Listeriosis

Zh Mikrobiol Epidemiol Immunobiol, 2000 Sep-Oct, (5), 3 - 6
{Autoregulation of expression of secreted proteins in Listeria monocytogenes}; Ermolaeva SA et al.; The spectrum of proteins secreted by L . monocytogenes greatly depends on the composition of the cultivation medium . The introduction of activated charcoal (AC) into brain heart infusion (BHI) leads to the secretion of a number of additional proteins with mol.wt . ranging between 20 and 100 kD, whose production is not observed in pure BHI . The effect depends on the absorption capacity of AC: when adsorption capacity is reduced due to a decrease in the concentration of AC or its preliminary saturation with the components of the cultivation medium a drop in the level of the production of additional proteins is observed . The preliminary treatment of the medium with AC with its subsequent elimination prior to inoculation doses not change the spectrum of secreted proteins, though greatly inhibits the growth of L . monocytogenes . The data obtained in this investigation indicate that the effect produced by AC is based on the elimination of some product of L . monocytogenes vital activity from the cultivation medium; this product acts as the autoregulator of the synthesis of a number of secreted proteins.

J Virol, 2001 Mar, 75(6), 2786 - 91
Systemic immunity and mucosal immunity are induced against human immunodeficiency virus Gag protein in mice by a new hyperattenuated strain of Listeria monocytogenes; Rayevskaya MV et al.; Vaccines designed to control chronic infections by intracellular agents such as human immunodeficiency virus type 1 (HIV-1) require the induction of cell-mediated immune responses to rid the host of pathogen-infected cells . Listeria monocytogenes has characteristics that make it an attractive vaccine vector for use against such infections . Here we show that parenteral immunization with a new highly attenuated strain of this organism provided complete protection against systemic and mucosal challenges with a recombinant vaccinia virus expressing HIV-1 gag . Immunization also generated a strong, long-term memory cytotoxic-T-lymphocyte (CTL) response in spleen, mesenteric lymph nodes, and Peyer's patches directed against the gag protein . Oral immunization with this attenuated strain also produced complete, long-lasting protection against the recombinant virus but only against mucosal virus challenge . Curiously, oral immunization was associated with a transient CTL response in the three lymphoid tissues examined.

Toxicol Appl Pharmacol, 2001 Mar 1, 171(2), 71 - 84
Ozone-induced modulation of cell-mediated immune responses in the lungs; Cohen MD et al.; Most pulmonary immunotoxicology studies of ambient pollutants have been broadly designed to discern if overall humoral or cell-mediated immunity (CMI) was altered; few have assessed effects on particular aspects of immune function . We hypothesized that effects from ozone (O3) exposure on pulmonary CMI are linked in part to changes in local immune cell capacities to form and/or to interact with immunoregulatory cytokines . Rats exposed to 0.1 or 0.3 ppm O3 4 h/day 5 days/week, for 1 or 3 weeks were assessed for resistance to, and pulmonary clearance of, a subsequent Listeria monocytogenes challenge . In situ cytokine release and immune cell profiles were also analyzed at different stages of the antilisterial response . Although O3 exposure modulated CMI, effects were not consistently concentration- or duration-dependent . Exposure did not effect cumulative mortality from infection, but induced concentration-related effects upon morbidity onset and persistence . All 1-week exposed rats had listeric burdens trending higher than controls; 0.3 ppm rats displayed continual burden increases rather than any onset of resolution . Rats exposed for 3 weeks had no O3-related changes in clearance . No exposure-related effect on neutrophil or pulmonary macrophage (PAM) numbers or percentages was noted . Bacterial burden analyses with respect to cell type showed that Listeria:PAM ratios in 0.3 ppm rats ultimately became greatest compared to all other rats . In situ IL-1alpha and TNFalpha levels were consistently higher in O3-exposed rats . All rats displayed increasing in situ IFNgamma levels as infection progressed, but no constant relationship was evident between IFNgamma and initial IL-1alpha/TNFalpha levels in O3-exposed hosts . It seems that short-term (i.e., 1 week) repeated O3 exposures imparted more effects upon CMI than a more prolonged (i.e., 3 week) regimen, with effects manifesting at the level of the PAM and in the cytokine network responsible for immunoactivation .

An Med Interna, 2000 Dec, 17(12), 649 - 51
{Listeriosis: an infrequent infection in patients with HIV}; Valencia Ortega ME et al.; Although resistance to Listeria monocytogenes infection requires intact T-cell mediated immunity, listeriosis is an infrequent problem in patients with HIV infection and only about 50 patients have been reported to date . Only two patients with HIV and L . monocytogenes have been attended in our hospital since the beginning of aids epidemic in 1981 . Case 1: a man with HIV and 364 CD4+ cells/mm3 presented fever and occipital headache . The cerebral scan was normal and L . monocytogenes grew in licuor culture . He was outcome after treatment with ampicillin and tobramycin . Case 2: a 47 years old man with HIV, 44 CD4+ cells/mm3 and hepatic virus C cirrhosis was admitted to the hospital because fever and abdominal distension . He was on menstrual pentamidine prophylaxis for Pneumocystis carinii pneumonia (PCP) . Bacterial peritonitis was diagnosed and the patient begun treatment with ceftriaxone . The patient dead 72 hours later with hepatic encepholopathy . Postmortem L . monocytogenes grew . Listeriosis is an infrequent disease in patients with HIV that causes difficult diagnostic problems, principally in patients without prophylaxis with cotrimoxazole for PCP.

Int J Food Microbiol, 2001 Jan 22, 63(1-2), 91 - 8
High incidence of Listeria monocytogenes in European red smear cheese; Rudol M et al.; The incidence of Listeria and Listeria monocytogenes in European red smear cheese was determined in order to assess whether the lack of recent outbreaks of listeriosis associated with cheese is due to improved hygenic conditions in the dairies . Out of European red-smear cheese samples of various types, 15.8% contained organisms of the genus Listeria, 6.4% of the samples were contaminated with L . monocytogenes, 10.6% with L . innocua, and 1.2% with L . seeligeri . Six cheese samples contained two or more Listeria species, including at least one L . monocytogenes isolate . The incidences of L . monocytogenes in cheeses from various countries were: Italy 17.4%, Germany 9.2%, Austria 10%, and France 3.3% . Listeria were found most frequently in soft and semi-soft cheese . Eight samples contained more than 100 L . monocytogenes cfu/cm2 cheese surface, 2 samples had counts above 10(4) cfu/cm2 cheese surface . Surprisingly, a higher incidence of L . monocytogenes was observed in cheeses made from pasteurized milk (8.0%) than in cheeses manufactured from raw milk (4.8%) . Phage-typing of isolated Listeria strains clearly confirmed that (i) contaminations within dairy plants were persistent over a period of several weeks to months and (ii) that cross-contamination within the dairy plant is and important factor . Comparison of our data with past surveys seems to indicate that contamination of red smear soft cheese with L . monocytogenes has not decreased sufficiently over the past 15 years . It is therefore strongly recommended that these products are monitored carefully by cheese-making companies.

Int J Food Microbiol, 2001 Jan 22, 63(1-2), 135 - 47
Factors influencing resuscitation and growth of heat injured Listeria monocytogenes 13-249 in sous vide cooked beef; Hansen TB et al.; The growth of Listeria monocytogenes 13-249 in vacuum-packed, minced beef was investigated as a function of degree of heat injury (including no injury i.e . uncooked beef), growth phase (logarithmic and late stationary phase), pH (5.6 and 6.2), and storage temperature (3, 10 and 20 degrees C) during a storage period of 30 days . Late logarithmic and late stationary phase cultures of L . monocytogenes 13-249 showed similar growth in refrigerated, vacuum-packed, raw minced beef with a high pH (6.2) . In normal pH (5.6) beef there was no growth at 3 degrees C while growth at 10 and 20 degrees C was only observed for logarithmic phase cultures . Heat injured late stationary phase cultures with 95-99.9% injured cells in the surviving population (as measured by differential plating on enriched vs . selective media after sous vide cooking) did not grow or repair sublethal injuries in sous vide cooked beef at 3 degrees C while repair and growth took place at 10 as well as at 20 degrees C . In logarithmic phase cultures heat injury occurred very rapidly and > or = 99.9% heat injury was observed in all trials in spite of much lower pasteurization values and fewer log10 reductions compared with late stationary phase cultures . Regardless of growth phase, all cultures where a high degree of heat injury (> or = 99.9%) was observed, did not subsequently grow in the beef product at 3 or 10 degrees C within 30 days . Growth of heat injured cultures preexposed to heat shock (46 degrees C, 30 min) or slowly rising temperatures (0.3 degrees C min(-1)) before heat injury was also investigated . Heat shocked or heat adapted cultures generally responded in the same manner as non-stressed cultures (no growth at 3 degrees C) except that a longer lag phase was observed in beef processed at slowly rising temperatures and in normal pH beef at 10 degrees C . Although processing at slowly rising temperatures may slightly increase the survival of L . monocytogenes 13-249 in cooked beef, there seem to be no indication of an increase in subsequent growth potential of the surviving cells.

MMWR Morb Mortal Wkly Rep, 2000 Dec 22, 49(50), 1129 - 30
Multistate outbreak of listeriosis--United States, 2000; Listeriolysin O-induced stimulation of mucin exocytosis in polarized intestinal mucin-secreting cells: evidence for toxin recognition of membrane-associated lipids and subsequent toxin internalization through caveolae; Institut National de la Sante et de la Recherche Medicale, Unite 510, Pathogenes et Fonctions des Cellules Epitheliales Polarisees, Faculte de Pharmacie Paris XI, Chatenay-Malabry, FranceLysteriolysin O (LLO) induces a microtubule-dependent activation of mucin exocytosis in the human mucin-secreting HT29-MTX . Cholesterol inhibits the LLO-induced mucin exocytosis, whereas the oxidized form of cholesterol had no inhibitory effect . LLO-induced mucin exocytosis inhibited by cholesterol can be restored by enzymatic treatment with cholesterol oxidase . Inhibition of cholesterol synthesis in HT29-MTX cells results in a decrease in the LLO-induced mucin exocytosis . Other lipids such as gangliosides are able to inhibit the LLO-induced mucin exocytosis, suggesting that the binding of the toxin occurs at a multiplicity of membrane-associated lipids acting as receptors . Incubation of the toxin with lipids such as cholesterol or gangliosides does not decrease binding of LLO to target membranes . The present work also provides evidence that the LLO-induced mucin exocytosis develops independently of the pore-forming activity of the toxin . Finally, we demonstrated that the toxin associates with detergent-insoluble glycolipid microdomains (DIGs) containing VIP/21 caveolin, allowing internalization of the toxin and subsequent activation of the mucin exocytosis.

Cell Microbiol, 2000 Dec, 2(6), 465 - 76
The invasion protein InIB from Listeria monocytogenes activates PLC-gamma1 downstream from PI 3-kinase; Bierne H et al.; Entry of the bacterial pathogen Listeria monocytogenes into non-phagocytic mammalian cells is mainly mediated by the InlB protein . Here we show that in the human epithelial cell line HEp-2, the invasion protein InlB activates sequentially a p85beta-p110 class I(A) PI 3-kinase and the phospholipase C-gamma1 (PLC-gamma1) without detectable tyrosine phosphorylation of PLC-gamma1 . Purified InlB stimulates association of PLC-gamma1 with one or more tyrosine-phosphorylated proteins, followed by a transient increase in intracellular inositol 1,4,5-trisphosphate (IP3) levels and a release of intracellular Ca2+ in a PI 3-kinase-dependent manner . Infection of HEp-2 cells with wild-type L . monocytogenes bacteria also induces association of PLC-gamma1 with phosphotyrosyl proteins . This interaction is undetectable upon infection with a deltainlB mutant revealing an InlB specific signal . Interestingly, pharmacological or genetic inactivation of PLC-gamma1 does not significantly affect InlB-mediated bacterial uptake, suggesting that InlB-mediated PLC-gamma1 activation and calcium mobilization are involved in post-internalization steps.

Cell Microbiol, 2000 Apr, 2(2), 127 - 36
A novel function of InIB from Listeria monocytogenes: activation of NF-kappaB in J774 macrophages; Mansell A et al.; Listeria monocytogenes causes a pro-inflammatory response on adhesion to macrophages . Upregulation of inflammation genes involves the transcription factor NF-kappaB . Several components of L . monocytogenes, including lipoteichoic acid (LTA), phospholipases and listeriolysin O (LLO), have since been shown to mediate NF-kappaB activation . Here, we report that purified recombinant InlB, but not internalin (InlA), is a potent activator of NF-kappaB in the mouse macrophage-like cell line J774 . Expression of InlB in Listeria innocua enhances its ability to activate NF-kappaB, while deletion of InlB from L . monocytogenes marginally decreases its effect on NF-kappaB, possibly because of the presence of NF-kappaB activators such as LTA and LLO . The effect correlates with the rapid degradation of IkappaBalpha, a sustained degradation of IkappaBbeta and increases in tumour necrosis factor alpha (TNF-alpha) and interleukin (IL) 6 production, two cytokines controlled by NF-kappaB . Using a series of anti-InlB monoclonal antibodies and domains of InlB, NF-kappaB activation was shown to be dependent upon the N-terminal 213-amino-acid leucine-rich repeat (LRR) domain of InlB, recently demonstrated to be responsible for InlB-mediated L . monocytogenes invasion and phosphoinositide-3 (PI-3) kinase activation . The effect of InlB was blocked by PI-3 kinase inhibitors, indicating the involvement of PI-3 kinase in this response . This report thus illustrates that InlB not only promotes invasion, but also contributes to the macrophage pro-inflammatory response.

Cell Microbiol, 2000 Apr, 2(2), 101 - 14
LaXp180, a mammalian ActA-binding protein, identified with the yeast two-hybrid system, co-localizes with intracellular Listeria monocytogenes; Pfeuffer T et al.; The Listeria monocytogenes surface protein ActA is an important virulence factor required for listerial intracellular movement by inducing actin polymerization . The only host cell protein known that directly interacts with ActA is the phosphoprotein VASP, which binds to the central proline-rich repeat region of ActA . To identify additional ActA-binding proteins, we applied the yeast two-hybrid system to search for mouse proteins that interact with ActA . A mouse cDNA library was screened for ActA-interacting proteins (AIPs) using ActA from strain L . monocytogenes EGD as bait . Three different AIPs were identified, one of which was identical to the human protein LaXp180 (also called CC1) . Binding of LaXp180 to ActA was also demonstrated in vitro using recombinant histidine-tagged LaXp180 and recombinant ActA . Using an anti-LaXp180 antibody and fluorescence microscopy, we showed that LaXp180 co-localizes with a subset of intracellular, ActA-expressing L . monocytogenes but was never detected on intracellularly growing but ActA-deficient mutants . Furthermore, LaXp180 binding to intracellular L . monocytogenes was asymmetrical and mutually exclusive with F-actin polymerization on the bacterial surface . LaXp180 is a putative binding partner of stathmin, a protein involved in signal transduction pathways and in the regulation of microtubule dynamics . Using immunofluorescence, we showed that stathmin co-localizes with intracellular ActA-expressing L . monocytogenes.

Cell Microbiol, 1999 Nov, 1(3), 249 - 57
Stability of the Listeria monocytogenes ActA protein in mammalian cells is regulated by the N-end rule pathway; Moors MA et al.; Upon infection of mammalian cells, Listeria monocytogenes lyses the phagosome and enters the cytosol, where it secretes proteins necessary for its intracellular growth cycle . Consequently, bacterial proteins exposed to the cytosol are potential targets for degradation by host cytosolic proteases . One pathway for degradation of host cytosolic proteins, the N-end rule pathway, involves recognition of the N-terminal amino acid and is mediated by the proteasome . However, very few natural N-end rule substrates have been identified . We have examined the L . monocytogenes ActA protein as a potential target for this pathway . ActA is an essential determinant of L . monocytogenes pathogenesis that is required to induce actin-based motility and cell-to-cell spread . We show that the half-life of a secreted form of ActA can be altered in the mammalian cytosol by changing the N-terminal amino acid . Moreover, the introduction of a destabilizing N-terminus into the functional, surface-bound form of ActA results in a small-plaque phenotype in L2 cells, which is partially reversible by an inhibitor of the proteasome . These results indicate that the L . monocytogenes ActA protein is a natural N-end rule substrate, and that optimal function of ActA in mediating cell-to-cell spread is dependent upon its intracellular turnover rate.

