aspect of a more global mechanism of catabolite repression in L . monocytogenes . Although cellobiose represses expression of hly and plcA at the level of transcript accumulation, quantitative Western blot analysis indicates that cellobiose has no effect on PrfA levels . These results are consistent with a model in which PrfA activity is controlled by interaction with a hypothetical cofactor, the synthesis or depletion of which is responsive to the presence of readily metabolized carbohydrates.

Appl Environ Microbiol, 1997 Mar, 63(3), 1155 - 9
Protamine-induced permeabilization of cell envelopes of gram-positive and gram-negative bacteria; Johansen C et al.; The inhibitory effect of the cationic peptide protamine on Listeria monocytogenes, Escherichia coli, and Shewanella putrefaciens has been studied in detail . The addition of protamine (10 to 1,000 micrograms/ml) resulted in inhibition of oxygen consumption after less than 1 min and loss of intracellular carboxyfluorescein and ATP after 2 to 5 min . Maximum antibacterial activity was reached at alkaline pH and in the absence of divalent cations . The efficient permeabilization of cell envelopes of both gram-positive and gram-negative bacteria suggests that protamine causes a general disruption of the cell envelope, leading to a rapid and nonspecific efflux of low- and high-molecular-weight compounds.

Appl Environ Microbiol, 1997 Mar, 63(3), 1077 - 82
DNA fragments from regions involved in surface antigen expression specifically identify Listeria monocytogenes serovar 4 and a subset thereof: cluster IIB (serotypes 4b, 4d, and 4e); Lei XH et al.; Listeria monocytogenes serotype 4b has frequently been implicated in sporadic as well as epidemic listeriosis . On the basis of pulsed-field fingerprinting, serotype 4b strains, along with strains of serotypes 4d and 4e, constitute one genomic cluster (IIB) . We have identified two genomic regions essential for the expression of surface antigens which previously were shown to be specific to cluster IIB strains . A DNA probe of 1.1 kb derived from one of the regions (probe 1) hybridized only with strains of serotypes 4b, 4d, and 4e in Southern blots and dot blots . A different DNA probe of 0.3 kb (probe 2), derived from the other region, hybridized with all serovar 4 strains (serotypes 4b, 4a, 4c, 4d, and 4e) . All other L . monocytogenes serotypes were negative with probe 1 or 2 . Use of probe 1 in Southern blots of EcoRI-digested genomic DNA revealed a restriction fragment length polymorphism in serotype 4b strains, with the hybridizing EcoRI fragments being 4.5 kb (strains of the epidemic clone) and either 4.5 or 5.0 kb (all other serotype 4b strains) . Although the probes hybridized with a special group of Listeria innocua strains which also expressed the surface antigens, the latter could be readily distinguished by the size of the hybridizing EcoRI fragment with probe 1 (ca . 2.2 kb) . These data suggest that the combined use of these probes with L . monocytogenes can readily and specifically identify cluster IIB strains as well as the entire serovar 4 complex.

J Bacteriol, 1997 Mar, 179(5), 1533 - 40
A Gly145Ser substitution in the transcriptional activator PrfA causes constitutive overexpression of virulence factors in Listeria monocytogenes; Ripio MT et al.; Virulence genes in Listeria monocytogenes are coordinately expressed under the control of the transcriptional activator PrfA, encoded by prfA, a member of the cyclic AMP (cAMP) receptor protein (CRP)/FNR family of bacterial regulators . Strain P14-A is a spontaneous mutant of L . monocytogenes serovar 4b which produces elevated levels of virulence factors (M . T . Ripio, G . Dominguez-Bernal, M . Suarez, K . Brehm, P . Berche, and J . A . Vazquez-Boland, Res . Microbiol . 147:371-384, 1996) . Here we report that P14-A and other variant strains with the same phenotype carry a point mutation in codon 145 of prfA, leading to a Gly-->Ser substitution . trans-complementation experiments with PrfA-deficient mutants demonstrated that the Gly145Ser prfA allele causes overexpression of virulence factors in L . monocytogenes, to the levels found in the virulence factor-overexpressing variants . In strain P14-A with a chromosomal Glyl45Ser prfA background, transcription of prfA and of PrfA-dependent virulence genes remained constitutively high under culture conditions in which virulence factor expression is downregulated in wild-type L . monocytogenes . The Glyl45Ser substitution is located in a PrfA stretch (residues 141 to 151) showing high sequence similarity to the D alpha-helix of CRP . Interestingly, well-characterized crp* mutations, which make CRP functionally active in the absence of cAMP, map in this region (i.e., Gly141Ser and Ala144Thr substitutions) . By analogy with the CRP model, the phenotype conferred to L . monocytogenes by the Gly145Ser substitution in PrfA could be due to the mutant regulatory protein being locked in a transcriptionally active, cofactor-independent conformational state . Our observations allow the construction of a model for PrfA-dependent virulence gene regulation in which the levels of virulence factor expression depend primarily on the conformational state of the PrfA protein, which alternates between active and inactive forms according to its interaction with an environmentally regulated signal molecule or cofactor.

Infect Immun, 1997 Mar, 65(3), 1095 - 7
Involvement of tubulin and inhibitory G proteins in the interaction of Listeria monocytogenes with mouse hepatocytes; Buchwalow IB et al.; Intracellular and cell-to-cell spread of Listeria monocytogenes has been considered exclusively actin dependent . By immunocytochemical techniques, we provide evidence for an involvement of inhibitory G proteins and tubulin in "comet tail" formation in L . monocytogenes-infected mouse hepatocytes.

Infect Immun, 1997 Mar, 65(3), 986 - 93
Elimination of resident macrophages from the livers and spleens of immune mice impairs acquired resistance against a secondary Listeria monocytogenes infection; Samsom JN et al.; During a secondary Listeria monocytogenes infection in mice, the bacteria are eliminated more rapidly from the liver and spleen than during a primary infection . This acquired resistance against a secondary infection is dependent on T lymphocytes, which induce enhanced elimination of bacteria via stimulation of effector cells such as neutrophils, resident macrophages, exudate macrophages, and hepatocytes . The aim of the present study was to determine the role of the resident macrophages in acquired resistance against a secondary L . monocytogenes infection in mice . Mice which had recovered from a sublethal primary infection with 0.1 50% lethal dose (LD50) of L . monocytogenes intravenously (i.v.), i.e., immune mice, received a challenge of 1 LD50 of L . monocytogenes i.v . to induce a secondary infection . At 2 days prior to challenge, immune mice were given an i.v . injection of liposomes containing dichloromethylene-diphosphonate (L-Cl2MDP) to selectively eliminate resident macrophages from the liver and spleen . Control immune mice received either phosphate-buffered saline (PBS) or liposomes containing PBS (L-PBS) . Treatment of mice with L-Cl2MDP effectively eliminated resident macrophages from the liver and spleen but did not affect the number of granulocytes, monocytes, or lymphocytes in peripheral blood or their migration to a site of inflammation . Phagocytosis and killing of L . monocytogenes by peritoneal exudate cells elicited with heat-killed L . monocytogenes were similar in all groups of immune mice . On day 3 of a secondary infection, the number of L . monocytogenes organisms in the livers and spleens of L-Cl2MDP-treated immune mice was 4 log10 units higher than in immune mice treated with PBS or L-PBS . The concentration of reactive nitrogen intermediates in plasma, a measure of the severity of infection, was 70-fold higher for L-Cl2MDP-treated immune mice than for PBS- or L-PBS-treated immune mice . Treatment with L-Cl2MDP significantly increased the number of inflammatory foci in the liver and spleen, decreased their size, and affected their structure . From these results, we conclude that resident macrophages are required for the expression of acquired resistance against a secondary L . monocytogenes infection in mice.

Infect Immun, 1997 Mar, 65(3), 978 - 85
Porcine polymorphonuclear leukocytes generate extracellular microbicidal activity by elastase-mediated activation of secreted proprotegrins; Panyutich A et al.; Antimicrobial peptides of several structural classes have been found in phagocytes and epithelial cells of many animals . The broadly microbicidal protegrins (PG1, -2, and -3) were originally isolated as 16 to 18-amino-acid peptides from pig neutrophil lysates, but the corresponding cDNA sequences encoded much larger precursors that belonged to the cathelicidin family of antimicrobial peptides . We explored the storage, secretion, and microbicidal activation of protegrins in porcine neutrophils and in a model system consisting of recombinant proprotegrin 3 (pPG3) and various serine proteases and their inhibitors . Protegrins were stored in neutrophils as inactive proforms that were cleaved by neutrophil elastase to mature protegrins during the preparation of granule lysate and during phorbol myristate acetate-stimulated granule secretion from intact neutrophils . Recombinant pPG3 was efficiently cleaved by trace amounts of human neutrophil elastase or equivalent amounts of elastase activity from porcine neutrophils, but pPG3 was relatively resistant to porcine pancreatic elastase or human neutrophil cathepsin G . The recombinant pPG3 and neutrophil proprotegrins lacked microbicidal activity, but the mature protegrins generated in the elastase-mediated cleavage reaction were as active against Listeria monocytogenes as the chemically synthesized protegrin . The secretion and elastase-mediated activation of proprotegrins accounted for much of the stable microbicidal activity of porcine neutrophil secretions against L . monocytogenes . Secreted proprotegrins and trace amounts of elastase constitute a binary microbicidal system that is likely to contribute to the antimicrobial activity of porcine inflammatory fluids.

J Immunol, 1997 Mar 1, 158(5), 2259 - 67
Both innate and acquired immunity to Listeria monocytogenes infection are increased in IL-10-deficient mice; Dai WJ et al.; IL-10-deficient mice were highly resistant to Listeria monocytogenes during the course of infection . An increased innate immunity was suggested by reduced bacterial burdens (as much as 50-fold) early (days 2 and 3) in the infection, as compared with control mice . In addition, in vitro stimulation of both IL-10-deficient peritoneal exudate cells and spleen cells with heat-killed Listeria resulted in a dramatically enhanced proinflammatory cytokine response (e.g., IL-12, IFN-gamma, TNF-alpha, IL-1alpha, and IL-6) . During later stages of a primary Listeria infection, the reduced bacterial burden in the infected organs of IL-10-deficient mice was accompanied by decreased tissue damage and earlier clearance of the pathogen, as well as a stronger Th1 polarization . The absence of IL-10 did not influence membrane-bound factors that stimulate Th cell responses, demonstrated by the finding of normal MHC class II, B7.1, and B7.2 surface expression on F4/80+ macrophages in vivo . IL-10-deficient mice were also more resistant to a secondary infection, accompanied by an enhanced Th1 response . The results presented in this work demonstrate that the absence of IL-10 augments innate and acquired immunity during primary and secondary L . monocytogenes infection by up-regulating proinflammatory type 1 cytokine responses . The resulting protective Th1 responses lead to an effective reduction of bacterial growth and tissue destruction and to an earlier clearance of the bacteria . The physiologic role of IL-10 during L . monocytogenes infection studies is discussed and compared with pathogenic infections that induce a more systemic cytokine response in IL-10-deficient mice.

Biochem Biophys Res Commun, 1997 Feb 24, 231(3), 686 - 91
ABM-1 and ABM-2 homology sequences: consensus docking sites for actin-based motility defined by oligoproline regions in Listeria ActA surface protein and human VASP; Purich DL et al.; Actin-based motility involves a cascade of binding interactions designed to assemble actin regulatory proteins into functional locomotory units . Listeria ActA surface protein contains a series of nearly identical EFPPPPTDE-type oligoproline sequences for binding vasodilator-stimulated phosphoprotein (VASP) . The latter is a tetrameric protein with numerous GPP-PPP docking sites for profilin, a 15 kDa regulatory protein that promotes actin filament assembly . Analysis of known actin regulatory proteins led to the identification of distinct Actin-Based Motility homology sequences ABM-1; (D/E)FPPPPX(D/E); and ABM-2, XPPPPP (where X denotes G, A, L, and S).

J Biol Chem, 1997 Feb 7, 272(6), 3259 - 65
A novel non-heme iron-binding ferritin related to the DNA-binding proteins of the Dps family in Listeria innocua; Bozzi M et al.; A multimeric protein that behaves functionally as an authentic ferritin has been isolated from the Gram-positive bacterium Listeria innocua . The purified protein has a molecular mass of about 240,000 Da and is composed of a single type of subunit (18,000 Da) . L . innocua ferritin is able to oxidize and sequester about 500 iron atoms inside the protein cage . The primary structure reveals a high similarity to the DNA-binding proteins designated Dps . Among the proven ferritins, the most similar sequences are those of mammalian L chains that appear to share with L . innocua ferritin the negatively charged amino acids corresponding to the iron nucleation site . In L . innocua ferritin, an additional aspartyl residue may provide a strong complexing capacity that renders the iron oxidation and incorporation processes extremely efficient . This study provides the first experimental evidence for the existence of a non-heme bacterial ferritin that is related to Dps proteins, a finding that lends support to the recent suggestion of a common evolutionary origin of these two protein families.

Scott Med J . 1997 Feb;42(1):18.
Listeria monocytogenes: a rare cause of pleural effusion in a patient with congestive cardiac failure; Hood S et al.; We report the case of a 65 year old immunocompetent man with a listerial pleural effusion . Infection of the pulmonary parenchyma and pleura with listeria monocytogenes has been reported in small numbers of immunocompromised patients but there have been only two previous reports of pulmonary listeria in non-compromised hosts.

Mol Biotechnol, 1997 Feb, 7(1), 85 - 8
Detection and identification of Listeria monocytogenes from milk and cheese by a single-step PCR; Manzano M et al.; Primers of iap gene were used as a target to develop a PCR technique for detecting Listeria monocytogenes in milk and cheese . The PCR technique gives good results in the detection of Listeria monocytogenes either in artificially or naturally contaminated foodstuffs and has a high sensitivity and specificity . Application of this rapid diagnostic tool could provide further information about the spread of L . monocytogenes in milk and cheese.

Nutr Rev, 1997 Feb, 55(2), 57 - 60
Food poisoning, listeriosis, and febrile gastroenteritis; Abscess formation in Listeria monocytogenes-infected gamma delta T cell deficient mouse mutants involves alpha beta T cells; Department of Immunology, University of Ulm, GermanyAlthough mutant mice lacking gamma delta T cells resolve Listeria monocytogenes infection, extensive abscesses are formed . Manifestation of these inflammatory lesions is prevented by in vivo depletion with monoclonal antibodies of CD4, CD8 or both T cell subsets . We conclude that these inflammatory tissue reactions develop when alpha beta T cells of either CD4 or CD8 phenotype are released from control by gamma delta T cells.

Microb Pathog, 1997 Feb, 22(2), 79 - 88
Involvement of inflammatory cytokines and nitric oxide in the expression of non-specific resistance to Listeria monocytogenes in mice induced by viable but not killed Mycobacterium bovis BCG; Yang J et al.; The non-specific defense against Listeria monocytogenes could be induced by viable BCG but not by killed BCG in mice . In order to understand the mechanism of antilisterial activity, viable and killed BCG were compared for their ability of inducing cytokine gene expression in spleen cells . Both viable and killed BCG induced the same level of mRNA expression of interleukin 10 (IL-10), transforming growth factor beta (TGF-beta), IL-12 and tumor necrosis factor alpha (TNF-alpha) . Gene expression and production of IL-1 alpha and gamma interferon (IFN-gamma) could be induced by stimulation only with viable BCG . Viable BCG but not killed BCG induced the mRNA expression of inducible nitric oxide synthase (iNOS) . Treatment of mice with NG-monomethyl-L-arginine acetate (NMMA) significantly impaired the non-specific antilisterial action induced by viable BCG . These results demonstrated that NO is an important mediator for the non-specific antilisterial activity induced by viable BCG, and IFN-gamma, IL-1 alpha and TNF-alpha may play a critical role in the non-specific antilisterial activity.

Microb Pathog, 1997 Feb, 22(2), 67 - 78
Mutants in the CtpA copper transporting P-type ATPase reduce virulence of Listeria monocytogenes; Francis MS et al.; The CtpA protein from pathogenic Listeria monocytogenes, is a P-type adenosine triphosphatase involved in copper homeostasis . To establish a role in pathogenicity for CtpA, a mutant strain was constructed by insertion of an antibiotic resistance cartridge into the ctpA gene . This mutant was then compared to the wild-type in tissue culture invasion assays and mouse infection studies . Mutants in CtpA, were unaltered for intracellular growth in J774 and HeLa cell lines . However, recovery of mutants from tissue of infected mice was dramatically reduced compared with the wild-type, and a significant impairment in terms of in vivo persistence in mixed-infection competition experiments was observed . These results demonstrate the significance of CtpA in establishing an in vivo infection by L . monocytogenes, and highlight some inadequacies of in vitro tissue culture monolayer assays for determining invasion and intracellular growth of a pathogen.

Can J Neurol Sci, 1997 Feb, 24(1), 70 - 2
Musical auditory hallucinosis from Listeria rhombencephalitis; Douen AG et al.; BACKGROUND: Complex auditory hallucinations have rarely been reported in cases of brainstem stroke or tumor . METHOD: Case study . RESULTS: A patient with acute Listeria rhombencephalitis complained of formed musical auditory hallucinations on the side of recent sensorineural deafness . MRI revealed an abscess in the middle cerebellar peduncule with extensive surrounding edema . CONCLUSIONS: Disruption of brainstem auditory pathways may cause complex auditory hallucinations . Potential pathogenetic mechanisms are discussed and a diagnostic approach is proposed.

Curr Opin Immunol, 1997 Feb, 9(1), 35 - 43
Inter-relationship among macrophages, natural killer cells and neutrophils in early stages of Listeria resistance; Unanue ER; Reports in the past few years have shown the involvement of different cells and cytokines in controlling the infection with the intracellular facultative pathogen Listeria monocytogenes . A synergistic interaction of T-cell-independent and -dependent processes takes place but the nature of these interactions and of the relevant cells and cytokines depends on both the stage of the infection and the tissue that is involved.

Int J Food Microbiol, 1997 Feb, 34(2), 171 - 7
Temperature distribution and prevalence of Listeria spp . in domestic, retail and industrial refrigerators in Greece; Sergelidis D et al.; The present paper examined the presence of Listeria spp . in the environment of domestic, retail and industrial refrigerators . From 136 household refrigerators, 136 surface samples were taken from the walls or shelves, and 125 from cheese compartments . Only two refrigerators harboured L . monocytogenes . From 228 food store refrigerators, 335 samples were taken . Of these, 118 were in in contact with cheeses, 69 with sausages, 21 with cheese and sausages, 20 with miscellaneous products and 107 from refrigerator handles . Listeria spp . and L . monocytogenes were found in 3.1% and 1.7%, of the samples respectively . Listeria spp . was not detected in any of the nine dairy plant refrigerators examined . Listeria monocytogenes and L . innocua were found in 4.5 and 36.4%, respectively, of the 22 refrigerators inside meat processing plants, with only one of 22 refrigerators handles being positive for L . monocytogenes . Temperature distribution in the refrigerators was also investigated . Fifty five per cent of the 136 domestic and 32% of the 228 retail store refrigerators had temperatures of greater than or equal to 9 degrees C . The range of refrigeration temperatures of the industrial refrigerators was 0-2 degrees C for meat plants and 2-7 degrees C for dairy plants . No correlation of any kind could be established between the prevalence of Listeria spp . and the temperature of the various refrigerators due to the low number of positive samples.

FEMS Microbiol Lett, 1997 Feb 1, 147(1), 45 - 50
Effect of sampling procedure and strain variation in Listeria monocytogenes on the discrimination of species in the genus Listeria by Fourier transform infrared spectroscopy and canonical variates analysis; Lefier D et al.; The ability to discriminate successfully among cultures of all species of the Listeria genus by infrared spectroscopy in combination with canonical variate analysis was confirmed . The robustness of the method was demonstrated by showing that the separation of L . monocytogenes and L . grayi was hardly affected by variations in broth medium, incubation temperature, incubation time and cell washing procedure . Discrimination among 24 strains of L . monocytogenes according to serotype allowed two groups to be recognised, one comprising serotypes 4 and 4b and the other containing serotypes 1, 1/2b and 1/2c . When strain variation was included in the species discrimination model, the classification of all the L . monocytogenes strains was virtually 100% correct.

Appl Environ Microbiol, 1997 Feb, 63(2), 543 - 6
Listeria monocytogenes Scott A transports glucose by high-affinity and low-affinity glucose transport systems; Parker C et al.; Listeria monocytogenes transported glucose by a high-affinity phosphoenolpyruvate-dependent phosphotransferase system and a low-affinity proton motive force-mediated system . The low-affinity system (Km = 2.9 mM) was inhibited by 2-deoxyglucose and 6-deoxyglucose, whereas the high-affinity system (Km = 0.11 mM) was inhibited by 2-deoxyglucose and mannose but not 6-deoxyglucose . Cells and vesicles artificially energized with valinomycin transported glucose or 2-deoxyglucose at rates greater than those of de-energized cells, indicating that a membrane potential could drive uptake by the low-affinity system.

Appl Environ Microbiol, 1997 Feb, 63(2), 524 - 31
Functional characterization of pediocin PA-1 binding to liposomes in the absence of a protein receptor and its relationship to a predicted tertiary structure; Chen Y et al.; The physicochemical interaction of pediocin PA-1 with target membranes was characterized using lipid vesicles made from the total lipids extracted from Listeria monocytogenes . Pediocin PA-1 caused the time- and concentration-dependent release of entrapped carboxyfluorescein (CF) from the vesicles . The pediocin-induced CF efflux rates were higher under acidic conditions than under neutral and alkaline conditions and were dependent on both pediocin and lipid concentrations . A binding isotherm constructed on the basis of the Langmuir isotherm gave an apparent binding constant of 1.4 x 10(7) M-1 at pH 6.0 . The imposition of a transmembrane potential (inside negative) increased the CF efflux rate by 88% . Pediocin PA-1 also permeablized synthetic vesicles composed only of phosphatidylcholine . Sequence alignments and secondary-structure predictions for the N terminus of pediocin PA-1 and other class IIa bacteriocins predicted that pediocin PA-1 contained two beta-sheets maintained in a hairpin conformation stabilized by a disulfide bridge . The structural model also revealed patches of positively charged residues, consistent with the argument that electrostatic interactions play an important role in the binding of pediocin PA-1 to the lipid vesicles . This study demonstrates that pediocin PA-1 can function in the absence of a protein receptor and provides a structural model consistent with these results.

Curr Opin Cell Biol, 1997 Feb, 9(1), 54 - 61
Actin dynamics in vivo; Welch MD et al.; Actin dynamics in lamellipodia are driven by continuous cycles of actin polymerization, retrograde flow, and depolymerization . In the past year, advances have been made in identifying signaling pathways that regulate actin-filament uncapping and polymerization, in determining the role of myosin motor proteins in retrograde flow, and in evaluating the role of severing proteins in actin depolymerization . Both Listeria monocytogenes and Saccharomyces cerevisiae have emerged as powerful model organisms for studying actin dynamics in cells.

Ned Tijdschr Geneeskd, 1997 Jan 25, 141(4), 202 - 4
{Green amniotic fluid as initial symptom of high intestinal obstruction in infants}; Swarte RM et al.; At the birth of two children the amniotic fluid was green colored . The Apgar scores were good . Because of bilious vomiting and food retention, respectively, an open stomach tube was inserted, out of which bilious stomach contains were drained . The cause of green amniotic fluid was not meconium production or infection with Listeria monocytogenes, but mixing with green bile . At further investigation the children both proved to have a high intestinal obstruction distal of the papilla duodeni major.

Nature, 1997 Jan 16, 385(6613), 265 - 9
Actin polymerization is induced by Arp2/3 protein complex at the surface of Listeria monocytogenes; Welch MD et al.; The pathogenic bacterium Listeria monocytogenes is capable of directed movement within the cytoplasm of infected host cells . Propulsion is thought to be driven by actin polymerization at the bacterial cell surface, and moving bacteria leave in their wake a tail of actin filaments . Determining the mechanism by which L . monocytogenes polymerizes actin may aid the understanding of how actin polymerization is controlled in the cell . Actin assembly by L . monocytogenes requires the bacterial surface protein ActA and protein components present in host cell cytoplasm . We have purified an eight-polypeptide complex that possesses the properties of the host-cell actin polymerization factor . The pure complex is sufficient to initiate ActA-dependent actin polymerization at the surface of L . monocytogenes, and is required to mediate actin tail formation and motility . Two subunits of this protein complex are actin-related proteins (ARPs) belonging to the Arp2 and Arp3 subfamilies . The Arp3 subunit localizes to the surface of stationary bacteria and the tails of motile bacteria in tissue culture cells infected with L . monocytogenes; this is consistent with a role for the complex in promoting actin assembly in vivo . The activity and subunit composition of the Arp2/3 complex suggests that it forms a template that nucleates actin polymerization.

FEMS Microbiol Lett, 1997 Jan 15, 146(2), 303 - 10
Complementation of Listeria seeligeri with the plcA-prfA genes from L . monocytogenes activates transcription of seeligerolysin and leads to bacterial escape from the phagosome of infected mammalian cells; Karunasagar I et al.; Infection experiments have shown that the avirulent species Listeria seeligeri invaded the enterocyte-like cell line Caco-2 with low efficiency but was unable to escape from the phagosome . Introduction of the listeriolysin gene (hly) from L . monocytogenes into L . seeligeri via a recombinant plasmid did not change these characteristics . No measurable transcription of this gene or of the structurally intact chromosomal seeligerolysin gene (lso) was detected . Transformation with a plasmid carrying the bicistronically transcribed plcA-prfA genes from L . monocytogenes resulted in the efficient expression of the plasmid-encoded transcription activator PrfA, a readily detectable synthesis of seeligerolysin and the escape of the bacteria from the phagosome of infected mammalian cells, followed by intracytoplasmic multiplication.

N Engl J Med, 1997 Jan 9, 336(2), 100 - 5
An outbreak of gastroenteritis and fever due to Listeria monocytogenes in milk; Dalton CB et al.; BACKGROUND: After an outbreak of gastroenteritis and fever among persons who attended a picnic in Illinois, chocolate milk served at the picnic was found to be contaminated with Listeria monocytogenes . METHODS: In investigating this outbreak, we interviewed the people who attended the picnic about what they ate and their symptoms . Surveillance for invasive listeriosis was initiated in the states that receive milk from the implicated dairy . Stool and milk samples were cultured for L . monocytogenes . Serum samples were tested for IgG antibody to listeriolysin O . RESULTS: Forty-five persons had symptoms that met the case definition for illness due to L . monocytogenes, and cultures of stool from 11 persons yielded the organism . Illness in the week after the picnic was associated with the consumption of chocolate milk . The most common symptoms were diarrhea (present in 79 percent of the cases) and fever (72 percent) . Four persons were hospitalized . The median incubation period for infection was 20 hours (range, 9 to 32), and persons who became ill had elevated levels of antibody to listeriolysin O . Isolates from stool specimens from patients who became ill after the picnic, from sterile sites in three additional patients identified by surveillance, from the implicated chocolate milk, and from a tank drain at the dairy were all serotype 1/2b and were indistinguishable on multilocus enzyme electrophoresis, ribotyping, and DNA macrorestriction analysis . CONCLUSIONS: L . monocytogenes is a cause of gastroenteritis with fever, and sporadic cases of invasive listeriosis may be due to unrecognized outbreaks caused by contaminated food.

World Health Stat Q, 1997, 50(1-2), 67 - 73
Foodborne listeriosis; Rocourt J et al.; Various epidemiological investigations of outbreaks and sporadic cases have clearly demonstrated that the consumption of contaminated food is responsible for a high proportion of listeriosis cases and Listeria monocytogenes has been increasingly recognized as an important foodborne pathogen over the last 15 years . The emergence of listeriosis is the result of complex interactions of different factors: medical progress which increases the lifespan and allows immunodeficient people to survive, expansion of the food industry and cold storage systems as well as changes in food habits . None of these factors on its own is entirely responsible . Considerable research has attempted to characterize the organism, define the magnitude of the public health problem and its impact on the food industry, identify the risk factors associated with the disease, and devise appropriate control strategies . Nevertheless, a number of crucial questions remains incompletely elucidated (extent of the foodborne transmission of listeriosis, health status of apparently "healthy patients" with the possible role of an intercurrent infection or genetic susceptibility, how to distinguish highly virulent from less virulent strains of L . monocytogenes, factors contributing to the emergence of outbreaks, the possible role of healthy carriers in the epidemiology of listeriosis, etc.) . To investigate the complexity of listeriosis requires the close collaboration of clinicians, epidemiologists, clinical and food microbiologists, food scientists and the food industry . A large amount of data has been accumulated during the past 10 years but more research is required to elucidate the epidemiology of the disease and the virulence of the causative agent.

Scand J Infect Dis, 1997, 29(3), 308 - 9
Fatal Listeria meningitis, endocarditis and pericarditis in a patient with haemochromatosis; Manso C et al.; A 65-year-old man with primary haemochromatosis was admitted because of fever and confusion . He was found to have bacteraemia and meningitis due to Listeria monocytogenes . Treatment with ampicillin plus tobramycin was instituted, and despite an initial improvement, the patient experienced an unfavourable course and died . At postmortem examination, tricuspid valve endocarditis and purulent pericarditis with tamponade were detected . Listeria monocytogenes grew in the culture of the pericardial fluid . Documentation of Listeria monocytogenes pericarditis is extremely rare, and data on the patient described and on seven published cases are reported.

Annu Rev Nutr, 1997, 17, 255 - 75
Emerging issues in microbiological food safety; Meng J et al.; Many microorganisms previously unrecognized as food-borne or harmful are emerging as human pathogens transmitted by food . This is a result of recent acquisition of key virulence factors, detection by newly developed isolation procedures, or astute detective-like laboratory skills of microbiologists . Six microbial pathogens, including Shiga toxin-producing Escherichia coli, Listeria monocytogenes, Arcobacter butzleri, Helicobacter pylori, Cryptosporidium parvum, and Cyclospora, have become recognized as significant causes of human illness . Although the ecology and epidemiology of illness caused by some of these pathogens have not been fully elucidated, food has the potential of being an important vehicle in their dissemination . Existing technologies and new approaches such as irradiation and hazard analysis critical control point (HACCP) programs are useful tools in the control of food-borne hazards . However, because of ever-changing products, processes, food-handling practices, societal habits, and pathogens, emerging food-borne diseases will continue to be an important public health concern.

J Clin Dent, 1997, 8(2 Spec No), 54 - 61
A comparison of intraoral antimicrobial effects of stabilized stannous fluoride dentifrice, baking soda/peroxide dentifrice, conventional NaF dentifrice and essential oil mouthrinse; Bacca LA et al.; The intraoral antimicrobial activity of four commercial oral products-conventional NaF dentifrice (Crest), baking soda/peroxide/NaF dentifrice (Mentadent), essential oil mouthrinse (Listerine) and SnF2 dentifrice (Crest Plus Gum Care)-have been compared in three test regimens . Formulations were compared for their ability to suppress the regrowth and apical extension of dental plaque following toothbrushing during thirty hours of non-brushing where products were used as oral rinses (30-hour plaque regrowth model) . Formulations were also compared for their ability to suppress the colony-forming units (cfu) of facultative anaerobic bacteria sampled from buccal gingival surfaces following use (Gingival Surface Microbial Index-GSMI model) . Lastly, formulations were compared for effects in suppressing the glycolytic metabolic activity and regrowth activity of in vivo-treated dental plaques sampled at various periods following topical use and incubated under controlled ex vivo conditions (Plaque Glycolysis and Regrowth-PGRM model) . In thirty-hour plaque regrowth testing, the rank ordered antimicrobial efficacy of formulations followed SnF2 > essential oils > NaF = water = baking soda/peroxide . In GSMI testing, all formulations were shown to suppress the cfu of facultative anaerobic bacteria relative to baseline, although SnF2 treatment was observed to reduce bacterial levels to a significantly greater degree than NaF dentifrice or baking soda/peroxide dentifrice up to two hours following brushing . In PGRM testing, the SnF2 dentifrice provided significant inhibition of bacterial metabolism and regrowth following topical application when compared with the NaF dentifrice as control . The baking soda/peroxide dentifrice provided no reduction in either bacterial metabolism or regrowth in PGRM . Previous studies had demonstrated modest effects for essential oil rinse in reducing PGRM plaque regrowth, with no effects for this treatment on plaque metabolism . Overall, these results demonstrate that SnF2 dentifrice provides substantial intraoral antimicrobial effects . The essential oil mouthrinse also exhibits significant intraoral antimicrobial effects, albeit apparently less than SnF2 dentifrice . The baking soda/peroxide dentifrice did not produce any antimicrobial effects following in vivo use compared with conventional dentifrice . These results provide mechanistic rationale for the chemotherapeutic efficacy of SnF2 and essential oil formulations in reducing gingivitis, while providing no support for the expectation of clinical efficacy for formulations containing baking soda and peroxide.

J Clin Dent, 1997, 8(2 Spec No), 46 - 53
The comparative efficacy of stabilized stannous fluoride dentifrice, peroxide/baking soda dentifrice and essential oil mouthrinse for the prevention of gingivitis; Beiswanger BB et al.; This double-blind parallel-design clinical study compared the efficacy of a stabilized stannous fluoride dentifrice (Crest Plus Gum Care), baking soda and peroxide (NaF) dentifrice (Mentadent), and essential oil mouthrinse (Listerine) to a conventional NaF dentifrice (Crest) for the control of plaque, gingivitis and gingival bleeding over six months . Following an initial baseline examination and stratification, subjects received a complete oral prophylaxis and were distributed assigned test products . Following three and six months, subjects re-visited the clinic for examinations . Evaluations at baseline and at 3 and 6 months included soft tissue status . Loe-Silness gingivitis/gingival bleeding, Silness-Loe plaque and dental stain . Results subsequent to six months of product use were as follows: At six months, the stabilized stannous fluoride dentifrice was observed to produce statistically significant 17.5% reductions in gingivitis and 27.5% reductions in gingival bleeding relative to the NaF dentifrice . The combination of sodium fluoride dentifrice and essential oil mouthrinse produced statistically significant reductions of 7.4% in gingivitis and 10.8% in plaque as compared with the NaF dentifrice . The stabilized stannous fluoride dentifrice produced statistically significant reductions in both gingivitis (10.8%) and gingival bleeding (23.0%) relative to the combination of sodium fluoride dentifrice and essential oil mouthrinse . The baking soda and peroxide (NaF) dentifrice did not provide reductions in gingivitis, plaque or gingival bleeding as compared with the conventional NaF dentifrice . The stabilized stannous fluoride dentifrice provided statistically significant reductions in gingivitis as compared with the baking soda and peroxide dentifrice following six months of use, and both the essential oil mouthrinse and stabilized stannous fluoride dentifrice provided statistically significant reductions in gingivitis as compared with the baking soda and peroxide dentifrice following three months of use . These results support: 1) the efficacy of stabilized stannous fluoride dentifrice and the combination of sodium fluoride dentifrice and essential oil mouthrinse for the prevention of gingivitis; 2) the superior activity of stabilized stannous fluoride dentifrice as compared with a combination of sodium fluoride dentifrice and essential oil mouthrinse for the control of gingivitis and gingival bleeding; and 3) the lack of efficacy for baking soda and peroxide dentifrice for the control of plaque, gingivitis and gingival bleeding as compared with conventional fluoridated dentifrice.

Anim Reprod Sci, 1997 Jan, 45(4), 311 - 27
Effect of experimental infection with Listeria monocytogenes on the development of pregnancy and on concentrations of progesterone, oestrone sulphate and 15-ketodihydro-PGF2 alpha in the goat; Engeland IV et al.; The effect of Listeria monocytogenes infection on hormone levels in pregnant goats was studied . Four goats (Group I) received an intravenous inoculation of a bacterial culture (Type 1) on Days 69-77 and another four goats (Group II) received a similar inoculation on Days 105-106 of gestation . Five non-inoculated goats were used as controls . Plasma was analysed for progesterone, oestrone sulphate and 15-ketodihydro-PGF2 alpha . The status of the foetus was followed using real-time ultrasonography . Three of the four goats in Group I aborted 8-10 days after inoculation . The fourth goat gave birth to a normal live kid at term . The three goats which aborted showed clinical signs of disease in connection with abortion . In Group II, all goats aborted after 9-11 days . All the goats showed clinical symptoms of disease from a few days after inoculation and the symptoms continued until abortion . The clinical symptoms of disease were more pronounced in Group II than in Group I . L . monocytogenes was isolated from all aborted foetuses . None of the control goats aborted . Ultrasound examination revealed foetal death either immediately before or up to 2 days before abortion . Mummification had begun in the foetus that had been dead for 2 days before expulsion . In comparison with pre-inoculation plasma levels in Group I, a significant decrease (P < 0.05) in progesterone levels and an increase in 15-ketodihydro-PGF2 alpha levels were observed from Days 4 and 6 after inoculation, respectively . In Group II, a significant decrease (P < 0.05) in progesterone levels and an increase in 15-ketodihydro-PGF2 alpha levels in plasma were observed from Days 8 and 6, respectively . The oestrone sulphate levels decreased slightly in the inoculated goats a few days before abortion . The pattern of changes in levels around abortion was similar to the pattern present in the control animals around parturition . However, oestrone sulphate levels did not increase in the inoculated groups before abortion in contrast to goats which delivered healthy kids . The changes in levels of 15-ketodihydro-PGF2 alpha in goats that aborted indicated that the endocrine foetal-placental function was disturbed, which was most likely due to the establishment and development of L . monocytogenes in the placenta and foetus.