J Immunol, 2001 Mar 1, 166(5), 3402 - 9
Organ-specific regulation of the CD8 T cell response to Listeria monocytogenes infection; Pope C et al.; The intestinal mucosal CD8 T cell response to infection with Listeria monocytogenes was measured using MHC class I tetramers and was compared with the response in peripheral blood, secondary lymphoid tissue, and liver . To assess the vaccination potential of Listeria and to analyze responses in C57BL/6 mouse strains, a recombinant Listeria expressing OVA (rLM-ova) was generated . The response peaked at 9 days postinfection with a much larger fraction of the intestinal mucosa and liver CD8 T cell pool OVA specific, as compared with the spleen . However, these differences were not linked to bacterial titers in each site . The higher responses in lamina propria and liver resulted in a larger CD8 memory population in these tissues . Furthermore, the level of memory induced was dependent on infectious dose and inversely correlated with the magnitude of the recall response after oral challenge . Recall responses in the tissues were most robust in the lamina propria and liver, and reactivated Ag-specific T cells produced IFN-gamma . Infection of CD40- or MHC class II-deficient mice induced poor CD8 T cell responses in the intestinal mucosa, but only partially reduced responses in the spleen and liver . Overall, the results point to novel pathways of tissue-specific regulation of primary and memory antimicrobial CD8 T cell responses.

Infect Immun, 2001 Mar, 69(3), 1883 - 8
Interference between host resistance to Listeria monocytogenes infection and ovalbumin-induced allergic responses in mice; Mizuki D et al.; Listeria monocytogenes promotes the induction of the T-helper 1 (Th1) cell response, while ovalbumin (OVA) induces a Th2 cell response and allergic reactions, such as airway hyperreactivity and immunoglobulin E (IgE) production . When mice were immunized with OVA on day 7 after L . monocytogenes infection, eosinophilia in bronchoalveolar lavage and the production of total IgE, OVA-specific IgE, interleukin-4 (IL-4), and IL-5 in the circulation were markedly suppressed . Cytokine responses, including IL-4, IL-5, IL-10, IL-13, and gamma interferon, to OVA were decreased in the spleen cell cultures obtained from OVA-immunized mice that had been infected with L . monocytogenes . Conversely, when OVA-immunized mice were infected with L . monocytogenes, conversion from the nonlethal infection to the lethal infection occurred . Host resistance to L . monocytogenes infection in OVA-immunized mice was enhanced by the administration of anti-IL-10 monoclonal antibody . The present study indicates that striking interference is observed between Th1-inducing L . monocytogenes infection and Th2-driven OVA-induced airway hyperreactivity.

Infect Immun, 2001 Mar, 69(3), 1795 - 807
Aberrant macrophage and neutrophil population dynamics and impaired Th1 response to Listeria monocytogenes in colony-stimulating factor 1-deficient mice; Guleria I et al.; Listeria monocytogenes, a facultative intracellular bacterium, has been used extensively to study innate immune responses . Macrophages act as hosts for this bacterium as well as a major defense against it . Using mice homozygous for a null mutation (Csf1(op)) in the gene for the mononuclear phagocytic growth factor colony-stimulating factor 1 (CSF-1), we have demonstrated that CSF-1-regulated macrophages were essential to defend against a listerial infection . In the absence of CSF-1, monocytes were not recruited to the sites of infection due to the lack of synthesis of the macrophage chemoattractant chemokine MCP-1 . In addition, there was no burst of interleukin-10 (IL-10) synthesis that has been shown to result in the egress of neutrophils from sites of infection . Consequently, neutrophils were not replaced by macrophages, and numerous neutrophil-filled microabscesses developed, followed by tissue destruction and death of the mice . In the CSF-1 nullizygous mice compared to wild-type mice, there was also a very low synthesis of gamma interferon (IFN-gamma), resulting in reduced macrophage activation . However, the concentrations of the IFN-gamma-inducing cytokines IL-12 and IL-18 at this bacterial load were similar in these mutant mice . In contrast, IL-6 concentrations were dramatically reduced . Administration of IL-6 to Csf1(op)/Csf1(op) mice significantly increased the synthesis of IFN-gamma and reduced the bacterial burden to a greater extent than treatment with IFN-gamma alone . These data indicate that IL-6 occupies a central role in the CSF-1-regulated macrophage response to L . monocytogenes.

Infect Immun, 2001 Mar, 69(3), 1708 - 13
Non-major histocompatibility complex control of antibody isotype and Th1 versus Th2 cytokines during experimental infection of mice with Mycobacterium avium; Nagabhushanam V et al.; Infection of different strains of mice with Mycobacterium avium has revealed genetic control of the immunoglobulin isotype induced and of the balance between Th1 and Th2 cytokines . Female BALB/c or C57BL/10 mice were infected intranasally with 10(5) M . avium organisms . The antibody response was measured over 18 weeks by enzyme-linked immunosorbent assay and Western blotting, while numbers of cytokine-producing cells were assessed at 12 to 15 weeks by ELISPOT assay . Upon infection, C57BL/10 mice produced a clear Th1 response with strong gamma interferon (IFN-gamma) production, no interleukin-4 (IL-4), and almost entirely immunoglobulin G2a (IgG2a) antibody . In contrast, BALB/c mice developed T cells producing IL-4, as well as those producing IFN-gamma, while the antibody response was a mixture of IgG1 and IgG2a . Antibodies from BALB/c mice were also able to recognize a greater range of antigens than were C56BL/10 mice . B10D2 mice, which carry the BALB/c major histocompatibility complex haplotype on a C57BL/10 background, followed the C57BL/10 cytokine pattern . Mice infected with Listeria monocytogenes did not show a similar response dichotomy.

Infect Immun, 2001 Mar, 69(3), 1344 - 50
Listeria monocytogenes-infected phagocytes can initiate central nervous system infection in mice; Drevets DA et al.; Listeria monocytogenes-infected phagocytes are present in the bloodstream of experimentally infected mice, but whether they play a role in central nervous system (CNS) invasion is unclear . To test whether bacteria within infected leukocytes could establish CNS infection, experimentally infected mice were treated with gentamicin delivered by surgically implanted osmotic pumps . Bacterial inhibitory titers in serum and plasma ranged from 1:16 to 1:256, and essentially all viable bacteria in the bloodstream of treated mice were leukocyte associated . Nevertheless, CNS infection developed in gentamicin-treated animals infected intraperitoneally or by gastric lavage, suggesting that intracellular bacteria could be responsible for neuroinvasion . This was supported by data showing that 43.5% of bacteria found with blood leukocytes were intracellular and some colocalized with F-actin, indicating productive intracellular parasitism . Experiments using an L . monocytogenes strain containing a chromosomal actA-gfpuv-plcB transcriptional fusion showed that blood leukocytes were associated with intracellular and extracellularly bound green fluorescent protein-expressing (GFP+) bacteria . Treatment with gentamicin decreased the numbers of extracellularly bound GFP+ bacteria significantly but did not affect the numbers of intracellular GFP+ bacteria, suggesting that the latter were the result of intercellular spread of GFP+ bacteria to leukocytes . These data demonstrate that infected leukocytes and the intracellular L . monocytogenes harbored within them play key roles in neuroinvasion . Moreover, they suggest that phagocytes recruited to infected organs such as the liver or spleen are themselves parasitized by intercellular spread of L . monocytogenes and then reenter the bloodstream and contribute to the systemic dissemination of bacteria.

Trends Microbiol, 2001 Feb, 9(2), 86 - 92
Hijacking and exploitation of IL-10 by intracellular pathogens; Redpath S et al.; Macrophages play a central role in infections, as a target for pathogens and in activation of the immune system . Interleukin-10 (IL-10), a cytokine produced by macrophages, is a potent immunosuppressive factor . Some intracellular pathogens specifically target macrophages for infection and use IL-10 to dampen the host immune response and stall their elimination from the host . Certain viruses induce production of cellular IL-10 by macrophages, whereas other viruses encode their own viral IL-10 homologs . Additionally, specific bacteria, including several Mycobacteria spp . and Listeria monocytogenes, can survive and replicate in macrophages while inducing cellular IL-10, highlighting a potential role for IL-10 of macrophage origin in the immunosuppressive etiology of these pathogens . Thus, the exploitation of IL-10 appears to be a common mechanism of immunosuppression by a diverse group of intracellular pathogens that can infect macrophages.

Lett Appl Microbiol, 2001 Feb, 32(2), 78 - 82
A new chromogenic medium for the isolation of Listeria spp; Smith PA et al.; A new medium is described for the isolation of Listeria spp . from foods and environmental samples . It is based on a modified Oxford medium in which 3,4-cyclohexenoesculetin-beta-D-glucoside replaces aesculin . Positive colonies are intensely black with the advantage that the pigment does not diffuse into the medium . The medium, when tested alongside the US Department of Agriculture (spiked samples) and Food and Drug Administration (naturally contaminated samples) isolation procedures, performed significantly better than the current formulations (34% more confirmed positives from naturally contaminated samples) with a reduction of 1 d in the assay time for most samples.

Immunology, 2001 Jan, 102(1), 94 - 102
Persistent infection with Listeria monocytogenes in the kidney induces anti-inflammatory invariant fetal-type gammadelta T cells; Ikebe H et al.; After intraperitoneal inoculation with Listeria monocytogenes, gammadelta T cells appear in the peritoneal cavity preceding the appearance of alphabeta T cells . Such gammadelta T cells predominantly express T-cell receptor (TCR)Vgamma1/Vdelta6, develop through an extrathymic pathway, and contribute to host defence against the bacteria . We have observed a gradual increase in gammadelta T cells in kidneys of mice after intrarenal inoculation with L . monocytogenes, which resulted in an unusually long-lasting local infection . In this study, we examined the characteristics and the roles of the gammadelta T cells induced in this model . It was found that these gammadelta T cells predominantly expressed TCRVgamma6/Vdelta1 with canonical junctional sequences identical to those expressed on fetal thymocytes . Although depletion of such gammadelta T cells in vivo did not affect the number of bacteria, it resulted in histologically exacerbated inflammation in the kidneys . These results indicate that a persistent infection with L . monocytogenes in kidneys induces a different kind of gammadelta T cell from that induced after intraperitoneal infection . The former expresses invariant fetal-type Vgamma6/Vdelta1+TCR and plays a regulatory role in resolution of inflammation.

Clin Microbiol Infect, 2000 Oct, 6(10), 525 - 35
Natural antibiotic susceptibility of Listeria species: L . grayi, L . innocua, L . ivanovii, L . monocytogenes, L . seeligeri and L . welshimeri strains; Troxler R et al.; OBJECTIVE: To investigate the natural susceptibility to 71 antimicrobial agents of 103 Listeria strains belonging to all known Listeria species (L . monocytogenes (N = 21), L . innocua (N = 21), L . seeligeri (N = 21), L . ivanovii (N = 19), L . welshimeri (N = 11), and L . grayi (N = 10)) . METHODS: MICs were determined using a microdilution procedure in H-Medium . RESULTS: All listeriae were naturally sensitive or intermediate to tetracyclines, aminoglycosides, penicillins (except oxacillin), loracarbef, cefazoline, cefaclor, cefotiam, cefoperazone, carbapenems, macrolides, lincosamides, glycopeptides, dalfopristin/quinupristin, chloramphenicol and rifampicin (probably except L . grayi) . Listeria spp . were naturally resistant or intermediate to most 'modern' cephalosporins (cefetamet, cefixime, ceftibuten, ceftazidime, cefdinir, cefpodoxime, cefotaxime, ceftriaxone, cefuroxime), aztreonam, pipemidic acid, dalfopristin quinupristin and sulfamethoxazole . Significant differences in natural susceptibility among the species were seen with the quinolones, trimethoprim, co-trimoxazole, rifampicin, fosfomycin and fusidic acid . It seems likely that L . grayi is naturally resistant to all antifolates; the species was least susceptible to rifampicin and most susceptible to quinolones, whereas L . ivanovii was naturally resistant to most quinolones . L . ivanovii was naturally sensitive to fosfomycin, whereas L . innocua and L . monocytogenes were naturally resistant . L . ivanovii was also the most susceptible species to fusidic acid . CONCLUSIONS: The present study describes a database on the natural susceptibility of Listeria spp . to a wide range of antibiotics, which can be used to validate susceptibility testing results of these microorganisms.

Trends Microbiol, 2001 Jan, 9(1), 23 - 8
From evil to good: a cytolysin in vaccine development; Dietrich G et al.; Current vaccination strategies mainly target antigens into the phagosomal, major histocompatibility complex class II antigen-processing pathway and thus lead predominantly to humoral immune responses . The elicitation of cytotoxic T-cell responses instead requires introduction of antigens into the cytosol of professional antigen-presenting cells (APCs) . The intracellular bacterium Listeria monocytogenes gains access to the host cell cytosol by means of a cytolysin, listeriolysin O . Vaccine researchers have successfully employed listeriolysin in novel vaccination approaches to provide access to the cytosol of professional APCs for purified protein antigens, attenuated bacterial vaccine strains, DNA vaccines and liposome contents.

Free Radic Biol Med, 2001 Feb 1, 30(3), 268 - 76
Comparison of control of Listeria by nitric oxide redox chemistry from murine macrophages and NO donors: insights into listeriocidal activity of oxidative and nitrosative stress; Ogawa R et al.; The physiological function of nitric oxide (NO) in the defense against pathogens is multifaceted . The exact chemistry by which NO combats intracellular pathogens such as Listeria monocytogenes is yet unresolved . We examined the effects of NO exposure, either delivered by NO donors or generated in situ within ANA-1 murine macrophages, on L . monocytogenes growth . Production of NO by the two NONOate compounds PAPA/NO (NH2(C3H6)(N{N(O)NO}C3H7) and DEA/NO (Na(C2H5)2N{N(O)NO}) resulted in L . monocytogenes cytostasis with minimal cytotoxicity . Reactive oxygen species generated from xanthine oxidase/hypoxanthine were neither bactericidal nor cytostatic and did not alter the action of NO . L . monocytogenes growth was also suppressed upon internalization into ANA-1 murine macrophages primed with interferon-gamma (INF-gamma) + tumor necrosis factor-alpha (TNF-alpha or INF-gamma + lipid polysaccharide (LPS) . Growth suppression correlated with nitrite formation and nitrosation of 2,3-diaminonaphthalene elicited by stimulated murine macrophages . This nitrosative chemistry was not dependent upon nor mediated by interaction with reactive oxygen species (ROS), but resulted solely from NO and intermediates related to nitrosative stress . The role of nitrosation in controlling L . monocytogenes was further examined by monitoring the effects of exposure to NO on an important virulence factor, Listeriolysin O, which was inhibited under nitrosative conditions . These results suggest that nitrosative stress mediated by macrophages is an important component of the immunological arsenal in controlling L . monocytogenes infections.

Vaccine, 2001 Jan 8, 19(11-12), 1435 - 45
Evaluation of a recombinant Listeria monocytogenes expressing an HIV protein that protects mice against viral challenge; Mata M et al.; Vaccine strategies that utilize cell mediated immunity to control infection will be a necessary component of human immunodeficiency virus (HIV) vaccines . In previous studies we have shown that a Listeria monocytogenes recombinant expressing HIV-Gag elicits strong CD8+ and CD4+ T cell responses against HIV Gag in addition to its own secreted proteins . Here, we show that Lm-Gag can protect mice against a viral challenge with a recombinant vaccinia virus expressing Gag, in an antigen specific manner, and that this protection is T cell mediated . These results further support the use of L . monocytogenes as a vaccine approach for HIV through the induction of T cell immunity.

Curr Opin Cell Biol, 2001 Feb, 13(1), 85 - 91
Actin filament nucleation by endosomes, lysosomes and secretory vesicles; Taunton J; Intracellular pathogens such as Listeria monocytogenes and vaccinia virus propel themselves through the cytoplasm of mammalian cells by nucleating actin filaments . Recently, actin assembly has also been shown to power the movement of intracellular vesicles, and this may be a mechanism underlying endomembrane movement in a variety of physiological contexts . Surprisingly, class I myosins have been found to play important roles in both actin nucleation and endomembrane trafficking.

Cell Immunol, 2001 Jan 10, 207(1), 13 - 8
Relationships between IFNgamma, IL-6, corticosterone, and Listeria monocytogenes pathogenesis in BALB/c mice; Kim D et al.; The relationships between Listeria monocytogenes (LM) pathogenesis, based on bacterial load, and serum levels of IL-6, IFNgamma, and corticosterone (CORT) were quantified . Serum IFNgamma levels increased along with the LM burden; however, with LM burdens > or =3 x 10(6) CFU per spleen, the serum IFNgamma level decreased along with a decrease in splenic weight . Serum IL-6 levels exponentially increased with increases of LM, and the CORT level positively correlated with the increase in IL-6 and LM . The serum level of IFNgamma appeared to be a good biomarker of the host's ability to combat the infection only when the LM burden did not exceed a critical level (>3 x 10(6) CFU per spleen) . Interestingly, the LM load at which the IFNgamma level began to decline was near the dose at which the IL-6 concentration exponentially increased, suggesting a transition point shift from stress (assessed as CORT level) being immunoenhancing to becoming immunosuppressive . The IL-6:IFNgamma ratio may be a good indicator of disease severity and/or the ability to cope with an infection .

J Immunol, 2001 Feb 15, 166(4), 2651 - 7
Lipopolysaccharide-induced IL-18 secretion from murine Kupffer cells independently of myeloid differentiation factor 88 that is critically involved in induction of production of IL-12 and IL-1beta; Seki E et al.; IL-18, produced as biologically inactive precursor, is secreted from LPS-stimulated macrophages after cleavage by caspase-1 . In this study, we investigated the mechanism underlying caspase-1-mediated IL-18 secretion . Kupffer cells constantly stored IL-18 and constitutively expressed caspase-1 . Inhibition of new protein synthesis only slightly reduced IL-18 secretion, while it decreased and abrogated their IL-1beta and IL-12 secretion, respectively . Kupffer cells deficient in Toll-like receptor (TLR) 4, an LPS-signaling receptor, did not secrete IL-18, IL-1beta, and IL-12 upon LPS stimulation . In contrast, Kupffer cells lacking myeloid differentiation factor 88 (MyD88), an adaptor molecule for TLR-mediated-signaling, secreted IL-18 without IL-1beta and IL-12 production in a caspase-1-dependent and de novo synthesis-independent manner . These results indicate that MyD88 is essential for IL-12 and IL-1beta production from Kupffer cells while their IL-18 secretion is mediated via activation of endogenous caspase-1 without de novo protein synthesis in a MyD88-independent fashion after stimulation with LPS . In addition, infection with Listeria monocytogenes, products of which have the capacity to activate TLR, increased serum levels of IL-18 in wild-type and MyD88-deficient mice but not in caspase-1-deficient mice, whereas it induced elevation of serum levels of IL-12 in both wild-type and caspase-1-deficient mice but not in MyD88-deficient mice . Taken together, these results suggested caspase-1-dependent, MyD88-independent IL-18 release in bacterial infection.

J Immunol, 2001 Feb 15, 166(4), 2348 - 56
Direct analysis of the dynamics of the intestinal mucosa CD8 T cell response to systemic virus infection; Masopust D et al.; The CD8 T cell response to vesicular stomatitis virus infection was characterized in the spleen and intestinal mucosa using MHC tetramers . Surprisingly, the primary response persisted in the lamina propria long after the splenic response had declined . Furthermore, the response was characterized by a protracted effector phase in which cytolytic activity in the lamina propria, but not in the spleen, was maintained . The appearance of Ag-specific cells in the intestinal mucosa was largely, though not exclusively, a result of beta(7) integrin-mediated migration . Infection with Listeria monocytogenes or with vaccinia virus also led to sustained mucosal responses . After reinfection of vesicular stomatitis virus-primed mice with a serotypically distinct virus, a sustained recall response was detected in all tissues . In CD40(-/-) mice, the mucosal, but not the splenic, response was compromised, resulting in diminished mucosal memory . The recall response was CD40 independent and correlated with memory levels, indicating that the mucosal and systemic responses operated independently . These findings illustrated the integrated yet distinct nature of systemic vs mucosal immune responses.

J Immunol, 2001 Feb 1, 166(3), 1877 - 84
A novel approach of direct ex vivo epitope mapping identifies dominant and subdominant CD4 and CD8 T cell epitopes from Listeria monocytogenes; Geginat G et al.; We used a novel approach for the direct ex vivo identification and characterization of T cell epitopes based on the screening of peptide spot libraries with freshly isolated splenocytes in a sensitive enzyme-linked immunospot (ELISPOT) assay . This technique was applied for the analysis of splenocytes from Listeria monocytogenes-infected BALB/c and C57BL/6 mice . The screening of peptide spot libraries covering the whole listeriolysin O and p60 of L . monocytogenes confirmed all known CD4 and CD8 T cell epitopes of these proteins and additionally revealed six new H-2(d) and six new H-2(b)-restricted T cell epitopes . New epitopes were categorized into CD4 and CD8 T cell epitopes by ex vivo ELISPOT analysis with separated T cell populations . The quantitative analysis of cells reactive with these CD4 and CD8 T cell epitopes revealed the existence of dominant and subdominant CD4 and CD8 T cell populations during L . monocytogenes infection . As a consequence of these data we suggest that ELISPOT-based screening of peptide spot libraries could be a general approach for the rapid identification and characterization of pathogen-specific T cell populations during various infectious diseases.

Infect Immun, 2001 Feb, 69(2), 1093 - 100
Neural route of cerebral Listeria monocytogenes murine infection: role of immune response mechanisms in controlling bacterial neuroinvasion; Jin Y et al.; The pathologic features of cerebral Listeria monocytogenes infection strongly suggest that besides hematogenous spread, bacteria might also spread via a neural route . We propose that after snout infection of recombination activating gene 1 (RAG-1)-deficient mice, L . monocytogenes spreads to the brain via a neural route . The neural route of invasion is suggested by (i) the immunostaining of L . monocytogenes in the trigeminal ganglia (TG) and brain stem but not in other areas of the brain; (ii) the kinetics of bacterial loads in snout, TG, and brain; and (iii) the increased resistance of mice infected with a plcB bacterial mutant (unable to spread from cell to cell) . Gamma interferon (IFN-gamma) plays a protective role in neuroinvasion; inducible nitric oxide synthase (iNOS) accounts only partially for the protection, as shown by a comparison of the susceptibilities of IFN-gamma receptor (IFN-gamma R)-deficient, iNOS-deficient, and wild-type mice to snout infection with L . monocytogenes . The dramatically enhanced susceptibility of RAG-1-deficient, IFN-gamma R gene-deficient mice indicated the overall importance of innate immune cells in the release of protective levels of IFN-gamma . The source of IFN-gamma appeared to be NK cells, as shown by use of RAG-1-deficient, gamma-chain receptor gene-deficient mice; NK cells played a relevant protective role in neuroinvasion through a perforin-independent mechanism . In vitro evidence indicated that IFN-gamma can directly induce bacteriostatic mechanisms in neural tissue.

Infect Immun, 2001 Feb, 69(2), 897 - 905
Human endothelial cell activation and mediator release in response to Listeria monocytogenes virulence factors; Rose F et al.; The interaction of Listeria monocytogenes with endothelial cells represents a crucial step in the pathogenesis of listeriosis . Incubation of human umbilical vein endothelial cells (HUVEC) with wild-type L . monocytogenes (EGD) provoked immediate strong NO synthesis, attributable to listerial presentation of listeriolysin O (LLO), as the NO release was missed upon employment of a deletion mutant for LLO (EGD hly mutant) and was reproduced by purified LLO . Studies of conditions lacking extracellular Ca(2+) suggested LLO-elicited Ca(2+) flux as the underlying mechanism . In addition, HUVEC incubation with EGD turned out to be a potent stimulus for sustained (>12-h) upregulation of proinflammatory cytokine generation (interleukin 6 {IL-6}, IL-8, and granulocyte-macrophage colony-stimulating factor) . Use of deletion mutants for LLO (EGD hly mutant), listerial phosphatidylinositol-specific phospholipase C (EGD plcA mutant), broad-spectrum phospholipase C (EGD plcB mutant) and internalin B (EGD inlB mutant), as well as purified LLO, identified LLO as largely responsible for the cytokine response . Endothelial cells responded with diacylglycerole and ceramide generation as well as nuclear translocation of NF-kappa B to the stimulation with the LLO-producing strains EGD and Listeria innocua . The endothelial PC-phospholipase C inhibitor tricyclodecan-9-yl-xanthogenate as well as two independent inhibitors of NF-kappa B activation, pyrolidine dithiocarbamate and caffeic acid phenethyl ester, suppressed both the NF-kappa B translocation and the upregulation of cytokine synthesis . We conclude that L . monocytogenes is a potent stimulus of NO release and sustained upregulation of proinflammatory cytokine synthesis in human endothelial cells, both events being largely attributable to LLO presentation . LLO-induced transmembrane Ca(2+) flux as well as a sequence of endothelial phospholipase activation and the appearance of diacylglycerole, ceramide, and NF-kappa B are suggested as underlying host signaling events . These endothelial responses to L . monocytogenes may well contribute to the pathogenic sequelae in severe listerial infection and sepsis.

J Clin Microbiol, 2001 Feb, 39(2), 485 - 93
Purification and characterization of PCR-inhibitory components in blood cells; Al-Soud WA et al.; In a recent study, immunoglobulin G in human plasma was identified as a major inhibitor of diagnostic PCR (W . Abu Al-Soud, L . J . Jonsson, and P . Radstrom . J . Clin . Microbiol . 38:345-350, 2000) . In this study, two major PCR inhibitors in human blood cells were purified using size exclusion and anion-exchange chromatographic procedures . Based on N-terminal amino acid sequencing and electrophoretic analysis of the purified polypeptides, hemoglobin and lactoferrin were identified as PCR-inhibitor components in erythrocytes and leukocytes, respectively . When different concentrations of hemoglobin or lactoferrin were added to PCR mixtures of 25 microl containing 10 different thermostable DNA polymerases and 1 ng of Listeria monocytogenes DNA as template DNA, AmpliTaq Gold, Pwo, and Ultma were inhibited in the presence of < or = 1.3 microg of hemoglobin and < or = 25 ng of lactoferrin, while rTth and Tli were found to resist inhibition of at least 100 microg of hemoglobin . In addition, the quantitative effects of seven low-molecular-mass inhibitors, present in blood samples or degradation products of hemoglobin, on real-time DNA synthesis of rTth using the LightCycler Instrument were investigated . A reaction system based on a single-stranded poly(dA) template with an oligo(dT) primer annealed to the 3' end was used . It was found that the addition of 0.25 to 0.1 mg of bile per ml, 2.5 mM CaCl2, 0.25 mM EDTA, 5 microM FeCl3, and 0.01 IU of heparin per ml reduced the fluorescence to approximately 76, 70, 46, 17, and 51%, respectively . Finally, the effects of nine amplification facilitators were studied in the presence of hemoglobin and lactoferrin . Bovine serum albumin (BSA) was the most efficient amplification facilitator, so that the addition of 0.4% (wt/vol) BSA allowed AmpliTaq Gold to amplify DNA in the presence of 20 instead of 1 microg of hemoglobin and 500 instead of 5 ng of lactoferrin . Including 0.02% (wt/vol) gp32, a single-stranded-DNA binding protein, in the reaction mixture of AmpliTaq Gold was also found to reduce the inhibitory effects of hemoglobin and lactoferrin.

J Bacteriol, 2001 Feb, 183(4), 1133 - 9
A novel serotype-specific gene cassette (gltA-gltB) is required for expression of teichoic acid-associated surface antigens in Listeria monocytogenes of serotype 4b; Lei XH et al.; Listeria monocytogenes serotype 4b strains account for about 40% of sporadic cases and many epidemics of listeriosis . Mutations in a chromosomal locus resulted in loss of reactivity with all three monoclonal antibodies (MAbs) which were specific to serotype 4b and the closely related serotypes 4d and 4e . Here we show that this locus contains a serotype 4b-4d-4e-specific gene cassette (3,071 bp) which consists of two genes, gltA and gltB, and is flanked by palindromic sequences (51 and 44 nucleotides) . Complete loss of reactivity with the three serotype-specific MAbs resulted from insertional inactivation of either gltA or gltB . The gltA and gltB mutants were characterized by loss and severe reduction, respectively, of glucose in the teichoic acid, whereas galactose, the other serotype-specific sugar substituent in the teichoic acid, was not affected . Within L . monocytogenes, only strains of serotypes 4b, 4d, and 4e harbored the gltA-gltB cassette, whereas coding sequences on either side of the cassette were conserved among all serotypes . Comparative genomic analysis of a serotype 1/2b strain showed that the 3,071-bp gltA-gltB cassette was replaced by a much shorter (528-bp) and unrelated region, flanked by inverted repeats similar to their counterparts in serotype 4b . These findings indicate that in the evolution of different serotypes of L . monocytogenes, this site in the genome has become occupied by serotype-specific sequences which, in the case of serotype 4b, are essential for expression of serotype-specific surface antigens and presence of glucose substituents in the teichoic acids in the cell wall.

Appl Environ Microbiol, 2001 Feb, 67(2), 840 - 7
Characterization of recurrent and sporadic Listeria monocytogenes isolates from raw milk and nondairy foods by pulsed-field gel electrophoresis, monocin typing, plasmid profiling, and cadmium and antibiotic resistance determination; Harvey J et al.; Following previous surveys to assess the incidence of Listeria monocytogenes in raw milk and nondairy foods processed in Northern Ireland, isolates were characterized as recurrent or sporadic on the basis of multilocus enzyme electrophoresis (MEE) analysis and restriction fragment length polymorphism typing . In the present study, 45 representative recurrent and sporadic electrophoretic types (ETs) previously identified by MEE were subjected to pulsed-field gel electrophoresis (PFGE) of genomic DNA macrorestriction fragments, monocin typing, plasmid profiling, and an examination of resistance to cadmium and nine different antibiotics . Although PFGE proved to be capable of subdividing a number of recurrent and sporadic ETs, the grouping of strains arrived at by PFGE and MEE were in broad agreement, and previous conclusions regarding the designation of L . monocytogenes strains as recurrent or sporadic remained unaltered . It is considered that PFGE was able to detect minor genetic changes in recurrent ETs which occurred during the time period in which food surveys were carried out . Production of type E monocin (Types A to E were found among the 45 strains), plasmid carriage, and resistance to cadmium occurred more frequently in recurrent than in sporadic strains and may be important with regard to the ability of L . monocytogenes to persist in food and food-processing environments . Only 2 of 45 strains showed resistance to any of the nine antibiotics tested: two sporadic strains were resistant to tetracycline (MIC, 64 microg x ml(-1)).