Crit Rev Microbiol, 1997, 23(2), 77 - 107
Antibodies to Listeria monocytogenes; Bhunia AK; Listeria monocytogenes is one of the leading foodborne pathogens and has been implicated in numerous outbreaks in the last 2 decades . Immunocompromised populations are usually the most susceptible to Listeria infections . Although the pathogenic mechanism is a complex process, significant progress has been made in unravelling the mechanism in recent years . It is now clear that numerous extracellular and cell-associated proteins, such as internalin, listeriolysin, actin polymerization protein, phospholipase, metalloprotease, and possibly p60 proteins, are essential for L . monocytogenes entry into mammalian cells, survival inside the phagosome, escape into the cytoplasm, and cell-to-cell spread . Other proteins may be responsible for growth and physiology or to maintain the structural integrity of the bacteria . Monoclonal and polyclonal antibodies have been developed against many of those antigens or their synthetic derivatives that have helped greatly to determine the structure and function of these antigens . The antibodies were also used for the diagnosis and detection, immunocytochemical staining, and serotyping of Listeria . Humoral immune response to live L . monocytogenes cells was examined in naturally or experimentally infected hosts . Studies revealed that only extracellular antigens induced the humoral response, whereas cell-associated antigens had apparently no response . It is speculated that during the occasional bacteremic phase, L . monocytogenes releases extracellular antigens that are then processed by the immune system for antibody production . As L . monocytogenes is an intracellular pathogen, the cell-associated antigens are not persistent in the blood circulation and thus fail to stimulate the humoral immune response.

Stomatologiia (Mosk), 1997, 76(2), 26 - 7
{The comparative characteristics of the antibacterial activity of new antiseptics and the prospects for their use in dental practice}; Dmitrieva LA et al.; Antibacterial activities of modern antiseptics listerine, myramistine, cidipol, octenisept, tantum verde, matecide, and rautine drugs chlorhexidine and dioxidine are compared . The prospects of their use in dentistry for the treatment of inflammations associated with anaerobes are discussed . Metacide, listerine, chlorhexidine, and dioxidine are characterized by the widest spectrum of activity towards obligate anaerobic bacteria; moreover, these drugs inhibit bacterial growth when used in lower concentrations than other drugs.

Folia Microbiol (Praha), 1997, 42(1), 65 - 71
Primary Listeria monocytogenes infection in gestating mice; Abram M et al.; The facultative intracellular Gram-positive bacterium Listeria monocytogenes is a food-borne pathogen of frequently underestimated importance . Pregnant women represent the high-risk group for L . monocytogenes infection . Abortion, stillbirth or neonatal infection can be the serious outcome of such an infection . Recovery from listeriosis, resistance mechanisms of the host and the effect of L . monocytogenes on fetal development still remain to be fully understood . The results of our experiments showed an increased susceptibility of gestating BALB/c mice to primary L . monocytogenes infection . The duration of listeriosis in gestating animals was almost twice longer than in the control group . Furthermore, it was clearly shown that the detrimental effect of L . monocytogenes on fetal development was more pronounced if the infection was acquired earlier during gestation.

Leuk Lymphoma, 1997 Jan, 24(3-4), 335 - 9
2-Chlorodeoxyadenosine as initial therapy for advanced low grade lymphomas; Canfield VA et al.; In order to evaluate efficacy and safety of 2-chlorodeoxyadenosine (2-CdA) as primary therapy of low grade non Hodgkin's lymphoma, a phase II trial of 2-CdA was initiated in patients with previously untreated advanced low grade lymphoma . Fourteen previously untreated patients with stage III and IV low grade lymphoma were enrolled . Patients received 2-CdA 0.1 mg/kg/d by continuous infusion for 7 days every 28 days, for 1-6 cycles of therapy (median 3.5) . Results showed one complete response and nine partial responses for an overall response rate of 75% . Until now there have only been three responding patients who have had progressive disease, with a median follow-up time of 18 months . The major toxicity was bone marrow suppression and nine patients stopped therapy prior to a planned six cycles because of prolonged cytopenias, primarily thrombocytopenia . Fifteen of 50 cycles of therapy were associated with neutropenic febrile episodes and there was one septic death secondary to Listeriosis . It seems from this small group of patients that 2-CdA is an active agent in previously untreated low grade lymphoma . Myelosuppression is cumulative and limits the number of cycles of therapy which can be given . Future exploration of different doses or schedules of this active agent is warranted.

Vet J, 1997 Jan, 153(1), 9 - 29
A review of Listeria monocytogenes and listeriosis; Low JC et al.; Following the initial isolation and description in 1926 Listeria monocytogenes has been shown to be of world-wide prevalence and is associated with serious disease in a wide variety of animals, including man . Our knowledge of this bacterial pathogen and the various forms of listeriosis that it causes has until recently been extremely limited, but recent advances in taxonomy, isolation methods, bacterial typing, molecular biology and cell biology have extended our knowledge . It is an exquisitely adaptable environmental bacterium capable of existing both as an animal pathogen and plant saprophyte with a powerful array of regulated virulence factors . Most cases of listeriosis arise from the ingestion of contaminated food and in the UK the disease is particularly common in ruminants fed on silage . Although a number of forms of listeriosis are easily recognized, such as encephalitis, abortion and septicaemia, the epidemiological aspects and pathogenesis of infection in ruminants remain poorly understood . The invasion of peripheral nerve cells and rapid entry into the brain is postulated as a unique characteristic of its virulence, but relevant and practical disease models are still required to investigate this phenomenon . This review offers an up to date introduction to the organism with a description of virulence determinants, typing systems and a detailed account of listeriosis in animals . Experimental and field papers are reviewed and further sections deal with the diagnosis, treatment and control of listeriosis in animals . A final part gives an overview of listeriosis in man.

J Dairy Sci, 1997 Jan, 80(1), 220 - 9
Molecular diagnostics for dairy-borne pathogens; Batt CA; Advances in diagnostic assays based on nucleic acids will revolutionize the ability of the industry to maintain the safety of dairy foods . Two complementary assay formats are explored, one of which permits the rapid detection of bacterial pathogens and the other the identification of reservoirs of these pathogens . The first format is an assay based on the polymerase chain reaction that employs homogeneous detection (TaqMan polymerase chain reaction detection; Perkin Elmer, Applied Biosystems Division, Foster City, CA) of the target sequence . This assay has been applied to the detection of Listeria monocytogenes . A primary problem with current assays that are based on polymerase chain reaction is the complexity of sample handling and the quantification of the initial target number . This fluorogenic assay takes advantage of the endogenous 5',3'-endonuclease activity in Taq DNA polymerase . Approximately 100 samples can be analyzed in 2 to 3 h with a sensitivity of < 50 cells and a dynamic range of > 1000-fold . The TaqMan polymerase chain reaction detection assay is a robust format that is readily applicable to a wide array of other pathogens found in foods and in the environment . The second format is an instrument for automated ribosomal RNA analysis (Riboprinter; DuPont, Wilmington, DE) that can be used to locate the reservoirs harboring the bacterial pathogen . Use of this typing method it has been shown that, although a number of different ribotypes can be isolated from a single environmental sample, only a selected number of these strains apparently have the ability to cause disease . The future of food microbiology lies in the development and integration of molecular methods that can be automated into a testing regimen that extends from the farm to finished products.

J Appl Microbiol, 1997 Jan, 82(1), 32 - 8
Nisin induces changes in membrane fatty acid composition of Listeria monocytogenes nisin-resistant strains at 10 degrees C and 30 degrees C; Mazzotta AS et al.; Listeria monocytogenes isolates resistant to 10(5) IU ml-1 nisin were obtained at 30 degrees C (NR30) and at 10 degrees C (NR10) . Nisin prolonged the lag phase of isolate NR30 at 10 degrees C . Isolates NR30 and NR10 did not produce a nisinase . Protoplasts of isolate NR30 were unaffected by exposure to nisin . The fatty acid composition from the wild-type strain and NR isolates was determined . As expected, temperature-induced differences in the C15/C17 fatty acid ratios were found . Growth of the NR strains in the presence of nisin resulted in significantly different C15/C17 ratios and a significant increase in the percentage of C16:0, C16: 1, C18:0 and C18: 1 fatty acids at 10 degrees C and 30 degrees C . Both the NR10 and NR30 isolates had similar growth rates at low temperatures, but these were slower than the wild-type strain . These results indicate that 'nisin resistance' is an environmentally defined phenotype and that nisin induces changes in the fatty acid composition of the membrane in L . monocytogenes nisin-resistant isolates regardless of the growth temperature.

Arch Immunol Ther Exp (Warsz), 1997, 45(1), 49 - 54
Interleukin 12 and direct cytotoxicity of spleen lymphocytes to Listeria innocua-phagocyting syngeneic macrophages in C57BL/6 and BALB/c mice; Szeliga J et al.; Production of interleukin 12 (IL-12) during cytotoxic reaction of C57BL/6 and BALB/c spleen lymphocytes or their subpopulations: T+B, T, CD4+ and CD8+ cells to L . innocua-phagocyting syngeneic macrophages was examined . The effector cell donors were untreated or L . innocua-infected . The number of surviving bacteria in phagocytes was tested and IL-12 level in culture supernatants of reacting cells was determined . C57BL/6 mice, resistant to Listeria infection, were found to develop stronger cell cytotoxicity to bacteria-phagocyting syngeneic macrophages than BALB/c mice . The lymphocytes responsible for that phenomenon were of CD8+ phenotype . IL-12 was produced only during nonspecific cytotoxic reaction of CD4+ and CD8+ T cells . It is suggested that the innate resistance of mice to Listeria is dependent on their ability to develop a specific cytotoxic reaction and IL-12 production.

J Cell Sci, 1997 Jan, 110 ( Pt 2), 191 - 200
Transfer of phagocytosed particles to the parasitophorous vacuole of Leishmania mexicana is a transient phenomenon preceding the acquisition of annexin I by the phagosome; Collins HL et al.; The eukaryotic intracellular pathogen Leishmania mexicana resides inside macrophages contained within a membrane bound parasitophorous vacuole which, as it matures, acquires the characteristics of a late endosomal compartment . This study reports the selectivity of fusion of this compartment with other particle containing vacuoles . Phagosomes containing zymosan or live Listeria monocytogenes rapidly fused with L . mexicana parasitophorous vacuoles, while those containing latex beads or heat killed L . monocytogenes failed to do so . Fusigenicity of phagosomes was not primarily dependent on the receptor utilized for ingestion, as opsonization with defined ligands could not overcome the exclusion of either latex beads or heat killed organisms . However modulation of intracellular pH by pharmacological agents such as chloroquine and ammonium chloride increased delivery of live Listeria and also induced transfer of previously excluded particles . The absence of fusion correlated with the acquisition of annexin I, a putative lysosomal targeting, molecule, on the phagosome membrane . We propose that the acquisition of cellular membrane constituents such as annexin I during phagosome maturation can ultimately direct the fusion pathway of the vesicles formed and have described a model system to further document changes in vesicle fusigenicity within cells.

Int Immunol, 1997 Jan, 9(1), 105 - 15
Active catabolism of glucocorticoids by 11 beta-hydroxysteroid dehydrogenase in vivo is a necessary requirement for natural resistance to infection with Listeria monocytogenes; Hennebold JD et al.; The results from the present study demonstrate that the innate defense mechanisms which control the progressive growth of Listeria monocytogenes in normal animals in vivo are dependent upon the active catabolism of endogenous glucocorticoids by the enzyme 11 beta-hydroxysteroid dehydrogenase (11 beta-HSD) . When 11 beta-HSD activity was pharmacologically inhibited in vivo, host susceptibility to progressive bacterial disease was markedly increased . Depressed natural resistance following 11 beta-HSD inhibition correlated with changes in the patterns of inducible cytokines by macrophages and T cells . Similar changes were observed when normal adult animals were treated with low doses of dexamethasone prior to experimental infection with Listeria.

Immunopharmacology, 1997 Jan, 35(3), 273 - 82
Effect of hot water extract of Chlorella vulgaris on cytokine expression patterns in mice with murine acquired immunodeficiency syndrome after infection with Listeria monocytogenes; Hasegawa T et al.; We have previously reported that oral administration of hot water extract of Chlorella vulgaris (CVE) enhances resistance to Listeria monocytogenes through augmentation of Listeria-specific cell-mediated immunity in normal mice and mice with murine acquired immunodeficiency syndrome (MAIDS) caused by murine leukemia virus (MuLV) LP-BM5 . To elucidate the mechanisms whereby CVE augments the cell-mediated immunity, we examined the expression patterns of mRNA for cytokines in normal and MAIDS mice given CVE orally after L . monocytogenes infection . The expression levels of IL-1 alpha, IL-12, GM-CSF, MIP and TNF alpha genes were significantly augmented in the peritoneal adherent cells by oral administration of CVE for 2 weeks before Listeria infection . The expression levels of gamma IFN and IL-12 mRNA were significantly higher in the spleen after Listeria infection in CVE-treated mice than in normal mice, while the expression of IL-10 mRNA in the spleen was decreased by CVE administration . In MAIDS mice, oral administration of CVE also augmented the expression of gamma IFN and IL-12 mRNA in the spleen after Listeria infection, while it rather reduced the expression of IL-10 mRNA . These results suggest that CVE may preferentially augment THI responses against Listeria via activation of macrophages to produce IL-12 and enhance host defence against Listeria infection both in normal and MAIDS mice.

Life Sci, 1997, 60(8), 545 - 54
Effect of dietary flaxseed on fatty acid composition, superoxide, nitric oxide generation and antilisterial activity of peritoneal macrophages from female Sprague-Dawley rats; Babu US et al.; The impact of ground flaxseed (FS) or flaxseed meal (FSM) diets on the fatty acid composition and functions of rat peritoneal exudate cells (PEC) was determined . Female weanling Sprague-Dawley rats (10/group) were fed isocaloric AIN-76 diets supplemented with 0.0, 10.0% (w/w) FS or 6.2% (w/w) FSM . At the end of 56-days, rat serum and thioglycollate-elicited PEC were analyzed for total lipid fatty acids . Production of nitric oxide (NO) and superoxide (O2-), Listeria monocytogenes (LM) phagocytic index and antilisterial activity of resident PEC were also assessed . A significant increase in alpha-linolenic (C18:3), eicosapentanoic (C20:5) and docosahexanoic (C22:6) acids, as well as a significant reduction in arachidonic acid (C20:4) was observed in the serum of rats fed 10% FS . Dietary FS caused a significant reduction in palmitic acid (C16:0) and an increase in stearic acid (C18:0) of PEC . Defatted FSM produced a significant increase in long chain fatty acids, which included eicosadienoic acid (C20:2) in PEC and C22:6 in serum . PEC from rats fed 10.0% FS produced significantly less (about 50%) O2- in response to phorbol myristate acetate (PMA), than did PEC from control animals; dietary treatment had no effect on O2- in response to LM . FSM had no impact on the O2- production by PEC in response to PMA or LM . Antilisterial activity of PEC was determined by comparing bacterial uptake after 1 hr with recovery 24 hrs later . Despite comparably equivalent bacterial uptake, few viable intracellular LM were recovered at T = 24 for all test samples, indicating that, regardless of the dietary treatment, PEC were able to handle the in vitro LM infection . This bacterial clearance was accompanied by equivalent NO generation by PEC from each dietary group in response to LM . Summarily, dietary FS produced significant changes in fatty acid composition of serum and PEC, inhibited O2- generation by PEC, and was ineffectual to both NO production by and antilisterial activity of PEC.

Clin Sci (Lond), 1997 Jan, 92(1), 95 - 101
Dietary fish oil reduces survival and impairs bacterial clearance in C3H/Hen mice challenged with Listeria monocytogenes; Fritsche KL et al.; 1 . To investigate the effect of dietary fat source on host resistance to intracellular pathogens, weanling female C3H/Hen mice were fed one of three experimental diets containing, 20% by weight, lard, soybean oil or 17% menhaden fish oil plus 3% corn oil . After 4 weeks, survival of mice (n = 12/treatment group) injected intraperitoneally with 2 x 10(6) colony forming units of live Listeria monocytogenes was determined . In a second study, bacterial clearance from the liver and spleen at 2, 4 and 7 days post-challenge was determined (n = 8/treatment group) . 2 . We found that the survival of mice fed the diets with soybean oil or menhaden fish oil was significantly lower than those fed lard (P < 0.05) . Survival rates were 58% (7/12), 33% (4/12) and 100% (12/12), respectively, for mice fed soybean oil, menhaden fish oil and lard . In the second study, mice fed menhaden fish oil had approximately 1 log10 greater bacteria in their spleens at day 4 than mice fed lard or soybean oil (P < 0.001) . There were no significant treatment differences in the number of bacteria recovered from liver samples . 3 . In summary, dietary fat source significantly affects murine resistance to Listeria, with diets rich in n-3 polyunsaturated fatty acids, such as from fish oil, having the most detrimental effect.

Lett Appl Microbiol, 1997 Jan, 24(1), 65 - 8
A case of foodborne listeriosis in Sweden; Loncarevic S et al.; A 70-year-old woman fell seriously ill overnight with meningitis and was admitted to hospital . Cerebrospinal fluid culture yielded Listeria monocytogenes . One of the first problems in solving a human case of listeriosis suspected to be foodborne is to find the foods likely to have been transmitting L . monocytogenes . Two enrichment procedures and a direct plating procedure were used for isolation of the bacteria from different food items collected from the patient's refrigerator, local retail store and producer . Samples of vacuum-packed products of sliced pork brawn, sliced cooked medwurst and berliner wurst of the same brand harboured L . monocytogenes . Serotyping and restriction enzyme analysis (REA) with pulsed-field gel electrophoresis (PFGE) were used to characterize and compare 41 isolates, including the human strain . At least three clones were present in the foods investigated, and one of these was identical to the human clone . This clone was present in samples of medwurst from the patient's refrigerator and the local retail store . This is, to our knowledge, the first proven foodborne case of listeriosis reported in Sweden.

Lett Appl Microbiol, 1997 Jan, 24(1), 51 - 4
Optimization of the detection of bacteriophages induced from Listeria sp; Lemaitre JP et al.; It is necessary to isolate new phages in order to improve the rate of typeability of Listeria monocytogenes strains . We propose a method which increases the detection of induced phages in the presence of inhibitory substances synthesized or liberated by the cells during phage production . Of the 29 phages isolated, 11 (38%) were detected by the spot-on-the-lawn technique and 18 (62%) were revealed by the soft-agar technique . To increase the rate of phage detection, both techniques appear useful . Listeria cultures were subjected to phage typing procedures utilizing these newly isolated phages and the French International set of phages . It appears that the newly isolated phages are good tools for the differentiation of Listeria strains . Among them, one phage seems to be complementary to the French International set.

Eur J Haematol, 1997 Jan, 58(1), 46 - 50
2-Chlorodeoxyadenosine in the treatment of relapsed/refractory chronic lymphoproliferative disorders; Rondelli D et al.; 2-Chlorodeoxyadenosine (2-CdA) is a purine analog with cytotoxic activity on both resting and cycling lymphocytes which has been used as salvage therapy in advanced/resistant chronic lymphoproliferative disorders . In our study 39 patients (19 B-CLL, 5 B-PLL, 9 low-grade B-NHL, 5 CTCL and 1 high-grade T-NHL) who relapsed or became resistant after 1-4 chemotherapy regimens were treated with 2-CdA 6 mg/m2 per day by 2 h infusion for 5 d every 28 d . The overall clinical response rate, including complete remission (CR) and partial remission (PR), was 66% . Two of 19 (10%) B-CLL patients achieved a CR lasting 9 months, while 11/19 B-CLL (58%) and 4/5 B-PLL (3 B-PLL/B-CLL and 1 B-PLL) (80%) achieved a PR . Interestingly, 5 of 6 patients who had been previously treated with fludarabine obtained a clinical response (2 CR and 3 PR) . One of 9 (11%) low-grade B-NHL patients achieved a CR and relapsed after 26 months, and 5/9 (55%) achieved a PR . One of 5 (20%) CTCL achieved a CR lasting 32 months, while 2/5 (40%) achieved a PR . The overall mean duration of PR was 7.4 months and no differences were observed among different groups of patients . Toxicity was acceptable, as only a transient severe hematological impairment was observed in 20% of the patients while nonhematological toxicity was not documented . Two patients died because of bacterial pneumonia, 1 of meningitis due to Listeria and 9 from progression of the disease . In conclusion, treatment with 2-CdA in heavily pretreated patients with chronic lymphoproliferative disorders is well tolerated and obtains high response rates, even in patients relapsed after treatment with fludarabine.

Antimicrob Agents Chemother, 1997 Jan, 41(1), 60 - 5
Comparative activities of new fluoroquinolones, alone or in combination with amoxicillin, trimethoprim-sulfamethoxazole, or rifampin, against intracellular Listeria monocytogenes; Michelet C et al.; We studied the activities of the new fluoroquinolones clinafloxacin, levofloxacin, ofloxacin, and sparfloxacin alone or in combination on the intracellular growth of Listeria monocytogenes . Against intracellular growth of the four strains tested, a similar reduction of the bacterial count was obtained with clinafloxacin at the dose of 10 x MIC (delta log10 CFU/ml = -2.19 +/- 0.24), with levofloxacin at 8 x MIC (delta log10 CFU/ml = -2.28 +/- 0.25), and with sparfloxacin at 4 x MIC (delta log10 CFU/ml = -2.16 +/- 0.21) after 24 h of incubation . The combination of the quinolones with trimethoprim-sulfamethoxazole or amoxicillin did not show a substantial increase in activity compared to the fluoroquinolone alone . Antagonism with rifampin was strongly suggested . No modification of the MIC was observed after 20 successive infections of HeLa cells and contact with subinhibitory concentrations of clinafloxacin, levofloxacin, and sparfloxacin for 24 h . We conclude that clinafloxacin, levofloxacin, or sparfloxacin could represent a therapeutic alternative to amoxicillin for the treatment of Listeria infections in adults, especially clinafloxacin, whose MIC is low (0.06 to 0.12 micrograms/ml), and whose best activity against intracellular L . monocytogenes was obtained at a concentration of 1.2 micrograms/ml, which is similar to clinically achievable levels . The results must be confirmed in an experimental model.

Appl Environ Microbiol, 1997 Jan, 63(1), 310 - 3
A nucleic acid sequence-based amplification system for detection of Listeria monocytogenes hlyA sequences; Blais BW et al.; A nucleic acid sequence-based amplification system primarily targeting mRNA from the Listeria monocytogenes hlyA gene was developed . This system enabled the detection of low numbers (< 10 CFU/g) of L . monocytogenes cells inoculated into a variety of dairy and egg products after 48 h of enrichment in modified listeria enrichment broth.

J Immunol, 1997 Jan 1, 158(1), 359 - 66
Antigen-driven but not lipopolysaccharide-driven IL-12 production in macrophages requires triggering of CD40; DeKruyff RH et al.; We demonstrated that two distinct pathways exist for the induction of IL-12 in APC . The first pathway for IL-12 production occurred during responses to T cell-dependent Ags such as OVA and required triggering of CD40 molecules on the APC . IL-12 production in this T cell-dependent system increased in direct proportion to Ag concentration and required TCR ligation but not CD28 costimulation . The second pathway occurred when bacterial products such as LPS or heat-killed Listeria monocytogenes were used to activate macrophages to produce IL-12 in the complete absence of T cells . In this second pathway, IL-12 production was completely independent of CD40 triggering . In both pathways, the presence of IFN-gamma was not required for induction of IL-12 synthesis when splenic adherent cells (SAC) from normal mice were used . However, addition of IFN-gamma to cultures of Th2 T cells and SAC increased IL-12 production two- to fivefold, and addition of rTNF-alpha with IFN-gamma further enhanced IL-12 production . The addition of TNF-alpha in the absence of IFN-gamma, however, had no effect on IL-12 production in the T cell-dependent pathway . Similarly, addition of TNF-alpha in the presence or the absence of IFN-gamma to cultures of LPS or heat-killed Listeria and SAC did not increase IL-12 production, but addition of IFN-gamma alone greatly enhanced IL-12 production, consistent with the idea that bacterial stimuli induce significant quantities of endogenous TNF-alpha production . These results indicate that the requirements for the induction of IL-12 production in T cell-dependent and T cell-independent responses differs mainly with regard to CD40 triggering . Furthermore, these results suggest that IL-12 production can be induced by bacterial products in patients with hyper-IgM syndrome who lack CD40 ligand expression and in those treated with soluble gp39 to interrupt CD40-CD40 ligand interactions.

J Immunol, 1997 Jan 1, 158(1), 287 - 93
Immune CD8+ T lymphocytes lyse Listeria monocytogenes-infected hepatocytes by a classical MHC class I-restricted mechanism; Jiang X et al.; Hepatocytes constitute the principal site of listerial replication in the livers of mice infected i.v . CD8+ T lymphocytes play a predominant role in the host defenses to Listeria monocytogenes . In vitro experiments by others undertaken to delineate the functions of CD8+ T lymphocytes have focused primarily on their interaction with Listeria-infected macrophages . Such experiments do not address directly the role of CD8+ T lymphocytes in eliminating the bulk of Listeria replicating within the liver . Here, we report that immune CD8+ T cells at an E:T cell ratio > or = 10:1 lysed Listeria-infected hepatocytes as judged by the following two criteria . Aspartate aminotransferase activity in the culture supernatants, indicative of hepatocyte damage, increased significantly . Conversely, infected hepatocytes cocultured with immune CD8+ T cells exhibited a marked reduction in viable intracellular Listeria assessed by CFUs . Neither immune CD4+ T cells nor nonimmune CD8+ T cells caused a similar increase in aspartate aminotransferase activity released or a decrease in intracellular bacteria . Immune CD8+ T cell-mediated lysis of infected hepatocytes was restricted by classical MHC class I (H-2Kb) molecules and was inhibited by the presence of either brefeldin A or mAb specific for CD8 . These results suggest that the predominant role of CD8+ T lymphocytes in host resistance to listerial infections of the liver may be due to their capacity to lyse infected hepatocytes.

Infect Immun, 1997 Jan, 65(1), 101 - 9
Identification and characterization of a novel PrfA-regulated gene in Listeria monocytogenes whose product, IrpA, is highly homologous to internalin proteins, which contain leucine-rich repeats; Domann E et al.; The expression of all virulence factors in Listeria monocytogenes characterized to date is controlled by the virulence regulator protein, PrfA . To identify further PrfA-regulated proteins, we examined supernatants of L . monocytogenes EGD harboring additional copies of the PrfA regulator for the presence of novel proteins . This led to the identification and biochemical purification of a hitherto uncharacterized PrfA-dependent 30-kDa protein (A . Lingnau, T . Chakraborty, K . Niebuhr, E . Domann, and J . Wehland, Infect . Immun . 64:1002-1006, 1996) . Oligonucleotide primers derived from internal peptide sequences of this protein allowed the cloning and determination of the entire sequence of the respective gene . The protein comprised 297 amino acids with strong overall homology to the internalins, InlA and InlB, particularly in the region harboring the leucine-rich repeats . The gene has been designated irpA for internalin-related protein A gene . Transcriptional studies revealed that the gene was monocistronic and, like the inlA and inlB genes, was transcribed by PrfA-dependent and PrfA-independent mechanisms . Monoclonal antibodies raised against IrpA indicated that it was produced by L . monocytogenes but not by the nonpathogenic species Listeria innocua . To examine the role of IrpA in pathogenesis, we constructed an isogenic in-frame deletion mutant that removed all but 116 amino acids of the IrpA protein . This mutant was neither defective for invasion into many tissue culture cell lines nor did it demonstrate reduced intracellular survival . However, in vivo studies using the mouse infection model revealed that the irpA mutant showed reduced virulence compared to the parental strain . These results suggest a role for IrpA during disseminated infection by L . monocytogenes.

Infect Immun, 1997 Jan, 65(1), 78 - 88
Host cell heparan sulfate proteoglycans mediate attachment and entry of Listeria monocytogenes, and the listerial surface protein ActA is involved in heparan sulfate receptor recognition; Alvarez-Dominguez C et al.; The mechanisms by which the intracellular pathogen Listeria monocytogenes interacts with the host cell surface remain largely unknown . In this study, we investigated the role of heparan sulfate proteoglycans (HSPG) in listerial infection . Pretreatment of bacteria with heparin or heparan sulfate (HS), but not with other glycosaminoglycans, inhibited attachment and subsequent uptake by IC-21 murine macrophages and CHO epithelial-like cells . Specific removal of HS from target cells with heparinase III significantly impaired listerial adhesion and invasion . Mutant CHO cells deficient in HS synthesis bound and internalized significantly fewer bacteria than wild-type cells did . Pretreatment of target cells with the HS-binding proteins fibronectin and platelet factor 4, or with heparinase III, impaired listerial infectivity only in those cells expressing HS . Moreover, a synthetic peptide corresponding to the HS-binding ligand in Plasmodium falciparum circumsporozoite protein (pepPf1) inhibited listerial attachment to IC-21 and CHO cells . A motif very similar to the HS-binding site of pepPf1 was found in the N-terminal region of ActA, the L . monocytogenes surface protein responsible for actin-based bacterial motility and cell-to-cell spread . In the same region of ActA, several clusters of positively charged amino acids which could function as HS-binding domains were identified . An ActA-deficient mutant was significantly impaired in attachment and entry due to altered HS recognition functions . This work shows that specific interaction with an HSPG receptor present on the surface of both professional and nonprofessional phagocytes is involved in L . monocytogenes cytoadhesion and invasion and strongly suggests that the bacterial surface protein ActA may be a ligand mediating HSPG receptor recognition.

Infect Immun, 1997 Jan, 65(1), 72 - 7
Requirement of the initial production of gamma interferon in the generation of protective immunity of mice against Listeria monocytogenes; Yang J et al.; Protective immunity of mice against Listeria monocytogenes, which is mediated mainly by gamma interferon (IFN-gamma)-producing T cells, was induced by immunization with viable bacteria but not with killed bacteria . By comparing mice immunized with either viable or killed L . monocytogenes, it was found that IFN-gamma was produced at the initial stage only after immunization with viable bacteria . This finding prompted us to investigate the effect of neutralizing the IFN-gamma on the final generation of protective T cells against L . monocytogenes . When endogenous IFN-gamma was neutralized by administration of anti-IFN-gamma monoclonal antibody for the initial 2 days in mice immunized with viable bacteria, the generation of protective T cells on day 6 was completely blocked, as revealed by T-cell adoptive transfer . The generation of listeria-specific IFN-gamma-producing T cells was also abolished . These results clearly demonstrated that endogenous IFN-gamma, which is produced at the initial stage of immunization, actually plays a critical role in the generation of protective T cells against L . monocytogenes in vivo . Moreover, this study suggested that the lack of IFN-gamma-inducing ability is responsible for the inability of killed L . monocytogenes to induce protective T cells in mice.

J Clin Microbiol, 1997 Jan, 35(1), 179 - 83
Isolation of catalase-negative Listeria monocytogenes strains from listeriosis patients and their rapid identification by anti-p60 antibodies and/or PCR; Bubert A et al.; Two catalase-negative Listeria monocytogenes serovar 1/2b strains were isolated from listeriosis patients in 1995 in Germany . The infections appeared in individuals from different cities at different seasons and were caused by L . monocytogenes strains of different clonal types . In particular, the catalase reaction of one strain isolated from blood was consistently negative, whereas this reaction was only reversibly blocked when the strain was freshly isolated from ascitic fluid . After subculturing, the catalase-positive reaction was restored . Initially, identification of these isolates was difficult to achieve not only because of the lack of a catalase reaction, which generally distinguishes L . monocytogenes from other morphologically similar pathogenic gram-positive bacteria, but also because other routinely used biochemical tests such as CAMP and the commercial API test gave unclear results . However, rapid and unequivocal identification of these strains was possible by analyzing secretions of the p60 protein in culture supernatants by enzyme-linked immunosorbent assay or Western blot (immunoblot) analysis with our recently developed Listeria- and L . monocytogenes-specific anti-p60 antibodies . Additionally, the identifications were confirmed by Listeria- and L . monocytogenes-specific PCR analyses with primers derived from the iap, hly, and prfA genes . Immunoanalyses also allowed for the differentiation of these two strains, whereas no differentiation was possible by PCR when the internal, variable repetitive iap gene portion was analyzed . However, size variations of the PCR products comprising these gene portions which were obtained from a number of L . monocytogenes strains belonging to the same serotypes indicated that this type of PCR is not only useful for specific identifications but may be used in parallel as an additional marker for epidemiological studies . In conclusion, the data suggest that catalase production should not be taken as a strict criterion for the identification of listeriae . Furthermore, at least the infection caused by the stably catalase-negative strain supports the notion that catalase does not seem to be necessary for the intracellular growth of L . monocytogenes.

FEMS Immunol Med Microbiol, 1996 Dec 31, 16(3-4), 291 - 8
The protective role of endogenous cytokines in host resistance against an intragastric infection with Listeria monocytogenes in mice; Nishikawa S et al.; It has been demonstrated that endogenous cytokines including gamma-interferon (IFN-gamma), tumour necrosis factor-alpha (TNF-alpha), and interleukin-6 (IL-6) play a protective role but that IL-4 plays a detrimental role in systemic Listeria monocytogenes infection in mice . The diverse roles of IL-10 have been reported in antilisterial resistance . In this paper, we studied the role of endogenous cytokines in host resistance against an intragastric infection with L . monocytogenes in mice . The expression of cytokine mRNAs including IFN-gamma, TNF-alpha, IL-4, IL-6, or IL-10, which were amplified by reverse transcription-PCR, was observed in intestinal intraepithelial lymphocytes irrespective of L . monocytogenes infection . Increased numbers of L . monocytogenes were detected in the ileal contents of infected mice which received monoclonal antibodies (mAbs) against IFN-gamma, TNF-alpha, IL-4, IL-6, or IL-10 . By contrast, mAbs against IL-4 or IL-6 showed little effect on the growth of L . monocytogenes in the mesenteric lymph nodes (MLNs), spleen, and liver, but anti-IFN-gamma mAb and anti-TNF-alpha mAb suppressed the defense in these organs . Anti-IL-10 mAb enhanced bacterial elimination from the MLNs but not from the spleen or liver . These results suggest that the role of endogenous cytokines may differ between systemic and intestinal defenses.

FEMS Immunol Med Microbiol, 1996 Dec 31, 16(3-4), 257 - 66
Involvement of various combinations of endogenous inflammatory cytokines in Listeria monocytogenes-induced expression of inducible nitric oxide synthase in mice; Xiong H et al.; Using a in vitro infection of spleen cells with Listeria monocytogenes, the relationship between endogenous cytokines and the expression of inducible nitric oxide synthase (iNOS) was examined . When all interferon (IFN)-gamma, tumor necrosis factor (TNF)-alpha and interleukin (IL)-1 alpha, or the combination of IFN-gamma with either TNF-alpha or IL-1 alpha were neutralized by antibodies, there was a significant reduction of iNOS expression and nitrite production in culture . However, there was no reduction of iNOS expression and nitrite production when these cytokines were individually neutralized . After the depletion of natural killer cells, there was no change in the expression of Listeria-induced iNOS and nitrite production although the IFN-gamma production was abrogated . Neutralization of TNF-alpha and IL-1 alpha in natural killer cell-depleted culture resulted in the reduction of iNOS expression . Thus, various combinations of cytokines to play an important role in iNOS induction by L . monocytogenes.

FEMS Immunol Med Microbiol, 1996 Dec 31, 16(3-4), 213 - 22
Expression of listeriolysin O by intracellular Listeria monocytogenes following infection of lipopolysaccharide-treated or untreated J774.1 macrophage-like cells; Moriishi K et al.; Listeria monocytogenes replicates in a phagocytic cell following escape into the host cytoplasm . Listeriolysin O, secreted by L . monocytogenes, which belongs to the thiol-activated hemolysin family, is known to play an important role in the escape of the bacterium into the host cytoplasm . In this study, we demonstrated that expression of listeriolysin O by infecting L . monocytogenes was lightly induced in J774.1 macrophage-like cells pretreated with lipopolysaccharide, although the growth of the bacteria was suppressed . The number of viable L . monocytogenes decreased until 4 h post-infection and then increased between 4 and 8 h post-infection in untreated J774.1 host cells, but it decreased until 8 h post-infection in lipopolysaccharide-treated host cells . However, expression of listeriolysin O by L . monocytogenes was not induced in the untreated host cells, while it increased 0 and 4 h post-infection in the lipopolysaccharide-treated host cells . Expression of listeriolysin O mRNA in the lipopolysaccharide-like cells . These results suggest that macrophage activation induced with lipopolysaccharide could lead to the expression of the listeriolysin O gene and the synthesis of listeriolysin O protein under suppression of the intracellular growth of L . monocytogenes.