Appl Environ Microbiol, 2001 Feb, 67(2), 646 - 53
Characterization and pathogenic potential of Listeria monocytogenes isolates from the smoked fish industry; Norton DM et al.; This study was designed to evaluate the hypothesis that some of the Listeria monocytogenes subtypes associated with foods, specifically smoked fish, may have an attenuated ability to cause human disease . We tested this hypothesis by using two different approaches: (i) comparison of molecular subtypes found among 117 isolates from smoked fish, raw materials, fish in process, and processing environments with subtypes found among a collection of 275 human clinical isolates and (ii) the evaluation of the cytopathogenicity of industrial isolates . Ribotyping and PCR-restriction fragment length polymorphism typing of the hlyA and actA genes differentiated 23 subtypes among the industrial isolates and allowed classification of the isolates into three genetic lineages . A significantly higher proportion of human isolates (69.1%) than industrial isolates (36.8%) were classified as lineage I, which contains human sporadic isolates and all epidemic isolates . All other industrial isolates (63.2%) were classified as lineage II, which contains only human sporadic isolates . Lineage I ribotypes DUP-1038B and DUP-1042B represented a significantly higher proportion of the human isolates than industrial isolates (5.1%) . Lineage II ribotypes DUP-1039C, DUP-1042C, and DUP-1045, shown previously to persist in the smoked fish processing environment, represented nearly 50% of the industrial isolates, compared to 7.6% of the human isolates . Representatives of each subtype were evaluated with a tissue culture plaque assay . Lineage I isolates formed plaques that were significantly larger than those formed by lineage II isolates . Isolates from the smoked fish industry representing three ribotypes formed no plaques or small plaques, indicating that they had an impaired ability to infect mammalian cells . While L . monocytogenes clonal groups linked to human listeriosis cases and outbreaks were isolated, our data also suggest that at least some L . monocytogenes subtypes present in ready-to-eat foods may have limited human-pathogenic potential.

J Immunol, 2000 Apr 15, 164(8), 4063 - 70
Differing roles of inflammation and antigen in T cell proliferation and memory generation; Busch DH et al.; Recent studies have demonstrated that viral and bacterial infections can induce dramatic in vivo expansion of Ag-specific T lymphocytes . Although presentation of Ag is critical for activation of naive T cells, it is less clear how dependent subsequent in vivo T cell proliferation and memory generation are upon Ag . We investigated T cell expansion and memory generation in mice infected alternately with strains of Listeria monocytogenes that contained or lacked an immunodominant, MHC class I-restricted T cell epitope . We found substantial differences in the responses of effector and memory T cells to inflammatory stimuli . Although effector T cells undergo in vivo expansion in response to bacterial infection in the absence of Ag, memory T cells show no evidence for such bystander activation . However, Ag-independent expansion of effector T cells does not result in increased memory T cell frequencies, indicating that Ag presentation is critical for effective memory T cell generation . Early reinfection of mice with L . monocytogenes before the maximal primary T cell response induces typical memory expansion, suggesting that the capacity for a memory T cell response exists within the primary effector population . Our findings demonstrate that T cell effector proliferation and memory generation are temporally overlapping processes with differing requirements for Ag.

J Biol Chem, 2000 Apr 14, 275(15), 11181 - 90
Monitoring cellular responses to Listeria monocytogenes with oligonucleotide arrays; Cohen P et al.; Listeria monocytogenes is a pathogenic intracellular microorganism whose infection induces pleiotropic biological changes associated with host cell gene expression regulation . Here we define the gene expression profiles of the human promyelocytic THP1 cell line before and after L . monocytogenes infection . Gene expression was measured on a large scale via oligonucleotide microarrays with probe sets corresponding to 6,800 human genes . We assessed and discussed the reproducibility of the hybridization signatures . In addition to oligonucleotide arrays, we also performed the large scale gene expression measurement with two high-density membranes, assaying for 588 and 18,376 human genes, respectively . This work allowed the reproducible identification of 74 up-regulated RNAs and 23 down-regulated RNAs as a consequence of L . monocytogenes infection of THP1 . The reliability of these data was reinforced by performing independent infections . Some of these detected RNAs were consistent with previous results, while some newly identified RNAs encode gene products that may play key roles in L . monocytogenes infection . These findings will undoubtedly enhance the understanding of L . monocytogenes molecular physiology and may help identify new therapeutic targets.

Int J Food Microbiol, 2000 Dec 20, 62(3), 267 - 74
Control options for Listeria monocytogenes in seafoods; Huss HH et al.; At least three outbreaks of listeriosis associated with seafood have been reported . Listeria monocytogenes is widely distributed in the general environment including fresh water, coastal water and live fish from these areas . Contamination or recontamination of seafood may also take place during processing and low levels (< 100 cfu/g) of L . monocytogenes are frequently found on seafood including ready-to-eat (RTE) products . Apart from heat treatment, which is very effective, there are few options for eliminating L . monocytogenes from foods and equipment . It is essential therefore, that growth of L . monocytogenes in the final product be inhibited . The preventive measures include the formulation of a cleaning and sanitising program specifically designed at reducing the presence of L . monocytogenes in the factory environment, the safe elimination of L . monocytogenes from heat treated products and prevention of growth in RTE products within the normal shelf life and conditions stated on the label . If any sampling is required, the sampling plans suggested by the International Commission on Microbiological Specifications for Foods {Int . J . Food Microbiol., 22 (1994) 89-96} are useful.

Int J Food Microbiol, 2000 Dec 20, 62(3), 253 - 60
Risk assessment used to evaluate the US position on Listeria monocytogenes in seafood; Elliot EL et al.; Human listeriosis has been associated with consumption of food including seafood . Surveillance information on the presence of Listeria monocytogenes in seafood products is presented as a background for steps that are being taken to inform risk managers of risks associated with particular food products . United States policy for L . monocytogenes in food has been shaped by our increasing knowledge of the epidemiology of outbreaks and sporadic cases of human listeriosis, the potentially severe public health consequences, and the characteristics of the organism . A quantitative risk assessment of the scientific knowledge we have about the organism and the epidemiology of listeriosis should be the basis for changes in this policy . Risk assessment uses quantitative scientific and epidemiological information in a structured format to determine the risks associated with particular hazards . A quantitative risk assessment is being performed using currently available data by the US Food and Drug Administration, in collaboration with the US Food Safety and Inspection Service, to determine the risk of listeriosis from various foods, including seafood, for specific intervention methods, and for general and at-risk population groups . The questions being considered include those on level of consumption, epidemiology, dose response, and the virulence, biology, and ecology of the organism . Risk managers can use the resulting information to form a defendable science-based policy on L . monocytogenes in food.

Int J Food Microbiol, 2000 Dec 20, 62(3), 247 - 51
Present situation in Canada regarding Listeria monocytogenes and ready-to-eat seafood products; Farber JM; The present situation regarding Listeria monocytogenes and ready-to-eat (RTE) seafood is discussed . An updated regulatory policy on L . monocytogenes directs inspection and compliance action to those RTE foods capable of supporting growth of the organism and is based on a combination of inspection, environmental sampling and product testing . The incidence of L . monocytogenes in imported seafood products in 1996-1997 and 1997-1998 was 0.88 and 0.3%, respectively . With respect to domestic products, an analysis of 347 RTE foods in 1997-1998 and 1998-1999, at one of the large fish inspection labs in the Maritimes, revealed an absence of L . monocytogenes . The only seafood product linked to suspect cases of listeriosis in Canada was imported.

Int J Food Microbiol, 2000 Dec 20, 62(3), 231 - 45
Predictive modelling of the growth and survival of Listeria in fishery products; Ross T et al.; Predictive microbiology provides a powerful tool to aid the exposure assessment phase of 'quantitative microbial risk assessment' . Using predictive models changes in microbial populations on foods between the point of production/harvest and the point of eating can be estimated from changes in product parameters (temperature, storage atmosphere, pH, salt/water activity, etc.) . Thus, it is possible to infer exposure to Listeria monocytogenes at the time of consumption from the initial microbiological condition of the food and its history from production to consumption . Predictive microbiology models have immediate practical application to improve microbial food safety and quality, and are leading to development of a quantitative understanding of the microbial ecology of foods . While models are very useful decision-support tools it must be remembered that models are, at best, only a simplified representation of reality . As such, application of model predictions should be tempered by previous experience, and used with cognisance of other microbial ecology principles that may not be included in the model . Nonetheless, it is concluded that predictive models, successfully validated in agreement with defined performance criteria, will be an essential element of exposure assessment within formal quantitative risk assessment . Sources of data and models relevant to assessment of the human health risk of L . monocytogenes in seafoods are identified . Limitations of the current generation of predictive microbiology models are also discussed . These limitations, and their consequences, must be recognised and overtly considered so that the risk assessment process remains transparent . Furthermore, there is a need to characterise and incorporate into models the extent of variability in microbial responses . The integration of models for microbial growth, growth limits or inactivation into models that can predict both increases and decreases in microbial populations over time will also improve the utility of predictive models for exposure assessment . All of these issues are the subject of ongoing research.

Int J Food Microbiol, 2000 Dec 20, 62(3), 223 - 9
Risk assessment of Listeria monocytogenes in fish products: some general principles, mechanism of infection and the use of performance standards to control human exposure; Notermans S et al.; Risk assessment is increasingly used as a scientific process to assess the potential for adverse health effects to occur and as a basis for management of unacceptable risks . For each risk assessment activity, the purpose of the assessment should be clearly stated . For Listeria monocytogenes, the purpose of risk assessment may be providing information on the relative contribution of listeriosis to infectious diseases . For control purposes, the emphasis may be put on factors contributing to the risk of occurrence in a food or to inform risk managers that they should be setting food safety objectives . For an adequate risk assessment of L . monocytogenes, sound scientific data are necessary . This especially applies both to exposure assessment and hazard characterisation . Surveillance data indicates that cold storage to prolongs product shelf-life has opened an ecological window for the growth of L . monocytogenes . Assessment of dose-response relationship is often regarded as a key element in risk characterisation . Due to the large variability of the current assessed dose-response data, their contribution to assessing risks is low . The use of epidemiological data on incidence rate, types of food involved in listeriosis, etc . may be good alternatives . The use of performance standards or criteria, such as inactivation by heat or by fermentation, combined with processes that prevent outgrowth of the organism should be reconsidered . Presently, performance standards can simply be assessed since mathematical tools for their calculations are becoming increasingly available.

Int J Food Microbiol, 2000 Dec 20, 62(3), 217 - 21
Microbiological criteria for Listeria monocytogenes in foods under special consideration of risk assessment approaches; Norrung B; This paper shortly summarizes data related to risk assessment of Listeria monocytogenes . From available data on risk assessment, it is concluded that the levels of L . monocytogenes consumed is an important factor affecting the incidence of listeriosis . Foods that do not support the growth of L . monocytogenes are unlikely to be a source of listeriosis, whereas foods that support the growth to high levels, should be the target of risk management efforts . Based on current epidemiological information from several countries, a concentration of L . monocytogenes not exceeding 100/g of food at the time of consumption is of low risk to the consumers . In order not to exceed these levels at the point of consumption, lower levels may need to be applied at the port of entry, for those foods in which growth can occur within the shelf life . In order to establish such levels, knowledge of the shelf life and behaviour of L . monocytogenes in the food during prevailing storage and distribution conditions is needed.

Int J Food Microbiol, 2000 Dec 20, 62(3), 211 - 5
Potential of Listeria hazard in African fishery products and possible control measures; Ababouch L; Africa contributes 5.54 million MT (4.5%) to the world harvest of aquatic organisms . Fisheries represent a vital sector for many countries in Africa, both for domestic food supply, employment opportunities and foreign exchange earnings . Despite the low level of African fish production and export in comparison with the other continents, fish represent the major protein Source in many countries (36-58% of animal proteins in C te d'Ivoire, Congo, Senegal, Angola) and fishing is a vital activity for Senegal, Mauritania, Morocco, Ghana, Tunisia and other countries . In fact, it is the main sector for foreign exchange earnings in countries such as Senegal and Mauritania (Ababouch, 1998b; 1999) . Consequently, expansion of export and development and production of value-added products in Africa for export are strategic keys for future economic development . This will require the implementation of reliable in-plant HACCP-based quality and safety control systems . Unfortunately, very little in known about the prevalence and ecology of Listeria in food, especially as it relates to seafood safety . This paper discusses the potential of Listeria hazard from African fishery products and speculates on some possible control measures.

Int J Food Microbiol, 2000 Dec 20, 62(3), 197 - 209
Epidemiology of human listeriosis and seafoods; Rocourt J et al.; While rarely diagnosed prior to 1960, more than 10,000 cases of listeriosis were recorded in the medical literature between 1960 and 1982, and thousands more have been reported annually world-wide {Rocourt J., 1991 . Human listeriosis, 1989 . WHO/HPP/FOS/91.3, World Health Organization, Geneva, Switzerland; Rocourt, J., Brosch, R., 1992 . Human listeriosis, 1990 . WHO/HPP/FOS/92.3, World Health Organization, Geneva, Switzerland; Rocourt, J., Jacquet, Ch., Bille, J., 1997 . Human listeriosis, 1991/1992 . WHO/FNU/FOS/97.1, World Health Organization, Geneva, Switzerland} . This widespread increase in reporting is most likely due to demographic trends and changes in food production, processing and storage, especially the extended cold food chain and the ability of Listeria monocytogenes to grow at low temperatures: L . monocytogenes is a bacterium responsible for opportunistic infections, preferentially affecting individuals whose immune system is perturbed, including pregnant women, newborns, people over 65 years, immunocompromised patients, such as cancer victims, transplant recipients, people on hemodialysis and AIDS patients . Thus, the increasing lifespan and medical progress allowing immunodeficient individuals to survive, partially explains the increasing incidence of listeriosis . Moreover, L . monocytogenes is ubiquitous and can grow at temperatures as low as 0 degrees C . At this temperature growth is very slow . The expansion of the agro-food industry, the widespread use of systems of cold storage and changes in consumers demands have led to a large increase in the pool of Listeria that can cause foodborne infections.

Int J Food Microbiol, 2000 Dec 20, 62(3), 191 - 6
Incidence and significance of Listeria in fish and fish products from Latin America; Destro MT; The incidence and importance of Listeria spp . in fish and fishery products in Latin American countries is reviewed . There are very few papers dealing with this subject, however it is known that Listeria can be an important problem even for fisheries of tropical countries . The importance of GMP and HACCP implementation is also discussed.

Int J Food Microbiol, 2000 Dec 20, 62(3), 183 - 90
Listeria monocytogenes in the smoked salmon industry; Rorvik LM; Smoked salmon is sporadically contaminated with Listerial monocytogenes . Contamination levels are normally low and consumers are probably seldom exposed to risk concentrations . No clones of L . monocytogenes seem to be specific to smoked salmon, some clones found in smoked salmon having been isolated from several sources, including patients . Cold-smoking has been shown to eliminate L . monocytogenes in challenge tests at temperatures from 17.1 to 21.1 degrees C, while from 22.2 to 30 degrees C the bacteria survived . Under natural cold-smoking conditions (19 to 22 degrees C) the frequency and level of L . monocytogenes seems to decrease . Hot-smoking seems to eliminate the bacteria when smoke is applied during the whole heating process . The prevention of recontamination of both cold-smoked and hot-smoked salmon is therefore of great importance . L . monocytogenes multiply considerably in smoked salmon during storage . Growth is faster in challenge tests than in naturally-contaminated smoked salmon . The declared shelf-life under refrigeration should be shorter than that customarily stipulated by many producers . While the sources of L . monocytogenes in smoked salmon processing plants have still to be determined, raw salmon does not seem to be an important source . The main issue for producers is to prevent colonization of the processing environment and spread of the bacteria to products . This should be achieved by the systemic implementation of hygienic measures, including the HACCP approach.