J Dairy Sci, 1996 Dec, 79(12), 2189 - 95
Bovine mastitis caused by Listeria monocytogenes: kinetics of antibody responses in serum and milk after experimental infection; Bourry A et al.; The kinetics of antibodies in serum and milk directed against proteins from Listeria monocytogenes were studied using 4 lactating cows after infection was experimentally induced in the udder with four strains of serotypes 4b or 1/2a . Antibodies (IgG and IgA) in samples of composite quarter milk and serum of the cow were measured by indirect ELISA . Microtiter plates were coated with proteins obtained from the culture supernatant of L . monocytogenes 4b . After challenge, an IgG response in serum and milk to listerial infections in the udder occurred for all cows, although the response varied among cows . In sera, the IgG titers reached a peak at 9 to 13 wk after challenge and remained elevated until 21 to 33 wk after challenge . In milk, the IgG titer increased significantly 3 wk after the challenge for all cows . A weak and nonpersistent increase in IgA antibodies also occurred . These results indicate that IMI by L . monocytogenes induced an increase of antibodies in milk, which could be detected with an ELISA test using our antigenic preparation . Therefore, this antigenic preparation could be used for the evaluation of a new method of diagnosis for bovine mastitis caused by L . monocytogenes.

Immunology, 1996 Dec, 89(4), 532 - 8
Th0-like CD4+ T cells protect mice with murine retrovirus-induced immunodeficiency syndrome (MAIDS) against co-infection with Listeria monocytogenes; Hiromatsu K et al.; We examined the host defence mechanism against infection with Listeria monocytogenes, a facultative intracellular bacterium, in mice with murine acquired immunodeficiency syndrome (MAIDS) caused by LP-BM5 murine leukaemia virus (MuLv) infection . Although LP-BM5 MuLV infection in C57BL/6 mice leads to a stage of immunodeficiency characterized by severe compromise of cell-mediated immunity, the mice with established MAIDS infected with LP-BM5 8 weeks previously, showed resistance to an intraperitoneal infection with Listeria monocytogenes . These MAIDS mice also showed resistance to a lethal dose of secondary listerial challenge, while the delayed-type hypersensitivity response to heat-killed Listeria (HKL.) was severely impaired in MAIDS mice . The resistance of MAIDS mice to listerial infection was mediated by CD4+ alpha beta T cells but neither by gamma delta T cells nor natural killer (NK) cells . Interferon-gamma (IFN-gamma) and interleukin-10 (IL-10) were produced by CD4+ T cells from Listeria-infected MAIDS mice in response to the in vitro stimulation with HKL, whereas IFN-gamma but not IL-10 were produced by those from Listeria-infected control mice . These results suggest that T-helper 0 (Th0)-like immune responses of CD4+ T cells occur and participate in host defence mechanisms against listerial infection in MAIDS mice.

Epidemiol Infect, 1996 Dec, 117(3), 437 - 42
Listeria species in domestic environments; Beumer RR et al.; Using a direct isolation method Listeria spp . were detected in 101 (47.4%) of 213 houses investigated . L . monocytogenes was present in 45 houses (21.1%) . Listeria spp . occurred at all sampling sites . Dish-cloths (37%) and surface samples round the drain in the bathroom (27.2%) were most frequently contaminated . Highest numbers (c . 10(4) c.f.u./object) were found in dish-cloths and washing-up brushes . Lower levels (up to 10(3) c.f.u./object) were obtained from kitchen sinks, refrigerator vegetable compartment samples and tooth brushes . In total, 132 isolations of Listeria spp . were made from 871 samples . L . innocua (53%) and L . monocytogenes (41%) were the predominant species in the positive samples . Other Listeria spp . were found in only 6% of the positive samples.

Epidemiol Infect, 1996 Dec, 117(3), 429 - 36
A foodborne outbreak of gastroenteritis involving Listeria monocytogenes; Salamina G et al.; An outbreak of gastroenteritis occurred in Italy among 39 persons who had attended a private supper . All guests were previously healthy, young, non-pregnant adults; 18 (46%) had symptoms, mostly gastrointestinal (78%), with a short incubation period . Four were hospitalized with acute febrile gastroenteritis, two of whom had blood cultures positive for Listeria monocytogenes . No other microorganisms were recovered from the hospitalized patients' specimens . Epidemiological investigation identified rice salad as the most likely vehicle of the food-borne outbreak . L . monocytogenes was isolated from three leftover foods, the kitchen freezer and blender . Isolates from the patients, the foods and the freezer were indistinguishable: serotype 1/2b, same phage type and multilocus enzyme electrophoretic type . Eight (36%) of 22 guests tested were found to have antibodies against L . monocytogenes, compared with none of 11 controls from the general population . This point source outbreak was probably caused by infection with L . monocytogenes . Unusual features included the high attack rate among immunocompetent adults and the predominance of gastrointestinal symptoms.

J Appl Bacteriol, 1996 Dec, 81(6), 641 - 50
The incidence and level of Listeria monocytogenes contamination of food sources at primary production and initial processing; Fenlon DR et al.; Listeria monocytogenes was isolated in low numbers from a variety of environmental samples associated with the primary production of food, including vegetation, faeces and meat . The organism was rarely detected on growing grass and vegetables prior to processing . The excretion of L . monocytogenes by farm animals was linked to their diet, with animals fed entirely on hay or manufactured diets not excreting detectable levels of Listeria (i.e . absence in 25 g) . However, animals fed on silage, which is frequently contaminated with L . monocytogenes, commonly excreted the organism . Transport of live animals over long distances (> 100 km) significantly increased the level of excretion of Listeria, but the contamination of carcasses of sheep and cattle was not high . Pigs and poultry faeces were free of Listeria prior to slaughter and pig carcasses were not found to have Listeria present . Frozen and chilled chicken did show detectable levels reflecting the greater potential for contamination during poultry processing . Samples of minced beef were tested and 21 of 23 samples were positive for L . monocytogenes, demonstrating that processing significantly increases the level of contamination compared to whole carcasses . Multilocus enzyme electrophoresis of a representative selection of the isolates showed that there was a wide range of electrophoretic types present in the primary production environment, relatively few of which have been linked to cases of human listeriosis . However, these types do arise on farms and occasional contamination of food raw material by potentially virulent strains may be sufficient to allow adaptable strains to become established in the processing environment and thus be responsible for more widespread contamination of the food available to the consumer.

Biophys J, 1996 Dec, 71(6), 3030 - 45
Cell motility driven by actin polymerization; Mogilner A et al.; Certain kinds of cellular movements are apparently driven by actin polymerization . Examples include the lamellipodia of spreading and migrating embryonic cells, and the bacterium Listeria monocytogenes, that propels itself through its host's cytoplasm by constructing behind it a polymerized tail of cross-linked actin filaments . Peskin et al . (1993) formulated a model to explain how a polymerizing filament could rectify the Brownian motion of an object so as to produce unidirectional force (Peskin, C., G . Odell, and G . Oster . 1993 . Cellular motions and thermal fluctuations: the Brownian ratchet . Biophys . J . 65:316-324) . Their "Brownian ratchet" model assumed that the filament was stiff and that thermal fluctuations affected only the "load," i.e., the object being pushed . However, under many conditions of biological interest, the thermal fluctuations of the load are insufficient to produce the observed motions . Here we shall show that the thermal motions of the polymerizing filaments can produce a directed force . This "elastic Brownian ratchet" can explain quantitatively the propulsion of Listeria and the protrusive mechanics of lamellipodia . The model also explains how the polymerization process nucleates the orthogonal structure of the actin network in lamellipodia.

Fundam Appl Toxicol, 1996 Dec, 34(2), 228 - 39
Immune function and host defense in rodents exposed to 60-Hz magnetic fields; House RV et al.; This study was conducted to evaluate the influence of subchronic exposure to pure, linearly polarized 60-Hz magnetic fields (MF) on the host immune response in mice . The experimental design was as follows: three groups were exposed continuously (18.5 hr/day) to MF at field strengths of 0.02, 2, or 10 gauss (G), one group was exposed intermittently (1 hr on/1 hr off) to MF at a field strength of 10 G, and one group served as a sham control . Experimental endpoints included spleen and thymus weights and cellularity, antibody-forming cell (AFC) response, delayed-type hypersensitivity (DTH) response, splenic lymphocyte subset analysis, susceptibility to infection with Listeria monocytogenes, and natural killer (NK) cell activity . No differences in body weight, lymphoid organ weight, or lymphoid organ cellularity were observed in any MF-exposed group in comparison to sham controls . Likewise, no statistically significant differences were found in comparisons of AFC responses . Isolated statistically significant differences from control were observed in MF-exposed mice in the DTH assay, although no clear dose-related pattern of altered activity was seen . Splenic lymphocyte subset parameters examined were within normal limits in all groups, and no differences between control and MF-exposed mice were found . Host resistance to bacterial infection was not altered at any MF exposure examined in this study . Finally, although apparently dose-related, statistically significant alterations were observed in an initial study of NK cell function, repeat studies failed to demonstrate a consistent pattern of alteration.

Appl Environ Microbiol, 1996 Dec, 62(12), 4410 - 6
Purification and amino acid sequences of piscicocins V1a and V1b, two class IIa bacteriocins secreted by Carnobacterium piscicola V1 that display significantly different levels of specific inhibitory activity; Bhugaloo-Vial P et al.; Two bacteriocins produced by Carnobacterium piscicola V1 were purified and characterized . Piscicocin V1a (molecular mass = 4,416 Da) and piscicocin V1b (molecular mass = 4,526 Da) are nonlantibiotic, small, heat-stable antibacterial peptides . Piscicocin V1b is identical to carnobacteriocin BM1, while piscicocin V1a is a new bacteriocin . Its complete sequence of 44 amino acid residues has been determined . Piscicocin V1a belongs to the class IIa bacteriocins having the consensus YGNGV motif . These peptides inhibit various gram-positive bacteria, including Listeria monocytogenes . Piscicocin V1a is approximately 100 times more active than piscicocin V1b against indicator strains . However, the antagonistic spectrum is the same for both piscicocins . Comparison of these results with the analysis of the amino acid sequence and secondary structure predictions suggests that (i) the conserved N-terminal conserved domain is involved in the receptor recognition and therefore in an "all-or-none" response against target bacterial cells and (ii) the C-terminal variable and hydrophobic domain determines membrane anchoring and therefore the intensity of the antagonist response.

Infect Immun, 1996 Dec, 64(12), 5439 - 41
Either B7-1 or B7-2 is required for Listeria monocytogenes-specific production of gamma interferon and interleukin-2; Zhan Y et al.; Listeria infection results in the induction of gamma interferon (IFN-gamma)-producing T lymphocytes . Blocking of the costimulatory molecule B7 in vivo led to a marked decrease in antigen-specific production of IFN-gamma and interleukin-2 by lymphocytes . Blocking of both B7-1 (CD80) and B7-2 (CD86) was required in order to inhibit cytokine production, indicating that either molecule could act alone . Although IFN-gamma production by cultured spleen cells was significantly suppressed by B7 blocking, mice cleared primary and secondary Listeria infection as effectively as control mice.

Infect Immun, 1996 Dec, 64(12), 5430 - 3
Antibodies to the leucine-rich repeat region of internalin block entry of Listeria monocytogenes into cells expressing E-cadherin; Mengaud J et al.; Internalin, a surface protein essential for entry of Listeria monocytogenes EGD into epithelial cells, was used as an antigen to raise nine monoclonal antibodies . These monoclonal antibodies recognized seven distinct epitopes which were located in three different regions of the protein . Three of them inhibited internalin-mediated entry and recognized the amino-terminal leucine-rich repeat region of the protein, suggesting that this region is essential for entry.

J Immunol, 1996 Dec 1, 157(11), 4746 - 50
IL-4 neutralization or TNF-alpha treatment ameliorate disease by an intracellular pathogen in IFN-gamma receptor-deficient mice; Szalay G et al.; Successful control of infectious disease depends on aquisition of an appropriate protective immune response . IFN-gamma, first produced by NK cells and then by Th1 cells, is central to acquired resistance against intracellular bacteria, including Listeria monocytogenes . In contrast, IL-4 is not generated to a measurable degree . Here we show that IL-4 is produced during listeriosis by IFN-gamma receptor gene disruption (IFN-gammaR(-/-)) mutant mice . Production of TNF was diminished, whereas IL-12 production was virtually unchanged in these mutants . Neutralization of IL-4 with anti-IL-4 mAb, as well as TNF-alpha reconstitution with rTNF-alpha, ameliorated listeriosis . These findings demonstrate the detrimental effects of IL-4 in listeriosis independent of IFN-gamma down-regulation and document the far-reaching consequences of a single cytokine deficiency on other cytokines . In cases where the primary gene defect cannot be restored, precise identification of secondary effects will promote rational immunotherapy based on neutralization or reconstitution of secondary immune deviations.

Endocrinology, 1996 Dec, 137(12), 5250 - 4
Induced illness in interleukin-6 (IL-6) knock-out mice: a causal role of IL-6 in the development of the low 3,5,3'-triiodothyronine syndrome; Boelen A et al.; Interleukin-6 (IL-6) administration to human subjects or experimental animals induces changes in thyroid hormone metabolism resembling those in the sick euthyroid syndrome . Furthermore, the decrease in serum T3 during illness is significantly related to serum IL-6 concentrations . These findings suggest, but do not prove, a causal role for IL-6 in the development of the low T3 syndrome . The aim of the present study was to evaluate the role of IL-6 in the development of the sick euthyroid syndrome in IL-6 knock-out (IL-6(-/-)) mice compared to that in wild-type mice (IL-6(+/+)) . Illness was induced in IL-6(-/-) and IL-6(+/+) mice by 1) administration of bacterial endotoxin (LPS), 2) infection with Listeria monocytogenes, and 3) turpentine injection in both hind limbs . Food intake was kept similar in both groups in all three experiments . Serial measurements were made of serum IL-6, tumor necrosis factor-alpha, T3, T4, corticosterone, and liver 5'-deiodinase (5'-DI) messenger RNA (mRNA) for 24 h (LPS), 96 h (L . monocytogenes), and 48 h (turpentine) . Serum IL-6 increased in response to all stimuli in IL-6(+/+) mice, but not in IL-6(-/-) mice . Serum tumor necrosis factor-alpha was induced by LPS in both groups to a similar extent, but did not rise after L . monocytogenes or turpentine administration . Serum T3 and T4 decreased after all three stimuli . The decrease in serum T4 in IL-6(-/-) was similar to that in IL-6(+/+) mice . The decrease in serum T3, however, was smaller in the IL-6(-/-) mice than in the IL-6(+/+) mice; T3 levels were 1.56 +/- 0.29 and 0.99 +/- 0.15 nmol/liter, respectively, 24 h after LPS treatment (P < 0.01), 2.39 +/- 0.17 and 1.75 +/- 0.24 nmol/liter 96 h after L . monocytogenes treatment (P < 0.01), and 1.46 +/- 0.18 and 1.10 +/- 0.25 nmol/liter 48 h after turpentine treatment (P < 0.05) . The smaller fall in serum T3 in IL-6(-/-) mice could not be attributed to differences in the severity of the induced illness, food intake, or corticosterone response, which were all similar in IL-6(-/-) mice and IL-6(+/+) mice . Liver 5'-deiodinase mRNA decreased after all three stimuli; the decrease after LPS and L . monocytogenes infection was smaller in the IL-6(-/-) mice, but the difference in IL-6(+/+) mice just failed to reached statistical significance . Liver 5'-deiodinase activity after turpentine injection administration decreased in the wild-type animals by 36%, but did not change in the knock-out mice . In conclusion, acutely induced illness generates the low T3 syndrome, which is less marked in IL-6 knock-out mice than in wild-type mice . The data suggest a causal role of IL-6 in the development of the low T3 syndrome.

Int J Food Microbiol, 1996 Dec, 33(2-3), 293 - 300
Multiplex PCR assay for the routine detection of Listeria in food; Bansal NS et al.; The development and validation of a multiplex PCR assay for the detection of Listeria that can be employed in routine investigation of food samples are described . The assay, which employs a short culture enrichment step followed by isolation of bacterial cells and detection by multiplex PCR reaction, is highly sensitive and specific for the detection of Listeria monocytogenes and all other Listeria species . Over 350 food samples were tested in parallel by standard cultural procedures and the PCR assay, with no false-positive or false-negative results obtained with the PCR assay . Compared to the standard cultural methods the PCR assay is highly sensitive, cost effective and extremely rapid with results obtained within 48 h from sample receipt.

Int J Food Microbiol, 1996 Dec, 33(2-3), 195 - 207
Antimicrobial activity of hop extracts against Listeria monocytogenes in media and in food; Larson AE et al.; Growth of Listeria monocytogenes was inhibited in culture media and in certain foods by four hop extracts (I-IV) containing varying concentrations of alpha-and beta-acids . Extracts (II and III) containing the highest concentrations of beta-acids were inhibitory at 0.01 mg/l in trypticase soy broth . In food, these hop extracts showed varying magnitudes of inhibition . In coleslaw, hop extract III at 1 mg/g enhanced the rate of inactivation of L . monocytogenes Scott A . Hop extract II was inhibitory at 0.1 and 1 mg/ml in skim and 2% milk, and was inhibitory at 1 mg/ml in whole milk . Hop extract II was listericidal in cottage cheese at 0.1 to 3 g/kg . No inhibition of L . monocytogenes by hop extract III was observed in Camembert cheese . Overall, the antimicrobial activity of hop extracts in food appeared to increase with acidity and lower fat content . Our results indicate that hop extracts could be used to control L . monocytogenes in minimally processed food with low fat content.

J Immunol Methods, 1996 Nov 29, 199(1), 5 - 25
A method to recover, enumerate and identify lymphomyeloid cells present in an inflammatory dermal site: a study in laboratory mice; Belkaid Y et al.; We describe a new method to recover and study cells present in the dermis of mouse ear at homeostasis or after intradermal injection of disturbing agents (lipopolysaccharide or Listeria monocytogenes) . The ears either left untreated or inoculated were handled and processed as culture explants of the dorsal and ventral leaflets, their dermal sides being spread on a buffered medium . Within this medium emigrate/sediment, with different kinetics: neutrophils, mononuclear phagocytes, dendritic leucocytes, T lymphocytes expressing either gamma delta or alpha beta TCRs, and other minor subsets, the identification of which deserves more relevant reagents: they are likely to be NK, mast cells, eosinophils and their local progenitors . All the major subsets were identified through a combination of immunocytochemical and flow cytometry labeling . Two examples illustrating the advantages and limitations of this new method are given: either 1 microgram of LPS or 10(4) Listeria monocytogenes were injected within the ear 48, 24, 12, 6, 3 h before ear explant culture . This ear explant culture has been further compared to the ear sheet treatment with collagenase/disease for three cell populations, the epidermal dendritic leucocytes, the gamma delta epidermal T cells as well as the alpha beta T cells recirculating within the steady state dermis . This method provides the first evidence of the existence of recirculating T CD4 lymphocytes in the mouse dermis.

Dtsch Tierarztl Wochenschr, 1996 Nov, 103(11), 460 - 2
{Listeriosis in a rabbitry}; Peters M et al.; An enzootic of listeriosis in a rabbitry is reported . Listeria monocytogenes serotype 1/2a was isolated from the organs of a doe, which had died of septic metritits . From aborted fetuses of two other does Listeria monocytogenes serotype 1/2b and 4b were cultured, respectively . In feed samples of the rabbitry Listeria monocytogenes strains of the serotypes 1/2b and 4b besides the apathogenic Listeria species Listeria seeligeri and Listeria innocua were detected . Serological studies with agglutination test and complement fixation test on double serum samples of does, which had aborted, pointed to listeric infections as the cause of abortion . A doe, which had aborted and failed to become pregnant again, showed serosal adhesions of both uterine tubes and a sterile pyometra . Therefore, previous infection of the uterus by Listeria monocytogenes should be considered as a cause of infertility.

Med Microbiol Immunol (Berl), 1996 Nov, 185(3), 131 - 7
Superinfection by Listeria monocytogenes of cultured human enterocyte-like cells infected with poliovirus or rotavirus; Superti F et al.; A mixed infection with either rotavirus or poliovirus and Listeria monocytogenes was analysed in Caco-2 cells, a tumour-derived cell line, highly susceptible to these pathogens . The multiplication of these pathogens, whose usual site of entry and/or replication is the intestine, was also followed by electron microscopy . Results obtained showed an increase of L . monocytogenes internalisation in cells infected with rotavirus, whereas the preinfection with poliovirus had only a slight interfering effect on bacterial entry . Analysis of L . monocytogenes multiplication in virus-infected cells revealed that rotavirus also promoted bacterial replication, which poliovirus hampered replication . Concerning the effect of Caco-2 cell invasion by L . monocytogenes on viral replication, we observed an increase in rotavirus antigen synthesis but no significant effect on poliovirus yield under our experimental conditions.

Appl Environ Microbiol, 1996 Nov, 62(11), 4293 - 5
Hemolytic activity reevaluation of putative nonpathogenic Listeria monocytogenes strains; Lachica RV; Identification of 12 strains originally characterized as nonpathogenic Listeria monocytogenes was reassured following the evaluation of their hemolytic capability with a newly developed horse blood agar plate . Seven of the strains were observed consistently to be hemolytic and confirmed as L . monocytogenes with the use of two commercial systems: the Gene-Trak L . monocytogenes-specific colorimetric DNA hybridization assay and the API Listeria system . Except for one strain that formed typical smooth colonies, these hemolytic strains formed rough colonies on a selective medium, lithium chloride-ceftazidime agar . The rest of the strains were nonhemolytic and did not hybridize with the DNA probe; they were identified as Listeria innocua on the basis of their API Listeria system biochemical profile . All but one of these nonhemolytic strains formed smooth colonies on lithium chloride-ceftazidime agar.

Pathol Biol (Paris), 1996 Nov, 44(9), 816 - 24
{Prevention of Listeria monocytogenes contamination on dairy farms and in the cheese industry}; Stahl V et al.; Listeria monocytogenes remains a pathogen bacteria the prevention of which, in food products, stays delicate . A complete organization, from the farmer's production to the industry and the consumer is necessary to eliminate Listeria in a type of food product . Listeria monocytogenes is susceptible of contaminate raw milk . The silage may be a major source of the occurrence of Listeria monocytogenes in raw milk . In this case, the contamination sources in a dairy farm and the good hygienic practices must be well-defined . In dairy industry, the contamination must be managed by the application of a systematic and methodically system like H.A.C.C.P . (Hazard Analysis Critical Control Points) . It is useful for the study of Listeria monocytogenes contamination and involve the hazard analysis of each industry plant . In fact, the raw products, food products, manufacturing process, environmental conditions, process equipment, materials and staff organizational are specific and characteristic.

Pathol Biol (Paris), 1996 Nov, 44(9), 808 - 15
{Incidence of Listeria in food}; Lahellec C et al.; It is only recently that the role of food in the appearance of human listeriosis has been shown up . However, the increasing number of studies made, up to date, don't let us appreciate the influence of Listeria, and more particularly Listeria monocytogenes, in a somehow satisfying way . The problems set by the evaluation of this incidence are called up firstly, and afterwards the data concerning different food-stuffs (meat and meat products, milk and milk products, sea foods, vegetal products) are reviewed, trying to explain the origin for each of it . To conclude, some research axes, susceptible of being developed are called up.

Pathol Biol (Paris), 1996 Nov, 44(9), 790 - 807
{Resistance of Listeria monocytogenes to physical exposure}; Augustin JC; The resistance of Listeria monocytogenes to physical processing, particularly heat resistance and radioresistance, is widely dependent on the method involved, the physiological state of the strain used, and, obviously, the substrate in which the organism is . HTST pasteurization of milk would allow at least 11 decimal reductions of the potentially present population of L . monocytogenes, and then greatly minimizes the risks of survival of the organism . On the other hand, high and low pasteurizations of egg products may involve only 4 to 5 decimal reductions and appear then not very reliable towards Listeria . Similarly, meat products cooking can, in some conditions, be inadequate to allow the total inactivation of contaminant L . monocytogenes . A 3 kGy irradiation of meat products should allow, on an average, 6 decimal reductions . These results must incite the manufacturers to take into account factors present in their products which allow L . monocytogenes to better resist and this in order to adapt processing to these conditions of increased resistance.

Pathol Biol (Paris), 1996 Nov, 44(9), 783 - 9
Comparative virulence between different strains of Listeria in zebrafish (Brachydanio rerio) and mice; Menudier A et al.; Listeriosis is a disease found in most animal species but is relatively uncommon in fish . We studied the relationship between Listeria and zebrafish by injecting Brachydanio rerio intraperitoneally with different Listeria strains having pathological or food-stuff origins . We then compared these results with those obtained in Swiss mice . Experimental Listeriosis in Zebrafish differs greatly from that observed in mice . The 50% lethal dose (LD50) previously determined was much higher than that observed in mice . In fish, a good correlation exists between infection found in renal tissue, an important lymphoid organ and that present in whole fish (p < 0.001) . Infection kinetics showed that, in contrast with mice, L . monocytogenes was unable to multiply in fish . Differential blood counts showed the development of an immune response in fish . The difference in the expression of Listeria virulence between Zebrafish and mice was also seen in their reactions to different wild strains inoculate i.p . Strains belonging the innocua, ivanovii, seeligeri and welshimeri were weakly or not virulent in mice but virulent in fish . Nevertheless, as in mice, differences in virulence existed between strains of L . monocytogenes belonging to serovars 4b, 1/2a, 1/2b and 1/2c.

Pathol Biol (Paris), 1996 Nov, 44(9), 775 - 82
Pathogenesis and immunology of Listeria monocytogenes; Schlech WF; Listeriosis is primarily a foodborne disease and the pathogenesis of infection is determined by passage of the organism from the gastrointestinal lumen to the reticuloendothelial cells of the liver and spleen . Subsequent invasive events such as sepsis and meningitis develop . The immune response to Listeria is characterized by early macrophage mediated killing followed by the development of a brisk cell mediated immune response . Humoral immunity appears to play no role in infection in the protected response . Organism specific virulence factors such as hemolysin and actin polymerization factor may play important roles in pathogenesis and also illicit specific immune responses . Immunization against listeriosis has been carried in animals but does not appear feasible for this rare infection in human populations.

Pathol Biol (Paris), 1996 Nov, 44(9), 769 - 74
Listeria monocytogenes--aspects of pathogenicity; Schwarzkopf A; The genus Listeria includes different species of ubiquitary present gram-positive rod shaped bacteria . The species Listeria monocytogenes causes severe diseases like meningitis and meningoencephalitis in humans . Additional groups of syndromes associated with this microorganism are the listeriosis of the pregnant woman, mostly appearing as an abortion or septic premature birth and the meningitis of the newborn . Transmission of Listeria may occur on the oral route due to infected food like raw milk and cheese, raw meat or soil contaminated food like prepacked salads, respectively . The understanding of Listeria virulence was improved by different investigations employing cell cultures and molecular methods like knockout of genes encoding potential virulence factors . Nowadays the procedure of infection of cells is divided in four different parts: internalisation, escape from intracellular vacuole, nucleation of actin filaments and cell-to-cell spread . So called Internalins are produced by Listeria and are obviously needed for cell invasion . Listeria could escape intracellular vacuoles producing a hemolysin, Listeriolysin O, and proliferate inside the host cells . The surface bounded protein Actin A mediates the contact to the actin filament system of the host cell . This is important for the intracellular spread of Listeria . In the next step a cell-to-cell spread supported by phospholipase and lecithinase occurs . Despite the high incidence of contaminated food only a little incidence of listeriosis is observed . This may be explained in an indirect vaccination due to less virulent strains . However, the immune response of patients even with well documented listeriosis may be poor and causes false negative serological results sometimes . In this paper the know virulence factors of the interesting species L . monocytogenes are demonstrated and the course of infection is discussed.

Pathol Biol (Paris), 1996 Nov, 44(9), 757 - 68
{Critical analysis of isolation, counting and identification methods of Listeria in food industry}; Bind JL et al.; Stimulated by epidemic outbreaks in years 80's and 90's detection methods for Listeria, and L . monocytogenes particularly, have undergone many important progresses . New selective media for isolation and enrichment have been formulated with the aim to improve bacteriological methods and decrease time delays . For identification of Listeria at the species level, some biochemical miniaturised tests allow response within 24 h . Within the immuno-chemical methods as ELISA or ELFA, the revelation step has been shortened and automated . The elaboration of L . monocytogenes specific antibodies begins to upset immunological methods . As far as concern simplification of detection tests, a new generation of small immunological plate-shaped tests has been marketed . Whatever the immunological method considered, intrinsic sensibility is about 10(5) at 10(6) CFU/ml . Only one method allows more sensibility: the immuno-magnetic separation . With a sensibility of 1 CFU/ml, immunocapture allows shortening of enrichment time of 24 h or eliminates this step altogether if the aim is to count the Listeria directly in the sample . In the biological molecular methods, some hybridization tests with nuclear probes allow rapid and specific detection of L . monocytogenes . The polymerase chain reaction has been improved to simplify and shorten the DNA preparation and the revelation of amplified fragments . This method will be soon used in food samples analysis . The elaboration of new methods that could allow the specific detection of L . monocytogenes pathogenic strains of is one of future stake.

Pathol Biol (Paris), 1996 Nov, 44(9), 749 - 56
{Taxonomy of the Listeria genus and typing of L . monocytogenes}; Rocourt J; The genus Listeria contains six species (L . monocytogenes, L . innocua, L . ivanovii, L . seeligeri, L . welshimeri and L . grayi) among which only L . monocytogenes can cause infections in humans . Typing of L . monocytogenes includes phenotypic methods, serotyping and phage-typing, and molecular methods, mainly ribotyping, multilocus enzyme analysis, DNA micro- and macrorestriction analysis and RAPD (Random Amplified Polymorphic DNA).

J Dairy Sci, 1996 Nov, 79(11), 1936 - 41
Occurrence of Listeria monocytogenes and other Listeria spp . in raw caprine milk; Gaya P et al.; Samples of caprine milk from bulk tanks of 405 farms in central Spain were analyzed for Listeria spp . once per season over a 1-yr period . Listeria monocytogenes and Listeria innocua were detected in 2.56 and 1.73% of the 1445 samples, respectively . Listeria ivanovii (0.21% samples) and Listeria seeligeri (0.07% samples) were rarely isolated . Only 6 milk samples were contaminated by more than one Listeria species . Most farms (92.59%) produced milk that was apparently free from L . monocytogenes throughout the sampling period, and 88.40% produced milk that was apparently free from Listeria spp . Milk contamination by Listeria spp . was seasonal; incidence in autumn (9.33%) and winter (5.14%) samples was higher than incidence in spring (0.85%) and summer (0.85%) samples . Occurrence of Listeria spp . was lower in samples from mountain farms (1.25%) than in samples from plateau farms (7.03%).

Immunology, 1996 Nov, 89(3), 442 - 8
Neutrophils are involved in the non-specific resistance to listeriosis induced by mycobacterial infections; Leal IS et al.; A major role has been recently ascribed to the neutrophil in the resistance to infection by Listeria monocytogenes (L . monocytogenes) . Here we evaluated whether such neutrophils played a role in the non-specific resistance to listeriosis that develops in hosts infected by mycobacteria . We found that the depletion of neutrophils completely abrogated the resistance conferred by the activated macrophages induced during the mycobacterial infection . The lack of killing by activated Kupffer cells and the visualization of bacteria proliferating inside peritoneal macrophages in neutrophil-depleted mice allowed us to postulate a role for the cooperation between neutrophils and macrophages in the killing of L . monocytogenes . We also found listerial proliferation in hepatocytes of neutrophil-depleted, mycobacteria-infected mice showing that the neutrophils may be involved in the control of listeria infection of parenchymal cells.

Can J Microbiol, 1996 Nov, 42(11), 1155 - 62
Genus- and species-specific detection of Listeria monocytogenes using polymerase chain reaction assays targeting the 16S/23S intergenic spacer region of the rRNA operon; Graham T et al.; In this study, the 16S/23S rRNA intergenic spacer (IGS) regions of six Listeria species were examined . DNA bands of 590 and 340 bp were observed following polymerase chain reaction (PCR) amplification of DNA from Listeria monocytogenes, Listeria innocua, Listeria seeligeri, Listeria welshimeri, and Listeria ivanovii strains with generic rRNA IGS oligonucleotide primers . For strains of Listeria grayi subspp . grayi and murrayi, DNA band sizes of 550 and 340 bp were observed with this primer pair . DNA bands of these sizes were not observed for other Gram-negative or- positive bacteria in this PCR assay . Four RsaI digestion profiles were noted for the Listeria PCR products . Listeria monocytogenes strains had one profile; L . innocua strains had a second; L seeligeri, L . welshimeri, and L ivanovii strains had a third; and L . grayi strains had a fourth . The small and large 16S/23S rRNA IGSs of L . monocytogenes ATCC 15313 were identical in the first 58 5' and the last 169 3' nucleotides . However, the large rRNA IGS contained a central 267-bp region with tRNA(Ile) and tRNA(Ala) genes . Large rRNA 16S/23S IGS nucleotide sequence data has not been previously reported . This data was used to develop novel Listeria genus-specific and L.monocytogenes species-specific PCR assays.

J Dairy Res, 1996 Nov, 63(4), 593 - 606
Effect of medium-chain fatty acids in mould ripened cheese on the growth of Listeria monocytogenes; Kinderlerer JL et al.; Listeria monocytogenes and List . innocua were isolated from commercial soft ripened and blue-veined cheeses manufactured in France, mainly from Brie cheese made from unpasteurized milk . Five isolates were List . monocytogenes serotype 1/2 and two were List . innocua . Examination of Bleu d'Auvergne cheese with the cryoscanning electron microscope showed that many conidia spores were present in the blue veins in close contact with the cheese surface . There were few conidia spores in the Brie, mostly on the outside of the cheese but not in contact with the surface . High concentrations of free dodecanoic (lauric) acid (1.77-2.50 g/kg cheese) and tetradecanoic (myristic) acid (2.54-6.38 g/kg cheese) were found in the veins of the blue cheese, but concentrations in the white regions were much lower . Free lauric and myristic acids were not detected in the Brie cheeses . There was no difference in the overall fatty acid composition of the fat in the surface ripened and blue-veined cheeses, although higher concentrations of free medium-chain fatty acids were found in a blue cheese compared with a surface ripened cheese . The pH and fat content were higher in regions with obvious fungal growth, the blue veins of Fourme d'Ambert and the rind of Brie . Free lauric acid dissolved in butteroil inhibited multiplication in broth at pH 7.0 of a test strain of List . monocytogenes isolated from Bleu d'Auvergne . Some inhibition was seen with hexanoic, octanoic, decanoic and tetradecanoic acids . We suggest that the presence of localized concentrations of free medium-chain fatty acids (dissolved in the fat) in the blue veins of blue mould ripened cheese could act as natural preservatives and inhibit the growth of listerias in conditions where (if present), one would otherwise expect them to grow.

J Med Microbiol, 1996 Nov, 45(5), 323 - 30
Effect of multiplicity of infection on Listeria monocytogenes pathogenicity for HeLa and Caco-2 cell lines; Francis MS et al.; The significance of multiplicity of infection (moi) for invasiveness and intracellular multiplication of Listeria monocytogenes in Caco-2 and HeLa cell monolayers was investigated . A low moi (1:1) resulted in recovery of significantly more L . monocytogenes when these bacteria were used to infect either cell line . At high moi (100:1), the percentage recovery of bacteria was comparatively low, even after extensive invasion and intracellular multiplication . Microscopic analysis of Giemsa- and immunofluorescent-stained infected monolayers revealed extensive cell disruption and exposure of the internalised bacteria to the bactericidal effect of gentamicin . By contrast, a low moi resulted in minimal cytopathic effects and evidence of cell to cell spread by L . monocytogenes was consistently observed in HeLa and J774, but not in Caco-2 cell lines . Nevertheless, the use of HeLa and Caco-2 cell monolayers enabled a clear distinction to be made between invasive (L . monocytogenes) and non-invasive Listeria spp . (L . innocua, L . ivanovii, L . seeligeri, L . grayi, L . welshimeri and L . monocytogenes LLO19) . The use of a low moi with HeLa cell monolayers provided a reliable tissue-culture model of infection for L . monocytogenes.

J Cell Biol, 1996 Nov, 135(3), 647 - 60
The tandem repeat domain in the Listeria monocytogenes ActA protein controls the rate of actin-based motility, the percentage of moving bacteria, and the localization of vasodilator-stimulated phosphoprotein and profilin; Smith GA et al.; The ActA protein is responsible for the actin-based movement of Listeria monocytogenes in the cytosol of eukaryotic cells . Analysis of mutants in which we varied the number of proline-rich repeats (PRR; consensus sequence DFPPPPTDEEL) revealed a linear relationship between the number of PRRs and the rate of movement, with each repeat contributing approximately 2-3 microns/min . Mutants lacking all functional PRRs (generated by deletion or point mutation) moved at rates 30% of wild-type . Indirect immunofluorescence indicated that the PRRs were directly responsible for binding of vasodilator-stimulated phosphoprotein (VASP) and for the localization of profilin at the bacterial surface . The long repeats, which are interdigitated between the PRRs, increased the frequency with which actin-based motility occurred by a mechanism independent of the PRRs, VASP, and profilin . Lastly, a mutant which expressed low levels of ActA exhibited a phenotype indicative of a threshold; there was a very low percentage of moving bacteria, but when movement did occur, it was at wild-type rates . These results indicate that the ActA protein directs at least three separable events: (1) initiation of actin polymerization that is independent of the repeat region; (2) initiation of movement dependent on the long repeats and the amount of ActA; and (3) movement rate dependent on the PRRs.

Am J Pathol, 1996 Nov, 149(5), 1737 - 43
Human HLA-B27 gene enhances susceptibility of rats to oral infection by Listeria monocytogenes; Warner TF et al.; Germfree rats transgenic for the human genes HLA-B27 and beta 2-microglobulin were colonized with hemolysin-positive (Hly+) or hemolysin-negative (Hly-) strains of Listeria monocytogenes . HLA-B27 rats were very susceptible to infection with Hly+ L monocytogenes none survived beyond 6 days . Conversely, nontransgenic control rats survived alimentary tract colonization with the Hly+ strain, and both transgenic and nontransgenic rats survived colonization with the Hly- strain of L monocytogenes . After colonization with Hly+ L monocytogenes, both transgenic and nontransgenic rats developed severe bowel inflammation which consisted histologically of microab scesses, granulomatous lesions, and ulcers; however, whereas the transgenic rats died within 6 days, only very mild intestinal lesions were seen in nontransgenic rats 10 to 42 days after colonization . Liver and splenic lesions were small and transient in nontransgenic rats . Transgenic and nontransgenic control rats infected with Hly- Listeria developed mild transient diarrhea but showed no histological changes in the intestine . This study thus documents an association between a particular bacterial product (hemolysin produced by L monocytogenes) and the induction of severe inflammatory disease and death in rats expressing HLA-B27 and beta 2-microglobulin.

J Infect Dis, 1996 Nov, 174(5), 1073 - 9
Lymphokine-activated killer cells lyse Listeria-infected hepatocytes and produce elevated quantities of interferon-gamma; Gregory SH et al.; The bulk of Listeria monocytogenes injected intravenously into mice is taken up in the liver, where hepatocytes serve as the principal site of intracellular replication . NK cells have been implicated in host defenses to a variety of intracellular pathogens . To explore the role of NK cells in resistance to listerial infections of the liver, lymphokine-activated natural killer (LAK) cells were cocultured with Listeria-infected hepatocytes . The aspartate aminotransferase activity in the medium (evidence of cytotoxicity and hepatocyte damage) was elevated significantly in these cultures . Conversely, the viability of intracellular Listeria organisms was reduced . Increased quantities of interferon-gamma (IFN-gamma) were also detected . IFN-gamma production by LAK cells was modulated by interleukin (IL)-2 and IL-12 . These findings suggest that the response of LAK cells to infected hepatocytes may play a critical role in host defenses to Listeria organisms taken up in the liver.

J Bacteriol, 1996 Nov, 178(21), 6105 - 9
Sodium-driven, osmotically activated glycine betaine transport in Listeria monocytogenes membrane vesicles; Gerhardt PN et al.; Transport of the osmoprotectant and cryoprotectant glycine betaine was investigated in membrane vesicles of Listeria monocytogenes . Uptake-driving transmembrane potentials ranging from 111 to 122 mV within the pH range of 5.5 to 7.5 could be generated by the electron donor system ascorbate-phenazine methosulfate but not by the electron donor system ascorbate-N,N,N',N'-tetramethyl-p-phenylenediamine . Transport was dependent on both high concentrations of sodium ion and the presence of a hypertonic solute gradient . Arrhenius-type temperature activation was observed . Lineweaver-Burk plots indicated a Km of 4.4 microM for glycine betaine and a Vmax of 700 pmol/min x mg of protein . The Michaelis constant for NaCl depended on the solute used to maintain a constant hyperosmotic pressure, and the Km values were 200 and 75 mM when KCl and sucrose were employed, respectively . Transport was 65% lower in vesicles derived from cells grown under stress provided by KCI rather than NaCl and approximately 94% lower in vesicles derived from cells that were not grown under osmotic stress . This porter appears to be specific for glycine betaine, since neither proline, carnitine, nor choline inhibited uptake effectively . Kinetic studies using ionophores and artificial gradients indicate that glycine betaine is cotransported with sodium ion.

Science, 1996 Nov 1, 274(5288), 780 - 2
A role for phosphoinositide 3-kinase in bacterial invasion; Ireton K et al.; Listeria monocytogenes is a bacterial pathogen that invades cultured nonphagocytic cells . Inhibitors and a dominant negative mutation were used to demonstrate that efficient entry requires the phosphoinositide (PI) 3-kinase p85alpha-p110 . Infection with L . monocytogenes caused rapid increases in cellular amounts of PI(3, 4)P2 and PI(3,4,5)P3, indicating that invading bacteria stimulated PI 3-kinase activity . This stimulation required the bacterial protein InlB, host cell tyrosine phosphorylation, and association of p85alpha with one or more tyrosine-phosphorylated proteins . This role for PI 3-kinase in bacterial entry may have parallels in some endocytic events.

Ann N Y Acad Sci, 1996 Oct 25, 797, 207 - 27
Protective immunity to Listeria monocytogenes elicited by immunization with heat-killed Listeria and IL-12 . Potential mechanism of IL-12 adjuvanticity; Miller MA et al.; The results presented here demonstrate the striking potentiating effects of IL-12 when it is combined with listerial immunogens . Although HKLM alone does not elicit strong T-cell responses, the results presented here demonstrate that the combination of HKLM and IL-12 elicited vigorous Listeria-specific Th1-type T-cell responses when administered intraperitoneally . The intensity of these responses, as well as the cytokine profiles of the Listeria-specific peritoneal T cells and macrophages, was remarkably similar to that of Listeria-infected/immune mice . These studies also revealed that typically nonimmunogenic forms of soluble listerial antigen preparations (cLLO, SLP) and LLO peptide homologs (M . A . Miller et al., manuscript in preparation) elicited intense Listeria-specific T-cell responses when administered with IL-12 . In conjunction with the generation of specific T-cell responses following injection of IL-12 in combination with either killed Listeria or soluble listerial antigen preparations, macrophages from these mice expressed upregulated quantities of class II MHC and produced increased amounts of IL-12 following restimulation in vitro . Protection studies established that the Listeria-specific T-cell responses elicited by the HKLM + IL-12 mixture conferred protective immunity of mice to a lethal dose of viable L . monocytogenes . Studies designed to investigate the regulation of IL-12 production by peritoneal macrophages revealed that activated macrophages are particularly sensitive to bacterial products . However, nonviable or replication-incompetent bacteria or bacterial products injected alone were unable to influence the ability of macrophages to produce IL-12 . The ability of activated macrophages to respond to HKLM was dramatically upregulated upon addition of IFN-gamma and markedly downregulated in the presence of the Th2 cytokines, IL-4 and IL-10 . In light of what is known about the ability of IL-12 to induce IFN-gamma production by NK cells and gamma delta T cells, these results suggest that the exogenous addition of IL-12 may help initiate a cytokine cascade which enables the immune system to interact productively with an antigen that is typically nonimmunogenic when administered alone . These findings demonstrate that IL-12 may prove to be a powerful and broadly useful adjuvant component of particulate and soluble antigen-based vaccines directed towards many types of intracellular pathogenic microorganisms . Studies aimed at determining the generality of these findings in other infectious disease models as well as experiments designed to further elucidate the mechanism(s) of IL-12 adjuvanticity are continuing.

Cell, 1996 Oct 18, 87(2), 227 - 39
Mena, a relative of VASP and Drosophila Enabled, is implicated in the control of microfilament dynamics; Gertler FB et al.; Drosophila Enabled is required for proper formation of axonal structures and is genetically implicated in signaling pathways mediated by Drosophila AbI . We have identified two murine proteins, Mena and Evl, that are highly related to Enabled as well as VASP (Vasodilator-Stimulated Phosphoprotein) . A conserved domain targets Mena to localized proteins containing a specific proline-rich motif . The association of Mena with the surface of the intracellular pathogen Listeria monocytogenes and the G-actin binding protein profilin suggests that this molecule may participate in bacterial movement by facilitating actin polymerization . Expression of neural-enriched isoforms of Mena in fibroblasts induces the formation of abnormal F-actin-rich outgrowths, supporting a role for this protein in microfilament assembly and cell motility.

Ugeskr Laeger, 1996 Oct 14, 158(42), 5949 - 50
{Septic infection of hip joint prosthesis with Listeria monocytogenes}; Hansen PS et al.; A case of Listeria monocytogenes septicaemia and infection of a prosthetic hip joint is presented in a patient with non-insulin-dependent diabetes mellitus . The patient developed the infection five and a half years after primary alloplastic operation . The prosthesis was removed and a temporary prosthesis with gentamicin was placed ("spacer") . The antibiotic treatment included ampicillin, pivampicillin and sulfamethoxazole-trimetroprim . Six weeks after removal of the prosthesis an un-cemented prosthesis was placed, and the patient had a full functional recovery.

Res Microbiol, 1996 Oct, 147(8), 637 - 40
Identification of Listeria species by a semi-nested polymerase chain reaction; Manzano M et al.; Three primers derived from the lap gene were used to distinguish Listeria monocytogenes from L.innocua and other Listeria species . L . monocytogenes and L . innocua yielded a PCR product of 600 and 300 bp, respectively, whereas a typical pattern of three amplimers was observed with L . ivanovii, L . seeligeri and L . welshimeri.

Arzneimittelforschung, 1996 Oct, 46(10), 1012 - 5
Treatment of an acute bacterial infection with a combination of acetylsalicylic acid/ibuprofen and interferon gamma; Hockertz S et al.; The bacterial infection with Listeria monocytogenes is associated with an inhibition of the macrophage function, the first-line defense against bacterial infection . We studied the effect of acetylsalicylic acid (ASA, CAS 50-78-2) and ibuprofen (CAS 15687-21-1) alone and in combination with a suboptimal dose of recombinant interferon gamma . (IFN gamma) on the acute infection with Listeria monocytogenes in the Balb/c mouse . Animals were intravenously infected with a sublethal dose of Listeria monocytogenes . The therapy was carried out I) at the time of the infection, II) 30 min, III) 60 min, IV) 3 h and V) 24 h post infection . Six groups of mice were treated: i) untreated control, ii) 10(4) units IFN gamma, iii) 10 mg/kg ASA, i.v.) 10 mg/kg ASA + IFN gamma, i.v.) 12 mg/kg ibuprofen, and vi) 12 mg/kg ibuprofen + IFN gamma . The data shown that treatment with ibuprofen and ASA resulted in a significant reduction of viable bacteria in spleen and liver, the main organs of this infection . In combination with low dose interferon gamma, both non-steroidal anti-inflammatory drugs (NSAID) reduced the parasite burden in the examined organs by a factor of more than 10 . The therapeutic efficacy showed its maximum 1 h after challenge with Listeria monocytogenes . These results suggest that ibuprofen and ASA possess antibacterial activity . In addition, IFN gamma significantly increases the antibacterial activity of ASA and ibuprofen . Presumably, these effects are due to an influence on the host immune system.

Infect Immun, 1996 Oct, 64(10), 4008 - 19
Differences in virulence and in expression of PrfA and PrfA-regulated virulence genes of Listeria monocytogenes strains belonging to serogroup 4; Sokolovic Z et al.; Listeria monocytogenes isolates belonging to serogroup 4 (subtypes 4a, 4ab, 4b, 4c, 4d, and 4e) exhibit different levels of virulence in mice . Molecular studies indicate that in comparison with the control strain EGD (serotype 1/2a), these strains differ in the expression of the PrfA-regulated virulence genes, including prfA itself . Strains of serotypes 4c, 4d, 4e, and especially 4a show a low level of invasiveness in Caco-2 cells, which correlates in part with the low level of expression of the inlA gene . All serotypes reach the cytoplasm, at the latest, 2 h postinfection and become surrounded by polymerized actin within the next hour, but actin tail formation by serotype 4a, 4c, 4d, and 4e strains is drastically reduced . The actA genes in these serogroup 4 strains are expressed in minimum essential medium and within the phagocytic cell line J774 . However, the amounts and (in part) the sizes of the ActA proteins in these strains differ under these conditions . The reduced actin tail formation by serotype 4a, 4c, 4d, and 4e strains may be due to the low level of in vivo expression of ActA . In addition, the loss of one repeat unit in the ActA proteins of serotype 4a and 4e strains may also contribute to the less efficient actin tail formation observed with these strains.

Infect Immun, 1996 Oct, 64(10), 3983 - 6
Expression of the inlAB operon by Listeria monocytogenes is not required for entry into hepatic cells in vivo; Gregory SH et al.; Listeria monocytogenes injected intravenously into mice is taken up in the liver, where hepatocytes serve as the principal site of intracellular replication . The factors effecting entry of L . monocytogenes into hepatic cells remain to be determined . Others have shown that the protein products of the inlAB (internalin) operon are required for maximum entry of L . monocytogenes into a number of cell lines in vitro . Likewise, we report here that expression of the inlAB operon was required for maximum uptake of L . monocytogenes by primary cultures of mouse hepatocytes . Uptake of an inlAB mutant strain of L . monocytogenes was approximately 10-fold less than that of the isogenic wild-type control . In contrast, inlAB expression was not a factor in (i) clearance of L . monocytogenes injected intravenously into mice and taken up in the liver, (ii) the distribution of L . monocytogenes among hepatocytes and nonparenchymal cells in the liver, or (iii) internalization of L . monocytogenes by hepatic cells in vivo . These latter findings suggest that infection of hepatic cells by L . monocytogenes in vivo does not require the protein products of the inlAB operon.

Int J Food Microbiol, 1996 Oct, 32(3), 343 - 55
Genomic fingerprinting of 80 strains from the WHO multicenter international typing study of listeria monocytogenes via pulsed-field gel electrophoresis (PFGE); Brosch R et al.; An international multicenter typing study of Listeria monocytogenes was initiated by the World Health Organization (Food Safety Unit, Geneva) in order to evaluate the usefulness of various phenotypic and genotypic typing methods for L . monocytogenes, to select and standardize the most appropriate methods to define common nomenclature of varieties and to select specific reference strains . Pulsed-field gel electrophoresis was used in four laboratories for molecular characterization of a set of 80 'coded' strains distributed to all participating laboratories . The endonucleases ApaI and SmaI, used in all four laboratories, yielded between 21 and 28 restriction endonuclease digestion profiles (REDP) . AscI was used, in addition, in laboratory A and displayed 21 REDP . The combination of ApaI, SmaI or AscI REDP established 25 to 33 genomic groups . depending on the laboratory and the number of viable strains . Agreement of typing data among the four laboratories ranged from 79 to 90% . Forty-nine (69%) of the 71 strains viable in all four laboratories were placed into exactly the same genomic groups in all four laboratories . The epidemiological relevance of the strains became known after decoding and it was shown that most of the epidemiologically related strains were correctly identified by the four groups of investigators . i.e., most related strains were placed into the same genomic groups by all four laboratories . Similar results were obtained when 11 duplicate cultures were analyzed-on average 84% of the duplicates were identified . Comparison of REDP obtained by laboratory A with REDP from previously analyzed set of 176 L . monocytogenes strains allowed the prediction of the serovar-groups of the 80 strains . These predictions of serovar-groups were later confirmed by serotyping results obtained by laboratories involved in the WHO multicenter typing study of L . monocytogenes . In general this study reconfirmed that PFGE is a very accurate and reproducible method for fine structure comparison and molecular typing of L . monocytogenes.

Int J Food Microbiol, 1996 Oct, 32(3), 325 - 41
The WHO multicenter study on Listeria monocytogenes subtyping: random amplification of polymorphic DNA (RAPD); Wernars K et al.; As part of a WHO multicenter study on Listeria monocytogenes subtyping methods the random amplification of polymorphic DNA (RAPD)-technique was evaluated . Six participants were asked to use a standard protocol to analyse a set of 80 L . monocytogenes strains . This set contained 22 groups of epidemiologically linked isolates and 11 pairs of duplicate strains . Using three different 10-mer primers the median reproducibility of the RAPD-results obtained by the six participants was 86.5% (range 0-100%) . Failure in reproducibility was mainly due to results obtained with one particular primer . The number of epidemiological groups found to be homogeneous varied from 1-22 (median 16) . However, for some groups an inhomogeneity was found by the majority of participants . The overall correlation between the results from the different participants ranged from 32 to 85%.

Int J Food Microbiol, 1996 Oct, 32(3), 313 - 24
High-frequency endonuclease (REA) typing: results from the WHO collaborative study group on subtyping of Listeria monocytogenes; Gerner-Smidt P et al.; Eighty isolates of Listeria monocytogenes were typed by high-frequency restriction endonuclease analysis . Two laboratories participated in the study with two restriction enzymes each . The enzymes used were EcoRI, Hae1II, HhaI . and its isoschizomer Cfo1 . EcoRI was less discriminatory than the other enzymes . The profiles generated by Hha1 and CfoI were not fully stable for some closely related isolates . The size and the number of restriction bands generated by Hha1 in one laboratory and its isoschizomer Cfo1 in another laboratory were directly comparable . This indicates that REA-typing may be used as a definitive typing method for Listeria monocytogenes if the typing procedure is standardized . The stability of the REA-types needs further elucidation in order to establish firm differentiation criteria for comparison of isolates.

Int J Food Microbiol, 1996 Oct, 32(3), 301 - 11
Multilocus enzyme electrophoresis for characterization of Listeria monocytogenes isolates: results of an international comparative study; Caugant DA et al.; Multilocus enzyme electrophoresis (MEE) is a standard technique that is used to elucidate the epidemiology of a variety of bacterial species . Recently, the method has been employed by several laboratories for investigations of clinical and foodborne isolates of Listeria monocytogenes . To assess the sensitivity and reproducibility of MEE in characterising L . monocytogenes isolates for epidemiological purposes and, ultimately, to agree on a standard protocol, seven laboratories participated in a blinded study of 80 strains . The strain collection included both epidemiologically related and unrelated isolates . Each laboratory used its own protocol for MEE . The number of enzymes that were assayed by the laboratories ranged from 8 to 23, and the total number of identified electrophoretic types (ETs) varied between 14 and 25 . Of the II pairs of duplicate strains, the number of pairs recognised as identical by the seven laboratories ranged from 3 to 10 (median = 8) . From 10 to 18 (median = 15) of the 22 groups of epidemiological related strains were recognised as homogeneous by the different laboratories . The discriminatory power of the method, calculated using Simpson's index of diversity for 69 strains (80 strains minus the 11 duplicates), ranged from 0.827 to 0.925 . This relatively low discriminatory power is a consequence of a somewhat low genetic diversity of L . monocytogenes compared to other bacterial species . Efforts should be pursued to standardise the method in order to improve the intra- and inter-laboratory reproducibility.

Int J Food Microbiol, 1996 Oct, 32(3), 289 - 99
WHO study on subtyping Listeria monocytogenes: results of phage-typing; McLauchlin J et al.; A multi-centered study on phage typing of Listeria monocytogenes was carried out using 80 cultures sent under code and tested in six different laboratories . Phage typing was performed using an international phage set in five laboratories and phage sets unique to two laboratories . Testing of cultures sent in duplicate showed similar levels of reproducibility to that previously reported . Analysis of results from groups of epidemiologically related cultures showed a high level of agreement in all laboratories . Patterns of phage susceptibility were relatively stable on retesting strains in the same laboratory after long periods of time . However, there was limited comparability between results obtained from testing the same cultures using the same phages in different laboratories . It is recommended that the phages in the international set be reviewed, and that better inter-laboratory reproducibility may be achieved by standardisation of phage suspensions, propagation strains and methodology, together with the use of centrally propagated phages.

Int J Food Microbiol, 1996 Oct, 32(3), 279 - 87
Serotyping of 80 strains from the WHO multicentre international typing study of Listeria monocytogenes; Schonberg A et al.; Serotyping was carried out on 80 coded strains, distribute to all laboratories taking part in the WHO L . monocytogenes multicenter subtyping study . All six laboratories used the method recommended by their coordinator . All 80 strains were typeable . There was complete agreement between the six laboratories on 49 (61.3%) strains (21 serovar 1/2a and 28 serovar 4b strains) which in turn were identical to the expected serovars, known only after decoding . The intralaboratory reproducibility carried out on 11 duplicate strains, ranged from 82 to 100%, with a medium value of 91% . Reproducibility of serotyping L . monocytogenes strains according to serovar varied from 33.3 to 100% for serotypes 3b and 1/2a, respectively, with serovar 4b (x) being incorrectly identified in all six laboratories . Serotyping of L . monocytogenes is easy and simple and is a useful prerequisite for other finer and more discriminatory typing methods . Problems may however, be encountered mainly with the flagellar antigenic factors . There is a need, therefore, for preparing antisera of good quality from which efficient antigenic factors can be obtained.

Int J Food Microbiol, 1996 Oct, 32(3), 263 - 78
WHO-sponsored international collaborative study to evaluate methods for subtyping Listeria monocytogenes: restriction fragment length polymorphism (RFLP) analysis using ribotyping and Southern hybridization with two probes derived from L . monocytogenes chromosome; Swaminathan B et al.; Seven laboratories participated in a WHO-sponsored international collaborative study, to evaluate methods for subtyping Listeria monocytogenes, by performing restriction fragment length polymorph sm (RFLP) analysis-based subtyping of an international study set of 80 strains of L . monocytogenes that included 22 epidemiologically related groups . The RFLP analysis was done by Southern hybridization with one of two types of probes found in multiple copies on the chromosome of L . monocytogenes . Six laboratories performed ribotyping . These laboratories used EcoRI enzyme to restrict the L . monocytogenes DNA and ribosomal RNA or DNA as the probe for Southern hybridizations . The seventh laboratory used Ncil to restrict the DNA, and two probes, one randomly cloned and the other containing repeat sequences cloned from L . monocytogenes DNA . The overall discriminating power of ribotyping, as estimated by calculation of Simpson's index of diversity, ranged from 0.83 to 0.88 for the six laboratories . The discriminating power of the combination of two probes used by Laboratory 7 was 0.91 . Ribotyping and the cloned probes used by Laboratory 7 discriminated poorly between serotype 4b strains . Neither method identified three atypical strains (identified by other subtyping methods) included in three apparently epidemiologically related groups . Ribotyping did not discriminate between strains of serotypes 4b and 4b(X) in one epidemiologically related group of strains; one cloned probe used by Laboratory 7 discriminated between these strains . Intra-laboratory reproducibilities for the seven laboratories ranged from 80.0 to 100% . as determined by their abilities to correctly identify 11 pairs of duplicate strains included in the study set . Inter-laboratory reproducibilities were generally very good considering that no attempt was made to standardize protocols used by the participants.

Curr Opin Immunol, 1996 Oct, 8(5), 664 - 9
Recombinant Listeria monocytogenes cancer vaccines; Paterson Y et al.; Listeria monocytogenes has recently been exploited as a vector for targeting antigens to the immune system . In the past year it has been shown to be particularly effective as a tumor antigen vector . Here we set its potency as a cancer vaccine in the context of the type of immunity induced by this facultative intracellular bacterium.

J Appl Bacteriol, 1996 Oct, 81(4), 433 - 8
Significance of pre-incubation temperature and inoculum concentration on subsequent growth of Listeria monocytogenes at 14 degrees C; Gay M et al.; The influence of the bacterial concentration of an inoculum (10(1) or 10(3) cfu ml-1) of two strains of Listeria monocytogenes (Scott A: serotype 4b and V7: serotype 1) and one strain of L . innocua (Lin 11), and the time and temperature at which the inoculum was stored (cold storage: 4 degrees C for 4 weeks, or without cold storage: -20 degrees C before immediate transfer), and the temperature at which cells were pre-incubated (30 degrees C and 14 degrees C) on subsequent growth in Richard's broth at 14 degrees C was investigated . Richard's broth at a pH 5.9 was used to simulate potential growth in soft cheese (camembert type) and an incubation temperature of 14 degrees C was used to simulate storage-temperature ripening of cheese . Enumeration of the number of viable cells was by plate count method, except where viable cell numbers were less that 10(3) cfu ml-1, when the MPN (Most Probable Number) technique was used . With cold storage and an inoculum of 10(3) cfu ml-1 (high bacterial concentration) the pre-incubation temperatures (30 degrees C and 14 degrees C) did not significantly influence the subsequent growth curve: there was no significant lag (less that 21 h) and cell numbers peaked in about 8.5 d . However, with cold storage and an inoculum of 10(1) cfu ml-1 (low bacterial concentration) and a pre-incubation temperature of 30 degrees C a significant shift in the growth curve was observed over that pre-incubated at f14 degrees C, with the appearance of a lag of about 7.7 d . At a pre-incubation temperature of 14 degrees C with the low inoculum concentration, there was a measurable lag of about 1 d . Without cold storage and a pre-incubation temperature of 30 degrees C, there was a lag time of 2.3 d . Storage conditions, pre-incubation temperature and inoculum concentration therefore appear to influence the subsequent growth curve . Importantly, however, the growth curves for cultures from inocula, pre-incubated at either 30 degrees C or 14 degrees C, appeared to involve two distinct values of the exponential growth rate (k): the initial portion of the growth curve described by a low value of k and the subsequent portion by a consistently and significantly greater value . The appearance of two distinct growth phases was reproduced in further data determined for all the studied strains of the microorganism . Further study to explain these unexpected and reproducible findings is being conducted.

Microbiology, 1996 Oct, 142 ( Pt 10), 2975 - 82
Acid tolerance in Listeria monocytogenes: the adaptive acid tolerance response (ATR) and growth-phase-dependent acid resistance; Davis MJ et al.; Listeria monocytogenes acquired increased acid tolerance during exponential growth upon exposure to sublethal acid stress, a response designated the acid tolerance response (ATR) . Maximal acid resistance was seen when the organism was exposed to pH 5.0 for 1 h prior to challenge at pH 3.0, although intermediate levels of protection were afforded by exposure to pH values ranging from 4.0 to 6.0 . A 60 min adaptive period was required for the development of maximal acid tolerance; during this period the level of acid tolerance increased gradually . Full expression of the ATR required de novo protein synthesis; chloramphenicol, a protein synthesis inhibitor, prevented full induction of acid tolerance . Analysis of protein expression during the adaptive period by two-dimensional gel electrophoresis revealed a change in the expression of at least 23 proteins compared to the non-adapted culture . Eleven proteins showed induced expression while 12 were repressed, implying that the ATR is a complex response involving a modulation in the expression of a large number of genes . In addition to the exponential phase ATR, L.monocytogenes also developed increased acid resistance upon entry into the stationary phase; this response appeared to be independent of the pH-dependent ATR seen during exponential growth.

Int J Syst Bacteriol, 1996 Oct, 46(4), 1088 - 92
The genus Nocardiopsis represents a phylogenetically coherent taxon and a distinct actinomycete lineage: proposal of Nocardiopsaceae fam . nov; Rainey FA et al.; The genus Nocardiopsis was shown to be phylogenetically coherent and to represent a distinct lineage within the radiation of the order Actinomycetales . The closest relatives of the genus Nocardiopsis are members of the genera Actinomadura, Thermomonospora, Streptosporangium, and Microtetraspora . The intrageneric structure of the genus Nocardiopsis is shown to consist of a highly related species group containing Nocardiopsis dassonvillei, Nocardiopsis alborubida, and Nocardiopsis antarctica and a second group of less highly related species comprising Nocardiopsis alba subsp . alba, Nocardiopsis alba subsp . prasina, and Nocardiopsis listeri . Nocardiopsis lucentensis occupies a position intermediate between the two species groups . The results of a 16S ribosomal DNA sequence analysis are generally consistent with the available chemotaxonomic, phenotypic, and DNA-DNA hybridization data . The phylogenetic position and the morpho- and chemotaxonomic properties of Nocardiopsis species support the creation of a family for the genus Nocardiopsis, Nocardiopsaceae fam . nov.

Proc Natl Acad Sci U S A, 1996 Oct 1, 93(20), 11008 - 13
Functions of interleukin 1 receptor antagonist in gene knockout and overproducing mice; Hirsch E et al.; Interleukin 1 receptor antagonist (IL-1ra) is a cytokine whose only known action is competitive inhibition of the binding of interleukin 1 (IL-1) to its receptor . To investigate the physiological roles of endogenously produced IL-1ra, we generated mice that either lack IL-1ra or overproduce it under control of the endogenous promoter . Mice lacking IL-1ra have decreased body mass compared with wild-type controls . They are more susceptible than controls to lethal endotoxemia but are less susceptible to infection with Listeria monocytogenes . Conversely, IL-1ra overproducers are protected from the lethal effects of endotoxin but are more susceptible to listeriosis . Serum levels of IL-1 following an endotoxin challenge are decreased in IL-1ra nulls and increased in IL-1ra overproducers in comparison to controls . These data demonstrate critical roles for endogenously produced IL-1ra in growth, responses to infection and inflammation, and regulation of cytokine expression.

Blood, 1996 Oct 1, 88(7), 2458 - 64
Hematopoiesis in mice lacking the entire granulocyte-macrophage colony-stimulating factor/interleukin-3/interleukin-5 functions; Nishinakamura R et al.; Interleukin-3 (IL-3), granulocyte-macrophage colony-stimulating factor (GM-CSF), and IL-5 are major hematopoietic cytokines produced by activated T cells and exhibit similar biologic activities by signaling through a common receptor subunit (beta c) . Mice lacking beta c show a pulmonary alveolar proteinosis-like disease and reduced numbers of peripheral eosinophils, which are explained by the lack of GM-CSF and IL-5 function, respectively . However, beta c-deficient hematopoietic cells do respond to IL-3 normally, probably through an additional beta subunit of the IL-3 receptor (beta IL3) that is present in the mouse . Thus, almost normal hematopoiesis in beta c-deficient mice may be caused by functional redundancy between IL-3 and GM-CSF . To clarify the role of the entire IL-3/GM-CSF/IL-5 system in hematopoiesis in vivo, we crossed the beta c mutant mice with mice deficient for IL-3 ligand to generate mice lacking the entire IL-3/GM-CSF/IL-5 functions . The double-mutant mice were apparently normal and fertile . The severity of the lung pathology in the beta c/IL-3 double-mutant mice showed normal hemodynamic parameters except for reduced numbers of eosinophils and the lack of eosinophilic response to parasites, which were also found in beta c mutant mice . The immune response of the beta c/IL-3 double-mutant mice to Listeria mono-cytogenes was normal, as was hematopoietic recovery after administration of the cytotoxic drug, 5-fluorouracil . Although it has been believed that IL-3/GM-CSF/IL-5 produced by activated T cells play a major role in expansion of hematopoietic cells in emergency, our results indicate that the entire function of IL-3/GM-CSF/IL-5 is dispensable for hematopoiesis in emergency as well as in the steady state . Thus, there must be an alternative mechanism to produce blood cells in both situations.

Regul Pept, 1996 Sep 16, 65(3), 219 - 23
Catecholamines inhibit alpha/beta interferon production induced by lipopolysaccharide; Andrade-Mena CE; In vitro incubation of Listeria monocytogenes immune spleen cells in the presence of the catecholamines epinephrine or norepinephrine inhibited the alpha/beta-interferon (IFN alpha/beta) synthesis induced by the mitogen lipopolysaccharide, in a manner that appeared to be concentration-dependent . Moreover, the inhibitory effect of both catecholamines epinephrine and norepinephrine on the synthesis of IFN alpha/beta was prevented by incubating immune spleen cells in the presence of propranolol, a beta-adrenergic antagonist agent.

Zh Mikrobiol Epidemiol Immunobiol, 1996 Sep-Oct, (5), 10 - 2
{Listeria in plants: an experimental study of its colonization, numbers and variability}; Pushkareva VI et al.; The possibility for Listeria monocytogenes to penetrate into plants from the soil via the root system was experimentally proved . Listeria were shown to continuously persist for 30 days (the term of observation) in the vegetative organs of wheat (roots, stems and leaves) . The concentration of Listeria was 10(9) CFU/g in the environment (soil extract) and the roots of wheat, 10(6)-10(7) CFU/g in stems, 10(8)-10(9) CFU/g in leaves . Six days later the dissociation of colonies in the S-form into small (up to 1 mm) and large (3-4 mm) was observed; in contrast to Listeria in large colonies, those in small colonies had high catalase activity and pronounced cytopathogenic action . The problem of the possible role of plants as the natural reservoir of bacteria, pathogenic for humans and animals, is discussed.

Rinsho Shinkeigaku, 1996 Sep, 36(9), 1107 - 9
{Erythromycin-induced hearing loss in a patient with Listeria monocytogenes meningo-ventriculitis}; Moriyasu H et al.; We report a 43-year-old woman who suffered from Listeria monocytogenes meningitis . She was admitted to our hospital because of headache, nausea, vomiting, and fever . On admission she had no abnormal neurological signs except for severe nuchal stiffness . Cerebrospinal fluid (CSF) examination on the day of admission revealed pleocytosis and increased total protein level . The CSF culture demonstrated Listeria monocytogenes . Because ampicillin therapy was not effective, erythromycin (8 g/day) was added . After 12 hours of erythromycin therapy, the patient complained of moderate hearing difficulty . Erythromycin was then stopped on the next day . Her hearing improved and became normal within 48 hours after discontinuation of erythromycin . Contrast MRI of the brain revealed enhancement of the ependyma of the lateral ventricle, suggesting the presence of ventriculitis . By parenteral administration of ampicillin and cephazolin, clinical symptoms improved quickly, and abnormal CSF and MRI findings were normalized . Listeria meningitis accompanied with ventriculitis has been reported in neonates and infants, but not in adults . In addition, this is the first case with erythromycin-induced hearing loss in the Japanese literature . Hearing should be regularly examined in patients who are treated with high-dose erythromycin (> or = 4 g/day), and the drug should be immediately discontinued when the patient develops hearing loss.

J Infect, 1996 Sep, 33(2), 79 - 85
Is amoxicillin-cotrimoxazole the most appropriate antibiotic regimen for listeria meningoencephalitis? Review of 22 cases and the literature; Merle-Melet M et al.; From June 1983 to January 1994, 22 adult patients with severe Listeria monocytogenes meningoencephalitis were observed in our Intensive Care Unit . Listeria monocytogenes was obtained in culture in cerebrospinal fluid or blood for every patient . Seven patients were treated with the combination ampicillin-aminoglycoside (group A) and 15 patients with the combination ampicillin (or amoxicillin)-cotrimoxazole (group A + C) . Risk factors and gravity scores were similar in both groups . Failure of the 'gold standard' regimen (group A) was significantly higher (57%) compared to group A + C (6.7%) (P < 0.05) . Mortality related to L . monocytogenes was 23.5% in group A compared to 6.7% in group A + C . Morbidity was reduced in group A + C (13.3%) compared to group A (60%) (P = 0.15) . This unique study seems to demonstrate that amoxicillin-cotrimoxazole should be the most appropriate therapeutic regimen for Listeria meningoencephalitis.

Int J Food Microbiol, 1996 Sep, 32(1-2), 235 - 42
Effect of combined lysozyme and lipase treatment on the survival of Listeria monocytogenes; Liberti R et al.; The effectiveness of polyphosphates or lipases to increase the lytic activity of lysozyme was evaluated both on Listeria monocytogenes suspended in buffer and on growing cultures incubated at different temperatures . At 5 degrees C and 37 degrees C polyphosphates combined with lysozyme did not result in the decrease of the number of non-growing L . monocytogenes cells . At the same incubation conditions, the addition of lipase to lysozyme significantly enhanced the bactericidal activity of lysozyme to an extent determined by pH, NaCl concentration and temperature.

Int J Food Microbiol, 1996 Sep, 32(1-2), 209 - 16
Listeria monocytogenes in bovine mastitis . Possible implication for human health; Jensen NE et al.; During the 23-year period 1972 through 1994 quarter milk samples from 1,132,958 cows originating from 36199 herds were examined for the presence of Listeria monocytogenes . Through the period the reference population amounted to 12,742,600 cow years and 401,682 herd years . The percentage of cows infected with L . monocytogenes varied from 0.01 to 0.1% (mean 0.04%) and of herds with an infected cow from 0.2 to 4.2% (mean 1.2%) through the period, showing a low but constant level of infection . A comparison of 33 isolates from bovine mastitis and 27 human clinical isolates was made by sero- and ribotyping . Serotyping showed that all bovine and 17 (63%) of the human isolates belonged to serogroup 1, whereas 10 (37%) of the human isolates belonged to serogroup 4 . Ribotyping using EcoRI as restriction enzyme divided the 60 isolates into 16 different types, 7 of which were found among both the bovine and human types . The combination of the typing methods showed that 26 (79%) bovine and 13 (48%) human isolates shared common types . This study showed that a low but constant percentage of Danish dairy herds have cows infected with L . monocytogenes and that some of the bovine types could be found among types causing human infections.

Int J Food Microbiol, 1996 Sep, 32(1-2), 159 - 72
Effects of carbon dioxide on the fate of Listeria monocytogenes, of aerobic bacteria and on the development of spoilage in minimally processed fresh endive; Carlin F et al.; Minimally processed fresh broad-leaved endive (Cichorium endivia L.) were stored at 3 and 10 degrees C in modified atmospheres containing air, 10% CO2/10% O2, 30% CO2/10% O2, and 50% CO2/10% O2 . The effects of these modified atmospheres on the fate of both aerobic bacteria and three strains of Listeria monocytogenes, was investigated . Increases in CO2 concentrations significantly reduced the growth of the aerobic microflora . The best preservation of the visual quality occurred on endive leaves stored in 10% CO2/10% O2, whereas leaves stored in 30% CO2/10% O2 and 50% CO2/10% O2, and to a lesser extent in air, showed extensive spoilage after storage . Listeria monocytogenes was slightly affected at 3 degrees C by the modified atmospheres, as compared to air . At 10 degrees C, results varied between replicate experiments, but L . monocytogenes generally grew better as the CO2 concentration was increased . The three test strains behaved in a similar way . In conclusion, among the modified atmospheres tested, a modified atmosphere containing 10% CO2/10% O2 resulted in improved visual quality of minimally processed fresh endive, without a marked effect on the growth of the aerobic microflora or of L . monocytogenes.