Int J Food Microbiol, 2000 Dec 20, 62(3), 177 - 81
Listeria in tropical fish and fishery products; Karunasagar I et al.; Listeria monocytogenes is considered to be a ubiquitous organism occurring in both terrestrial and aquatic habitats . This organism has been isolated from fish and fishery products from different parts of the world and interestingly the incidence rate reported from tropical fish is rather low . Varying methodologies have been used by different investigators to study the incidence of L . monocytogenes in fish . Data on virulence of seafood-associated strains are lacking . For quality assurance in the fish processing industry, rapid and sensitive methods for the detection of L . monocytogenes are required.

Int J Food Microbiol, 2000 Dec 20, 62(3), 173 - 5
Lessons from an outbreak of listeriosis related to vacuum-packed gravad and cold-smoked fish; Tham W et al.; The first lesson learned from this outbreak was that vacuum-packed rainbow trout is not only an excellent medium for the growth of Listeria monocytogenes, but may also cause human listeriosis . Another lesson is that one single fish processing plant may spread multiple clonal types of L . monocytogenes by selling contaminated products to consumers . Thus, when investigating fish-borne outbreaks of listeriosis one should identify and type several isolates of L . monocytogenes from each food and environmental sample, since multiple clonal types might be present . The outbreak described in this paper involved at least eight human cases, three clonal types of L . monocytogenes, and lasted for 11 months . During the outbreak investigation, L . monocytogenes was also isolated from another brand of rainbow trout found in the refrigerator of one of the patients . These latter isolates belonged to a clonal type not associated with the outbreak . However, this clonal type is of considerable interest since it has been associated with foodborne outbreaks of listeriosis in several countries, and is also the second most common clonal type among human clinical isolates of L . monocytogenes in Sweden . Besides the described outbreak, it is likely that vacuum-packed, cold-smoked and gravad rainbow trout have been involved in additional cases of foodborne listeriosis in Sweden.

Curr Opin Immunol, 2001 Feb, 13(1), 96 - 103
The use of host cell machinery in the pathogenesis of Listeria monocytogenes; Cossart P et al.; The bacterial pathogen, Listeria monocytogenes, exploits the host cell's machinery, enabling the pathogen to enter into cells and spread from cell to cell . Three bacterial surface proteins are crucial for these processes: internalin and InlB, which mediate entry into cells, and ActA, which induces actin polymerisation at one pole of the bacterium and promotes intracellular and intercellular motility . Recent studies have identified several of the cellular factors involved in the entry process and major discoveries have unravelled the mechanisms underlying the actin-based motility . Increasing evidence shows that many cellular genes are up- or down-regulated during infection and probably play a role in the establishment of infection, inflammation and induction of the host immune response.

Inhal Toxicol, 2001 Jan, 13(1), 85 - 102
Strain-related differences of nonspecific respiratory defense mechanisms in rats using a pulmonary infectivity model; Antonini JM et al.; A number of animal studies have assessed pulmonary host defense mechanisms by inoculating the lungs with the bacterial agent, Listeria monocytogenes . Most studies use only a single strain of the animal to be tested; however, strain-related differences in responsiveness to pulmonary toxicants have been well documented . It was the goal of this current investigation to measure the pulmonary defense responses of two different strains of rats in a lung infectivity model . Fischer 344 (F344) and Sprague-Dawley (SD) rats were instilled intratracheally with 5 x 10(3) or 5 x 10(5) L . monocytogenes, and the effect on mortality, lung injury and inflammation, pulmonary bacterial clearance, and alveolar macrophage (AM) function was determined at 3, 5, and 7 days after bacteria treatment . Pulmonary inoculation with the higher (5 x 10(5) L . monocytogenes) dose proved to be highly pneumotoxic to the F344 rats as evidenced by an increase in mortality and more severe lung injury and inflammation when compared with the SD rats . After intratracheal instillation with the lower (5 x 10(3) L . monocytogenes) dose, pulmonary bacterial clearance was slowed and an increase in pulmonary responsiveness was observed for the F344 rats as compared to the SD rats . Specifically, the total number of neutrophils recovered from the lungs and tumor necrosis factor-alpha secreted by AMs were elevated for the F344 group throughout the 7 days, while cellular chemiluminescence, an index of reactive oxygen species production, and lung albumin and lactate dehydrogenase, indicators of injury, were increased at 3 and 5 days after bacterial instillation . This study demonstrated that respiratory defense function was compromised in F344 rats as evidenced by elevated mortality, slowed pulmonary bacterial clearance, and altered AM function . F344 rats may then represent a sensitive model for the examination of respiratory defense mechanisms after bacterial challenge.

Diagn Microbiol Infect Dis, 2000 Dec, 38(4), 259 - 61
In vitro activities of 22 antimicrobial agents against Listeria monocytogenes strains isolated in Barcelona, Spain . The Collaborative Study Group of Listeriosis of Barcelona; Marco F et al.; The in vitro activity of 22 antimicrobial agents against 82 human Listeria monocytogenes strains isolated in Barcelona from 1994 to 1998 was determined . Ampicillin and gentamicin showed good in vitro activity against all strains (MIC90: 1 and < or = 0.25 microg/ml, respectively) . No resistance to rifampin or co-trimoxazole was detected and only one strain was resistant to tetracycline . Of the nine fluoroquinolones tested, clinafloxacin and gemifloxacin were the most active compounds (MIC90: 0.12 and 0.25 microg/ml, respectively) . No increasing MICs values were observed during the five-year period.

J Immunol, 2001 Jan 15, 166(2), 1132 - 40
Variable immunodominance hierarchies for H2-M3-restricted N-formyl peptides following bacterial infection; Kerksiek KM et al.; H2-M3-restricted presentation of N-formyl methionine (f-Met) peptides to CD8(+) T cells provides a mechanism for selective recognition of bacterial infection . In this report we demonstrate that Listeria monocytogenes infection induces distinct CD8(+) T cell populations specific for each of the known Listeria-derived formyl methionine peptides presented by M3 . The sum H2-M3-restricted, Listeria-specific T cell response constitutes a major fraction of the total CD8(+) T cell response to primary infection . H2-M3-restricted T cell populations expand synchronously in vivo and achieve peak frequencies approximately 2 days earlier than MHC class Ia-restricted T cell populations . Although cross-recognition of different f-Met peptides by M3-restricted T cells was previously described, costaining of CD8(+) T cells ex vivo with H2-M3 tetramers complexed with different f-Met peptides shows that the majority of Listeria-specific, M3-restricted CD8(+) T cells are peptide specific . In contrast to the highly predictable size and immunodominance hierarchies of MHC class Ia-restricted T cell responses, the magnitudes of T cell responses specific for H2-M3-restricted peptides are remarkably variable between genetically identical mice . Our findings demonstrate that H2-M3-restricted T cell responses are distinct from classically restricted T cell responses to bacterial infection.

Am J Pathol, 2001 Jan, 158(1), 179 - 88
Role of macrophage scavenger receptors in response to Listeria monocytogenes infection in mice; Ishiguro T et al.; Type I and type II macrophage scavenger receptors (SR-A I/II) recognize a variety of polyanions including bacterial cell-wall products such as lipopolysaccharide, suggesting a role for SR-A I/II in immunity against bacterial infection . SR-A I/II-deficient (MSR-A-/-) mice were more susceptible to infection with listeriolysin-O (LLO)-producing Listeria monocytogenes . After infection, Kupffer cells in wild-type (MSR-A+/+) mice phagocytized larger numbers of Listeria than those in MSR-A-/- mice . The number and the diameter of hepatic granulomas were larger in MSR-A-/- mice than MSR-A+/+ mice . L . monocytogenes replicated at higher levels in the liver of MSR-A-/- mice compared with MSR-A+/+ mice, and macrophages from MSR-A-/- mice showed impaired ability to kill Listeria in vitro . However, macrophages from MSR-A+/+ and MSR-A-/- mice showed similar levels of listericidal activity against isogenic mutant L . monocytogenes with an inactivated LLO gene . The listerial phagocytic activities of MSR-A+/+ macrophages treated with an anti-SR-A I/II antibody (2F8) and MSR-A-/- macrophages were significantly impaired compared with untreated MSR-A+/+ macrophages, indicating that SR-A I/II function as a receptor for L . monocytogenes . Electron microscopy revealed that most L . monocytogenes had been eliminated from the lysosomes of MSR-A+/+ macrophages in vivo and in vitro . In contrast, L . monocytogenes rapidly lysed the phagosomal membrane and escaped to the cytosol in MSR-A-/- macrophages and in MSR-A+/+ macrophages treated with 2F8 before phagosome-lysosome fusion . These findings imply that SR-A I/II plays a crucial role in host defense against listerial infection not only by functioning as a receptor but also by mediating listericidal mechanisms through the regulation of LLO-dependent listerial escape from the macrophages.

Int J Food Microbiol, 2000 Dec 5, 62(1-2), 57 - 63
Occurrence of and a possible mechanism for resistance to a quaternary ammonium compound in Listeria monocytogenes; Aase B et al.; In a study of 200 Listeria monocytogenes isolates, 10% were determined to be resistant to benzalkonium chloride (BC) . Serial subcultivation of initially BC sensitive (BC(S)) and BC resistant (BC(R)) isolates in sublethal concentrations of BC resulted in enhanced and approximately equal resistance of all strains to the compound . Fifty per cent of the BC(R) isolates showed resistance to ethidium bromide (EB) as well . A proton motive force (pmf)-dependent efflux of EB was demonstrated in BC(R) isolates, and in originally sensitive strains adapted to grow in BC . This efflux was not found in BC(S) strains . The result indicate that BC can induce a broad resistance mechanism based on a pmf-driven efflux pump . There was no indication that this type of resistance was related to resistance to antibiotics.

Int J Food Microbiol, 2000 Dec 5, 62(1-2), 155 - 9
Pulsed-field gel electrophoresis (PFGE) typing of Listeria strains isolated from a meat processing plant over a 2-year period; Senczek D et al.; As part of a hygiene monitoring program in a meat processing plant a total of 131 Listeria isolates were detected by sampling different processing areas and meat products within a 2-year period . The isolates were differentiated by means of phenotypic characteristics . Furthermore, the genomic ApaI and SmaI fragment patterns of all isolates were examined by pulsed-field gel electrophoresis (PFGE) . PFGE using SmaI and ApaI yielded 15 (Listeria monocytogenes), 20 (Listeria innocua) and six (Listeria welshimeri) pulsotypes . Of the environmental Listeria monocytogenes isolates the predominating PFGE-type B was clearly associated with processing area A whereas PFGE-type E predominated in the meat products . Moreover, the study showed the persistence of closely related Listeria strains over a 2-year period in the environment of this meat processing plant.

Int J Food Microbiol, 2000 Dec 5, 62(1-2), 149 - 53
Behaviour of Listeria monocytogenes during the manufacture and ripening of Manchego and Chihuahua Mexican cheeses; Solano-Lopez C et al.; The ability of Listeria monocytogenes to survive the Mexican Manchego and Chihuahua cheese-making processes and its persistence during the ripening stages of both cheeses was examined . Commercial pasteurized and homogenized whole milk was inoculated with Listeria monocytogenes (strain ATCC 19114) to a level between 2 x 10(6) and 9 x 10(6) CFU/ml . The milk was used to make Mexican Manchego and Chihuahua cheeses in a 25-l vat . Mexican Manchego cheese was ripened for 5 days and Chihuahua cheese for 6 weeks at 12 degrees C and 85% RH . Listeria present in the cheese was enumerated by diluting samples in sterile 0.1% peptone water and plating on Oxford agar . Duplicate samples were taken at each step of the manufacturing process . During the first week of ripening samples were taken daily from both cheeses . For Chihuahua cheese, samples were taken weekly after the first week of the ripening stage . During the manufacture of Mexican Manchego cheese, Listeria counts remained relatively constant at 10(6) CFU/ml, while with Chihuahua cheese there was a one log decrease in numbers (10(6) to 10(5) CFU/ml) . After pressing both curds overnight, numbers of bacteria decreased in Mexican Manchego cheese to 8.2 x 10(5) but increased in Chihuahua cheese from 1.7 x 10(5) to 1.2 x 10(6) CFU/ml . During the ripening stage, counts of Listeria remained constant in both cheeses . However, since the Chihuahua cheese ripening stage is about 6 weeks, the number of bacteria decreased from 2 x 10(6) to 4 x 10(4) CFU/g . The results show that Listeria monocytogenes is able to survive the manufacture and ripening processes of both Mexican cheeses.

Appl Environ Microbiol, 2001 Jan, 67(1), 198 - 205
Molecular studies on the ecology of Listeria monocytogenes in the smoked fish processing industry; Norton DM et al.; We have applied molecular approaches, including PCR-based detection strategies and DNA fingerprinting methods, to study the ecology of Listeria monocytogenes in food processing environments . A total of 531 samples, including raw fish, fish during the cold-smoking process, finished product, and environmental samples, were collected from three smoked fish processing facilities during five visits to each facility . A total of 95 (17.9%) of the samples tested positive for L . monocytogenes using a commercial PCR system (BAX for Screening/Listeria monocytogenes), including 57 (27.7%) environmental samples (n = 206), 8 (7.8%) raw material samples (n = 102), 23 (18.1%) samples from fish in various stages of processing(n = 127), and 7 (7.3%) finished product samples (n = 96) . L . monocytogenes was isolated from 85 samples (16.0%) using culture methods . Used in conjunction with a 48-h enrichment in Listeria Enrichment Broth, the PCR system had a sensitivity of 91.8% and a specificity of 96.2% . To track the origin and spread of L . monocytogenes, isolates were fingerprinted by automated ribotyping . Fifteen different ribotypes were identified among 85 isolates tested . Ribotyping data established possible contamination patterns, implicating raw materials and the processing environment as potential sources of finished product contamination . Analysis of the distribution of ribotypes revealed that each processing facility had a unique contamination pattern and that specific ribotypes persisted in the environments of two facilities over time (P < or = 0.0006) . We conclude that application of molecular approaches can provide critical information on the ecology of different L . monocytogenes strains in food processing environments . This information can be used to develop practical recommendations for improved control of this important food-borne pathogen in the food industry.

J Appl Microbiol, 2000 Dec, 89(6), 944 - 50
Effect of various environmental parameters on the recovery of sublethally salt-damaged and acid-damaged Listeria monocytogenes; Gnanou Besse N et al.; The influence of supplementing the culture medium with magnesium sulphate, D-glucose, L-cysteine, catalase or lithium chloride, of incubation temperature and of oxygen availability on the recovery of salt- or acid-damaged Listeria monocytogenes, was studied on a solid repair medium according to a Hadamard matrix, with seven parameters varying between a high and a low level . The most important factors for repair of stressed Listeria were further studied with complete factorial design experiments . Results show that conditions promoting resuscitation of acid- or salt-injured cells are stress-specific, and differ in part from those described in the literature for heat-stressed Listeria.

J Immunol, 2001 Jan 1, 166(1), 466 - 72
Listeria monocytogenes modulates macrophage cytokine responses through STAT serine phosphorylation and the induction of suppressor of cytokine signaling 3; Stoiber D et al.; Macrophage activation as part of natural resistance to infection is caused by stimulation with IFN-gamma and by the invading microorganisms or microbial products . Infection of macrophages with the Gram-positive bacterium LISTERIA: monocytogenes for short periods before activation with IFN-gamma increased the phosphorylation of transcription factor STAT1 at S727 and thereby the expression of IFN-gamma-induced genes . By contrast, persistent infection with viable bacteria or treatment with heat-killed LISTERIA: diminished IFN-gamma-stimulated transcription and the phosphorylation of STAT1 at Y701 . Decreased IFN-gamma signaling correlated with the induction of suppressor of cytokine signaling 3 (SOCS3) mRNA and protein . Contrasting our previous findings with LPS, maximal synthesis of SOCS3 required both the immediate signals from LISTERIA: receptors on the cell surface and the activity of a polypeptide secreted in response to bacterial infection . SOCS3 induction by the secreted protein could not be blocked by neutralizing Abs to IL-10 and it did not require the presence of STAT1 . Consistent with the induction of SOCS3 activity, LISTERIA: also inhibited activation of STAT5 by GM-CSF . The p38 mitogen-activated protein kinase was rapidly activated upon infection of macrophages with L . monocytogenes . Inhibition of p38 mitogen-activated protein kinase with the pyridinyl imidazol SB203580 abrogated both STAT1 S727 phosphorylation and the expression of SOCS3 . The data suggest that STAT1 serine kinase and SOCS3 activity are hallmarks of immediate and delayed phases of influence by bacterial signals on signal transduction in response to IFN-gamma.

J Immunol, 2000 Dec 15, 165(12), 6833 - 9
Early programming of T cell populations responding to bacterial infection; Mercado R et al.; The duration of infection and the quantity of Ag presented in vivo are commonly assumed to influence, if not determine, the magnitude of T cell responses . Although the cessation of in vivo T cell expansion coincides with bacterial clearance in mice infected with Listeria monocytogenes, closer analysis suggests that control of T cell expansion and contraction is more complex . In this report, we show that the magnitude and kinetics of Ag-specific T cell responses are determined during the first day of bacterial infection . Expansion of Ag-specific T lymphocyte populations and generation of T cell memory are independent of the duration and severity of in vivo bacterial infection . Our studies indicate that the Ag-specific T cell response to L . monocytogenes is programmed before the peak of the innate inflammatory response and in vivo bacterial replication.

Brain Behav Immun, 2000 Dec, 14(4), 305 - 17
Immunotoxic effects of inorganic lead on host resistance of mice with different circling behavior preferences; Kim D et al.; We have observed differential immune responses in mice with different circling preferences, which are posited to reflect interindividual immune response differences influenced by brain laterality effects on neuroimmune circuits . In this study, we have investigated the influence of inorganic lead (Pb) and/or Listeria monocytogenes (LM) infection on the cytokine and corticosterone (CORT) levels of mice grouped by lateralized behavior . Pb increased the LM susceptibility of mice with both left (LC)- and right-circling (RC) preferences; however, Pb did not inhibit the host resistance of mice with no circling preference (NP mice) . The basal serum IFNgamma levels were lowered in all groups after Pb exposure, which coincided with a decrease in host resistance in LC and RC mice, but not NP mice . Pb also altered the basal serum CORT levels, and these changes appear to correlate better with changes in the host resistance of all groups . The basal CORT levels were significantly lowered by Pb in mice with a circling preference, and Pb significantly suppressed the host resistance of mice with a circling preference . However, Pb slightly increased the serum CORT level of NP mice, and their host resistance was slightly improved by Pb . After infection, the increase in CORT levels was associated with an increase in the serum IL-6 levels, which may reflect cytokine influences on the hypothalamic-pituitary-adrenal axis . At 3 days after infection, the serum IL-6 level seems to be a good indicator of the severity of the infection . We suggest that environmental stressors can reorder the observed differential susceptibility to LM in mice with different circling preferences, in that relatively resistant mice (RC mice) become more susceptible than NP mice after exposure to Pb . The results suggest that environmental stressors may have differential effects among individuals with endogenous differences in their neuroimmune circuits, since brain laterality is known to influence immune functions.

Epidemiol Infect, 2000 Oct, 125(2), 303 - 8
Comparative investigations of Listeria monocytogenes isolated from a turkey processing plant, turkey products, and from human cases of listeriosis in Denmark; Ojeniyi B et al.; Listeria monocytogenes was isolated from critical control points in a Danish turkey processing plant, from turkey products and from cases of human listeriosis . During processing in the plant the prevalence of L . monocytogenes ranged from 25.9 to 41.4% . Cleaning and disinfection decreased the prevalence to 6.4% . Isolates of L . monocytogenes were characterized by pulsed-field gel electrophoresis (PFGE) using restriction endonuclease ApaI . Identical DNA types were obtained from turkey products and the processing line even after cleaning and disinfection . Two identical DNA types were demonstrated among isolates from turkey products and human cases of listeriosis . The prevalence of L . monocytogenes in turkey products ranged from 7.3 to 17.4% for ready-to-eat products and raw products, respectively . Since none of the 27 flocks examined before slaughter sampled positive for L . monocytogenes and the prevalence increased during processing, the potential risk from turkey meat was apparently due to factory hygiene rather than intrinsic contamination of the turkeys.

Clin Immunol, 2000 Dec, 97(3), 193 - 202
Allergen immunotherapy: novel approaches in the management of allergic diseases and asthma; Campbell D et al.; Currently available pharmacotherapies for allergic diseases and asthma, which are serious public health problems, are aimed primarily at neutralizing effector molecules and inflammatory mediators such as histamine and leukotrienes or at inhibiting the function of inflammatory cells such as eosinophils and Th2 lymphocytes . While this approach is effective in controlling symptoms, these therapies have a limited capacity to alter the natural course of allergic diseases and asthma, and discontinuation of medications results in the redevelopment of symptoms on reexposure to the offending allergens . In contrast, immune-based allergen immunotherapies modify and correct the underlying pathological immune responses in allergy and asthma in an antigen-specific manner . These immunotherapies replicate the regulatory processes that occur in nonallergic individuals and allow patients to tolerate exposure to allergens . Current and future methodologies for immunotherapy involve immunization with allergen, modified allergen, peptides of allergen, cDNA of allergen, with adjuvants, including immunostimulatory DNA sequences, cytokines, and bacterial products such as Listeria monocytogenes . This form of therapy can provide a long-lasting cure for allergic diseases without the need for continuous therapeutic intervention and without causing generalized immunosuppression or immune augmentation .

Int Microbiol, 1998 Mar, 1(1), 11 - 8
The sophisticated survival strategies of the pathogen Listeria monocytogenes; Wehland J et al.; The function of the ActA protein of Listeria monocytogenes has been partially elucidated . These results illustrate the sophistication with which intracellular pathogens like Listeria use the host cell to their advantage, and have provided new insights into some of the molecular mechanisms of complex cell functions such as actin-promoted cell motility . The clarification of these processes is of fundamental importance not only for understanding elementary processes such as development and growth, but also for the treatment of both diseases caused by cytopathogenic bacteria such as Listeria and pathophysiological processes arising from disorders in cell motility and cell adhesion.

J Gastroenterol Hepatol, 2000 Oct, 15(10), 1145 - 50
Detection of Listeria monocytogenes by polymerase chain reaction in intestinal mucosal biopsies from patients with inflammatory bowel disease and controls; Chen W et al.; BACKGROUND AND AIMS: Components of the intestinal microflora are believed to play an important role in the pathogenesis of inflammatory bowel disease (IBD) in genetically susceptible hosts acting either as a non-specific antigenic stimulus or as a specific pathogen . Listeria monocytogenes has been suggested as an organism with the potential to cause IBD . The objective of the present study was to investigate the prevalence of L . monocytogenes DNA in intestinal biopsies from patients with IBD and from non-IBD controls by using nested polymerase chain reaction (PCR) . METHODS: The DNA was extracted from 274 colonoscopic biopsies, which were obtained from 23 patients with Crohn's disease (CD), 28 with ulcerative colitis (UC) and 39 non-IBD control patients . Nested PCR amplification was used to detect the presence of the L . monocytogenes listeriolysin O (hly) gene . The sequences of positive PCR products were determined and compared with databases . RESULTS: The sensitivity of our nested PCR was 10 fg L . monocytogenes DNA . Overall, L . monocytogenes DNA was detected in 13.0% patients with CD, 17.9% patients with UC and 25.6% non-IBD control patients or in 29 of 274 (10.6%) endoscopic biopsies . Among them, L . monocytogenes DNA was detected in four of 67 (6%) biopsies from patients with CD, five of 94 (5.3%) biopsies from patients with UC and 20 of 113 biopsies (17.7%) from non-IBD control patients . Sequence analysis of positive PCR products demonstrated more than 95% similarity to the hly gene sequence of L . monocytogenes, confirming the authenticity of our PCR products . CONCLUSION: Listeria monocytogenes DNA was detected in the intestine of both patients with IBD and in non-IBD control patients, probably reflecting the widespread presence of this organism in the environment . The low yield of positive biopsies in our IBD patients (5-6%) and the fact that the detection rate of L . monocytogenes DNA was similar in endoscopic biopsies from IBD patients and non-IBD controls does not support a direct role for L . monocytogenes in the pathogenesis of IBD, at least in New Zealand patients.

Immunopharmacol Immunotoxicol, 2000 Nov, 22(4), 721 - 40
Stimulatory action of Pluchea quitoc extract on the hematopoietic response during murine listeriosis; Queiroz ML et al.; The importance of both granulocytes and macrophages in the response to Listeria monocytogenes infection make this infection a suitable choice to investigate the effects of Pluchea quitoc on hematopoiesis . A significant depletion of bone marrow granulocyte-macrophage progenitor cells (CFU-GM) was observed at 48 and 72 h after intraperitoneal infection of mice with 1 x 10(4) L . monocytogenes . However, the treatment of infected animals with P . quitoc ethanolic extract (250, 500 or 1000 mg/kg) given orally for 3 consecutive days prior to infection produced a stimulatory effect on myelopoiesis, restoring the number of CFU-GM to normal . This same dose-schedule also increased colony formation in normal mice as compared to controls . In addition, P . quitoc significantly enhanced survival of infected mice . Thus, it is probable that the ability of P . quitoc to induce a higher reserve of granulocyte-macrophage precursors in the bone marrow is of major significance in determining early resistance to infection.

FEMS Microbiol Lett, 2000 Dec 1, 193(1), 155 - 9
Effect of acid-adaptation on Listeria monocytogenes survival and translocation in a murine intragastric infection model; Saklani-Jusforgues H et al.; Acid tolerance response mechanisms can greatly influence Listeria monocytogenes survival in low pH foods . In the present paper, the effect of acid-adaptation together with control of gastric pH level on L . monocytogenes survival and translocation was analyzed after intragastric inoculation in the BALB/c mouse model . Our results showed that acid-adaptation led to an increase in resistance to the first barrier constituted by the low gastric pH and that inoculation at alkaline pH had a synergistic effect . It resulted in a higher live bacterial load reaching the next intestinal compartments and was correlated with increased translocation rates to the mesenteric lymph nodes, both at the frequency and quantitative levels . Our results in this murine model suggest that acid-adaptation of L . monocytogenes in low pH foods, together with control of gastric pH level through dietary practices, or use of inhibitors of gastric acid secretion, may be potential aggravating risk factors to food-borne listeriosis.

Curr Treat Options Neurol, 1999 May, 1(2), 147 - 156
Bacterial Meningitis; Roos KL; Initial empiric therapy for community-acquired bacterial meningitis should be based on the possibility that penicillin-resistant pneumococci may be the etiologic organisms and, hence, should include a combination of third-generation cephalosporin (cefotaxime or ceftriaxone) and vancomycin . Ampicillin should be included if the patient has predisposing factors that are associated with a risk for infection with Listeria monocytogenes . Bacterial isolates from the cerebrospinal fluid should be tested for antimicrobial susceptibility . Understanding the significance of inflammatory cytokines in the pathophysiology of bacterial meningitis leads to an understanding of the need to prevent their formation . Dexa- methasone inhibits synthesis of the inflammatory cytokines, interleukin-1 and tumor necrosis factor . Results of clinical trials and meta-analysis suggest that dexamethasone therapy improves the outcome for patients with bacterial meningitis . Dexamethasone should be administered before or with the first dose of antibiotics . The development of therapeutic modalities to downregulate host inflammatory responses, such as those of monoclonal antibodies to cytokines, is of utmost importance.

Eur J Immunol, 2000 Dec, 30(12), 3447 - 56
Human dendritic cells infected by Listeria monocytogenes: induction of maturation, requirements for phagolysosomal escape and antigen presentation capacity; Paschen A et al.; An important feature of microbial infections is the ability of the microorganisms to interfere with and modulate the induction of host immune reactions . However, little is known about the effects of broad host range pathogens such as Listeria monocytogenes on similar cell types in different hosts . Here we examine the effects of the human and animal pathogen L . monocytogenes on human dendritic cells (DC) since this type of cells is essential for the initiation of immune responses . Listeria are phagocytosed efficiently by immature human DC and the bacteria escape from the phagolysosome quickly . Lack of the pore-forming activity of listeriolysin, which was found to be essential for the vacuolar escape of this bacterium in other cell types, retarded but did not prevent egress from the vacuole . Treatment of cultures of immature DC with L . monocytogenes resulted in rapid changes in morphology and cellular constitution followed by maturation of the DC . This could be judged by the appearance of maturation-specific cell surface markers . Antigen presentation to CD4 T cells was apparently not impaired by the infection . These results are in clear contrast to results obtained previously in the mouse system (Guzman et al., Mol . Microbiol . 1996 . 20: 119 - 126; Darji et al., Eur . J . Immunol . 1997 . 27: 1696 - 1703.).

J Bacteriol, 2000 Dec, 182(24), 7083 - 7
Role of sigma(B) in adaptation of Listeria monocytogenes to growth at low temperature; Becker LA et al.; The activity of sigma(B) in Listeria monocytogenes is stimulated by high osmolarity and is necessary for efficient uptake of osmoprotectants . Here we demonstrate that, during cold shock, sigma(B) contributes to adaptation in a growth phase-dependent manner and is necessary for efficient accumulation of betaine and carnitine as cryoprotectants.

J Immunol, 2000 Dec 1, 165(11), 6472 - 9
Depletion of a gamma delta T cell subset can increase host resistance to a bacterial infection; O'Brien RL et al.; Gammadelta T lymphocytes have been shown to regulate immune responses in diverse experimental systems . Because distinct gammadelta T cell subsets, as defined by the usage of certain TCR V genes, preferentially respond in various diseases and disease models, we have hypothesized that the various gammadelta T cell subsets carry out different functions . To test this, we compared one particular gammadelta T cell subset, the Vgamma1(+) subset, which represents a major gammadelta T cell type in the lymphoid organs and blood of mice, to other subsets and to gammadelta T cells as a whole . Using LISTERIA: monocytogenes infection as an infectious disease model, we found that bacterial containment improves in mice depleted of Vgamma1(+) gammadelta T cells, albeit mice lacking all gammadelta T cells are instead impaired in their ability to control LISTERIA: expansion . Our findings indicate that Vgamma1(+) gammadelta T cells reduce the ability of the innate immune system to destroy LISTERIA:, even though other gammadelta T cells as a whole promote clearance of this pathogen.

Infect Immun, 2000 Dec, 68(12), 7061 - 8
ClpC ATPase is required for cell adhesion and invasion of Listeria monocytogenes; Nair S et al.; We studied the role of two members of the 100-kDa heat shock protein family, the ClpC and ClpE ATPases, in cell adhesion and invasion of the intracellular pathogen Listeria monocytogenes . During the early phase of infection, a clpC mutant failed to disseminate to hepatocytes in the livers of infected mice whereas the invasive capacity of a clpE mutant remained unchanged . This was confirmed by a confocal microscopy study on infected cultured hepatocyte and epithelial cell lines, showing a strong reduction of cell invasion only by the clpC mutant . Western blot analysis with specific antisera showed that the absence of ClpC, but not that of ClpE, reduced expression of the virulence factors InlA, InlB, and ActA . ClpC-dependent modulation of these factors occurs at the transcriptional level with a reduction in the transcription of inlA, inlB, and actA in the clpC mutant, in contrast to the clpE mutant . This work provides the first evidence that, in addition to promoting escape from the phagosomes, ClpC is required for adhesion and invasion and modulates the expression of InlA, InlB, and ActA, further supporting the major role of the Clp chaperones in the virulence of intracellular pathogens.