Int J Food Microbiol, 1996 Sep, 32(1-2), 133 - 44
Predictive modeling of the growth of Listeria monocytogenes in CO2 environments; Farber JM et al.; The effects of pH (5.5, 6.5), temperature (4, 7 and 10 degrees C) and carbon dioxide (10, 30, 50, 70 and 90%) on the growth and/or survival of a five strain mixture of Listeria monocytogenes were examined in brain heart infusion broth . All three variables had a major influence on the growth characteristics of the organism . As expected, both the lag time and generation time increased as the CO2 level increased, and as pH and temperature decreased . Growth over a 30-day period was observed at all parameter combinations tested, except at pH 5.5, 4 degrees C in the presence of either 50, 70 or 90% carbon dioxide . Two primary models, the Gompertz and Baranyi equations, were compared for their ability to describe the growth of L . monocytogenes . In general, the Gompertz model predicted both longer lag and shorter generation times, compared to the Baranyi model . The Baranyi model appeared to fit the overall data better than the Gompertz model . However, these differences were often small . Response surface models were developed for predicting the effects and interactions of the three independent variables on the growth and/or survival of L . monocytogenes in the different modified atmospheres . Results demonstrate the importance of strict temperature control for maintaining the advantages of food shelf life extension in enriched carbon dioxide environments . The information obtained in this study could be used as a guide to manufacturers of modified-atmosphere packaged foods, especially when designing products in which this organism may be a concern.

Int J Food Microbiol, 1996 Sep, 32(1-2), 73 - 90
Predictive models of the effect of temperature, pH and acetic and lactic acids on the growth of Listeria monocytogenes; George SM et al.; The combined effect of temperature (1-20 degrees C), pH (4.5-7.2) and acetic acid (0-10,000 mg/l; model 1) or lactic acid (0-20,000 mg/l; model 2) on growth of Listeria monocytogenes in laboratory media was studied . Growth curves at various combinations of temperature, pH and acid concentration were fitted by the model of Baranyi and Roberts (1994), and specific growth rates derived from the curve fit were modelled . Predictions of growth from the models were compared with data in the literature, and this showed the models to be suitable for use in predicting growth of L . monocytogenes in a range of foods including meat, poultry, fish, egg and milk and dairy products . The two models are compatible, i.e . they give similar predictions for cases when no acid is present.

Poult Sci, 1996 Sep, 75(9), 1126 - 32
Thermal and biological treatments to control psychrotrophic pathogens; Sheldon BW et al.; Over the past decade, advances in egg processing technologies have permitted commercial production of ultrapasteurized liquid whole egg (LWE) products with a shelf-life of greater than 10 wk at 4 C . The inactivation and control of psychrotrophic pathogens such as Listeria monocytogenes and Aeromonas hydrophila in extended shelf-life LWE and conventionally pasteurized egg products is an ongoing food safety concern . This manuscript reports on the common features of these two psychrotrophic pathogens, their incidence in egg products, and their survival, growth potential, and heat resistance in liquid egg . Furthermore, this manuscript reports in detail on the results of two specific studies conducted in our laboratory whose objectives were: 1) to determine the heat resistance (D-values) of A . hydrophila in LWE using a low-volume immersed sealed glass capillary tube (ISCT) procedure; 2) to assess the impact of methodology (i.e., ISCT procedure vs a conventional capped test tube procedure) on the apparent thermal resistance of A . hydrophila; and 3) to report on the use of the bacteriocin nisin to restrict the survival of L . monocytogenes in ultrapasteurized LWE stored at refrigeration temperatures.

J Clin Microbiol, 1996 Sep, 34(9), 2148 - 53
Subtyping Listeria monocytogenes isolates genetically related to the Swiss epidemic clone; Boerlin P et al.; Macrorestriction analysis by pulsed-field gel electrophoresis was used to assess the diversity of strains within the epidemic-associated electrophoretic type 1 (ET1) clone of Listeria monocytogenes . For this purpose, a total of 144 isolates from Switzerland shown by multilocus enzyme electrophoresis to belong to the ET1 were examined . These isolates were subtyped by macrorestriction analysis using the enzymes ApaI and SmaI and field inversion gel electrophoresis . Among these 144 isolates, 45 were isolated in human listeriosis cases of the postepidemic period of 1988 to 1993 and 44 were isolated in animal listeriosis cases of the same period . Forty-seven isolates were from the epidemic period of 1983 to 1987, and eight additional isolates were from cattle from two different farms . Twenty-nine different subtypes could be identified among the 144 isolates tested . Five major subtypes were found more frequently than the others during the postepidemic period, both in humans and in animals . Two of these subtypes had been previously implicated in outbreaks of listeriosis, thus suggesting that particular pulsed-field gel electrophoresis subtypes may be frequently associated with disease in humans and animals . Two of these frequent subtypes were also suspected to be related to small clusters of listeriosis cases during the postepidemic period . The results obtained by typing epidemiologically related isolates from different animals within the same farms and from different body sites of a given patient confirmed the potential of macrorestriction analysis for epidemiological studies restricted to short periods of time and to small number of isolates . The analysis of 47 isolates related to the Swiss listeriosis epidemic period of 1983 to 1987 and the use of Southern blotting and hybridization experiments show that the interpretation of relatedness between isolates presenting slightly different macrorestriction patterns may be more complex than commonly accepted . In such cases, careful interpretation of the potential molecular mechanisms leading to the differences observed between patterns is necessary.

J AOAC Int, 1996 Sep-Oct, 79(5), 1083 - 94
TECRA Listeria Visual Immunoassay (TLVIA) for detection of Listeria in foods: collaborative study; Knight MT et al.; A collaborative study involving 26 laboratories and 5 food types was performed to compare the TECRA Listeria Visual Immunoassay (TLVIA) with standard culture methods . Three foods (lettuce, ice cream, and fish fillets), under the jurisdiction of the U.S . Food and Drug Administration, and 2 foods (cooked chicken and cooked ground turkey), under the jurisdiction of the U.S . Department of Agriculture, were used to determine the effectiveness of the TLVIA . Of the 900 samples tested, 300 were inoculated with low levels (1-5 cells/25 g) of Listeria spp . and 300 were inoculated with high levels of Listeria spp . (10-50 cells/25 g) . Method agreement between the conventional culture methods and TLVIA (visual) was 94.7% . Method agreement between the conventional culture methods and TLVIA (reader) was 93.6% . The colorimetric polyclonal enzyme immunoassay (TLVIA) for detection of Listeria in foods has been adopted first action by AOAC INTERNATIONAL.

Curr Biol, 1996 Sep 1, 6(9), 1084 - 6
Common entry mechanisms . Bacterial pathogenesis; Marra A et al.; The recent identification of E-cadherin as the cell-surface receptor for the Listeria monocytogenes adhesin, internalin, indicates that pathogenic bacteria exploit a variety of host surface molecules for entry and that they may share some common strategies for uptake into host cells.

Appl Environ Microbiol, 1996 Sep, 62(9), 3128 - 32
Acid adaptation of Listeria monocytogenes can enhance survival in acidic foods and during milk fermentation; Gahan CG et al.; We have previously shown that tolerance to severe acid stress (pH 3.5) can be induced in Listeria monocytogenes following a 1-h adaptation to mild acid (pH 5.5), a phenomenon termed the acid tolerance response (ATR) (B . O'Driscoll, C . G . M . Gahan, and C . Hill, Appl . Environ . Microbiol . 62:1693-1698, 1966) . In an attempt to determine the industrial significance of the ATR, we have examined the survival of adapted and nonadapted cells in a variety of acidic foods . Acid adaptation enhanced the survival of L . monocytogenes in acidified dairy products, including cottage cheese, yogurt, and whole-fat cheddar cheese . Acid-adapted L . monocytogenes cultures also demonstrated increased survival during active milk fermentation by a lactic acid culture . Similarly, acid-adapted cells showed greatly improved survival in low-pH foods (orange juice and salad dressing) containing acids other than lactic acid . However, in foods with a marginally higher pH, such as mozzarella cheese, a commercial cottage cheese, or low-fat cheddar cheese, acid adaptation did not appear to enhance survival . We have previously isolated mutants of L . monocytogenes that are constitutively acid tolerant in the absence of an induction step (O'Driscoll et al., Appl . Environ . Microbiol . 62:1693-1698, 1996) . In the present study, one such mutant, ATM56, demonstrated an increased ability to survive in low-pH foods and during milk fermentation when compared with the wild-type strain . Significant numbers of ATM56 could be recovered even after 70 days in both whole-fat and low-fat cheddar cheese . Collectively, the data suggest that ATR mechanisms, whether constitutive or induced, can greatly influence the survival of L . monocytogenes in low-pH food environments.

Appl Environ Microbiol, 1996 Sep, 62(9), 3088 - 93
Role of osmolytes in adaptation of osmotically stressed and chill-stressed Listeria monocytogenes grown in liquid media and on processed meat surfaces; Smith LT; Listeria monocytogenes is a food-borne pathogen that is widely distributed in nature and is found in many kinds of fresh and processed foods . The pervasiveness of this organism is due, in part, to its ability to tolerate environments with elevated osmolarity and reduced temperatures . Previously, we showed that L . monocytogenes adapts to osmotic and chill stress by transporting the osmolyte glycine betaine from the environment and accumulating it intracellularly (R . Ko, L . T . Smith, and G . M . Smith, J . Bacteriol . 176:426-431, 1994) . In the present study, the influence of various environmental conditions on the accumulation of glycine betaine and another osmolyte, carnitine, was investigated . Carnitine was shown to confer both chill and osmotic tolerance to the pathogen but was less effective than glycine betaine . The absolute amount of each osmolyte accumulated by the cell was dependent on the temperature, the osmolarity of the medium, and the phase of growth of the culture . L . monocytogenes also accumulated high levels of osmolytes when grown on a variety of processed meats at reduced temperatures . However, the contribution of carnitine to the total intracellular osmolyte concentration was much greater in samples grown on meat than in those grown in liquid media . While the amount of each osmolyte in meat was less than 1 nmol/mg (fresh weight), the overall levels of osmolytes in L . monocytogenes grown on meat were about the same as those in liquid samples, from about 200 to 1,000 nmol/mg of cell protein for each osmolyte . This finding suggests that the accumulation of osmolytes is as important in the survival of L . monocytogenes in meat as it is in liquid media.

J Infect Dis, 1996 Sep, 174(3), 651 - 4
Comparison of the antimicrobial activity of deactivated human macrophages challenged with Aspergillus fumigatus and Listeria monocytogenes; Meier-Osusky I et al.; The anticonidial activity of human monocytes deactivated by cytokines interleukin (IL)-4 and IL-10 and the hormone dexamethasone was studied and compared with antilisterial activity . Dexamethasone had the largest effect on the anticonidial activity and suppressed germination-inhibiting activity and elimination of ingested spores by macrophages more than the cytokines did . Maximally active concentrations of IL-10 had a similar but significantly smaller deactivating effect . IL-4, in contrast to IL-10 and dexamethasone, did not reduce anticonidial activity . However, IL-4 and IL- 10 were equally potent in deactivating human macrophages against Listeria monocytogenes, whereas dexamethasone was significantly less potent in the Listeria model . These observations indicate that all three mediators lessen antimicrobial activity but that this effect depends on the test organism studied and is apparently mediated through regulation of different antimicrobial systems operating against a particular microorganism.

Infect Immun, 1996 Sep, 64(9), 3946 - 9
Treatment with the antigranulocyte monoclonal antibody RB6-8C5 impairs resistance of mice to gastrointestinal infection with Listeria monocytogenes; Czuprynski CJ et al.; Treatment with the antigranulocyte monoclonal antibody (MAb) RB6-8C5 increased the severity of infection in mice intragastrically inoculated with Listeria monocytogenes . Most MAb RB6-8C5-treated mice died when inoculated intragastrically with as few as 4 x 10(4) L . monocytogenes bacteria, whereas most control mice survived intragastric inoculation with 4 x 10(8) L . monocytogenes bacteria . The increased severity of infection in MAb RB6-8C5-treated mice appeared to result from listerial multiplication in the spleen and liver rather than from local proliferation in the intestinal tract or mesenteric lymph nodes.

Infect Immun, 1996 Sep, 64(9), 3925 - 9
Iron availability affects entry of Listeria monocytogenes into the enterocytelike cell line Caco-2; Conte MP et al.; The influence of iron on the entry of Listeria monocytogenes into Caco-2 cells was studied . Iron availability was found to modify the surface hydrophobicity and protein profile of L . monocytogenes, with the result that cell invasion strongly increased upon bacterial growth in iron-rich medium . The enhanced invasive capability of iron-overloaded L . monocytogenes cells correlates to the higher-level expression of the inlAB virulence genes, which were positively iron regulated at the transcriptional level.

Infect Immun, 1996 Sep, 64(9), 3901 - 4
Transforming growth factor beta is protective in host resistance against Listeria monocytogenes infection in mice; Nakane A et al.; The role of transforming growth factor beta (TGF-beta) in host resistance against Listeria monocytogenes infection was studied with mice . The constitutive expression of TGF-beta 1 mRNA was observed in the spleens and livers of mice before and after infection . Injecting the mice with anti-TGF-beta 1 peptide serum resulted in diminished antilisterial resistance, whereas the administration of human platelet-derived TGF-beta 1 enhanced the resistance . Moreover, mice were protected against lethal infection when treated with TGF-beta 1 . These results suggest the TGF-beta 1 might be involved in antilisterial resistance . On the other hand, injecting the mice with TGF-beta 1 resulted in a decrease in the titers of endogenous gamma interferon, tumor necrosis factor alpha, and interleukin-6, which are crucial in antilisterial resistance, in sera and in extracts of spleen and liver . Thus, a complicated mechanism might be involved in the role of TGF-beta 1 in host resistance against L . monocytogenes infection.

Infect Immun, 1996 Sep, 64(9), 3728 - 35
Elimination of the listeriolysin O-directed immune response by conservative alteration of the immunodominant listeriolysin O amino acid 91 to 99 epitope; Bouwer HG et al.; A major H2-Kd-presented epitope for antilisterial cytotoxic T lymphocytes (CTLs) is the nanomer peptide which corresponds to the amino acid 91 to 99 (aa91-99) sequence from listeriolysin O (LLO) . Although the LLO sequence contains at least five additional nanomer peptides which also satisfy the H2-Kd binding motif, aa91-99 is the only LLO-derived target peptide that is recognized by antilisterial CTLs following infection of BALB/c mice with Listeria monocytogenes . In order to investigate further the immunodominance of the LLO aa91-99 epitope following endogenous processing of LLO, we introduced a point mutation in hly (the gene for LLO) which results in a conservative Y-to-F substitution for the anchor residue at position 2 within the aa91-99 sequence . This "92F" L . monocytogenes mutant produces biologically active LLO and is phenotypically indistinct from wild-type L . monocytogenes in terms of intracellular growth in vitro and virulence in vivo . BALB/c mice actively immunized with the 92F L . monocytogenes mutant are protected against challenge with wild-type L . monocytogenes . Antilisterial CTLs from mice immunized with the 92F mutant lyse targets infected with L . monocytogenes; however, these CTLs do not lyse target cells pulsed with either the LLO aa91-99 peptide, other LLO-derived peptides which satisfy the H2-Kd binding motif, or a peptide corresponding to the LLO aa91-92F-99 sequence . Target cells pulsed with the LLO aa91-92F-99 peptide are, however, lysed by wild-type LLO aa91-99-specific cytotoxic cells . Thus, a conservative amino acid change in the first anchor residue of the immunodominant aa91-99 sequence of LLO eliminates the induction of the cytotoxic cell response to this epitope as well as to any of the other candidate LLO-derived peptides which fit the H2-Kd binding motif . The lack of anti-LLO-specific CTLs following immunization with the 92F mutant does not appear, however, to influence the protective antilisterial immune response.

Infect Immun, 1996 Sep, 64(9), 3632 - 40
CD8 T-cell recognition of macrophages and hepatocytes results in immunity to Listeria monocytogenes; Harty JT et al.; CD8 T cells are effective mediators of specific immunity to infection by Listeria monocytogenes, a bacterial pathogen that initially infects macrophages in the spleen and liver and subsequently spreads to hepatocytes and unidentified parenchymal cells in the spleen . To identify the in vivo target cells of L . monocytogenes-immune CD8 T cells, adoptive transfer assays were performed with bone marrow chimeric or transgenic host mice which had been manipulated to alter the major histocompatibility complex molecules expressed on macrophages or hepatocytes . L . monocytogenes-immune CD8 T cells mediate significant immunity in BDF1-->beta 2 M-/- chimeras, comparable to that seen in unmanipulated BDF1 recipients . L . monocytogenes-immune CD8 T cells also mediate significant antilisterial immunity in parent-->F1 chimeras when the CD8 T cells are syngeneic with the bone marrow donor . These data demonstrate that bone marrow-derived macrophages are major targets for L . monocytogenes-immune CD8 T cells in adoptive transfer assays . Interestingly, significant immunity was observed in parent-->F1 chimeras when the L . monocytogenes-immune CD8 T cells were not syngeneic with the bone marrow donor, suggesting that recognition of Listeria-infected non-bone-marrow-derived cells such as hepatocytes may also occur in vivo . Consistent with this possibility, H-2Kb-restricted CD8 T cells specific for the listeriolysin O molecule mediate significant immunity in the liver, but not the spleen, in transgenic mice expressing H-2Kb only on hepatocytes . In addition, Listeria-specific CD8 T cells lyse Listeria-infected hepatocyte-like cells in vitro . Thus, Listeria-infected hepatocytes can be recognized by CD8 T cells in vivo and in vitro.

Infect Immun, 1996 Sep, 64(9), 3475 - 83
Differential regulation of cytokine and cytokine receptor mRNA expression upon infection of bone marrow-derived macrophages with Listeria monocytogenes; Demuth A et al.; Cytokine and cytokine receptor mRNA expression was analyzed by PCR-assisted amplification of RNA extracted from bone marrow-derived macrophages (BMM phi) at different time points after infection with Listeria monocytogenes . The mRNAs for the cytokines interleukin-1 alpha (IL-1 alpha), IL-1 beta, and tumor necrosis factor alpha (TNF-alpha) were induced early after infection, whereas IL-6 mRNA appeared later and even nonhemolytic Listeria strains, which are unable to grow inside eukaryotic cells, induced the same cytokine mRNAs at levels similar to those of the wild-type strain . In most cases, the amounts of cytokines determined by various bioassays correlated with the level of mRNA induction . Inhibition of phagocytic uptake of L . monocytogenes by cytochalasin D treatment resulted in adherent bacteria which still induced the proinflammatory cytokines . In BMM phi, the level of IL-1 receptor II mRNA was unaffected, whereas mRNA expression of the two subtypes of tumor necrosis factor receptors (TNF-RI and TNF-RII) was differentially regulated upon infection: transcription of TNF-RI was reduced, and that of TNF-RII mRNA was induced . Similar to the decreased TNF-RI mRNA expression, gamma interferon receptor mRNA was downregulated in L . monocytogenes-infected BMM phi . This dose- and time-dependent induction or downregulation of cytokine receptor mRNA following L . monocytogenes infection of BMM phi was not observed upon infection of established macrophage-like cell lines J774 and P388D1 . Induction of IL-6 mRNA as well as IL-1 alpha/beta and TNF-alpha mRNAs upon L . monocytogenes infection of BMM phi occurs independently of autocrine TNF-alpha signaling via TNF-RI or TNF-RII, as shown by infection of TNF-RI- and TNF-RII-deficient macrophages derived from mutant B6 x 129 mice . In contrast to gamma interferon receptor mRNA, both TNF receptor subtype mRNAs were not influenced by L . monocytogenes infection of hybrid (B6 x 129) mouse macrophages . Whereas the proinflammatory cytokine mRNAs were even induced after infection with the nonpathogenic species L . innocua, no alteration of cytokine receptor mRNA expression was observed after challenge of BMM phi with this nonpathogenic species, suggesting that the modulation of cytokine and cytokine receptor expression by L . monocytogenes could be an important way of inhibition of macrophage stimulation.

Cell Immunol, 1996 Aug 25, 172(1), 118 - 25
Suppression of IFN-gamma production from Listeria monocytogenes-specific T cells by endogenously produced nitric oxide; Xiong H et al.; The induction of nitric oxide (NO) by IFN-gamma has been well documented in a variety of experimental settings, but so far there has been no report on whether the endogenously produced NO can suppress IFN-gamma production . In the present study, CD4+ T cells from Listeria monocytogenes-immune mice produced IFN-gamma upon stimulation with specific antigen and NO was generated in culture . When NG-monomethyl-L-arginine (NMMA) was added to the culture at a dose sufficient for the complete blockade of NO production, there was a significant level of enhancement of IFN-gamma production, which was also dose dependently correlated with addition of NMMA . RT-PCR revealed that IFN-gamma mRNA per given amount of total RNA remained the same irrespective of NO blockade by NMMA; however, total RNA recovery was significantly higher in the culture with NMMA . The endogenously produced NO suppressed T-cell proliferation which can be restored by the addition of NMMA . Sodium nitroprusside, a spontaneous NO generator, inhibited T-cell proliferation dose dependently and suppressed IFN-gamma production . Taken together, it may be concluded that NO down-regulates IFN-gamma production mainly by inhibiting T-cell proliferation.

J Toxicol Environ Health, 1996 Aug 9, 48(5), 419 - 25
Differential inhibition of IL-1 alpha and TNF-alpha generation by ammonium metavanadate in murine macrophages; Vaddi K et al.; The relationship between immunotoxicity of ammonium metavanadate (NH4VO3) and levels of tumor necrosis factor-alpha (TNF-alpha) and interleukin-1 (IL-1) was studied with a NH4VO3-treated murine macrophage-like cell line, 1774 and resident peritoneal macrophages (PEM) obtained from treated mice . Lipopolysaccharide (LPS)-induced elevation of extracellular TNF-alpha in PEM and 1774 cells was not markedly affected by prior treatment with vanadate . However, PEM from treated mice at 10 mg V/kg (10V) had a significantly lower level of LPS-induced intracellular TNF-alpha . NH4VO3-treated 1774 cells at 3.6 (V1) and 7.2 micrograms V/10(7) cells (V2) had significantly higher levels of intracellular TNF-alpha than the PO4 and V3 (10.8 micrograms V/10(7) cells) groups . Although the four PEM groups showed no marked difference in extracellular IL-1 alpha levels, PEM from treated mice at 2.5V and 10V had significantly lower levels of intracellular IL-1 alpha than those from control groups . 1774 cells from PO4 and NH4Cl groups showed significant increases in intracellular IL-1 alpha following treatment with LPS . However, 1774 cells with prior treatment with vanadate revealed significant reduction in levels of LPS-induced intracellular IL-1 alpha when compared to control groups . Therefore, the previously reported reduced resistance of vanadate-treated mice to Listeria monocytogenes could be attributed to an inhibitory effect on the production of IL-1 alpha in macrophages.

Enferm Infecc Microbiol Clin, 1996 Aug-Sep, 14(7), 416 - 21
{Clinical characteristics and epidemiologic study of a listeriosis outbreak in Grand Canary}; Elcuaz R et al.; BACKGROUND AND METHODS: Human infections caused by Listeria monocytogenes often present as sporadic cases without any epidemiological relationship among them; however they also appear as outbreaks that are usually detected by an increase in the number of cases diagnosed by hospitals of the geographic area . Between December 1991 and May 1993, twenty four cases of listeriosis were detected in three hospitals of Las Palmas de Gran Canaria; and they were classified as an outbreak . Our report describes its clinical, epidemiological and microbiological aspects . RESULTS AND CONCLUSIONS: Twenty four cases of listeriosis were diagnosed, 12 occurred in pregnant women or neonates (5 and 7 respectively) and 12 in non pregnant adults . All adult infections were community-acquired . The incidence rate was, for the epidemic area, 76.3 cases per million population during the period considered (18 months) . Among non pregnant adults, 9/12 patients had some underlying disease and 9/12 presented CNS affection (meningitis and/or cerebritis) . In the group of pregnant women, 4 cases occurred in the second trimester and fetal loss was caused; one case was detected in the third trimester and four weeks later the patient delivered an unaffected infant . All cases of neonatal listeriosis presented as early-onset sepsis . Of the 24 strains of L . monocytogenes, 21 were serotype 4, two were serotype 1 and one was not typeable . Strains from 12 patients were available for epidemiological analysis, seven of which corresponded to the same pattern and there were three more different patterns.

Lett Appl Microbiol, 1996 Aug, 23(2), 125 - 8
Lactate and acetate production in Listeria innocua; Kelly AF et al.; Listeria innocua NCTC 11289 was grown aerobically in continuous culture in defined media at 30 degrees C . Both acetate and lactate were produced, the proportion of acetate decreased with increasing dilution rate . Enzymatic analysis showed lactate dehydrogenase was activated 10-fold by fructose-1, 6-bisphosphate . The presence of phosphate acetyltransferase and acetate kinase but not pyruvate oxidase was detected, suggesting the sequential action of phosphate acetyltransferase and acetate kinase to produce acetate from acetyl CoA via acetylphosphate.

J Appl Bacteriol, 1996 Aug, 81(2), 167 - 73
Adsorption of bacteriocins by ingestible silica compounds; Wan J et al.; Bacteriocins including nisin, pediocin PO2, brevicin 286 and piscicolin 126 were adsorbed from culture supernates by various food-grade porous silica anti-caking agents and the food colourant, titanium dioxide . All the porous silica (calcium silicate or silicon dioxide) materials showed substantial capacity in adsorbing bacteriocin activities from the culture supernate and biological activity was recovered in the adsorbents . In contrast, the food colourant titanium dioxide adsorbed most of the bacteriocin activity from the supernate, with minimal biological activity retained in the adsorbent . Experiments with piscicolin 126 showed that optimum adsorption could be achieved with Micro-Cel E within 30 min, independent of the supernate pH (2.0-10.0) . Piscicolin activity of up to 5 x 10(7) AU g(-1) of Micro-Cel E was obtained after adsorption from culture supernates and the adsorbed piscicolin demonstrated substantial biological activity against Listeria monocytogenes in both broth and a milk growth medium.

Immunology, 1996 Aug, 88(4), 544 - 50
CD4+ cytolytic effectors are inefficient in the clearance of Listeria monocytogenes; Serody JS et al.; Cytotoxic T lymphocytes (CTL) recognize and lyse target cells through the interaction of the T-cell receptor complex with the class I or class II major histocompatibility complex (MHC) . The production of class I-restricted CTL has been shown to be critical to the elimination of specific pathogens including Listeria monocytogenes . However, the function of class II-restricted CTL in the clearance of intracellular pathogens is poorly understood . H-2b beta 2-microglobulin-deficient mice (beta 2M-/-) are not able to produce CD8+ CTL in response to infection with L . monocytogenes . We used this model to evaluate the efficacy of class II-restricted CTL, in the absence of a class I-restricted response, during a primary infection with L . monocytogenes . We demonstrate that, despite their effectiveness in adoptive transfer of protection, Listeria-specific CD4+ class II-restricted cytotoxic lymphocytes are ineffective in decreasing titres of L . monocytogenes in the spleen was found established infection . In beta 2M-/- mice, persistence of L . monocytogenes in the spleen was found preferentially in class II-negative cells . Surprisingly, class I-restricted CTL from C57BL/6 mice were capable of decreasing bacterial titres during an established infection even in the absence of detectable class I on the surface of cells from beta 2M-/- mice . These data strongly suggest that, in the absence of a class I-restricted response, pathogens that elicit a class II-restricted cytotoxic response may escape prompt eradication by the immune system.

Int J Food Microbiol, 1996 Aug, 31(1-3), 349 - 55
The sub-typing of Listeria monocytogenes isolates from food, environments surrounding food manufacturing sites, and clinical samples in New Zealand using multilocus enzyme electrophoresis; Flint SH et al.; Listeria monocytogenes strains isolated from food (cheese, meat and fish), environments surrounding food manufacturing sites, and clinical samples from throughout New Zealand were analyzed by multilocus enzyme electrophoresis . One hundred and twenty four strains were divided into 56 electrophoretic types, containing primarily clinical isolates and environmental isolates.

Int J Food Microbiol, 1996 Aug, 31(1-3), 333 - 40
Incidence of Listeria spp . in tropical fish; Jeyasekaran G et al.; The incidence of Listeria spp . in tropical fish and shellfish was studied . The isolation protocol included a pre-enrichment, followed by two selective enrichment steps and plating on three selective agars . Listeria monocytogenes could be detected in 17.2% of finfish and 12.1% of shellfish . L . innocua was the most common species encountered . In 6.9% finfish and 5.6% shellfish, both L . monocytogenes and L . innocua were detected . Polymerase chain reaction (PCR)-based amplification of internal fragments of the iap gene was found to be useful in differentiation of L . monocytogenes from L . innocua.

Int J Food Microbiol, 1996 Aug, 31(1-3), 245 - 62
Typing of Listeria monocytogenes by monocin and phage receptors; Bannerman E et al.; One hundred strains of Listeria monocytogenes from both sporadic and epidemic cases were typed by monocin production combined with phage receptor and reverse phage receptor methods . The monocin-phage combination gave 72 types with 100% typability and 97% reproducibility . The results were compared to those of serotyping, phage typing, ribotyping, multilocus enzyme electrophoresis, restriction enzyme analysis and RAPD (random amplification of polymorphic DNA) . The monocin/phage types were comparable in terms of discrimination with other methods for epidemiological investigations . The index of discrimination of using the monocin typing and phage receptor/reverse phage receptor method combination (0.99) for both the 87 epidemiologically unrelated strains and the epidemiologically important serogroup 4 strains was the highest of the seven different methods analysed . This combination of methods was simple, highly discriminatory and reproducible and can be carried out in a non-specialized laboratory . However, like most of the other Listeria typing methods, both the method and the indicator test strains need to be standardized.

Int J Food Microbiol, 1996 Aug, 31(1-3), 161 - 71
Pathways of Listeria monocytogenes contamination in the meat processing industry; Nesbakken T et al.; One hundred and thirty-three isolates of Listeria monocytogenes from deboned fresh meat, production environment, cold cuts from five meat processing plants and from one plant producing cured dried sausages, were characterized using multilocus enzyme electrophoresis . On the basis of electrophoretically demonstrable allelic variation at 21 enzyme loci, 21 electrophoretic types (ETs) were distinguished . Analysis of the genetic relationships among the 21 ETs revealed two distinct clusters: Cluster A and Cluster B . With the exception of two isolates from one plant, all isolates from deboned fresh meat belonged to Cluster B . During processing of cold cuts, however, isolates belonging to Cluster A became more frequent, and only one of the 37 isolates from cold cuts belonged to Cluster B . In contrast, six of the nine isolates from cured dried sausages had ETs in Cluster B . One clone of Cluster A, ET-6 was isolated from cold cuts in four of six plants . This is one of the ETs most frequently recovered from patients in Norway . Isolates of ET-6 were further characterized using restriction fragment length polymorphism (RFLP) analysis of chromosomal DNA . Six distinct restriction patterns were distinguished among the 44 ET-6 strains . In one plant, four different RFLP patterns could be identified . Two clone variants seemed to have colonized different areas in this plant for at least four years . However, in each of the other plants, all ET-6 isolates had the same RFLP patterns.

Int J Food Microbiol, 1996 Aug, 31(1-3), 133 - 47
Listeriolysin O production and pathogenicity of non-growing Listeria monocytogenes stored at refrigeration temperature; Buncic S et al.; Three haemolytic, pathogenic strains of Listeria monocytogenes (a reference strain NCTC 7973, a food-derived strain L70 and a human strain L94) and a control strain of Listeria innocua L27 were held in phosphate-buffered saline (PBS) of pH 7.0 or 5.5 at 4 degrees C for 4 weeks . The number of viable cells did not change significantly during this storage (the cells were non-growing) . Titers of Listeria listeriolysin O (LLO) activity against washed human erythrocytes and the pathogenicity of non-growing bacterial cells for 14-day-old chick embryos were determined before storage and after 1, 2, 3 and 4 weeks of storage . Prolonged storage at 4 degrees C affected both LLO production and pathogenicity of the non-growing cells, but effects were strain- and pH-dependent . At pH 7.0, all three L . monocytogenes strains had lost LLO activity after 2 weeks of storage . At pH 5.5, the reference and the food strains lost LLO activity 1 week later than when stored at neutral pH, and the human strain maintained LLO activity throughout the 4-week period . Pathogenicity of the reference strain stored at pH 7.0 and 5.5 and that of the food strain stored at pH 7.0 decreased during storage at 4 degrees C . However, the human strain stored at pH 7.0 and 5.5, and the food strain stored at pH 5.5, maintained their pathogenicity throughout the 4-week period . In all cases, non-growing L . monocytogenes cells that had ceased LLO production and/or had a reduced pathogenicity, recovered these characteristics after growth in media at 37 degrees C . This study indicates that prolonged storage of chilled-foods in which L . monocytogenes is present, but not growing may have the desirable result that the L . monocytogenes has a reduced ability to cause illness in humans . As well, pathogenicity testing involving growth of L . monocytogenes in laboratory media may not reflect the actual pathogenicity of the organism in the food as eaten.

Mol Microbiol, 1996 Aug, 21(4), 823 - 37
A new PrfA-regulated gene of Listeria monocytogenes encoding a small, secreted protein which belongs to the family of internalins; Engelbrecht F et al.; A mutant of Listeria monocytogenes EGD was constructed that carries an extended deletion removing the entire PrfA-regulated gene cluster from plcA to plcB and a second deletion inactivating the inlA gene . Upon supplementation of this mutant with multiple gene copies of prfA, a protein of 30 kDa was detected in the supernatant of the mutant strain . The gene encoding this protein was obtained by direct and inverse polymerase chain reaction using oligonucleotide primers that were deduced from partial amino acid sequences of the purified 30 kDa protein . The amino acid sequence of the gene product revealed a protein of 297 amino acids that carried eight repeat units with high homology to those of the two known internalin proteins A and B . This secretory protein, termed internalin C, is much smaller than InlA or InlB and its complete sequence is related to the two known internalins . The gene InlC is transcribed into a monocistronic mRNA from a single promoter which shows a typical consensus sequence for PrfA-binding at the position -40 . In contrast to the transcription of the InlAB operon, which is downregulated after shift of an L . monocytogenes EGD culture from brain-heart infusion into minimum essential medium (MEM), transcription of inlC is induced in MEM like most of the other known PrfA-regulated virulence genes . In addition, InlC is strongly transcribed in the cytoplasm of phagocytic J774 cells whereas inlA is poorly transcribed under these conditions, suggesting that internalin C may play a role in a late stage of L . monocytogenes infection rather than in the uptake of L . monocytogenes by non-professional phagocytic cells . An InlC deletion mutant shows reduced virulence when tested in an intravenous mouse model, but intracellular replication of the mutant in Caco-2 and J774 cells appears to be comparable with that of the wild-type strain.

Mol Microbiol, 1996 Aug, 21(3), 579 - 92
Internalin must be on the bacterial surface to mediate entry of Listeria monocytogenes into epithelial cells; Lebrun M et al.; Entry of Listeria monocytogenes into cultured epithelial cells requires production of internalin, a protein with features characteristic of some Gram-positive bacterial surface proteins, in particular an LPXTG motif preceding a hydrophobic sequence and a few basic residues at its C-terminal end . By immunofluorescence and immunogold labelling, we show that in wild-type L . monocytogenes, internalin is present on the cell surface and has a polarized distribution similar to that of ActA, another surface protein of L . monocytogenes involved in actin assembly . Through a genetic analysis, we establish that the C-terminal region of internalin is necessary for cell-surface association, and that although internalin is partially released in the culture medium, its location on the bacterial surface is required to promote entry . Finally, using a 'domain-swapping' strategy-replacement of the cell wall anchor of IniA by the membrane anchor of ActA- we show that the reduced ability to adhere and enter cells of strains expressing IniA-ActA correlates with a lower amount of surface-exposed internalin . Taken together, these results suggest that internalin exposed on the bacterial surface mediates direct contact between the bacterium and the host cell.

Can J Neurol Sci, 1996 Aug, 23(3), 220 - 3
Listeria spinal cord abscess--clinical and MRI findings; Chu JY et al.; BACKGROUND: Intramedullary spinal cord abscess due to Listeria Monocytogenes is an uncommon condition usually affecting immunocompromised patients . METHOD: Case study . RESULTS: A 69-year-old man presented with 3 weeks history of subacute paralysis of both lower limbs and the left upper limb . Myelogram and CT scan showed a widened upper cervical cord . CSF revealed lymphocytosis, moderately elevated protein and depressed glucose . A gadolinium-enhanced MRI showed diffuse cervical cord edema with two ring-enhancing lesions at C2-C3 . Blood and CSF cultures grew Listeria Monocytogenes . He received IV ampicillin and gentamycin; the latter was discontinued after 1 month due to nephrotoxicity . Serial MRI over the next 3 months showed significant reduction in the size of these abscesses . The patient made a modest improvement in the power of his lower limbs, however he remained bed-ridden . Aside from being a mild, diet-controlled diabetic, there was no evidence of immunosuppression . CONCLUSION: Listeria spinal cord abscess is a treatable disorder and should be considered in the differential diagnosis in patients with a subacute onset of spinal cord dysfunction.