Science, 2000 Nov 17, 290(5495), 1354 - 8
Regulation of antigen-specific CD8+ T cell homeostasis by perforin and interferon-gamma; Badovinac VP et al.; T cell memory depends on factors that regulate expansion and death of these cells after antigenic stimulation . Mice deficient in perforin and interferon-gamma (IFN-gamma) exhibited increased expansion, altered immunodominance, and decreased death of antigen-specific CD8+ T cells after infection with an attenuated strain of Listeria monocytogenes, which was cleared from these mice . Expansion of CD8+ T cells was controlled by perforin, whereas IFN-gamma regulated immunodominance and the death phase . Thus, perforin and IFN-gamma regulate distinct elements of CD8+ T cell homeostasis independently of their role as antimicrobial effector molecules.

Cell, 2000 Oct 27, 103(3), 501 - 10
InIB-dependent internalization of Listeria is mediated by the Met receptor tyrosine kinase; Shen Y et al.; The Listeria monocytogenes surface protein InlB promotes bacterial entry into mammalian cells . Here, we identify a cellular surface receptor required for InlB-mediated entry . Treatment of mammalian cells with InlB protein or infection with L . monocytogenes induces rapid tyrosine phosphorylation of Met, a receptor tyrosine kinase (RTK) for which the only known ligand is Hepatocyte Growth Factor (HGF) . Like HGF, InlB binds to the extracellular domain of Met and induces "scattering" of epithelial cells . Experiments with Met-positive and Met-deficient cell lines demonstrate that Met is required for InlB-dependent entry of L . monocytogenes . InlB is a novel Met agonist that induces bacterial entry through exploitation of a host RTK pathway.

Int J Food Microbiol, 2000 Nov 1, 61(2-3), 169 - 75
Effects of combinations of lactoperoxidase system and nisin on the behaviour of Listeria monocytogenes ATCC 15313 in skim milk; Boussouel N et al.; Individual or combined effects of nisin (100 or 200 IU/ml) and the lactoperoxidase system (LPS) were analysed against 1 x 10(4) cfu/ml Listeria monocytogenes ATCC 15313 cells in skim milk, at 25 degrees C for 15 days . Nisin induced an immediate bactericidal effect and LPS a 48 h bacteriostatic phase which in both cases was followed by re-growth of L . monocytogenes . LPS and nisin added together at t0 showed a synergistic and lasting bactericidal effect which after 8 days and until 15 days resulted in no detectable cells in 1 ml of milk . When LPS was added to cells already in contact with 100 or 200 IU/ml nisin for a period of 4 h, the inhibitory activity was enhanced with no L . monocytogenes detectable after 72 or 48 h, respectively, and until 15 days . When LPS was added after 12 h, the nisin bactericidal phase was followed by re-growth . When nisin, 100 or 200 UI/ml, was added to cells already in contact with LPS over 24 h, L . monocytogenes was not detectable after 196 and 244 h, respectively, without any re-growth . For nisin addition after 72 h, cell counts were 8 log10 cycles lower than in the control milk after 196 h, but population levels were similar to the control within 15 days . The best combination to inhibit L . monocytogenes ATCC 15313 was nisin present at t0 followed by the LPS addition 4 h later, when the maximum inhibitory effect of nisin was reached.

Drug Chem Toxicol, 2000 Nov, 23(4), 621 - 44
Oxymetholone modulates cell-mediated immunity in male B6C3F1 mice; Karrow NA et al.; Oxymetholone is a synthetic androgen, structurally related to testosterone . It is currently used to treat anemias, but has also been abused as a performance enhancing anabolic steroid by the sport community . Concern about its suspected immunomodulatory properties provided the incentive for a detailed investigation into its effects on the mammalian immune system . In this study, male B6C3F1 mice were treated for 14 d with oxymetholone (0, 50, 150, and 300 mg/kg) by gastric intubation, then evaluated for immunotoxicity using a panel of immunotoxicity assays . Except for an increasing trend in kidney and liver weights, and a dose-dependent increase in serum blood urea nitrogen levels, no other signs of systemic toxicity were observed . Bone marrow DNA synthesis was reduced, though this did not translate into alterations in myeloid or monocyte colony forming units . Spleen B and T cell numbers, antibody response to sheep red blood cells, proliferative response to both mitogen and immunoglobulin receptor immunogens, and NK cell activity were all unaltered in mice treated with oxymetholone . Peritoneal macrophage activity was also unaffected by oxymetholone treatment . A 38% decrease in the spleen cell mixed leukocyte response, and a 15% decrease in cytotoxic T cell activity, measured in the highest oxymetholone treatment group, indicate that cell-mediated immunity was impaired following exposure . This immunomodulation did not however, translate into a change in host resistance to Listeria monocytogenes.

Nature, 2000 Oct 26, 407(6807), 1026 - 9
Steps and fluctuations of Listeria monocytogenes during actin-based motility; Kuo SC et al.; The actin-based motility of the bacterium, Listeria monocytogenes, is a model system for understanding motile cell functions involving actin polymerization . Although the biochemical and genetic aspects of Listeria motility have been intensely studied, biophysical data are sparse . Here we have used high-resolution laser tracking to follow the trailing ends of Listeria moving in the lamellae of COS7 cells . We found that pauses during motility occur frequently and that episodes of step-like motion often show pauses spaced at about 5.4 nm, which corresponds to the spatial periodicity of F-actin . We occasionally observed smaller steps (<3 nm), as well as periods of motion with no obvious pauses . Clearly, bacteria do not sense cytoplasmic viscoelasticity because they fluctuate 20 times less than adjacent lipid droplets . Instead, bacteria bind their own actin 'tails, and the anchoring proteins can 'step' along growing filaments within the actin tail . Because positional fluctuations are unusually small, the forces of association and propulsion must be very strong . Our data disprove the brownian ratchet models and limit alternative models, such as the 'elastic' brownian ratchet or the 'molecular' ratchet.

Lett Appl Microbiol, 2000 Oct, 31(4), 319 - 22
Cellular morphology of rough forms of Listeria monocytogenes isolated from clinical and food samples; Rowan NJ et al.; Transmission electron microscopy (TEM) studies revealed that rough cell-forms of L . monocytogenes (designated FR variants), isolated from clinical and food samples (and under conditions of sublethal heat stress), consist of either single or paired long-filaments . These FR variants markedly contrast in cell morphology from other previously described avirulent rough-mutants of L . monocytogenes that form long chains consisting of multiple cells of similar size (designated MCR variants) . The identity of these Listeria isolates was determined using a commercially available, anti-Listeria polyclonal KPL antibody and by the API Listeria biochemical gallery . This study shows that filamentous rough-forms of L . monocytogenes may occur in clinical and food samples that are of undetermined pathogenicity.

FEMS Immunol Med Microbiol, 2000 Nov, 29(3), 187 - 94
Effect of a matrix metalloproteinase inhibitor on host resistance against Listeria monocytogenes infection; Yamada K et al.; Hydroxy acid-based matrix metalloproteinase (MMP) inhibitors have been shown to inhibit tumor infiltration and growth, endotoxin shock, and acute graft-versus-host disease . Blockade of the release of soluble tumor necrosis factor-alpha (TNF-alpha) and CD95 ligand (CD95L; FasL) from cell-associated forms is reportedly involved in the mechanism of the drug effect . We investigated the effect of a MMP inhibitor, KB-R7785, on host resistance against Listeria monocytogenes infection, in which TNF-alpha is essentially required for the defense, in mice . The administration of KB-R7785 exacerbated listeriosis, while the drug prevented lethal shock induced by lipopolysaccharide and D-galactosamine . KB-R7785 inhibited soluble TNF-alpha production in spleen cell cultures stimulated by heat-killed L . monocytogenes and the drug treatment reduced serum TNF-alpha levels in infected mice, whereas the compound was ineffective on the modulation of interferon-gamma and interleukin-10 production . The effect of KB-R7785 was considered to be dependent on TNF-alpha because the drug failed to affect L . monocytogenes infection in anti-TNF-alpha monoclonal antibody-treated mice and TNF-alpha knockout mice . Anti-CD95L monoclonal antibody was also ineffective on the infection . These results suggest that induction of infectious diseases, to which TNF-alpha is critical in host resistance, should be considered in MMP inhibitor-treated hosts.

Science, 2000 Nov 3, 290(5493), 992 - 5
A PEST-like sequence in listeriolysin O essential for Listeria monocytogenes pathogenicity; Decatur AL et al.; Establishment and maintenance of an intracellular niche are critical to the success of an intracellular pathogen . Here, the pore-forming protein listeriolysin O (LLO), secreted by Listeria monocytogenes, was shown to contain a PEST-like sequence (P, Pro; E, Glu; S, Ser; T, Thr) that is essential for the virulence and intracellular compartmentalization of this pathogen . Mutants lacking the PEST-like sequence entered the host cytosol but subsequently permeabilized and killed the host cell . LLO lacking the PEST-like sequence accumulated in the host-cell cytosol, suggesting that this sequence targets LLO for degradation . Transfer of the sequence to perfringolysin O transformed this toxic cytolysin into a nontoxic derivative that facilitated intracellular growth.

New Microbiol, 2000 Oct, 23(4), 347 - 56
Virulence profiles and other biological characters in water isolated Aeromonas hydrophila; Bondi M et al.; Thirty water isolates of A . hydrophila were tested for potential virulence profiles, antibiotic resistance and Bacteriocin-Like Substances (BLS) production . Cytotoxic activity was present in all strains tested, 87% were hemolytic and 70% adhesive . Lysine decarboxylase reactions (LDC) positivity was correlated with virulence factors: 100% versus cytotoxicity, 84% versus adherence, 76% versus hemolytic activity . The correlation was also present in the LDC-negative strains . Hemolytic and cytotoxic activities were frequently associated: high cytotoxicity, corresponding to high hemolytic activity and vice versa . The in vitro susceptibility of A . hydrophila to 28 antibacterial agents showed that cefotaxime was the most active beta-lactam antibiotic, and Cefuroxime inhibited 90% of the strains . Isolates were resistant to Penicillin G, Ampicillin, Carbenicillin, Amoxicillin, Cephalotin and Cefaclor . Tetracycline, Chloramphenicol, Nitrofurantoine, the quinolones and the aminoglycosides (except Streptomycin) were consistently active . BLS production never emerged against closely-related microorganisms . On the contrary A . hydrophila presented a heteroinhibitory activity against non-taxonomically related genera such as Listeria spp . (L . seeligeri NCTC 11856, L . welshimeri NCTC 11857, L . ivanovii NCTC 11846) and S . aureus ATCC 25923 . Although a large number of strains showed virulence determinants together with other biological characters such as antibiotic resistance and BLS production, it was not possible to relate these factors to the observed plasmids.

Nature, 2000 Oct 19, 407(6806), 916 - 20
Development of Th1-type immune responses requires the type I cytokine receptor TCCR; Chen Q et al.; On antigen challenge, T-helper cells differentiate into two functionally distinct subsets, Th1 and Th2, characterized by the different effector cytokines that they secrete . Th1 cells produce interleukin (IL)-2, interferon-gamma (IFN-gamma) and lymphotoxin-beta, which mediate pro-inflammatory functions critical for the development of cell-mediated immune responses, whereas Th2 cells secrete cytokines such as IL-4, IL-5 and IL-10 that enhance humoral immunity . This process of T-helper cell differentiation is tightly regulated by cytokines . Here we report a new member of the type I cytokine receptor family, designated T-cell cytokine receptor (TCCR) . When challenged in vivo with protein antigen, TCCR-deficient mice had impaired Th1 response as measured by IFN-gamma production . TCCR-deficient mice also had increased susceptibility to infection with an intracellular pathogen, Listeria monocytogenes . In addition, levels of antigen-specific immunoglobulin-gamma2a, which are dependent on Th1 cells, were markedly reduced in these mice . Our results demonstrate the existence of a new cytokine receptor involved in regulating the adaptive immune response and critical to the generation of a Th1 response.

Eur J Clin Microbiol Infect Dis, 2000 Sep, 19(9), 711 - 4
Listeriosis in recipients of allogeneic bone marrow transplants from unrelated donors; Girmenia C et al.; Two cases of listeriosis in patients submitted to matched unrelated donor bone marrow transplantation are reported . The patients developed listerial septicemia and listerial septicemia with meningitis and encephalitis 39 and 29 days after transplantation, respectively . Including the present two cases, 19 Listeria monocytogenes infections in related and unrelated donor allogeneic bone marrow transplant recipients have been reported to date . Infection occurred earlier in unrelated donor transplant recipients . Listeriosis is a rare complication in allogeneic bone marrow transplant recipients; however, the widespread practice of performing transplants from a donor-alternative to a human leukocyte antigen-compatible sibling and, in this setting, the need for intensified immunosuppression may predict an increasing and earlier occurrence of listeriosis.

Appl Environ Microbiol, 2000 Nov, 66(11), 4979 - 87
Growth limits of Listeria monocytogenes as a function of temperature, pH, NaCl, and lactic acid; Tienungoon S et al.; Models describing the limits of growth of pathogens under multiple constraints will aid management of the safety of foods which are sporadically contaminated with pathogens and for which subsequent growth of the pathogen would significantly increase the risk of food-borne illness . We modeled the effects of temperature, water activity, pH, and lactic acid levels on the growth of two strains of Listeria monocytogenes in tryptone soya yeast extract broth . The results could be divided unambiguously into "growth is possible" or "growth is not possible" classes . We observed minor differences in growth characteristics of the two L . monocytogenes strains . The data follow a binomial probability distribution and may be modeled using logistic regression . The model used is derived from a growth rate model in a manner similar to that described in a previously published work (K . A . Presser, T . Ross, and D . A . Ratkowsky, Appl . Environ . Microbiol . 64:1773-1779, 1998) . We used "nonlinear logistic regression" to estimate the model parameters and developed a relatively simple model that describes our experimental data well . The fitted equations also described well the growth limits of all strains of L . monocytogenes reported in the literature, except at temperatures beyond the limits of the experimental data used to develop the model (3 to 35 degrees C) . The models developed will improve the rigor of microbial food safety risk assessment and provide quantitative data in a concise form for the development of safer food products and processes.

Appl Environ Microbiol, 2000 Nov, 66(11), 4779 - 84
Molecular epidemiological survey of Listeria monocytogenes in seafoods and seafood-processing plants; Rorvik LM et al.; To evaluate the role of seafoods in the epidemiology of human listeriosis and the role of the processing environment as a source of Listeria monocytogenes in seafood products, 305 L . monocytogenes isolates were characterized by multilocus enzyme electrophoresis using 21 genetic loci and restriction enzyme analysis of total DNA . Forty-four isolates were recovered from patients in Norway; 93 were isolated from seafoods, seafood-processing environments, and seawater from 55 different producers; and the remaining 168 isolates originated from six seafood-processing plants and one transport terminal examined in detail for L . monocytogenes . The patient isolates fell into 11 electrophoretic types, with four of them being responsible for 77% of the listeriosis cases in 1992 to 1996 . Isolates from Norwegian seafoods and processing environments showed great genetic diversity, indicating that seafoods and seafood-processing environments do not offer a niche for specific L . monocytogenes strains . On the other hand, isolates from individual processing plants were genetically more homogenous, showing that plants are likely to be colonized with specific subclones of L . monocytogenes . The isolation of identical subclones of L . monocytogenes from both human patients and seafoods, including ready-to-eat products, suggests that such products may have been possible sources for listeriosis cases in Norway.

Biophys J, 2000 Nov, 79(5), 2259 - 75
An elastic analysis of Listeria monocytogenes propulsion; Gerbal F et al.; The bacterium Listeria monocytogenes uses the energy of the actin polymerization to propel itself through infected tissues . In steady state, it continuously adds new polymerized filaments to its surface, pushing on its tail, which is made from previously cross-linked actin filaments . In this paper we introduce an elastic model to describe how the addition of actin filaments to the tail results in the propulsive force on the bacterium . Filament growth on the bacterial surface produces stresses that are relieved at the back of the bacterium as it moves forward . The model leads to a natural competition between growth from the sides and growth from the back of the bacterium, with different velocities and strengths for each . This competition can lead to the periodic motion observed in a Listeria mutant.