Australas Radiol, 1996 Aug, 40(3), 354 - 6
MRI appearances of Listeria rhombencephalitis; Davies RS et al.; Listeria monocytogenes is a rare cause of central nervous system infection in the non-immunocomprised patient and 10% of these patients develop a rhombencephalitis . We present such a case and discuss the clinical, pathological and radiological features.

Curr Opin Immunol, 1996 Aug, 8(4), 526 - 30
Primary and secondary immune responses to Listeria monocytogenes; Harty JT et al.; Recent studies have revealed the complexity of cytokine and cellular interactions required for resistance to primary Listeria monocytogenes infection and have illustrated that resistance to secondary infection may occur through multiple pathways . Analyses of Listeria epitope generation and the specificity of protective CD8(+) T cells have suggested that future research should focus on secreted protein antigens in specific resistance to infection and have increased our understanding of Listeria antigens presented by MHC class l-b molecules.

Epidemiol Infect, 1996 Aug, 117(1), 89 - 93
Occurrence of Listeria species in prepacked retail sandwiches; Wilson IG; A survey of 725 prepacked sandwiches was conducted examining for the presence on enrichment, and by plate count, of Listeria species . Sandwiches were found to contain Listeria sp . more frequently than their component foods . Chicken, beef and bacon fillings were associated with more frequent isolation . Salad also was associated with more frequent isolation, but the increase was not significant . On enrichment, over 15% of sandwiches contained Listeria species . L . innocua and L . monocytogenes were the only species isolated by plate count at numbers > or = 100 cfu/g (1.5% of total samples) . Potentially hazardous levels of L . monocytogenes (defined as > or = 10(3) cfu/g) were found in two sandwiches examined (0.3%), indicating that although Total Viable Counts (TVCs) may often be high, the risk of listeriosis to vulnerable individuals from sandwiches is relatively low . It is important to distinguish the risk of consuming potentially hazardous levels of a pathogen in food from the risk of contracting illness as a result of such an event.

Photochem Photobiol, 1996 Aug, 64(2), 269 - 74
Risk assessment of UVB effects on resistance to infectious diseases; Garssen J et al.; The aim of this study was to develop a quantitative risk assessment of lowered resistance to infections in humans due to (solar) ultraviolet B (UVB) exposure . We followed the steps for risk assessment as defined by the U.S . National Academy of Sciences: (1) hazard identification, (2) dose-response assessment, (3) exposure assessment, and (4) risk characterization . For step 1, the suppressory effects of UVB radiation on the immune system have been reviewed, supplemented with new data, and analyzed . Experiments on UV-induced immunosuppression cannot be performed with humans for ethical reasons, but herpes simplex virus infection appears to be the human paradigm . Thus, UVB radiation appears to be a potential hazard to immunologic functions . Step 2 is crucial, but dose-response relationships for infections have never been measured in humans . We used our earlier dose-response rat data for suppression of lymphocyte stimulation and computed that the UVB dose resulting in a 50% reduction of lymphocyte stimulation by Listeria monocytogenes is 6.800 J/m2 . Using mixed skin lymphocyte response assays we found that humans are 3.8 times less sensitive than rats (interspecies variation {IEV}) . To account for the 2.5 percentile of most susceptible individuals in a population, an additional factor (intraspecies variation {IAV}) was introduced (0.5 for humans) . Using these data, we computed that 13.100 J/m2 of UVB radiation emitted by FS40 lamps would suppress 50% of the proliferative response of lymphocytes to L . monocytogenes in most sensitive skin type 2 humans . In step 3, we assumed the action spectrum for the responses analyzed by us as identical to an action spectrum for suppression of contact hypersensitivity that is available in the literature . This led us to step 4, where we calculated that approximately 100 min of solar exposure at around noon in Italy or Spain would suppress the resistance to infections by L . monocytogenes in the most sensitive humans.

J Appl Bacteriol, 1996 Aug, 81(2), 147 - 53
Metabolic activities of Listeria monocytogenes in the presence of sodium propionate, acetate, lactate and citrate; Kouassi Y et al.; The effects of sodium propionate, acetate, lactate and citrate on cell proliferation, glucose and oxygen consumption, and ATP production in Listeria monocytogenes were investigated in growing and resting cells . Media pH was 6.7-6.8 . Growth inhibition increased while glucose consumption continued in the presence of > or = 1% propionate, > or = 3% acetate and > or = 5% lactate in broth during incubation at 35 degrees C, indicating that glucose consumption was uncoupled from cell proliferation . Acetate and propionate were the most effective antilisterials, whereas citrate (5%) was only slightly inhibitory . Of the four salts, only lactate supported growth, oxygen consumption and ATP production . While concentrations of 1 and 5% propionate, acetate and citrate did not have an effect on oxygen consumption, they inhibited ATP production . ATP production in the presence of the four salts was consistently lower at pH 6.0 than at neutral pH . Lactate served as an alternative energy source for L . monocytogenes in the absence of glucose but became toxic to the organism in the presence of the carbohydrate.

J Appl Bacteriol, 1996 Aug, 81(2), 139 - 46
Involvement of the cell envelope of Listeria monocytogenes in the acquisition of nisin resistance; Davies EA et al.; The involvement of the cell wall in the acquisition of nisin resistance by Listeria monocytogenes F6861 and its nisin-resistant mutant was investigated . Results indicated that without a cell wall, the acquired nisin resistance of the mutant was lost . Cell surface hydrophobicity was shown to correlate with nisin sensitivity; the wild type strain being more hydrophobic than its mutant . The possible role of S-layer proteins in nisin resistance was investigated . Examination of strains by freeze-etching and atomic force microscopy did not demonstrate the presence of S-layers in either strain while SDS-PAGE following S-layer extraction procedures revealed no major protein bands . Chloramphenicol did not adversely affect the frequency of isolation of nisin-resistant mutants, indicating that de novo protein synthesis was not involved . The involvement of other cell surface components, teichoic and lipoteichoic acids, was also examined . In contrast with other reports, comparison of the total phospholipid content of the mutant with its parental strain showed no significant difference (P > 0.05).

Infect Immun, 1996 Aug, 64(8), 3280 - 7
Increased susceptibility to primary infection with Listeria monocytogenes in germfree mice may be due to lack of accumulation of L-selectin+ CD44+ T cells in sites of inflammation; Inagaki H et al.; The host defense of germfree (GF) mice against primary infection with Listeria monocytogenes was compared with that of specific-pathogen-free (SPF) mice . In SPF mice, the numbers of bacteria in the peritoneal cavity, liver, and spleen decreased gradually to undetectable levels by day 8 after intraperitoneal infection with a sublethal dose (2 X 10(3) CFU) of L . monocytogenes . On the other hand, the elimination of bacteria in these organs of GF mice was significantly impaired at this stage after inoculation . We have reported previously that T cells coexpressing L-selectin and CD44 play an important role in protection against L . monocytogenes through trafficking to sites of inflammation . Consistent with our previous findings, the number of unique L-selectin+ CD44+ T cells in the peritoneal cavity was remarkably increased on day 8 after infection in SPF mice, whereas such an increase was not evident in GF mice at this stage . Listeria-specific T-cell proliferation was normally detected in the lymph node cells of GF mice inoculated with L . monocytogenes, whereas the T-cell-proliferative response of the peritoneal exudate cells of GF mice was significantly impaired compared with that of SPF mice . These results suggest that the priming of T cells against listerial antigens normally occurs in the peripheral lymphoid organs of GF mice but the trafficking of the activated T cells to the inflamed sites may be severely impaired in GF mice, resulting in increased susceptibility to infection with L . monocytogenes.

Infect Immun, 1996 Aug, 64(8), 3188 - 95
Induction of cytokine gene expression by listeriolysin O and roles of macrophages and NK cells; Nishibori T et al.; To determine the role of listeriolysin O (LLO) of Listeria monocytogenes in the host response at the initial stage of infection, cytokine gene expression in mouse peritoneal exudate macrophages and spleen cells was examined by reverse transcription-PCR . Expression of various cytokine mRNAs, especially those of interleukin-1 (IL-1), tumor necrosis factor alpha, gamma interferon (IFN-gamma), and IL-12, was observed to occur in spleen cells after direct stimulation with an LLO preparation purified to a single band on sodium dodecyl sulfate-polyacrylamide gel electrophoresis . Induction of mRNA expression by LLO was not blocked by cholesterol, which abrogated the hemolytic activity of LLO . After the depletion of NK cells in spleen cells by treatment with anti-asialo GM1 antibody plus complement, LLO-induced expression of IFN-gamma was decreased, indicating that NK cells were the main source of IFN-gamma . After depletion of macrophages by passing spleen cells over a Sephadex G-10 column, expression of macrophage-derived cytokines, including IL-1alpha, tumor necrosis factor alpha, and IL-12, was diminished . In addition, IFN-gamma mRNA expression was impaired, indicating that IFN-gamma mRNA expression from NK cells required signaling from macrophages . It is suggested that LLO is capable of inducing endogenous cytokines of mice, and both NK cells and macrophages are involved in the host cytokine response to LLO.

J Immunol, 1996 Aug 1, 157(3), 1163 - 75
The presentation of class I and class II epitopes of listeriolysin O is regulated by intracellular localization and by intercellular spread of Listeria monocytogenes; Hiltbold EM et al.; The hemolysin, listeriolysin 0 (LLO), produced by Listeria monocytogenes is both a virulence factor and an immunodominant Ag . In this study, we investigated how the lytic activity of LLO effects the context of presentation of two known LLO epitopes by either class I or class II MHC molecules . T cell hybridomas were used to monitor each peptide/MHC ligand . APCs infected with strains of Listeria expressing hemolytic LLO strongly presented the class I MHC epitope; however, this ligand was not well presented by cells infected with nonhemolytic Listeria . In contrast, there was almost no presentation of the class II-binding LLO epitope in cells infected with fully hemolytic Listeria . Only hemolysin-deficient Listeria were presented by class II MHC . Listeria expressing wild-type LLO but deficient in other virulence factors showed a presentation pattern equivalent to that of hemolytic Listeria . To address further the divergence of presentation, we used an intercellular spread assay to detect Ag presentation by cells neighboring the primarily infected one . We found that hemolytic Listeria were presented by both class I and II MHC on cells adjacent to the initially infected one(s) . Finally, our kinetic analysis of presentation revealed that the class II ligand is presented over 4 h before the class I ligand . We have demonstrated that LLO's lytic activity potentiates presentation of listerial Ags by class I MHC and inhibits presentation via class II MHC . LLO-mediated intracellular localization (cytoplasmic vs endosomal) of bacteria corresponds to the operative presentation pathway.

Mol Cell Biol, 1996 Aug, 16(8), 4566 - 72
Unimpaired macrophage differentiation and activation in mice lacking the zinc finger transplantation factor NGFI-A (EGR1); Lee SL et al.; The zinc finger protein NGFI-A (also called EGR1, Krox24, or zif268) is a candidate regulator of myeloid cell differentiation . Evidence supporting this hypothesis is twofold . First, NGFI-A antisense oligonucleotides prevent macrophage differentiation in HL-60 and U937 myeloid leukemia cell lines and in normal bone marrow cells . Second, enforced expression of NGFI-A blocks granulocytic differentiation and promotes macrophage differentiation in HL-60 cells and in the hematopoietic progenitor cell line 32D . We sought to determine the effect of NGFI-A deficiency on macrophage differentiation and function in vivo by examining native bone marrow cells from mice homozygous for a disrupted allele of NGFI-A derived from gene-targeted ES cells . Macrophages were observed in peripheral blood and several tissues, indicating that NGFI-A was not required for the formation of a variety of macrophage compartments . No differences in myeloid cell differentiation were observed between wild-type and NGFI-A-/- bone marrow cells cultured in the presence of macrophage, granulocyte-macrophage, or granulocyte colony-stimulating factor (M-CSF, GM-CSF, or G-CSF) . Activation of NGFI-A-/- macrophages was comparable to that of wild-type macrophages as determined by nitric oxide production and increased cell surface expression of class II major histocompatibility complex molecules . Moreover, NGFI-A-/- mice showed no increased mortality or bacteria} burden when challenged with Listeria monocytogenes . Together, these results indicate that NGFI-A is not required for macrophage differentiation or activation.

Toxicol Lett, 1996 Aug, 86(2-3), 163 - 7
Interaction of environmental chemicals with respiratory sensitization; Van Loveren H et al.; The acute effects of the inhalation of air polluting agents have been examined by many research groups in both animal models and human beings . For instance, it is evident that exposure to ozone has toxic effects and can lead to lung function disturbances . For this reason it is likely that individuals suffering from COPD or asthma are groups especially at risk with respect to the effects of ozone . The majority of studies dealing with effects of air pollutants on pulmonary allergy are restricted to IgE mediated allergy (type I allergy) . Again for ozone, in animal models for type I allergy it has been demonstrated that exposure can affect the induction as well as the effector phase of this type of hyperimmune reaction (e.g . allergic asthma) . Recently it has been demonstration in animal models that non-IgE mediated "asthma' T cells, and notably Th1 cells, may play a crucial role . In a murine model it was demonstrated that low molecular weight compounds can induce delayed type hypersensitivity-like reactions in the respiratory tract, and that these reactions are associated with the induction of airway hyperreactivity . Such compounds include toluene diisocyanate (TDI), to which immune responses can be readily mounted, and which can cause occupational asthma through its sensitizing capability, but to which IgE is only detected in a minority of patients suffering from TDI-associated asthma . Effects of air pollutants on Th1 responses in the respiratory tract have not been studied so far . We have demonstrated that ozone can inhibit resistance to a an intratracheal challenge with Listeria monocytogenes, indicating suppression of Th1 immune responses . In addition, we have shown that ozone exposure suppresses pulmonary delayed type hypersensitivity induced by small molecular weight compounds, as well as the tracheal hyperreactivity that is induced during the development of these immune responses, again supporting the hypothesis of suppression of Th1 responses by ozone exposure . These phenomena may be due to activation of Th2 cell dependent reactions that in turn lead to a downregulation of Th1 mediated immunity, or to a direct effect on Th1 cells or other cell types that are crucial for delayed type hypersensitivity and related airway hyperresponsiveness in this model . These data indicate that exposure to air pollutants may have differential consequences on different types of immune responses in the respiratory tract.

Appl Environ Microbiol, 1996 Aug, 62(8), 3057 - 60
Modified Listeria bacteriophage lysin genes (ply) allow efficient overexpression and one-step purification of biochemically active fusion proteins; Loessner MJ et al.; Listeria bacteriophage lytic enzymes are useful for in vitro applications such as rapid, gentle cell disruption, and they provide new approaches as selective antimicrobial agents for destruction of Listeria monocytogenes in contaminated foods . We describe here the amino-terminal modification of three cloned Listeria phage lysin genes (ply), resulting in fusion proteins with a 12-amino-acid leader containing six consecutive histidine residues . The recombinant enzymes retain their native specific activity and can be efficiently overproduced in Escherichia coli . By one-step metal chelate affinity chromatography, active lysins could be purified to more than 90% homogeneity.

J Immunol, 1996 Jul 15, 157(2), 827 - 35
Mice lacking the TNF receptor p55 fail to resolve lesions caused by infection with Leishmania major, but control parasite replication; Vieira LQ et al.; TNF is involved in host resistance to several pathogens . Recently it was found that mice lacking the p55 receptor for TNF (TNFRp55 -/-) do not control growth of the intracellular bacteria, Listeria monocytogenes and Mycobacterium tuberculosis . Here we report that the course of infection in TNFRp55 -/- mice with another intracellular pathogen, the protozoan parasite Leishmania major, is also quite different from normal mice . TNFRp55 -/- mice developed larger lesions than control mice and failed to resolve these lesions . However, they were able to eliminate parasites within the lesions . Histologic analysis indicated that at late stages lesions from TNFRp55 -/- mice appeared similar to lesions associated with cutaneous graft-vs-host disease . Both TNFRp55 -/- and control mice developed a normal Th1-type response during infection . We also found that IFN-gamma-activated macrophages from TNFRp55 -/- mice produced nitric oxide and killed L . major in vitro, which correlated with the ability of TNFRp55 -/- mice to eliminate the parasites in vivo . The production of nitric oxide by macrophages from TNFRp55 -/- mice required the presence of the parasites, however, since in their absence TNF could only synergize with IFN-gamma for nitric oxide production when added to normal, but not TNFRp55 -/-, macrophages . These results indicate that neither macrophage microbicidal activity nor nitric oxide production is absolutely dependent on the p55 receptor for TNF . Furthermore, they uncover a previously undefined role for TNFRp55 in resolution of parasite-induced inflammatory lesions.

Nature, 1996 Jul 11, 382(6587), 174 - 7
Impaired IL-12 responses and enhanced development of Th2 cells in Stat4-deficient mice; Kaplan MH et al.; Interactions between cytokine and receptor lead to the activation of multiple signalling molecules, including the family of signal transducer and activator of transcription (STAT) proteins . STAT4 is one member of this family, and is activated only in response to the cytokine interleukin (IL)-12 (refs 5, 6) . By gene targeting, we have generated mice deficient in STAT4 to determine whether the function of this transcription factor is redundant with other signalling molecules activated by IL-12 . IL-12-induced increases in the production of interferon (IFN)-gamma cellular proliferation and natural killer (NK) cell cytotoxicity are abrogated in lymphocytes from STAT4-deficient mice . The development of Th1 cells in response to either IL-12 of Listeria monocytogenes is also impaired in the absence of Stat4 . Furthermore, Stat4-deficient lymphocytes demonstrate a propensity towards the development of Th2 cells . These results demonstrate that Stat4 is essential for mediating responses to IL-12 in lymphocytes, and regulating the differentiation of both Th1 and Th2 cells.

Int J Food Microbiol, 1996 Jul, 30(3), 379 - 84
Comparison of the hydrophobic grid-membrane filter DNA probe method and the Health Protection Branch standard method for the detection of Listeria monocytogenes in foods; Yan W et al.; The standard Health Protection Branch (HPB) method for the detection of L . monocytogenes in foods involves lengthy enrichment, selection and biochemical testing, requiring up to 8 days to complete . A hydrophobic grid-membrane filter (HGMF) method employing a digoxigenin-labelled listeriolysin O probe required 5 days to complete, and included an image-analysis system for electronic data acquisition . A total of 200 food samples encompassing 8 high-risk food groups (soft and semi-soft cheeses, packaged raw vegetables, frozen cooked shrimp, ground poultry, ground pork, ground beef, jellied meats, and pate) were screened for the presence of L . monocytogenes by the two methods . Overall, 32 (16%) and 30 (15%) of the naturally-contaminated food samples tested positive for L . monocytogenes by the HPB and DNA methods, respectively . The DNA probe method was highly specific in discriminating L . monocytogenes from other Listeria spp . present in 50 of the samples tested . Results showed 94% sensitivity and 100% specificity between the two methods . The HGMF DNA probe method is an efficient and reliable alternative to the HPB standard method for detecting L . monocytogenes in foods.

Int J Food Microbiol, 1996 Jul, 30(3), 231 - 42
Mathematically modeling the repair of heat-injured Listeria monocytogenes as affected by temperature, pH, and salt concentration; Chawla CS et al.; Heat-injured cells of Listeria monocytogenes were inoculated into Listeria repair broth (LRB) adjusted to various pH levels (4.2, 5.0, 6.6, 8.0 and 9.6) and salt concentrations (0.5%, 2.5%, 5.0%, 7.5% and 10.0% w/v) at controlled temperatures (4, 10, 22, 37 and 43 degrees C) in a complete factorial manner (5(3)) . Repair of the injured microorganisms was evaluated using selective and non-selective plating media . The Gompertz parameters, which were generated by fitting the equation with the bacterial counts, were used to calculate the repair percentage as a function of time from which the repair time was estimated . All growth curves fit the Gompertz equation well (R(2) > or = 0.972) . A first-order model described the repair trend closely (R2 = 0.989 +/- 0.011) . Heat-injured Listeria could fully repair in LRB only under 63 of 125 conditions tested during 21 days of incubation . Refrigeration temperature was the most effective means to prevent the repair of heat-injured Listeria . The minimum temperature required for repair increased with an increase in NaCl concentration . The pH ranges at which the repair could occur were narrower at 4 and 10 degrees C than those at higher temperature . The repair was observed in media containing 10% NaCl between temperatures of 22 and 43 degrees C at pH 6.6.

Zentralbl Bakteriol, 1996 Jul, 284(2-3), 439 - 42
Effect of immunomodulation with galactoside-specific mistletoe lectin on experimental listeriosis; Stoffel B et al.; BALB/c-mice (n = 10 per experimental group) were intravenously infected with 5 x 10(4) and 5 x 10(5) viable cells of Listeria monocytogenes SLCC 4013 . About 50-80 h after this challenge, all mice of the untreated control groups succumbed to their infection . Pretreatment of experimental animals on the optimal immunoactive schedule with the galactoside-specific mistletoe lectin (ML-1; 1 ng/kg body weight; days 1, 4, 5, 6 before challenge), however, evidently reduced the lethality of listerial infection (survival rate 60%).

Zentralbl Bakteriol, 1996 Jul, 284(2-3), 263 - 72
Protein p60 participates in intestinal host invasion by Listeria monocytogenes; Hess J et al.; The role of p60 in intestinal invasion by Listeria monocytogenes was assessed after oral infection of mice with the p60 low-expressing mutant RIII, or with anti-p60 antibody coated wild-type EGD . Invasion by L . monocytogenes RIII bacteria has been unimpaired suggesting that a low density of p60 suffices for entry . Up to 24 h post infection (p.i.), intestinal penetration by L . monocytogenes EGD bacteria was markedly reduced by coating with anti-p60 antibodies . In histological sections, anti-p60 antibody-treated L . monocytogenes EGD, but not uncoated listeriae were still detectable 24 h p.i . at the apical surface of enterocytes in the intestine . We conclude that p60 contributes to host invasion through the natural port of listerial entry, the intestinal epithelium.

J Interferon Cytokine Res, 1996 Jul, 16(7), 547 - 54
Interferon-gamma and interleukin-10 have cross-regulatory roles in modulating the class I and class II MHC-mediated presentation of epitopes of Listeria monocytogenes by infected macrophages; Hiltbold EM et al.; IFN-gamma is an important cytokine in resistance to infection with Listeria monocytogenes, and interleukin 10 is known to exacerbate infection with Listeria and other intracellular pathogens . We examined the effects of these cytokines on antigen presentation by macrophages infected with live Listeria . Listeriolysin O, a hemolysin secreted by Listeria, is an immunodominant antigen presented by both class I and class II MHC on infected cells . Thioglycollate-elicited macrophages were pretreated with exogenous IFN-gamma, IL-10, or both cytokines overnight, infected with bacteria, and then fixed . Epitope-specific, MHC-restricted, T cell hybridomas were then added to detect the presentation of the class I or class II ligand . We found that IFN-gamma enhanced the presentation of both the class I and class II epitopes and IL-10 strongly inhibited the presentation of both ligands . The degree of inhibition of presentation caused by IL-10 was dose dependent . IL-10 was also able to inhibit the presentation of exogenously added class II-binding peptide but had a less dramatic effect on the presentation of the added class I-binding polypeptide epitope . Flow cytometric analysis of expression of class I and class II on treated macrophages demonstrated that the inhibitory effect of IL-10 on antigen presentation was not due to significant downregulation of MHC expression . This loss of antigen presentation was also not due to downregulation of the costimulatory molecule, B7-2 . We have found that IFN-gamma and IL-10 have opposing immunoregulatory effects on the presentation of antigens derived from an intracellular pathogen and that the class I vs . class II-mediated presentation of antigens is differentially regulated by IL-10.

J Cell Sci, 1996 Jul, 109 ( Pt 7), 1739 - 47
Vaccinia virus: a model system for actin-membrane interactions; Cudmore S et al.; Our understanding of the interactions between the actin cytoskeleton and cellular membranes at the molecular level is rudimentary . One system that offers an opportunity to examine these interactions in greater detail is provided by vaccinia virus, which induces the nucleation of actin tails from the outer membrane surrounding the virion . To further understand the mechanism of their formation and how they generate motility, we have examined the structure of these actin tails in detail . Actin filaments in vaccinia tails are organized so they splay out at up to 45 degrees from the centre of the tail and are up to 0.74 micron in length, which is considerably longer than those reported in the Listeria system . Actin filaments show unidirectional polarity with their barbed filament ends pointing towards the surface of the virus particle . Rhodamine-actin incorporation experiments show that the first stage of tail assembly involves a polarized recruitment of G-actin, and not pre-formed actin filaments, to the membrane surrounding the virion . Incorporation of actin into the tail only occurs by nucleation from the viral surface, suggesting filament ends in the tail are blocked against further actin addition . As virus particles fuse with the plasma membrane during the extention of projections, actin nucleation sites previously in the viral membrane become localized to the plasma membrane, where they are able to nucleate actin polymerization in a manner analogous to the leading edge of motile cells.

Vet Microbiol, 1996 Jul, 51(1-2), 151 - 9
The use of listeriolysin O in an ELISA, a skin test and a lymphocyte blastogenesis assay on sheep experimentally infected with Listeria monocytogenes, Listeria ivanovii or Listeria innocua; Baetz AL et al.; Purified listeriolysin O (LLO) was evaluated as a specific antigen to detect both humoral and cell mediated immune responses of sheep infected with Listeria monocytogenes . Six sheep (two in each group) were orally inoculated with 10(10) organisms of L . monocytogenes, L . ivanovii, or L . innocua . Only the L . monocytogenes inoculated sheep had an elevated temperature (> 42 degrees C) and after 15 days had anti-LLO antibodies as assessed by an ELISA . In a blastogenesis assay, only peripheral blood mononuclear cells (PBMC) from L . monocytogenes-infected sheep responded to LLO, while PBMC from all the sheep responded somewhat to heat-killed L . monocytogenes bacteria . In a skin test, only L . monocytogenes-infected sheep exhibited a positive reaction to injected LLO, while all the Listeria-infected sheep reacted to heat-killed bacteria . On day 120 postinfection, all of the sheep were orally inoculated with L . monocytogenes . Only the four that had not been previously given L . monocytogenes exhibited an elevated temperature (> 42 degrees C) . 80 days later, sera from all of the animals were positive for anti-LLO antibodies . Thus, prior exposure to L . ivanovii or L . innocua does not protect against a L . monocytogenes challenge . These results suggest LLO is an excellent antigen for use in detecting Listeria infection in sheep . However, whether LLO will be useful in differentiating chronically infected animals from animals that have recovered, has yet to be investigated.

Ecotoxicol Environ Saf, 1996 Jul, 34(2), 134 - 40
Copper and zinc exposure of zebrafish, Brachydanio rerio (Hamilton-Buchaman): effects in experimental Listeria infection; Rougier F et al.; To investigate the effects of heavy metals on susceptibility of fish to Listeriosis, normal zebrafish, Brachydanio rerio (Hamilton-Buchanan), were exposed to varying concentrations of zinc (0.05, 0.15, and 0.25 mg/liter) and copper (0.05, 0.10, and 0.15 mg/liter) . During copper exposure, this heavy metal did not accumulate in zebrafish kidney . Unlike copper, a small amount of zinc accumulated in kidneys of fish exposed at 0.25 mg/liter . To estimate the effects of this heavy metal on listerial infection, the mortality of fish and the number of viable bacteria in fish kidney were determined at various times (1, 4, 7, and 10 days) after ip challenge with Listeria monocytogenes (strain 31386, serotype 4b) . The results indicate that the number of colony-forming units in zinc-exposed fish decreased at 4, 7, and 10 days after challenge with 0.2 x LD50 of viable bacteria . In contrast, copper-exposed fish indicated both decreases and increases in the number of colony-forming units depending on the concentration of L . monocytogenes used.

Neurochem Int, 1996 Jul, 29(1), 55 - 64
IL-10 production by adult human derived microglial cells; Williams K et al.; Microglia, a population of central nervous system (CNS) macrophages, have been demonstrated to support immune accessory and effector functions in the CNS . Numerous studies support the role of microglia in CNS development and pathology, where activation of microglia is consistently noted . The current study investigated microglial immune functions under basal and activation conditions and assessed the ability of interleukin-10 (IL-10), added exogenously or produced by microglia, to down-regulate microglial functions . This report demonstrates that microglia from the adult human brain produce IL-10 following interferon-gamma/lipopolysaccharide activation . Functionally, recombinant human IL-10 down-regulated basal HLA-DR expression by microglia and inhibited, in a dose-dependent response, the ability of microglia to stimulate CD4+ T-cells in antigen presentation assays . These data, together with recent observations of the inhibition of experimental allergic encephalomyelitis (EAE) following IL-10 administration and reduced CNS infection by Listeria monocytogenes after anti-IL-10 treatment, suggest that IL-10 production by microglia may have important immune-regulatory functions in CNS disease and disease models.

J Radiol, 1996 Jul, 77(7), 489 - 96
{MRI and Listeria monocytogenes rhombencephalitis}; Soulie D et al.; Rhombencephalitidis is a serious form of brainstem inflammation, difficult to diagnose on the basis of clinical and laboratory findings alone . We describe the MR appearance of 3 cases of Listeria monocytogenes rhombencephalitidis and correlate the findings with clinical information . MR imaging is crucial for early diagnosis of this illness: patchy signal hyperintensity throughout the medulla and cerebellar peduncles on T2 weighted images, always in association with a hypointense dot; numerous gadolinium-enhanced microabcesses in the rhombencephalon . MR imaging is very useful for follow-up examinations.

Immunity, 1996 Jul, 5(1), 73 - 9
A Listeria monocytogenes pentapeptide is presented to cytolytic T lymphocytes by the H2-M3 MHC class Ib molecule; Gulden PH et al.; Polymorphism of MHC class Ia molecules severely constrains vaccine development against intracellular pathogens . Antigen presentation by MHC class Ib molecules, which are generally conserved between different individuals, may circumvent this obstacle . Herein, we use tandem mass spectrometry to identify a Listeria monocytogenes pentapeptide antigen that is presented to T lymphocytes by the H2-M3 MHC class Ib molecule . The peptide contains N-formyl methionine at the N terminus and exclusively hydrophobic amino acids . Mice of the H-2 d, H-2 b,and H-2 k haplotypes respond to this peptide upon infection with Listeria monocytogenes . Identification of antigens presented by MHC class Ib molecules is feasible and may provide opportunities for relatively unrestricted vaccine development.

Immunity, 1996 Jul, 5(1), 63 - 72
Identification of an H2-M3-restricted Listeria epitope: implications for antigen presentation by M3; Lenz LL et al.; Using expression cloning, we have identified an H2-M3-restricted epitope of the intracellular bacterial pathogen Listeria monocytogenes . Picomolar concentrations of an amino-terminal N-formylated hexapeptide, fMIGWII, targeted cells for lysis by CD8+ cytotoxic T cells, while the nonformylated peptide was approximately 100-fold less active . The sequence of the 185 aa protein source of this epitope predicts a transmembrane protein that retains its N terminus and assumes an N(out)-C(in) topology . This membrane orientation offers an explanation for the protection of the epitope from deformylases present in the bacterial cell and suggests an explanation for the ability of phagocytes to present H2-M3-restricted bacterial epitopes via a vacuolar TAP-independent mechanism.

Infect Immun, 1996 Jul, 64(7), 2666 - 72
Monocytes of individual human subjects display heterogeneous bacterial uptake and antilisterial activity; Zerlauth G et al.; Peripheral blood monocytes (Mo) of normal human donors simultaneously exhibit two subsets differing in their functional activity towards the facultative intracellular bacterium Listeria monocytogenes . One subset (on average, 25% of total Mo) was characteristically able to ingest a large number of L . monocytogenes bacteria and permitted intracellular growth of these bacteria . The other Mo subpopulation (on average, 75% of total Mo) was far less active in phagocytosing L . monocytogenes and restricted intracellular L . monocytogenes growth . Electron microscopy revealed that the Listeria-permissive Mo subset allowed the bacteria to escape to the cytosol, a mechanism by which these bacteria evade the lethal attack of phagocytes . The Listeria-restrictive Mo subset, on the other hand, confined the bacteria to the phagolysosomes, where they were exposed to the killing mechanisms of the Mo . Permissiveness for L . monocytogenes growth was further associated with differences in the capacity of the Mo subsets to synthesize tumor necrosis factor alpha TNF-alpha), an important mediator in the defense against intracellular bacteria . Following challenge with L . monocytogenes, the Listeria-restrictive Mo subset secreted two to six times more TNF-alpha than did the Listeria-permissive Mo subset . Enhanced TNF-alpha secretion was paralleled by increased accumulation of TNF-alpha mRNA as assessed by quantitative PCR . Despite these functional differences, the two Mo subsets were indistinguishable with respect to expression of cell surface markers known to be involved in adherence and phagocytosis of microbes . A speculative physiological role of the two Mo subsets may lie in the dual function of Mo as microbicidal effector cells and accessory cells for antigen-specific immune reactions.

Infect Immun, 1996 Jul, 64(7), 2515 - 22
Cytotoxic-T-lymphocyte responses to epitopes of listeriolysin O and p60 following infection with Listeria monocytogenes; Bouwer HG et al.; In order to test the influence of the cell surface density of a specific H2-Kd-presented epitope on the subsequent level of the cytotoxic-T-lymphocyte (CTL) response directed against the epitope, we investigated the CTL response to two secreted products of Listeria monocytogenes from mice immunized with viable L . monocytogenes . We determined the response to the H2-Kd-presented amino acid 91 to 99 (aa91-99) immunodominant peptide of listeriolysin O (LLO) and to the aa217-225 immunodominant peptide of p60 . The p60-derived peptide appears at the cell surface as an H2-Kd-complexed peptide at a level sixfold higher than that of LLO aa91-99 . CTL frequency analysis of anti-LLO- or anti-p60-specific CTLs from mice immunized with wild-type L . monocytogenes showed that the numbers of immune spleen cell-derived CTLs specific for the two peptides were essentially equivalent . We have also found that Listeria-specific CTL populations lyse target cells pulsed with the p60 aa217-225 peptide with a magnitude of the lytic response markedly less than that for targets pulsed with the LLO aa91-99 peptide . Additionally, immunization with mutants of L . monocytogenes which do not stimulate anti-LLO-specific CTLs does not alter the CTL frequency of anti-p60-specific effector cells, with levels of anti-p60-specific CTLs similar to those seen in mice immunized with wild-type L . monocytogenes . These results suggest that the relative cell surface density of major histocompatibility complex class I-presented L . monocytogenes-derived epitopes is but one of the criteria which determine the magnitude of the cytotoxic effector cell response that develops in antilisterial immunity.

J Immunol, 1996 Jul 1, 157(1), 247 - 54
The role of p56lck in the development of gamma delta T cells and their function during an infection by Listeria monocytogenes; Fujise S et al.; We investigated roles of p56lck tyrosine kinase (Lck) on the development and function of gamma delta T cells in adult mice using lck gene knockout (lck -/-) mice . The mature gamma delta T cells (heat-stable Ag negative) were generated significantly in the thymi of adult lck -/- mice . When Listeria monocytogenes was infected i.p., gamma delta T cells were induced in the peritoneal cavity of the lck -/- mice . Interestingly, the repertoire of gamma delta T cells was obviously different in the lck +/+ and lck -/- mice; i.e., the gamma delta T cells of the lck -/- mice induced by the listerial infection dominantly expressed V delta 1 while those of the lck +/+ mice dominantly expressed V delta 6 . The V delta 1 + gamma delta T cells in the lck -/- mice were extrathymically generated, supported by their appearance in thymectomized irradiated mice reconstituted with bone marrow cells from the lck -/- mice . Furthermore, the gamma delta T cells of the lck +/+ mice were protective in the early stage of the listerial infection, while the gamma delta T cells in the lck -/- mice were not protective against the listerial infection because the depletion of the gamma delta T cells from the lck -/- mice did not influence the bacterial burden in the spleens . These observations thus suggest that 1) gamma delta T cells can develop in adult mice through the intrathymic and extrathymic pathways even in the absence of Lck, 2) Lck influences the expansion and the repertoire of gamma delta T cells, and 3) the gamma delta T cells raised in the absence of Lck are not protective against L . monocytogenes.

Lett Appl Microbiol, 1996 Jul, 23(1), 18 - 22
Relationship between variations in pathogenicity and lag phase at 37 degrees C of Listeria monocytogenes previously stored at 4 degrees C; Buncic S et al.; Three haemolytic, pathogenic strains of Listeria monocytogenes (a reference strain, a food-derived strain and a human strain) were held at 4 degrees C for 4 weeks in phosphate-buffered saline pH 5.5 or 7.0, with and without 0.2% potassium sorbate or 0.3% sodium acetate . The number of viable cells did not change significantly during this storage . Pathogenicity of non-growing L . monocytogenes cells for 14-d-old chick embryos was determined before and after storage . Storage at 4 degrees C resulted in decreased pathogenicity, but effects were strain-, pH-and substrate-dependent . After 4 weeks storage at 4 degrees C non-growing bacterial cells were transferred to Brain Heart Infusion broth and growth characteristics were determined during incubation at 37 degrees C . Strains that showed decreased pathogenicity had significantly longer lag phases at 37 degrees C than strains that maintained pathogenicity . It is concluded that decreased pathogenicity of L . monocytogenes stored without growth at 4 degrees C for 4 weeks and subsequent long lag phase at 37 degrees C are correlated.

Arch Microbiol, 1996 Jul, 166(1), 51 - 7
Extracellular iron reductase activity produced by Listeria monocytogenes; Barchini E et al.; Little is known about how pathogenic microorganisms that do not produce low-molecular-weight iron-chelating agents, termed siderophores, acquire iron from their environment . We have identified an extracellular enzyme produced by Listeria monocytogenes that can mobilize iron from a variety of iron-chelate complexes via reduction of the metal . The iron reductase requires Mg2+, flavin mononucleotide (FMN), and reduced nicotinamide adenine dinucleotide (NADH) for activity . Saturation kinetics were found when initial velocity studies of iron reduction were carried out as a function of variable FMN concentrations in the presence of 100 microM NADH and 10 mM Mg2+ . Hyperbolic kinetics were also found when these studies were repeated as a function of variable NADH concentrations along with 20 microM FMN and 10 mM Mg2+ . This process of extracellular reduction, in all likelihood, could be involved in the mobilization of iron from soils and aqueous environments and from host tissues in pathogenic processes . This is the first report of the extracellular enzymic reduction of iron by microorganisms.

FEMS Microbiol Lett, 1996 Jun 15, 140(1), 29 - 35
Cell wall changes in nisin-resistant variants of Listeria innocua grown in the presence of high nisin concentrations; Maisnier-Patin S et al.; Two nisin-resistant variants of a strain of Listeria innocua were isolated after growth in the presence of 500 and 4000 IU ml-1 of nisin A showed increased cell wall hydrophobicity, resistance to phage attack and three different cell wall-acting antibiotics, as well as to the peptidoglycan hydrolytic enzymes lysozyme and mutanolysin, as compared to the parental strain . Transmission electron microscopy revealed marked thickening of the wall of nisin-resistant cells with an irregular surface . Differences in thickness were lost after cell wall purification and no significant difference in gross wall composition was observed between the parental and resistant variants . Cell wall changes in nisin-resistant listeriae are attributed to abnormal cell wall synthesis and autolysin inhibition, the latter possibly associated with subtle changes in cell wall structures and function.

J Biol Chem, 1996 Jun 7, 271(23), 13834 - 43
Phagocytosed live Listeria monocytogenes influences Rab5-regulated in vitro phagosome-endosome fusion; Alvarez-Dominguez C et al.; Survival or destruction of a pathogen following phagocytosis depends, in part, on fusion events between the phagosome and the endosomal or lysosomal compartments . Here we use an in vitro assay to show that phagosome-endosome fusion is regulated by the small GTPase rab5 and that fusion events are influenced by an internalized live organism, Listeria monocytogenes (LM) . We compare the in vitro fusion of phagosomes containing heat-killed organisms (dead LM) with that of phagosomes containing a live nonhemolytic mutant (live LMhly-) . Unlike the wild-type organism, LMhly- remains trapped inside the phagosome . Phagosome-endosome fusion was reconstituted using biotinylated organisms and endosomes containing horseradish peroxidase conjugated with avidin . With both live LMhly- and dead LM preparations, in vitro phagosome-endosome fusion was time-, temperature-, and cytosol-dependent . Live LMhly- phagosomes exhibited a faster rate of fusion . Fusion in both preparations was regulated by rab5 and possibly by other GTPases . Anti-rab5 antibodies and immunodepletion of cytosolic rab5 inhibited fusion . Addition of glutatione S-transferase-rab5 in the GTP form stimulated phagosome-endosome fusion, whereas addition of a dominant negative mutant of rab5 blocked fusion . Purified live LMhly- phagosomal membranes were enriched in rab5 as revealed by Western blotting, compared with dead LM phagosomes . Fusion of endosomes with dead LM containing phagosomes required ATP and was inhibited by ATP depletion and by N-ethylmaleimide (NEM) and anti-NEM-sensitive factor (NSF) antibodies . Unexpectedly, phagosome-endosome fusion with live LMhly--containing phagosomes was not inhibited by ATP depletion nor by NEM or anti-NSF antibodies . Western blot analysis revealed that live LMhly--containing phagosomes were enriched for membrane-bound NSF, while dead LM containing phagosomes contained low or undetectable quantities . Washing live LMhly--containing phagosomes with 0.5 M KCl removed NSF associated with the membranes and rendered them NEM, ATP, anti-NSF antibody sensitive for fusion . We conclude that rab5 regulates phagosome-endosome fusion and that live microorganisms can up-regulate this process by recruiting rab5 to the membrane.

Int J Food Microbiol, 1996 Jun, 30(1-2), 145 - 56
Health risk assessment of Listeria monocytogenes in Canada; Farber JM et al.; In this review, the major steps used in the formulation of a health risk assessment for Listeria monocytogenes in foods are discussed . Data is given on the numbers of human listeriosis cases reported in Canada along with the current Canadian regulatory policy on L . monocytogenes . Four major steps in the health risk assessment of this organism in foods, namely, hazard identification, hazard characterization, exposure assessment and risk characterization, were examined . For hazard characterization, since it is known that no direct human dose response data is available for L.monocytogenes, a flexible dose response model called the Weibull-Gamma model was evaluated . For the exposure assessment, pate and soft cheese, both high-risk foods in terms of listeriosis infection, were used as prototypes in some of the models that were used . Using disappearance data for cheese and 100 g as a typical serving, the data suggested an average of 102 servings per capita, per year in Canada . As a rough approximation, for L . monocytogenes, reference ID10 and ID90 dose levels of response for both normal and high risk populations were given as 10(7) and 10(9) for normal individuals, and 10(5) and 10(7) for high-risk people . The corresponding dose response models were graphically displayed . These models exhibited a higher degree of susceptibility and less host/pathogen heterogeneity for the higher risk group . The range of doses between the ID10 and ID90 reference values corresponded roughly to levels associated with cases of listeriosis . In the risk characterization stage, dose response data was combined with some predictive growth modeling data of L . monocytogenes on pate, assuming an initial exposure of a single cell for food stored at 4 degrees and 8 degrees C . Storage of pate at 4 degrees C for more than 35 days resulted in a rapidly increasing risk for the high risk population, while storage at 8 degrees C produced a similar risk after about 13 days . In addition, an equation, used to calculate the average probability of acquiring human listeriosis in Canada from soft and semi-soft cheese consumption, was formulated . Computations derived from this equation indicated a substantial level consistency between reported data and assumptions of the risk assessment model . An important part of risk characterization or possibly risk management is characterizing the economic and social consequences of estimated risks . The total annual estimated cost of listeriosis illnesses and deaths in Canada was estimated to be between 11.1 and 12.6 million dollars.

Int J Food Microbiol, 1996 Jun, 30(1-2), 71 - 85
Assessment of alimentary exposure to Listeria monocytogenes; Hitchins AD; Survey data on the frequency of foodborne occurrence and dietary exposure to Listeria monocytogenes were used to estimate the mininmal mean per person annual rate of exposure in the United States during the late 1980s . The estimate was restricted to ready-to-eat (RTE) foods because proper cooking was assumed to be listericidal . The mean amount of each food type per L . monocytogenes occurrence was calculated in about 100 sources, and dietary intake data were used to calculate the mean number of occurrences of L . monocytogenes consumption per person per year . The mean number of occurrences consumed annually per person was determined to be 10 to 100 for RTE food values of 2 to 20% of the total dietary intake, respectively . The frequency of foodborne listeriosis (approximately 10(-5)) was consistent with the estimated exposure rate only if the susceptible population was unexpectedly small or extremely high doses were necessary for infection . Because little evidence is available to support a high rate of unreported non-severe infections, this study was concerned only with severe listeriosis cases . Published frequencies of L . monocytogenes concentrations in food were used to convert occurrences to colony forming units (CFU) . Low L . monocytogenes concentrations (approximately 1 CFU/g) were too frequent to be responsible for listeriosis in susceptible subjects, would have caused listeriosis only with extremely low probability in a one-cell threshold infection model . The probability of exposure to a higher dose (> or = 10(3) CFU) was large enough to account for the observed rate of listeriosis.

Methods, 1996 Jun, 9(3), 445 - 52
Identification of CD4+ T-Cell-Stimulating Antigens by Expression Cloning
Sanderson S.
The antigens recognized by CD4(+) T cells are key to rational vaccine design, but have been difficult to identify due to limitations of conventional methods . A novel strategy for identifying CD4(+) T-cell-stimulating antigen genes is described here . Using antigen-specific, lacZ-expressing T cells as single-cell probes, a DNA library was screened as recombinant Escherichia coli . An antigen gene was isolated from the E . coli clone that, when ingested by the macrophages, allowed generation of the appropriate peptide/MHC class II complex and T-cell activation . This strategy was successfully applied to the identification of a previously unknown listeria gene product with characteristics of a membrane-bound lipoprotein.

Mol Microbiol, 1996 Jun, 20(6), 1189 - 98
Differential regulation of the virulence genes of Listeria monocytogenes by the transcriptional activator PrfA; Bohne J et al.; The two Listeria monocytogenes strains EGD and NCTC 7973 display a different regulation pattern of their PrfA-dependent genes . All PrfA-dependent genes from L . monocytogenes NCTC 7973 are much more efficiently transcribed in brain-heart infusion medium than those from strain EGD . Transcription of these genes in EGD is, however, induced after shift into Minimal Essential Medium (MEM) to a level that is comparable to that of strain NCTC 7973 . Expression of the internalin gene (inlA) is also influenced by PrfA, but only one (P2) out of three mapped promoters is strictly dependent on PrfA . In contrast to the other PrfA-regulated genes, transcription of inlA even from the P2 promoter is reduced in both strains after shift to MEM . The prfA deletion mutant SLCC 53 complemented with multiple copies of prfA synthesizes large amounts of monocistronic prfA transcript, but there is no concomitant increase in the transcripts of the PrfA-dependent genes . However, upon a shift into MEM, transcription of the PrfA-dependent genes (with the exception of the inlA gene) is highly induced even in the absence of de novo protein synthesis . The PrfA proteins of the two studied L . monocytogenes strains differ in their ability to activate PrfA-dependent genes . This difference is probably the result of amino acid exchange(s) in the C-terminal part of these proteins . Strain EGD supplemented with multiple copies of prfA-7973 shows a similar regulation of the PrfA-dependent genes as strain NCTC 7973, whereas multiple copies of prfA-EGD introduced into strain EGD hardly change the rate of transcription of the PrfA-dependent genes . Our data thus suggest that PrfA-mediated gene expression depends not only on the amount of the PrfA protein and the 'quality' of the putative PrfA-binding sites, but also on the 'quality' of the PrfA protein which seems to be influenced by its amino acid composition and by environmental parameters.

FEMS Immunol Med Microbiol, 1996 Jun, 14(2-3), 103 - 7
Enhanced in vitro engulfment of Listeria monocytogenes by rabbit polymorphonuclear leukocytes in the presence of sera from immune rabbits; Vahidy R et al.; The role of immune serum in the engulfment of Listeria monocytogenes by polymorphonuclear leukocytes (PMNLs) of rabbits was documented employing an in vitro assay . Three serovarieties of L . monocytogenes, viz . serovars 1/2a, 4a and 4b, were separately incubated with PMNLs of nonimmune rabbit and high titre homologous or heterologous antisera . Normal rabbit serum was used as control . The number of L . monocytogenes per neutrophil was counted in stained smears in each assay and opsonic indices were calculated . Higher opsonic indices, i.e . 2.50, 2.09 and 2.56 for the three strains respectively, were obtained when bacteria were engulfed in the presence of homologous antisera as compared to when the bacterial cells were incubated with heterologous antisera, opsonic indices being in the range of 0.87 to 1.63 . These results are indicative of a possible role of specific serum factors in at least the internalization of L . monocytogenes by PMNls of rabbits and therefore in the host defenses against Listerial infections.

Br J Neurosurg, 1996 Jun, 10(3), 317 - 9
Listeria monocytogenes meningitis complicated by symptomatic spinal subarachnoid cysts; Abduljabbar T et al.; We report the case of a man who developed signs of compression of the spinal cord in the dorsal region over a year after treatment of Listeria monocytogenes meningitis . He proved to have mild hydrocephalus and a number of subarachnoid pouches compressing the upper dorsal cord . Insertion of a ventriculo-peritoneal shunt caused clinical improvement . We believe that this was caused by relief of tension in the spinal cysts rather than any reduction in ventricular size.

Lipids, 1996 Jun, 31(6), 635 - 40
Diversity of the polar lipids of the food-borne pathogen Listeria monocytogenes; Mastronicolis SK et al.; Listeria monocytogenes is a Gram-positive bacterium that can adapt to high salinity and cold . Because the membrane lipids may play a role in its survival and adaptation, we have examined the polar lipids of L . monocytogenes . Extraction of total lipids from L . monocytogenes yielded 7 +/- 1 mg/mL wet cells . Polar lipids represented 64% of total lipids and contained 9% lipid-phosphorus . Polar lipids were separated into 14 components by two-dimensional thin-layer chromatography . Eight components (88% of polar lipids) contained lipid-phosphorus; among these was one major component (34% of polar lipids) . Two other phospholipids were ninhydrin-positive components and accounted for 15% of the polar lipids . Orcinol staining revealed two glyco- or sulfo-lipids accounting for 9% of polar lipids . Five components (4% of polar lipids) were amino components free of phosphorus . The major component contained 46% of its fatty acids as 15:0 anteiso, 24% as 17: 0 anteiso, and 11% as 15:0 iso . The fatty acid profile of the remaining polar lipids was variable, consisting primarily of 16:0, 18:0, 15:0 anteiso, and 17:0 anteiso . Their unsaturation level was < or = 20%; however, the major phosphoaminolipid component was 46% unsaturated . The ratios of 15:0 anteiso/17:0 anteiso and 15:0 anteiso/15:0 iso were similar in all classes, averaging 1.5 and 4.5, respectively . Since the adaptation process to stressful environments involves activation of a membrane transport system for the protectant glycine betaine, the membrane lipids may play a role in enabling transport.

Microbiologia, 1996 Jun, 12(2), 245 - 58
The pathogenesis of infection by Listeria monocytogenes; Rouquette C et al.; Listeria monocytogenes is a Gram-positive bacterium responsible for severe infections in human and a large variety of animal species . It is a facultative intracellular pathogen which invades macrophages and most tissue cells of infected hosts where it can proliferate . The molecular basis of this intracellular parasitism has been to a large extent elucidated . The virulence factors, including internalin, listeriolysin O, phospholipases and a bacterial surface protein, ActA, are encoded by chromosomal genes organised in operons . Following internalisation into host cells, the bacteria escape from the phagosomal compartment and enter the cytoplasm . They then spread from cell to cell by a process involving actin polymerisation . In infected hosts, the bacteria cross the intestinal wall at Peyer's patches to invade the mesenteric lymph nodes and the blood . The main target organ is the liver, where the bacteria multiply inside hepatocytes . Early recruitment of polymorphonuclear cells lead to hepatocyte lysis, and thereby bacterial release . This causes prolonged septicaemia, particularly in immunocompromised hosts, thus exposing the placenta and brain to infection . The prognosis of listeriosis depends on the severity of meningoencephalitis, due to the elective location of foci of infection in the brain stem (rhombencephalitis) . Despite bactericidal antibiotic therapy, the overall mortality is still high (25 to 30%).

Microbiologia, 1996 Jun, 12(2), 237 - 44
The molecular mechanisms of actin-based intracellular motility by Listeria monocytogenes; Chakraborty T; A key virulence trait of bacteria and viruses that multiply in the cytoplasm of the infected cell is their ability to direct movement intracellularly and to spread from cell-to-cell . Intracellular movement is effected by harnessing components of the host microfilament system . This mode of locomotion by intracytoplasmic parasites has recently gained much interest as a model to examine microfilament assembly and function . Of the intracellular bacteria employing association with the host cytoskeleton to effect movement, the Gram-positive pathogen Listeria monocytogenes is the most well studied . This review summarizes the current state of the understanding, at the molecular level, of how L . monocytogenes subverts the host cell contractile machinery to meet its own need to move and spread within infected host cells.

Microbiologia, 1996 Jun, 12(2), 219 - 36
Regulation of virulence gene expression in pathogenic Listeria; Brehm K et al.; Dynamic interactions between host and pathogen are characteristic of infections caused by intracellular bacteria . This has favoured the evolution of highly effective control systems by which these pathogens regulate the expression of different virulence factors during sequential steps of the infection process . In the case of the facultative intracellular bacterium Listeria monocytogenes, these steps involve internalization by eukaryotic cells, lysis of the resulting phagosome, replication as well as movement within the host cytoplasm, direct cell-to-cell spread, and subsequent lysis of a double-membrane vacuole when entering neighbouring cells . Virulence factors which are involved in each of these steps have been identified and the expression of these factors is subject to a co-ordinate and differential control exerted by the major listerial virulence regulator PrfA . This protein belongs to the Crp/Fnr-family of transcriptional activators and recognizes specific target sequences in promoter regions of several listerial virulence genes . Differential expression of these genes during sequential steps of the infection seems to be at least partially mediated by different binding affinities of PrfA to its target sequences . Activity of PrfA-dependent genes and of prfA itself is under the control of several environmental variables which are used by the pathogen to recognize its transition from the free environment into a eukaryotic host.

Res Microbiol, 1996 Jun, 147(5), 371 - 84
Transcriptional activation of virulence genes in wild-type strains of Listeria monocytogenes in response to a change in the extracellular medium composition; Ripio MT et al.; A panel of 103 Listeria monocytogenes strains of different origins was examined for haemolysin and lecithinase production in brain-heart infusion (BHI) . Three distinct phenotypes were observed . Phenotype 1 was characterized by low to undetectable levels of expression and was exhibited by almost all strains tested . Phenotype 2 expressed high levels of haemolysin and lecithinase and was displayed by five strains: one (P14-A) was a spontaneous mutant derived from a type 1 isolate (P14); the four others (EGD-A, NCTC 7973, SLCC 2373 and CLIP 545) were all laboratory strains kept under in vitro conditions for a long period . Phenotype 3 was intermediate and was exhibited by another laboratory strain (L028) . We therefore concluded that phenotype 1 corresponded to the wild type, whereas phenotypes 2 and 3 represented mutant or variant phenotypes . Interestingly, wild-type strains were able to dramatically increase the expression of virulence factors when cultured in BHI treated with activated charcoal (BHIC), up to levels similar to those constitutively expressed by the hyperhaemolytic/lecithinase variants in BHI . Experiments with P14 and P14-A demonstrated that both charcoal and the hyperhaemolytic/lecithinase mutation exerted their effect by inducing (or derepressing) transcription of prfA, the pleiotropic transcriptional activator of the L . monocytogenes virulence regulon . Moreover, P14 and P14-A were equally virulent for mice despite the different levels of virulence factor expression in BHI . Taken together, these observations indicate that L . monocytogenes turns off virulence gene expression when growing in vitro in a rich medium, and suggest that the increased levels of virulence factors in the hyperhaemolytic/lecithinase mutants and in wild-type strains grown in BHIC might represent the levels of expression needed in vivo by L . monocytogenes for infecting host tissues.

J Clin Microbiol, 1996 Jun, 34(6), 1391 - 5
Serodiagnosis of listeriosis based upon detection of antibodies against recombinant truncated forms of listeriolysin O; Gholizadeh Y et al.; Amino-terminal fragments of listeriolysin O (LLO) of 240 and 411 residues (fragments LLO240 and LLO411, respectively) were expressed in Escherichia coli as fusion polypeptides with maltose-binding protein (MBP) with the aim of producing specific antigens for use in serological tests . In Western blots (immunoblots) with crude bacterial extracts of the fusion polypeptides, the reactivities of MBP-LLO240 and MBP-LLO411 with anti-LLO antibody (ALLO)- and anti-streptolysin O antibody (ASLO)-positive human sera were first compared with that of the entire LLO (LLO530) also fused to MBP (MBP-LLO530) . Sixteen of 17 (94.1%) ALLO-positive samples reacting with MBP-LLO530 also reacted with MBP-LLO411, whereas this proportion dropped to 11 of 17 (64.7%) with MBP-LLO240 . Alternatively, 18 of 19 (94.7%) ASLO-positive samples giving an interpretable result reacted with MBP-LLO530, whereas 1 of 19 (5.3%) of these samples reacted with MBP-LLO240 or MBP-LLO411 . The fusion polypeptide MBP-LLO411 was purified by maltose affinity chromatography and was further evaluated as a diagnostic antigen in a Western blot assay . Twenty-one of 21 (100%) serum samples obtained from patients with listeriosis and found to be positive for ALLO by a reference dot blot test reacted with MBP-LLO411, whereas 1 of 20 (5%) ASLO-positive serum samples and 1 of 100 (1%) serum samples from healthy adults were reactive . Thus, a polypeptide limited to the 411 amino-terminal residues of LLO is a specific and sensitive antigen for the detection of ALLO.

Vet Hum Toxicol, 1996 Jun, 38(3), 186 - 90
The effect of lead on the bone marrow stem cells of mice infected with Listeria monocytogenes; Bincoletto C et al.; We investigated the effects of lead exposure on the growth and differentiation of bone marrow hematopoietic cells, the so called colony-forming cells, in normal and Listeria monocytogenes infected mice (resistant and susceptible strains) . We also studied the effects of lead on the serum colony-stimulating activity (CSA), as well as on the survival of the mice after the infection . The doses of lead acetate were 13, 130 and 1300 ppm for 10, 30 and 70 d . At the end of this dosing, mice were infected with Listeria monocytogenes and killed 24, 48 or 72 h after inoculation of the bacteria . A dose-response suppressive effect of lead was observed in both strains in the 3 periods studied . However, in the resistant strain of mice the suppressive effects were overcome 48 h after the administration of the bacteria, whereas in the susceptible mice the suppressive effect of the infection was evident in all 3 time periods . The administration of lead caused no changes in serum hematopoietic growth factors, thus suggesting this metal acts by direct action on the myelopoietic cells . A significant decrease in host resistance, as measured by the mortality rate, was found when both strains of mice were challenged with sub-lethal doses of Listeria monocytogenes . Lethality was determined for a period of 10 d after dosing with 1300 ppm lead for 30 d.

Lett Appl Microbiol, 1996 Jun, 22(6), 448 - 52
Confirmation and identification of Listeria spp; Beumer RR et al.; All confirmation and identification methods used in this study can be used for the screening of suspected colonies on isolation media for Listeria spp . In traditional enrichment procedures the Microscreen Listeria latex test gives fast results . The DNA probes (Accuprobe and Gene-Trak) are very specific in detecting Listeria monocytogenes . For identification of Listeria spp . both tests (API and Micro-ID) performed equally well . Preference may be given to the API test, since differentiation of L . monocytogenes from L . innocua is based on the absence of arylamidase, through which tests for haemolytic activity and/or CAMP reactions can be omitted . However, the use of Enhanced Haemolysis Agar as isolation medium makes further testing essentially superfluous, since L . monocytogenes strains can be differentiated from L . innocua.

Lett Appl Microbiol, 1996 Jun, 22(6), 433 - 8
The effect of nisin on Listeria monocytogenes in culture medium and long-life cottage cheese; Ferreira MA et al.; The sensitivity to nisin of 27 strains of Listeria monocytogenes, four of L . innocua and one of L . ivanovii was estimated at pH 6.8 and pH 5.5 . Strains of L . monocytogenes showed differences in sensitivity which were not correlated with serotype . Strains of L . innocua were as resistant as the most resistant strains of L . monocytogenes, whereas the strain of L . ivanovii was relatively sensitive . Two of the most resistant strains of L . monocytogenes multiplied in aerated liquid medium adjusted to pH 5.0 with HCl, incubated at 20 degrees C; nisin, 500 IU ml-1, prevented multiplication and caused death . Following inoculation of a resistant strain into long-life cottage cheese, pH 4.6-4.7, the number of viable L . monocytogenes decreased approximately 10-fold during storage at 20 degrees C for 7 d; addition of nisin, 2000 IU g-1, to the cottage cheese increased the rate of inactivation to approximately a 1000-fold decrease in 3 d.

Lett Appl Microbiol, 1996 Jun, 22(6), 425 - 8
Thermal inactivation of Listeria monocytogenes during rapid and slow heating in sous vide cooked beef; Hansen TB et al.; Heating at slowly rising temperatures is suspected to enhance thermotolerance in Listeria monocytogenes and, since anaerobic environments have been shown to facilitate resuscitation of heat-injured cells of this micro-organism, concern may arise about the possibility of L . monocytogenes surviving in minimally preserved products . The effect of rapid ( > 10 degrees C min-1) and slow (0.3 and 0.6 degrees C min-1) heating on survival of L . monocytogenes in sous vide cooked beef was therefore examined at mild processing temperatures of 56 degrees, 60 degrees and 64 degrees C . No statistically significant difference (P = 0.70) was observed between the tested heating regimes . Since the average pH of beef was low (5.6), and little or no effect was observed, a pH-dependency of heat shock-induced thermotolerance in L . monocytogenes is suggested to account for this result.

Infect Immun, 1996 Jun, 64(6), 2359 - 61
Listeriolysin O activates mitogen-activated protein kinase in eucaryotic cells; Tang P et al.; Infection with Listeria monocytogenes induces the activation of mitogen-activated protein (MAP) kinase in several tissue culture cell lines (P.Tang, I . Rosenshine, and B . B . Finlay, Mol . Biol . Cell 5:455-464, 1994) . After various mutants were examined, the bacterial factor responsible for MAP kinase activation was identified as listeriolysin O (LLO) . Growth supernatant containing LLO or purified LLO alone can induce MAP kinase tyrosine phosphorylation in HeLa cells . Single-amino-acid mutations in LLO that do not affect its membrane binding capacity but reduce its cytolytic activity also reduced its ability to induce MAP kinase activity in HeLa cells . Streptolysin O, another sulfhydryl-activated hemolysin, and the detergent saponin are also able to activate MAP kinase in target cells . Thus, the increased MAP kinase activity observed in L . monocytogenes-infected cells is most likely a result of the permeabilization of the host cell membrane by LLO and may not be linked with invasion.

Infect Immun, 1996 Jun, 64(6), 2356 - 8
Neutralizing monoclonal antibodies against listeriolysin: mapping of epitopes involved in pore formation; Darji A et al.; Six different mouse monoclonal antibodies (MAbs) and a specific rabbit polygonal antibody were raised against listeriolysin . Four of the MAbs also recognized seeligeriolysin, and five cross-reacted with ivanolysin . The hemolytic activity could be neutralized by the polygonal antibody as well as by five of the MAbs . None of the neutralizing antibodies interfered with the binding of listeriolysin to the cellular membrane . The epitopes recognized by the MAbs were localized by using overlapping synthetic peptides between positions 59 and 279, a region hitherto not implicated in mediating hemolytic activity.

Infect Immun, 1996 Jun, 64(6), 1929 - 36
The ActA polypeptides of Listeria ivanovii and Listeria monocytogenes harbor related binding sites for host microfilament proteins; Gerstel B et al.; The surface-bound ActA polypeptide of the intracellular bacterial pathogen Listeria monocytogenes acts as a nucleator protein, generating the actin cytoskeleton around intracellularly motile bacteria . In this work, we examined the functional similarity of ActA from Listeria ivanovii (iActA) ATCC 19119 to its L . monocytogenes counterpart . The amino acid sequence of iActA predicts a molecular mass of 123 kDa and harbors eight proline-rich repeats . For functional analysis, various iActA derivatives and hybrid constructs of L . ivanovii and L . monocytogenes ActA polypeptides were transiently expressed in epithelial cells and examined for recruitment of host microfilament proteins by a mitochondrial targeting assay . As has been demonstrated with ActA, iActA also spontaneously inserted into the surface of mitochondria and induced recruitment of actin, alpha-actinin, and the vasodilator-stimulated phosphoprotein (VASP) to these subcellular organelles . By comparison of amino-terminally truncated iActA derivatives for their ability to recruit cytoskeletal proteins, a region essential for actin filament accumulation was identified between amino acid residues 290 and 325 . Such derivatives, however, retained their ability to bind VASP . Replacement of the proline-rich repeats in ActA with those of iActA also resulted in VASP recruitment . Hence, despite the limited overall sequence homology between ActA and iActA, the two molecules consist of at least two similar domains: a highly positively charged N-terminal domain that is directly involved in actin filament recruitment and a proline-rich repeat region required for VASP binding.

J Immunol, 1996 Jun 1, 156(11), 4280 - 9
Bias in the gamma delta T cell response to Listeria monocytogenes . V delta 6.3+ cells are a major component of the gamma delta T cell response to Listeria monocytogenes; Belles C et al.; Despite extensive research, the role that gamma delta T cells play in the immune response to infectious disease has yet to be established . Here we report the generation of a mAb specific for the V delta 6.3 TCR and investigate the gamma delta+ and V delta 6.3+ T cell responses to the intracellular bacterium Listeria monocytogenes in BALB/c mice . By infecting animals with various doses of Listeria and analyzing the components of the cellular immune response at the two primary sites of infection, the liver and spleen, we have shown that the kinetics, composition, and magnitude of the gamma delta and V delta 6.3 T cell responses are dependent upon the injected dose of bacteria and the organ in which the infection is established . At low doses of infection, the gamma delta T cell response occurs late in the disease course, while at high doses, the response is earlier and of greater magnitude, particularly in the liver . At all infectious doses and in both tissues, the V delta 6.3+ population predominates and together with V delta 4+ cells composes the bulk of the gamma delta T cell response . Changes in the morphology of gamma delta+ and V delta 6.3+ cells at the site of infection are consistent with cellular activation and suggest that these cells are active participants in the Listeria-induced immune response . The results of our study suggest that many features of the gamma delta T cell response to Listeria are dose and tissue related.

J Med Microbiol, 1996 Jun, 44(6), 418 - 24
The effects of inhibitors of vacuolar acidification on the release of Listeria monocytogenes from phagosomes of Caco-2 cells; Conte MP et al.; To evaluate the role of the acidic pH of phagosomes on the invasive ability and fate of Listeria monocytogenes within host cells, entry and replication of this gram-positive bacterium in a human enterocyte-like cell line (Caco-2) were investigated by a combination of biochemical and ultrastructural approaches . The effects of inhibitors of vacuolar acidification--the lipophilic weak base ammonium chloride, the carboxylic ionophore monensin and the vacuolar proton ATPase inhibitor bafilomycin A1--on the bacterial invasion pathway were analysed . These agents, which raise the intracellular vesicle acidic pH of living cells by different mechanisms, affected L . monocytogenes replication in Caco-2 cells . Bacteria internalised by bafilomycin-treated cells were unable to escape from phagosomes, as demonstrated by electronmicroscopy . The results provide evidence that low pH is required for efficient intracellular growth of L . monocytogenes.

J Chromatogr B Biomed Appl, 1996 May 17, 680(1-2), 165 - 70
Use of aqueous two-phase systems in sample preparation for polymerase chain reaction-based detection of microorganisms; Lantz PG et al.; An aqueous two-phase system, consisting of poly(ethylene glycol) (PEG) and dextran, was employed to separate polymerase chain reaction (PCR)-inhibitory substances from bacterial cells . The PCR inhibition of four soft cheeses was examined and three of them were found to be strongly PCR-inhibitory . Extraction of the PCR-inhibitory soft cheeses inoculated with Listeria monocytogenes in an aqueous two-phase system containing 8% (w/w) PEG 4000 and 8% (w/w) dextran 500, was found to lower the PCR detection level of L . monocytogenes by more than four orders of magnitude in two of the cheeses compared to the case where no such sample pretreatment was performed . Depending on the type of cheese used, the PCR-inhibitory factors were found to be enriched in either the top or bottom phase in the aqueous two-phase system . These results show that different soft cheeses contain different types and amounts of PCR-inhibitory substances.

J Am Vet Med Assoc, 1996 May 15, 208(10), 1695 - 9
Epidemiologic evaluation of encephalitic listeriosis in goats; Johnson GC et al.; OBJECTIVE--To evaluate host and environmental factors associated with the development of encephalitic listeriosis in goats . DESIGN--Retrospective analysis of diagnostic laboratory records and survey of veterinarians and goat producers . SAMPLE POPULATION--355 goat herds accessible through laboratory records; 38 veterinarians who treated goats and 76 goat producers . PROCEDURE--Data regarding breed and use for goats affected with encephalitic listeriosis were obtained from surveys and case follow-up information . Listeria monocytogenes isolates from the brains of 7 affected goats were serotyped and subjected to DNA restriction analysis . RESULTS--Odds ratio for the development of encephalitis listeriosis in Angora (mohair-producing) goats was 22.9 by use of diagnostic laboratory records . Survey also revealed a high prevalence in herds of Angora and other breeds that subsisted on woody browse, although Angora goats feeding predominantly on hay or pasture were not affected . Listeria monocytogenes isolates from 4 Angora goats in 3 herds differed in DNA restriction patterns, although the pattern was identical in 3 other goats from another herd . CLINICAL IMPLICATIONS--Encephalitic listeriosis can be observed in all goat breeds, but a lifestyle of heavy browse consumption seems important to the development of disease in some herds.

J Appl Bacteriol, 1996 May, 80(5), 557 - 64
Development of a predictive model for growth of Listeria monocytogenes in a skim milk medium and validation studies in a range of dairy products; Murphy PM et al.; A predictive model based on growth of Listeria monocytogenes in milk is described . The main aim of this work was to generate a predictive model in milk acidified with lactic acid to mimic conditions found in a range of dairy products . A complete factorial design was employed to determine the effects of pH (4.5-7.5), temperature (3-35 degrees C) and salt concentration (0-8%) on growth of the organism . There were 210 design points and growth curves were individually fitted for the Gompertz function using non-linear regression . Descriptors of the curves, such as lag phase duration (LPD), exponential growth rate (EGR) and generation time (GT) were calculated and polynomial models were developed relating these to pH, temperature and salt concentration . The selected cubic polynomial model gave acceptable predictive estimates of growth and was stable, i.e . predictions were repeatable over the range of environmental variables studied . The model was further tested to determine its capacity for predicting growth of listeria in a range of dairy foods and these validation studies confirm its usefulness as a rapid means of estimating growth of the organism under specified environmental conditions.

Mikrobiol Z, 1996 May-Jun, 58(3), 10 - 7
{The characteristics of the biological properties of Listeria strains isolated in Ukraine and Belgium}; Krasovskii VV et al.; Biological characteristics of 21 strains of bacteria of Listeria genus have been studied in Ukraine and Belgium . Morphological, cultural biochemical properties of cultures have been described . It has been proved that 85.7% produced bacteriocins . Antigenic titration of Listeria has been conducted and sensitivity to Listeria bacteriophage 2 LA and 4 LA has been estimated.

Microb Pathog, 1996 May, 20(5), 287 - 95
Inhibition of the multiplication of Listeria monocytogenes in a murine hepatocyte cell line (ATCC TIB73) by IFN-gamma and TNF-alpha; Haponsaph R et al.; The effects of IFN-gamma and TNF-alpha on intracellular multiplication of Listeria monocytogenes in a murine enbryonic hepatocyte cell line (ATCC TIB 73) were investigated . Neither IFN-gamma nor TNF-alpha alone (10, 25, or 100 ng/ml) significantly inhibited intracellular multiplication of L . monocytogenes . In contrast, addition of both IFN-gamma and TNF-alpha (10, 25, or 100 ng/ml) significantly inhibited intracellular listerial multiplication . The anti-listerial effects of IFN-gamma and TNF-alpha were not blocked by adding aminoguanidine or catalase . Nor did IFN-gamma and TNF-alpha treated hepatocyte monolayers produce detectable amounts of nitric oxide or hydrogen peroxide . These findings suggest that the effects of IFN-gamma and TNF-alpha may be independent of reactive oxygen (ROI) and nitrogen (RNI) intermediates.

J Biolumin Chemilumin, 1996 May-Jun, 11(3), 169 - 73
Bioluminescence measurements of the antilisterial activity of nisin: comparison with ampicillin and streptomycin; Ukuku DO et al.; The influence of nisin on intracellular ATP and cell numbers of Listeria monocytogenes strain Scott A was determined and compared with the effect of amplicillin and streptomycin under similar conditions . In the presence of nisin (3-12 micrograms/ml), intracellular ATP and cell numbers decreased rapidly during the first hour at 35 degrees C and extracellular ATP increased . Cell numbers and intracellular ATP increased after 3 h of incubation . No effect was observed in cells treated with ampicillin (3-12 micrograms/ml) and streptomycin (15-60 micrograms/ml) during the first hour . However, concentrations of > or = 3 micrograms/ml ampicillin and > or = 30 micrograms/ml streptomycin were listeriostatic after 3 h of incubation . Progressive loss of viability and reduction of intracellular ATP were observed in resting cells in PBS (pH 7.2) containing increasing concentrations of the antimicrobials . Rapid accumulation of extracellular ATP, observed immediately after treatment with nisin but not with the antibiotics, supports the reported collapse of proton motive force in L . monocytogenes by nisin.

Mol Microbiol, 1996 May, 20(4), 785 - 97
A single substitution in the putative helix-turn-helix motif of the pleiotropic activator PrfA attenuates Listeria monocytogenes virulence; Sheehan B et al.; PrfA, the regulator of virulence-gene expression in the pathogenic bacterium Listeria monocytogenes, displays sequence similarity to members of the CAP-FNR family of transcriptional regulators . To test the functional significance of this similarity, we constructed and analysed substitutions of two amino acids of PrfA predicted to contact DNA, i.e . Ser-184 and Ser-183 . Substitution of Ser-184 by Ala reduced DNA binding and virulence-gene activation, and attenuated the virulence in a mouse model of infection . In contrast, substitution of Ser-183 by Ala had the opposite effect in these functional assays . A 17bp DNA sequence, which includes a putative PrfA site, was shown to be sufficient for target-site recognition by PrfA and PrfA-S183A . Our results strongly support the hypothesis that PrfA is a structural and functional homologue of CAP . In addition, they establish a clear correlation between DNA binding by PrfA, virulence-gene activation, and virulence.

J Clin Periodontol, 1996 May, 23(5), 444 - 51
Effects of sublethal exposure to an antiseptic mouthrinse on representative plaque bacteria; Fine DH et al.; Although the mechanism responsible for the clinical antiplaque efficacy of oral antiseptics is generally considered to be primarily one of bactericidal activity, it has been suggested that oral antiseptics may have additional effects on bacteria exposed to sublethal levels . Studies reported herein, investigated the effects of sublethal levels of an essential oil-containing antiseptic mouthrinse (Listerine Antiseptic, Warner-Lambert Co., Morris Plains, NJ) on selected activities of representative plaque microorganisms using in vitro models . These studies demonstrated that sublethal exposure to the tested oral antiseptic can have significant effects in reducing intergeneric coaggregation, increasing bacterial generation time, and extracting endotoxin from Gram-negative bacteria . These in vitro activities can be correlated with features of plaque formation and pathogenicity seen in vivo; however, additional studies will be necessary to confirm that these mechanisms are, in fact, operative clinically.

Zh Mikrobiol Epidemiol Immunobiol, 1996 May-Jun, (3), 60 - 4
{Characteristics of Listeria monocytogenes strains isolated in Russia and their typing using pulse electrophoresis}; Marakusha BI et al.; On the basis of specially developed scheme for the isolation of Listeria strains comprising 2 enrichment stages and the use of growth inhibitors, 128 L . monocytogenes cultures were isolated from clinical material, foodstuffs and sewage water . Highly virulent L.monocytogenes strains isolated from clinical material belonged to serovar 4b (54%) and 1/2a (38%), while those isolated from foodstuffs and sewage water belonged to 4b (74%) . The restriction analysis of the chromosomal DNA of the isolated cultures with the use of restrictase EcoR1 on the basis of pulsed-field gel electrophoresis (PFGE) made it possible to distinguish Listeria strains in accordance with 5 types of restrictograms . The restrictograms of highly virulent L . monocytogenes strains, serovar 4b, belonged to types 1 and 2, while those of L . monocytogenes strains, serovar 1/2a, belonged to types 2 and 3 . The comparative use of different methods for typing L . monocytogenes (sero-, phago-, bio- and resistotyping, the analysis of plasmid composition and restriction analysis) revealed that the combination of serotyping and restriction analysis on the basis of PFGE proved to be most promising for the characterization of the isolated L . monocytogenes strains and the assessment of their epidemic importance.

Zh Mikrobiol Epidemiol Immunobiol, 1996 May-Jun, (3), 53 - 6
{The immunogenic and protective properties of the cell wall proteins of Listeria monocytogenes}; Pronin AV et al.; Two protein antigens with molecular weights of 58 kD (antigen Lm58) and 79/39 kD (antigen Lm79/ 39) were isolated from Listeria monocytogenes cell wall . Only Lm79/39 was shown to protect mice from L . monocytogenes infection, increasing their LD50 and survival time . The protective activity of Lm79/39 correlated (r = 0.64) with its mitogenic properties and its capacity for activating the production of interleukin-1- and interleukin-2-like factors . More over Lm79/ 39 induced more strong than Lm58 specific lymphocyte proliferation . The two antigens had practically no difference in their capacity for cytotoxic cell activation . The protective activity of Lm79/39 is probably linked with its immunomodulating properties, which opens a perspective for its use as a component of an antilisteriosis vaccine.

J Clin Microbiol, 1996 May, 34(5), 1086 - 90
Ribotype diversity of Listeria monocytogenes strains associated with outbreaks of listeriosis in ruminants; Wiedmann M et al.; Ribotyping is a molecular method for the characterization, identification, and typing of bacterial isolates that has value in epidemiological studies . To demonstrate the utility of this technique for typing of Listeria monocytogenes, four outbreaks of epizootic listeriosis in ruminants were investigated through coordinated detection and characterization methods utilizing classical microbiology and nucleic acid-based techniques . L . monocytogenes strains isolated from clinical samples and the silage consumed by the affected animals were ribotyped to establish the causal relationship between feed and the disease outbreak . For all but one outbreak, we were able to isolate L . monocytogenes strains represented by the same ribotype from both clinical and silage samples . Additional L . monocytogenes strains with ribotypes different from those of the respective clinical samples were isolated from all silage samples . This indicates that a diverse population of L . monocytogenes strains exists in farm environments, of which some may be more likely than others to cause disease.

J Interferon Cytokine Res, 1996 May, 16(5), 381 - 7
Deficient tumor necrosis factor secretion by cord blood mononuclear cells upon in vitro stimulation with Listeria monocytogenes; Serushago B et al.; We examined the production of tumor necrosis factor (TNF) by mononuclear cells (MNC) after incubating adult or cord blood MNC with Listeria monocytogenes in vitro . With adult MNC cultures, we found that TNF activity reached a peak at 6 h (606 +/- 120 x 10(3) units/liter) and declined to the baseline by day 3 . In contrast, using cord blood MNC, we found that TNF activity increased gradually reaching a peak at 24 h . In addition, the peak TNF activity using newborn MNC (189 +/- 26 x 10(3) U/liter) at 24 h was still lower than the peak using adult MNC at 6 h (p < 0.0002) . In seeking an explanation for the decreased TNF secretion from newborn MNC, we examined the possibility that newborn cells produce TNF but failed to secrete it . However, lysates of newborn cells contained functionally and antigenically less TNF than adult cells . Based on these observations, we conclude that the overall TNF production by newborn cells incubated with L monocytogenes is decreased compared with similarly stimulated adult cells.

Am J Vet Res, 1996 May, 57(5), 677 - 83
Protection of BALB/c mice against homologous and heterologous species of Brucella by rough strain vaccines derived from Brucella melitensis and Brucella suis biovar 4; Winter AJ et al.; OBJECTIVE--To evaluate stable rough mutants derived from Brucella melitensis 16M and B suis 2579 (biovar 4) as vaccines against homologous and heterologous Brucella spp in the BALB/c mouse model . DESIGN, ANIMALS, AND PROCEDURE--Rough mutants VTRM1 and VTRS1 were obtained from B melitensis 16M and B suis 2579, respectively, by allelic exchange of rfbU gene encoding mannosyltransferase with a Tn5-disrupted rfbU gene . Mice were vaccinated with VTRM1 or VTRS1 and challenge exposed 8 weeks later . RESULTS--VTRM1 and VTRS1 replicated extensively in the spleen during the first 3 weeks of infection, then decreased rapidly . Antibodies specific for the O polysaccharide were not detected in sera of mice inoculated with either rough strain . Vaccination with VTRM1 or VTRS1 induced protection against virulent strains of B abortus (2308), B melitensis (16M), B suis biovar 1 (750), and B suis biovar 4 (2579) . VTRM1 also protected against B ovis (PA) and against 4 field isolates of B abortus from bison or elk . VTRS1 conferred protection against 4 field isolates of B suis biovar 4 from reindeer . Vaccines prepared from live VTRM1 or VTRS1 provided significantly greater protection than that afforded by vaccines of killed cells in QS-21 adjuvant . Vaccination with VTRM1 containing VTRS1 gave minimal protection against the antigenically unrelated Listeria monocytogenes, thus demonstrating the immunologic specificity of protection against Brucella spp . CONCLUSIONS AND CLINICAL RELEVANCE--Results encourage evaluation, in primary host species, of VTRM1 and VTRS1, along with RB51, as alternative vaccines to strain 19, Rev 1, or other smooth phase vaccines.

Antimicrob Agents Chemother, 1996 May, 40(5), 1225 - 30
Effect of recombinant human gamma interferon on intracellular activities of antibiotics against Listeria monocytogenes in the human macrophage cell line THP-1; Scorneaux B et al.; Listeria monocytogenes is a facultative intracellular pathogen which enters cells by endocytosis and reaches phagolysosomes from where it escapes and multiplies in the cytosol of untreated cells . Exposure of macrophages to gamma interferon (IFN-gamma) restricts L . monocytogenes to phagosomes and prevents its intracellular multiplication . We have tested whether IFN-gamma also modulates the susceptibility of L . monocytogenes to antibiotics . We selected drugs from three different classes displaying marked properties concerning their cellular accumulation and subcellular distribution, namely, ampicillin (not accumulated by cells but present in cytosol), azithromycin (largely accumulated by cells but mostly restricted to lysosomes), and sparfloxacin (accumulated to a fair extent but detected only in cytosol) . We used a continuous line of myelomonocytic cells (THP-1 macrophages), which display specific surface receptors for IFN-gamma, and examined the activity of these antibiotics against L . monocytogenes Hly+ (virulent variant) and L . monocytogenes Hly- (a nonvirulent variant defective in hemolysin production) . Untreated THP-1 and phorbol myristate acetate-differentiated THP-1 were permissive for infection and multiplication of intracellular L . monocytogenes Hly+ (virulent variant) . All three antibiotics tested were bactericidal against this Listeria strain when added to an extracellular concentration of 10x their MIC . After preexposure of THP-1 to IFN-gamma, L . monocytogenes Hly+ was still phagocytosed but no longer grew intracellularly . The activity of ampicillin became almost undetectable (antagonistic effect), and that of azithromycin was unchanged (additive effect with that of IFN-gamma), whereas that of sparfloxacin was markedly enhanced (synergy) . A similar behavior (lack of bacterial growth, associated with a loss of activity of ampicillin, an enhanced activity of sparfloxacin, and unchanged activity of azithromycin) was observed in cells infected with L . monocytogenes Hly- . This modulation of antibiotic activity, which we ascribe to the change of subcellular localization of L . monocytogenes caused by IFN-gamma or by the lack of virulence factor, could result from a change in bacterial responsiveness to antibiotics, a modification of the drug activity, or differences in drug bioavailabilities between cytosol and phagosomes.

Lett Appl Microbiol, 1996 May, 22(5), 381 - 4
The clones of Listeria monocytogenes detected in food depend on the method used; Loncarevic S et al.; Restriction enzyme analysis (REA) with pulsed-field gel electrophoresis (PFGE) has been used to characterize and compare Listeria monocytogenes strains isolated from foods by two methods, an enrichment procedure and a direct plating procedure . In total 151 isolates from nine foods were investigated . In six of the foods (101 strains investigated) only one clone of L . monocytogenes was found irrespective of the method used . In three foods (50 strains investigated) the direct plating procedure yielded more clones than the enrichment procedure . At the most, five clones were detected in the same food . The results presented here indicate that direct plating from the food reveals more L . monocytogenes clones than revealed by an enrichment procedure.

Lett Appl Microbiol, 1996 May, 22(5), 357 - 60
Behaviour of Listeria monocytogenes during the traditional manufacture of water-buffalo Mozzarella cheese; Villani F et al.; The behaviour of a four-strains mixture of Listeria monocytogenes (strains Scott A, V7, OH and Cal) during the traditional manufacture of water-buffalo Mozzarella cheese was investigated at two levels of inoculation: ca 10(5) and 10(3) cfu ml-1 of vat milk . No significant change in Listeria counts was observed during the curd ripening (4.0-4.5 h), at the end of which the pH ranged between 4.83 and 4.91 . A decrease of about 2 log was observed after stretching of the curd in hot water (95 degrees C), followed by complete elimination of Listeria after 48 and 24 h of storage of the final cheese in the conditioning liquid (skim water resulting from the stretching, pH ca 4.0) with initial high and low contamination of the cheese milk respectively . Results also indicated that a 1.7 log reduction of L . monocytogenes could be achieved during the preparation of the natural whey culture utilized as starter in cheesemaking.

Lett Appl Microbiol, 1996 May, 22(5), 353 - 6
Development of a polymerase chain reaction assay for the detection of Listeria monocytogenes in foods; Bansal NS; Species-specific oligonucleotide primers were selected from the coding region of the listeriolysin O gene of Listeria monocytogenes and were used in conjunction with genus-specific primers and an internal control fragment for polymerase chain reaction amplification . The specificity of the primers was confirmed by testing 40 isolates of L . monocytogenes, other Listeria species and other micro-organisms which are ubiquitous in the environment . The reliability of these primers was further tested in parallel with standard cultural methods . In a preliminary study, over 250 different food samples were examined and PCR results were in complete agreement with those obtained from standard cultural procedures.

J Leukoc Biol, 1996 May, 59(5), 683 - 90
Differential regulation of Ia expression and antigen presentation by listeriolysin-producing versus non-producing strains of Listeria monocytogenes; Vazquez MA et al.; Listeria monocytogenes is an intracellular bacterial pathogen . A single gene product, listeriolysin (LLO), is critical for the induction of protective immunity . We now show that listeria that produce functional LLO augment Ia expression by macrophages and are better presented to a Th1, CD4+ anti-listeria T cell line . We used two genetically engineered strains of listeria which differed only in their ability (Ly+) or inability (Ly-) to produce functional LLO . Ia-negative murine macrophages ingested either Ly+ or Ly-, and then were stimulated by interferon-gamma (IFN-gamma) . Increasing numbers of live Ly+, but not Ly-, augmented IFN-gamma-induced Ia expression . Ly+ by itself did not induce Ia expression . Heat-killed Ly+ and Ly- did not augment IFN-gamma-induced Ia expression . The abundance of Ia on the macrophage cell surface is one major determinant of antigen presentation to CD4+ T cells . Consistent with their ability to augment la expression, Ly+ were better presented than Ly- to a CD4+, Th1, anti-listeria T cell line . When macrophages and T cells were from different inbred mouse strains, antigen presentation required identity at the class II region of the MHC gene complex . This indicated that antigen presentation occurred via Ia molecules . The increased ability of macrophages to present Ly+ is a product of the macrophage-listeria interaction, not a property of the T cell tine 86 . If Ia-negative macrophages ingested Listeria and were then stimulated by IFN-gamma, Ly+ was presented more efficiently than Ly- . On the other hand, if Ia-positive macrophages ingested Listeria, then Ly+ and Ly- were presented equally well to T cells . Altogether our data is consistent with the hypothesis that macrophages interact differently with Ly+, and that this contributes to the ability of only live Ly+ to induce protective immunity.

Appl Environ Microbiol, 1996 May, 62(5), 1781 - 7
Recovery of different Listeria ribotypes from naturally contaminated, raw refrigerated meat and poultry products with two primary enrichment media; Ryser ET et al.; Isolation rates for Listeria monocytogenes and the other Listeria spp . typically improve when samples are enriched in more than one primary enrichment medium . This study evaluated the abilities of two primary enrichment media, University of Vermont-modified Listeria enrichment broth (UVM) and Listeria repair broth (LRB), to recover different ribotypes of Listeria spp . from raw meat and poultry samples . Forty-five paired 25-g retail samples of ground beef, pork sausage, ground turkey, and chicken (160 samples) underwent primary enrichment in UVM and LRB (30 degrees C for 24 h) followed by secondary enrichment in Fraser broth (35 degrees C for 24 and 40 h) and plating on modified Oxford agar . After 24 h of incubation of 35 degrees C, 608 Listeria colonies from selected positive samples were biochemically confirmed as L . monocytogenes (245 isolates), L innocua (276 isolates), and L . welshimeri (89 isolates) and then ribotyped with the automated Riboprinter microbial characterization system (E . I . du Pont de Nemours & Co., Inc.) . Thirty-six different Listeria strains comprising 16 L . monocytogenes (including four known clinical ribotypes), 12 L . innocua, and 8 L . welshimeri ribotypes were identified from selected positive samples (15 samples of each product type; two UVM and two LRB isolates per sample) . Twenty-six of 36(13 L . monocytogenes) ribotypes were detected with both UVM and LRB, whereas 3 of 36 (1 L . monocytogenes) and 7 of 36 (3 L . monocytogenes) Listeria ribotypes were observed with only UVM or LRB, respectively . Ground beef, pork sausage, ground turkey, and chicken yielded 22 (8 L . monocytogenes), 21 (12 L . monocytogenes), 20 (9 L . monocytogenes), and 19 (11 L . monocytogenes) different Listeria ribotypes, respectively, with some Listeria ribotypes confined to a particular product . More importantly, major differences in both the number and distribution of Listeria ribotypes, including previously recognized clinical and nonclinical ribotypes of L . monocytogenes, were observed when 10 UVM and 10 LRB isolates from five samples of each product were ribotyped . When a third set of six samples per product type was examined from which two Listeria isolates were obtained by using only one of the two primary enrichment media, UVM and LRB failed to detect L . monocytogenes (both clinical and nonclinical ribotypes) in two and four samples, respectively . These findings stress the importance of using more than one primary enrichment medium and picking a sufficient number of colonies per sample when attempting to isolate specific L . monocytogenes strains during investigations of food-borne listeriosis.

Appl Environ Microbiol, 1996 May, 62(5), 1693 - 8
Adaptive acid tolerance response in Listeria monocytogenes: isolation of an acid-tolerant mutant which demonstrates increased virulence; O'Driscoll B et al.; The ability of Listeria monocytogenes to tolerate low-pH environments is of particular importance because the pathogen encounters such environments in vivo, both during passage through the stomach and within the macrophage phagosome . In our study, L . monocytogenes was shown to exhibit a significant adaptive acid tolerance response following a 1-h exposure to mild acid (pH 5.5), which is capable of protecting cells from severe acid stress (pH 3.5) . Susceptibility to pH 3.5 acid is growth phase dependent . Stationary-phase Listeria cultures are naturally resistant to the challenge pH (pH 3.5), while exponential-phase cultures require adaptation at pH 5.5 to induce acid tolerance . Adaptation requires protein synthesis, since treatment with chloramphenicol prevents the development of acid tolerance . Induction of the acid tolerance response also protects L . monocytogenes against the effect of other environmental stresses . Acid-adapted cells demonstrate increased tolerance toward thermal stress, osmotic stress, crystal violet, and ethanol . Following prolonged exposure of L . monocytogenes to pH 3.5, we isolated mutants which constitutively demonstrate increased acid tolerance at all stages of the growth cycle . These mutants do not display full acid tolerance, but their resistance to low pH can be further increased following adaptation to mild-acid conditions . The mutants demonstrated increased lethality for mice relative to that of the wild type when inoculated by the intraperitoneal route . When administered as lower inocula, the mutants reached higher levels in the spleens of infected mice than did the wild type . The data suggest that low-pH conditions may have the potential to select for L . monocytogenes mutants with increased natural acid tolerance and increased virulence.

Appl Environ Microbiol, 1996 May, 62(5), 1616 - 22
Model for the combined effects of temperature, pH, and sodium lactate on growth rates of Listeria innocua in broth and Bologna-type sausages; Houtsma PC et al.; A modified Monod equation was successfully applied to describe the maximum specific growth rate of Listeria innocua in a broth model in the presence of various concentrations of sodium lactate or NaCl . The combined effects of temperature and pH were assessed by translating the parameters of the modified Monod equation mu(m), alpha, and p') as functions of pH and/or temperature . As a result, the area in which the growth rate could be predicted was extended to include as a variable not only the salt concentration but also pH and temperature . The number of parameters needed to describe the experimental data was thereby reduced from 48 to 4 (NaCl) and from 42 to 5 (sodium lactate) . The decline in the goodness of fit that accompanied the reduction in the number of parameters was within statistically acceptable ranges . The resulting model was compared with a polynomial fit, and it was proposed that the former was more suitable for the purpose of this study . The broth model for sodium lactate was evaluated with Bologna-type sausages . Because of the "worst-case" design of the broth model, it was necessary to reestimate one or all parameters to obtain a good description of the growth rate of L . innocua in the meat product . However, the simplicity of the model and the practical usefulness of its parameters offer considerable prospects for its use in predictive microbiology.

Photochem Photobiol, 1996 May, 63(5), 672 - 9
Effects of ultraviolet-B exposure on the resistance to Listeria monocytogenes in the rat; Goettsch W et al.; A rat infection model using the bacterial pathogen Listeria monocytogenes was employed to analyze the immunosuppressive activity of UVB radiation . Rats were exposed to suberythemal doses of UVB radiation for 5 or 7 consecutive days, using Kromayer or FS40 lamps respectively . Subsequently, the rats were infected subcutaneously or intravenously with Listeria . Exposure to UVB resulted in an increased number of bacteria in the spleen 4 days after infection . Listeria-specific lymphocyte proliferation assays as well as delayed-type hypersensitivity reactions demonstrated that T cell-mediated immunity to Listeria was impaired by UVB as measured 4 and 8 days after infection . In addition, UVB exposure decreased phagocytotic activity of peripheral blood macrophages . This study demonstrated that suberythemal doses of UVB radiation caused a delay in the clearance of Listeria bacteria from the spleen of the rats and that this was probably caused by impaired nonspecific phagocytosis of Listeria by macrophages in addition to an impaired activity of Listeria-specific T cells.

J Virol, 1996 May, 70(5), 2902 - 10
Antiviral cytotoxic T-cell memory by vaccination with recombinant Listeria monocytogenes; Slifka MK et al.; Listeria monocytogenes is a facultative intracellular bacterium that is able to escape phagocytic vesicles and replicate in the cytoplasm of infected cells . As with viral vectors, this intracytoplasmic life cycle provides a means for introducing foreign proteins into the major histocompatibility complex class I pathway of antigen presentation . Using recombinant L . monocytogenes (rLM) strains expressing the full-length nucleoprotein (NP) or a single cytotoxic T-lymphocyte (CTL) epitope from lymphocytic choriomeningitis virus (LCMV), we analyzed antiviral CTL responses induced by rLM vaccination . After vaccination, rLM was cleared from the host within 7 days while inducing an LCMV-specific ex vivo CD8+ effector CTL response . Virus-specific CTL memory was maintained for 6 months postvaccination, as demonstrated by vigorous secondary CTL responses after in vitro stimulation . A single immunization with rLM that expressed either the full-length NP gene or the CTL epitope alone resulted in LCMV NP-specific CTL precursor frequencies of approximately 1/10(4) CD8+ T cells . A second rLM vaccination resulted in enhanced virus-specific CTL activity and in vitro proliferation . rLM-vaccinated mice were protected against chronic viral infection by an accelerated virus-specific memory CTL response . These mice cleared infectious virus as well as viral antigen, suggesting that sterilizing immunity was achieved . In contrast to mice that received wild-type LM, rLM-vaccinated mice were protected from virally induced immunosuppression and splenic atrophy associated with chronic LCMV infection . The ability to elicit long-term cell-mediated immunity is fundamental in designing vaccines against intracellular pathogens, and these results demonstrate the efficacy of recombinant LM vaccination for inducing protective antiviral CTL memory.

Infect Immun, 1996 May, 64(5), 1870 - 2
Peptide epitopes from noncytosolic Listeria monocytogenes can be presented by major histocompatibility complex class I molecules; Zwickey HL et al.; Listeria monocytogenes is an intracellular pathogen which escapes the phagosome and resides in the cytosol of the host cell . Using Listeria innocua and a mutant strain of L . monocytogenes (listeriolysin O negative), which do not enter the cytosol of the host cell, we demonstrate class I presentation of an epitope of p60, a protein secreted by L . monocytogenes, to a class I-restricted CD8+ cytotoxic T lymphocyte clone.

Infect Immun, 1996 May, 64(5), 1744 - 9
Control of natural killer cell-mediated innate resistance against the intracellular pathogen Listeria monocytogenes by gamma/delta T lymphocytes; Ladel CH et al.; Listeria monocytogenes is an intracellular bacterium which causes an acute infectious disease in mice . Initial host resistance depends on innate immunity mediated primarily by natural killer (NK) cells followed by specific alpha/beta T cells, which are central to acquired specific immunity . Gamma/delta T lymphocytes seem to provide a link between the innate and the specific immune response . All these lymphocyte populations produce gamma interferon (IFN-gamma), which, because of its macrophage-activating potential, is central to antibacterial protection . IFN-gamma from NK cells not only contributes to early host resistance but also promotes development of protective T-cell responses of helper T type 1 (Th1) type . Here, we show that innate resistance and early IFN-gamma production in listeriosis are markedly impaired in T-cell receptor (TCR)-delta-/- but not TCR-beta-/- gene disruption mutant mice . By two-color cytofluorimetry, we demonstrate that NK cells rather than gamma/delta T lymphocytes are the major cellular source of IFN-gamma in immunocompetent mice and that IFN-gamma production by NK cells is impaired in the TCR-delta-/- mutants . Probably, reduced tumor necrosis factor production in listeria-infected TCR-delta-/- mutants contributed to impaired NK cell activation . Our data reveal a novel function of gamma/delta T cells as regulators of innate resistance against sublethal infection with an intracellular pathogen.

Infect Immun, 1996 May, 64(5), 1685 - 93
A recombinant minigene vaccine containing a nonameric cytotoxic-T-lymphocyte epitope confers limited protection against Listeria monocytogenes infection; An LL et al.; We have previously shown that vaccines expressing virus-derived cytotoxic-T-lymphocyte (CTL) epitopes as short minigenes can confer effective protection against virus challenges, and here we extend these studies to the bacterium Listeria monocytogenes . Host defense against this important human pathogen appears largely T cell mediated, and a nonamer CTL epitope from the listeriolysin O (LLO) protein has been identified in BALB/c mice . We have synthesized this nonamer as a minigene, expressed it in a recombinant vaccinia virus (VV-list), and used this to immunize mice . Memory CTLs cultured from VV-list-immunized mice specifically lyse target cells pulsed with a nonamer peptide identified at LLO amino acid residues 91 to 99 . Four weeks postimmunization, mice were challenged with L . monocytogenes . By day 6 following challenge with a sublethal dose of L . monocytogenes, mice immunized with VV-list showed a approximately 2,000- to 6,000-fold reduction in bacteria CFU in the spleen and liver . At this time point, with control mice, bacterial were readily detectable by Gram stain of the liver but were undetectable in the VV-list-immunized animals . Additionally, when a normally lethal dose of bacteria was given, death was delayed in VV-list-immunized animals . This study has demonstrated that a single immunization with a recombinant vaccinia virus bearing only nine amino acids from a bacterial pathogen can induce specific CTLs able to confer partial protection against bacterial challenge.

J Immunol, 1996 Apr 15, 156(8), 2979 - 84
Differential effects of viable and killed bacteria on IL-12 expression of macrophages; Song F et al.; Listeria monocytogenes-specific, IFN-gamma-producing CD4+ T cells are induced in 5-day in vitro cultures of naive spleen cells with viable L . monocytogenes (VLM) but are not induced in cultures with heat killed L . monocytogenes (HKLM) . Anti-IL-12 Abs abrogated the induction of the IFN-gamma-producing CD4+ T cells by VLM, suggesting an importance of IL-12 in the induction of IFN-gamma-producing CD4+ T cells . Accordingly, IL-12p40 was expressed by macrophages (M phi) from the cultures of whole spleen cells with VLM but not with HKLM, although HKLM induced IL-12p40 expression on M phi when nonadherent cells were removed before culture . In vivo analysis also showed that VLM induced IL-12p40 expression by M phi, whereas HKLM failed to induce it . On the other hand, the addition of anti-IL-10 mAb into cultures of whole spleen cells and HKLM resulted in an increase of IL-12p40 expression by M phi . Furthermore, we detected an expression of IFN-gamma by both adherent and nonadherent spleen cells at the early stage of stimulation with VLM before the appearance of IFN-gamma-producing CD4+ T cells . These data suggest that HKLM induce nonadherent spleen cells to produce IL-10 which may down-regulate IFN-gamma-producing CD4+ T cells by blocking IL-12 production by M phi . In contrast, VLM support IFN-gamma production by CD4+ T cells by stimulating M phi to produce IL-12 and IFN-gamma.

Cell Immunol, 1996 Apr 10, 169(1), 1 - 6
Complement receptor type 3 mediates phagocytosis and killing of Listeria monocytogenes by a TNF-alpha- and IFN-gamma-stimulated macrophage precursor hybrid; Drevets DA et al.; Previous work demonstrated that engagement of complement receptor type 3 (CR3) was required for inflammatory peritoneal macrophages to phagocytose and kill the facultative intracellular bacterium Listeria monocytogenes . The experiments described here tested the role of CR3 in phagocytosis and killing of Listeria by a clonal population of TNF-alpha/IFN-gamma-stimulated macrophage precursor hybrids . Stimulation with TNF-alpha and IFN-gamma increased CR3 expression 20-fold and induced a big increase in phagocytic activity . Phagocytosis and killing of Listeria by these cells were inhibited when bacteria were opsonized with complement-depleted serum or by incubation of the macrophages with anti-CR3 mAb . Furthermore, cytokine-stimulated macrophages could not kill Listeria opsonized with heat-inactivated anti-Listeria antiserum, indicating that macrophage receptors which mediate phagocytosis do not necessarily promote bactericidal activity . These data suggest that upregulation of CR3 and CR3-mediated phagocytosis are mechanisms by which TNF-alpha and IFN-gamma stimulate nonphagocytic, nonbactericidal macrophage precursors to kill intracellular bacterial pathogens.

Microbiology, 1996 Apr, 142 ( Pt 4), 985 - 92
Bacteriophage receptors on Listeria monocytogenes cells are the N-acetylglucosamine and rhamnose substituents of teichoic acids or the peptidoglycan itself; Wendlinger G et al.; Different approaches were used to examine the function of teichoic acids (TA) as phage receptors among selected Listeria strains, and to identify and characterize specific receptor structures of host cells belonging to different serovars . This included successive removal of cell wall constituents, preparation and purification of TA, and GLC analysis of TA components . Adsorption of Listeria monocytogenes bacteriophages could be inhibited by polyvalent antisera, specific lectins and addition of purified TA . The results confirmed the necessity of TA in general and of rhamnose and glucosamine in particular for adsorption of Listeria phage A118, which is a temperate Siphovirus (morphotype B1), attacking predominantly serovars 1/2 . Host binding of siphoviral phage A500 (predominantly lysing serovars 4b), was also dependent on cell wall TA . A phage-resistant L . monocytogenes strain was shown to lack glucosamine in its TA . These results support the view that TA substituents may play an important role not only in antigenicity of Listeria cells, but also in specificity of host recognition by two temperate Listeria phages . In contrast, the broad-host-range virulent phage A511 (Myovirus, morphotype A1) uses the listerial peptidoglycan as primary receptor . This corresponds well with the observation that A511 is capable of lysing the majority of L . monocytogenes strains.

Appl Environ Microbiol, 1996 Apr, 62(4), 1461 - 6
Characterization of Listeria monocytogenes isolates by esterase electrophoresis; Harvey J et al.; Multiple bands of alpha-naphthyl-propionyl esterase (alpha NPE) activity observed following starch gel electrophoresis of cell extracts allowed 219 Listeria monocytogenes isolates from milk, nondairy foods, and clinical and veterinary sources to be assigned to 17 different alpha NPE types . Multilocus enzyme electrophoresis (MEE) analysis was used to obtain electrophoretic mobility data for alpha NPEs and nine other metabolic enzymes; on the basis of these data, the 219 strains were assigned to 59 electrophoretic types . Each of the methods separated the strains into two main groups, and there was extensive agreement on assignment of the strains to the groups . Although the method is less discriminatory than MEE, the usefulness of alpha NPE electrophoresis alone as a rapid, simple typing method for L . monocytogenes for certain purposes is indicated by agreement among alpha NPE, MEE, and restriction fragment length polymorphism types as molecular markers for persistent and transient L . monocytogenes strains found in sequential raw-milk and nondairy food samples obtained from different processors.

Appl Environ Microbiol, 1996 Apr, 62(4), 1252 - 6
Influence of environmental parameters on phosphatidylcholine phospholipase C production in Listeria monocytogenes: a convenient method to differentiate L . monocytogenes from other Listeria species; Coffey A et al.; The ability to produce phosphatidylcholine phospholipase C (lecithinase) is associated with virulence in pathogenic species of Listeria . Levels of production vary greatly among members of the genus, and this virulence factor is not readily detectable in many members of the pathogenic species on conventional agar media containing egg yolk, a common substrate for the enzyme . In this study, the influence of a variety of environmental parameters, including temperature, pH, and salt concentration, on the production of lecithinase by a number of strains was evaluated . Lecithinase production by Listeria monocytogenes LO28 in brain heart infusion medium was optimal at 1.75 to 2.0% NaCl; pH 7.0 to 7.3, and 37 to 40 degrees C, and the presence of oxygen had no effect . In a chemically defined medium, the optimal NaCl concentration and temperature were lower at 0.75 to 1.0% NaCl and 33.5 degrees C . As detection of virulence factors is useful to assist in the identification and differentiation of Listeria species, this report shows that lecithinase activity can conveniently be detected within 36 h on a relatively inexpensive medium . Under the conditions described, L . monocytogenes could be distinguished from other members of the genus as a result of distinct lecithin degradation which was not evident in L . innocua, L . seeligeri, L . ivanovii, L . welshimeri, or L . murrayi/grayi.

Mol Microbiol, 1996 Apr, 20(1), 119 - 26
Apoptosis of mouse dendritic cells is triggered by listeriolysin, the major virulence determinant of Listeria monocytogenes; Guzman CA et al.; Infection of a murine-spleen dendritic cell line by Listeria monocytogenes was found to induce cell death through apoptosis . To characterize the bacterial product(s) involved in induction of apoptosis, dendritic cells were infected with the L . monocytogenes EGD strain and several isogenic mutants deficient in the production of individual listerial virulence factors . The ability to induce cellular apoptosis was retained by all mutants tested, except the prfA and delta hly mutants, both of which are unable to produce listeriolysin . Apoptosis was also induced by purified listeriolysin suggesting that this protein directly induces apoptosis . Purified recombinant listeriolysins rendered either weakly haemolytic by a C-484 to S mutation, or nonhaemolytic by a W-491 to A mutation exhibited little or no capacity to induce apoptosis, indicating that both activities are associated within the same protein region . Treatment with purified listeriolysin or L . monocytogenes infection also triggers apoptosis in explanted bone-marrow dendritic cells . Thus invasion of dendritic cells by L . monocytogenes, which results in cell death, may play an important role in the pathogenesis of listerial infections by impairing immune responses, hindering bacterial clearance and promoting spread of the infection.

J Appl Bacteriol, 1996 Apr, 80(4), 395 - 401
Listeria monocytogenes in poultry and poultry products: epidemiological investigations in seven Danish abattoirs; Ojeniyi B et al.; Listeria monocytogenes was isolated from 11/236 (4 x 7%) caecal samples from parent flocks, providing broilers to the abattoirs investigated . Caecal samples from 2078 broilers representing 90 randomly selected broiler flocks were negative for L . monocytogenes . A total of 3080 samples from seven abattoirs including poultry processing line samples, and final products were also examined for L . monocytogenes . Listeria monocytogenes was isolated in 0 x 3% to 18 x 7% of the samples collected in the different abattoirs . Epidemiological typing of 247 L . monocytogenes isolates, including serotyping, phage typing, pulsed-field gel electrophoresis and ribotyping revealed 62 different clones . Based upon typability and discriminatory power, DNA typing methods used were found equally suitable as epidemiological markers . Serotyping and phage typing were not found useful as epidemiological markers for poultry isolates of L . monocytogenes since only 120/247 (48 x 6%) isolates were typable by phage typing and 230/247 (93 x 1%) L . monocytogenes belonged to serotype 01 while 6/247 (2 x 4%) belonged to 04 . The discovery of a few dominating clones in each abattoir might indicate an endemic occurrence of L . monocytogenes . It is concluded that L . monocytogenes in the broiler production is primarily localized to the abattoirs . The incidence of L . monocytogenes may be reduced by improving the hygiene.

J Clin Microbiol, 1996 Apr, 34(4), 1007 - 10
Serotyping and esterase typing for analysis of Listeria monocytogenes populations recovered from foodstuffs and from human patients with listeriosis in Belgium; Gilot P et al.; Listeria monocytogenes strains isolated in Belgium from different foodstuffs and in sporadic cases of human listeriosis were analyzed . The distribution of serovars differed in each of these populations . The bacteria isolated from cheeses and from human patients with listeriosis were further studied by esterase typing . The twenty esterase patterns defined were not equally distributed in these two populations . The secretion of the virulence determinant phosphatidylinositol-specific phospholipase C and the pathogenicity level of strains in immunocompromised mice could not explain the unequal distribution of esterase types . The discrimination index of esterase typing (DI = 0.868) was compared with that of serotyping (DI = 0.666) and with that of the two combined methods (DI = 0.899).

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