Semin Neurol, 2000, 20(3), 361 - 73
Listeria and atypical presentations of Listeria in the central nervous system; Bartt R; Listeria monocytogenes infection of the central nervous system is often not recognized and treated appropriately in the crucial early stages of the disease . Most consider patients with underlying disease or immunocompromised states to be at risk, although healthy individuals may present with a neurologic syndrome caused by L . monocytogenes . Earlier suspicion and treatment remains our best means of reducing the morbidity and high mortality rate of this treatable disease . In addition to meningitis and meningoencephalitis, infection of the brainstem (rhomboencephalitis) is challenging to recognize and therefore initiate appropriate early therapy . Cerebritis and abscess can also occur . Furthermore, empirical therapy for meningitis or the other manifestations of nervous system involvement is often inadequate . This review addresses the clinical microbiology, pathogenesis, spectrum of neurological involvement, and treatment of central nervous system infection related to L . monocytogenes.

J Vet Med B Infect Dis Vet Public Health, 2000 Sep, 47(7), 497 - 502
Kinetics of antibody production and clinical profiles of calves experimentally infected with Listeria monocytogenes; Barbuddhe SB et al.; Clinical and serum antibody profiles were studied during oral Listeria monocytogenes infection of calves . No clinical signs, except for pyrexia with mild diarrhoea and staggering gait, were observed in the infected calves . Specific antibodies to listeriolysin O (LLO) appeared as early as day 8 of an oral infection and peaked by days 16-32 of infection . Antibodies to LLO were observed to persist over the period of 126 days observed in the study . LLO being a major virulence factor and capable of inducing a humoral response could therefore be used as an antigen for development of an immunoassay for diagnosis of Listeria monocytogenes infections in animals.

J Immunol, 2000 Nov 1, 165(9), 5192 - 201
MHC class Ib-restricted CTL provide protection against primary and secondary Listeria monocytogenes infection; Seaman MS et al.; Infection of B6 mice with the intracellular pathogen Listeria monocytogenes (LM) results in the activation of CD8(+) T cells that respond to Ag presented by both MHC class Ia and class Ib molecules . Enzyme-linked immunospot analysis reveals that these CTL populations expand and contract at different times following a primary sublethal LM infection . Between days 4 and 6 postinfection, class Ib-restricted CTL exhibit a rapid proliferative response that is primarily H2-M3 restricted . The peak response of class Ia-restricted CD8(+) T cells occurs a few days later, after the majority of bacteria have been cleared . Although class Ia-restricted CTL exhibit a vigorous recall response to secondary LM infection, we observe limited expansion of class Ib-restricted memory CTL, even in MHC class Ia-deficient mice (B6.K(b-/-)D(b-/-)) . Despite this lack of enhanced expansion in vivo, class Ib-restricted memory CTL retain the ability to proliferate and expand when provided with Ag in vitro . Furthermore, we demonstrate that in vivo depletion of CD8(+) T cells in LM-immune B6.K(b-/-)D(b-/-) mice severely impairs memory protection . Together, these data demonstrate that class Ib-restricted CTL play an important role in clearing a primary LM infection and generate a memory population capable of providing significant protection against subsequent infection.

Int J Med Microbiol, 2000 May, 290(2), 167 - 74
Genome organization and the evolution of the virulence gene locus in Listeria species; Chakraborty T et al.; The chromosomal region of Listeria monocytogenes harboring the gene cluster prfA-plcA-hly-mpl-actA-plcB (virulence gene cluster; vgc) harbors virulence genes critical for the survival of the bacteria following infection . Previous studies have implicated it as an ancestral pathogenicity island, derivatives of which are present in the species L . ivanovii and L . seeligeri, but absent in non-pathogenic species such as L . innocua . We cloned the corresponding region from L . innocua and L . welshimeri and compared its sequences to those from L . monocytogenes, L . ivanovii and L . seeligeri . The analysis allowed exact determination of delineation and size of the vgc and suggests that these genes may have been acquired by bacteriophage transduction . Thus, here we present an alternative view of the evolution of Listeria spp . and suggest that L . monocytogenes may be the primordial species of this genus.

J Food Prot, 2000 Oct, 63(10), 1438 - 42
Listeria monocytogenes contamination pattern in pig slaughterhouses; Autio T et al.; Ten low-capacity slaughterhouses were examined for Listeria by collecting a total of 373 samples, of which 50, 250, and 73 were taken from carcasses, pluck sets, and the slaughterhouse environment, respectively . Six slaughterhouses and 9% of all samples were positive for Listeria monocytogenes . Of the samples taken from pluck sets, 9% were positive for L . monocytogenes, the highest prevalence occurring in tongue and tonsil samples, at 14% and 12%, respectively . Six of 50 (12%) carcasses were contaminated with L . monocytogenes . In the slaughterhouse environment, L . monocytogenes was detected in two, one, one, and one sample originating from the saws, drain, door, and table, respectively . Carcasses were contaminated with L . monocytogenes in those two slaughterhouses, where the mechanical saws, used for both brisket and back splitting, were also positive for L . monocytogenes . A total of 58 L . monocytogenes isolates were characterized by pulsed-field gel electrophoresis typing . The isolates were divided into 18 pulsotypes, 15 of which were detected in pluck sets . In two slaughterhouses, where the carcasses were contaminated with L . monocytogenes, the same pulsotypes were also recovered from splitting saws . In addition, identical pulsotypes were recovered from pluck sets . Our findings indicate that L . monocytogenes of tongue and tonsil origin may contaminate the slaughtering equipment that may in turn spread the pathogen to carcasses . Thus, it is of the utmost importance to follow good manufacturing practices and to have efficient cleaning and disinfection procedures to prevent equipment being contaminated with L . monocytogenes.

J Food Prot, 2000 Oct, 63(10), 1353 - 8
Influence of traditional brine washing of smear Taleggio cheese on the surface spreading of Listeria innocua; Carminati D et al.; The influence of a traditional procedure of washing of smear Taleggio cheese on surface spreading of Listeria innocua was studied . This practice is carried out during ripening to remove molds, to select the surface microflora, and to control the ripening process . One cheese, both of 2 (i) and 4 (ii) weeks of ripening, was surface-inoculated with approximately 3 log CFU of L . innocua per entire cheese surface . The inoculated cheeses and others of the same age were weekly washed with brine solution . Listeria was spread both on the surface of the inoculated cheese and on the other cheeses, and it was also found in the brines and on the wooden boxes where the cheeses were ripened . The time of ripening when contamination occurs influenced the behavior of Listeria . At the moment of contamination, the smear surface microflora of (i) cheese was approximately 2 log CFU/g higher than of (ii) cheese . Listeria inoculated on 2-week-ripened cheese was able to colonize the entire surface of the cheese and to cross-contaminate the other cheeses . On the contrary, Listeria inoculated on a 4-week-ripened cheese was partially spread on the surface of the originally inoculated cheese, and the transfer of contamination by the washing procedure was restrained . Because a random distribution of Listeria on cheese surface was observed, the importance of the mode of sampling was discussed . Because of the lack of critical control points during ripening of Taleggio cheese, the Listeria hazard needs to be controlled by taking appropriate control measures to break off the contamination cycle (cheese --> brine --> wooden boxes --> cheese).

Mayo Clin Proc, 2000 Oct, 75(10), 1039 - 54
Infection and immunity in chronic lymphocytic leukemia; Tsiodras S et al.; Patients having chronic lymphocytic leukemia (CLL) are at increased risk for infectious morbidity and mortality . The predisposition to infections in CLL patients has many components, including both immunodeficiency related to the leukemia itself (humoral and cellular immune dysfunction) and the results of cumulative immunosuppression related to CLL treatment . The risk of infectious complications increases with the duration of CLL, reflecting the natural history of the disease and the cumulative immunosuppression related to its treatment . Hence, in early, untreated CLL, the infectious risk is mainly related to hypogammaglobulinemia, and infections by encapsulated bacteria are common . However, in patients having advanced CLL, particularly those who receive the newer purine analogues, neutropenia and defects in cell-mediated immunity appear to be the major predisposing factors . An expanded spectrum of pathogens, including opportunistic fungi, Pneumocystis carinii, Listeria monocytogenes, mycobacteria, and herpesviruses, are seen in that setting . The changing spectrum of infections in this latter group of patients mandates a newer approach to prophylaxis and therapy.

FEMS Microbiol Lett, 2000 Nov 1, 192(1), 79 - 83
Effect of enterocin CRL35 on Listeria monocytogenes cell membrane; Minahk CJ et al.; The antimicrobial peptide Enterocin CRL35, a class II bacteriocin, produces at high concentrations (8 microg ml(-1)) localized holes in the wall and cellular membrane of Listeria monocytogenes, reflected in the efflux of macromolecules such as proteins and other ultraviolet-absorbing materials . At lower concentrations (0.5 microg ml(-1)), neither ultra structural changes nor macromolecules efflux were observed, however potassium and phosphate ions were released, dissipating the proton motive force . As a result the bacteria were killed.

J Leukoc Biol, 2000 Oct, 68(4), 487 - 94
Altered membrane trafficking in activated bone marrow-derived macrophages; Tsang AW et al.; Activation of macrophages with interferon-gamma (IFN-gamma) and lipopolysaccharide (LPS) leads to increased intracellular resistance to microbes and increased major histocompatibility complex class II-restricted antigen presentation, processes that both use the vacuolar compartment . Despite the requirement of the macrophage vacuolar compartment for microbicidal activities and antigen processing, the rates of endocytosis and membrane trafficking in activated macrophages are not clearly defined . In this study, vacuolar compartment dynamics were analyzed in murine bone marrow-derived macrophages activated with LPS and/or IFN-gamma, conditions that increased macrophage nitric oxide production and resistance to infection by Listeria monocytogenes . Relative to nonactivated cells, activated macrophages showed diminished rates of fluid-phase pinocytosis and phagocytosis and delayed progression of macropinosomes and phagosomes to late endosomes and lysosomes . In contrast to the slowing of membrane trafficking, rates of macropinosome acidification were similar between activated and nonactivated cells . One consequence of this slowed membrane trafficking in activated macrophages was a prolonged exposure of incoming molecules to an acidic nonlysosomal compartment, a condition which may facilitate microbicidal chemistries or antigen processing.

J Immunol, 2000 Oct 15, 165(8), 4575 - 80
Partially TAP-independent protection against Listeria monocytogenes by H2-M3-restricted CD8+ T cells; Rolph MS et al.; Effective protection against Listeria monocytogenes requires Ag-specific CD8(+) T cells . A substantial proportion of CD8(+) T cells activated during L . monocytogenes infection of C57BL/6 mice are restricted by the MHC class Ib molecule H2-M3 . In this study, an H2-M3-restricted CD8(+) T cell clone specific for a known H2-M3 epitope (fMIGWII) was generated from L . monocytogenes-infected mice . The clone was cytotoxic, produced IFN-gamma, and could mediate strong protection against L . monocytogenes when transferred to infected mice . Macrophages pulsed with heat-killed LISTERIAE: presented Ag to the clone in a TAP-independent manner . Both TAP-independent and -dependent processing occurred in vivo, as TAP-deficient mice infected with L . monocytogenes were partially protected by adoptive transfer of the clone . This is the first example of CD8(+) T cell-mediated, TAP-independent protection against a pathogen in vivo, confirming the importance of alternative MHC class I processing pathways in the antibacterial immunity.

J Exp Med, 2000 Oct 16, 192(8), 1135 - 42
Requirements for bone marrow-derived antigen-presenting cells in priming cytotoxic T cell responses to intracellular pathogens; Lenz LL et al.; Bone marrow (BM)-derived antigen-presenting cells (APCs) are potent stimulators of T cell immune responses . We investigated the requirements for antigen presentation by these cells in priming cytotoxic T lymphocyte (CTL) responses to intracellular bacterial and viral pathogens . {Parent-->F(1)} radiation BM chimeras were constructed using C57BL/6 donors and (C57BL/6 x BALB/c)F(1) recipients . Infection of chimeric mice with either Listeria monocytogenes or vaccinia virus expressing the nucleoprotein (NP) antigen from lymphocytic choriomeningitis virus (LCMV) primed H2-D(b)-restricted, but not H2-K(d)-restricted CTL responses, demonstrating the requirement for BM-derived APCs for successful priming of CTL responses to these pathogens . Surprisingly, this did not hold true for chimeric mice infected with LCMV itself . LCMV-infected animals developed strong CTL responses specific for both H2-D(b)- and H2-L(d)-restricted NP epitopes . These findings indicate that in vivo priming of CTL responses to LCMV is remarkably insensitive to deficiencies in antigen presentation by professional BM-derived APCs.

FEMS Microbiol Lett, 2000 Sep 15, 190(2), 323 - 8
Interaction of Listeria monocytogenes with the intestinal epithelium; Daniels JJ et al.; Listeria monocytogenes is a food-borne pathogen that must cross the intestinal epithelial barrier to reach its target organs . We have investigated the importance of M cells in translocation using an experimental mouse model and a novel, recently described in vitro coculture system that mimics the follicle-associated epithelium (FAE) . Our data demonstrate that L . monocytogenes does not require, nor specifically use, M cells of the FAE to cross the gut . We also show that bacterial translocation is rapid and L . monocytogenes can attach very efficiently to exposed basal lamina of the small intestine indicating an important role for extracellular matrix proteins.

Vopr Med Khim, 2000 May-Jun, 46(3), 256 - 64
{Listeria monocytogenes: a dangerous pathogen used as a vector for the new generation of vaccines}; Tkachuk MV et al.; Listeria monocytogenes (LM) has become a major pathogen of human foodborne illnesses eliciting meningitis, peritonitis, and abortions with a mortality rate of about 30% . During the course of the disease, LM infects a variety of tissues and cell types due to its capacity to induce its own phagocytosis even into non-phagocytic cells . For over 35 years LM continues to serve as a model to define general paradigms of immunology In this review we focus on the clinical characteristics of listeriosis, on the risk factors involved in the pathogenesis, and discuss the currently accepted approaches to prophylaxis and treatment . We report on novel strategies in vaccine development based on the LM-dependent delivering machinery for immune recognition and induction of immunological memory against desired antigens.

J Comp Pathol, 2000 Aug-Oct, 123(2-3), 104 - 9
Effect of selenium deficiency on the development of central nervous system lesions in murine listeriosis; Altimira J et al.; The effect of selenium (Se) deficiency, produced by feeding a Se-deficient diet, on the development of central nervous system (CNS) lesions was studied in mice infected with Listeria monocytogenes, administered in drinking water for 1 or 7 days in a daily dose of 10(9)organisms, or for 7 days in a daily dose of 10(7) . Se-deficient mice differed from Se-normal controls in developing CNS lesions significantly more frequently . Moreover, regardless of Se status, mice receiving repeated doses of 10(9)organisms differed from those receiving a single 10(9)dose in showing CNS lesions at least twice as often . The majority of animals with CNS lesions showed an inflammatory pattern of rhombencephalitis (17/24), while only two of 24 showed choroiditis-ventriculitis-meningitis; five of 24 animals showed both inflammatory patterns . Listeria monocytogenes antigen was identified within the areas of inflammation by an immunoperoxidase technique . Neuritis of the trigeminal nerve was present in eight animals . The relative lack of pathological changes in the liver and spleen validates this murine model for the study of CNS listeriosis .

Pharmazie, 2000 Sep, 55(9), 635 - 9
Prophylactic and therapeutic application of antimicrobial agents in the oral cavity; Pitten FA et al.; Antimicrobial substances are used for many prophylactic and therapeutic reasons in the oral cavity . They are used as mouthrinses, for the irrigation of specific oral locations, in form of gels, or varnishes . Different antimicrobial agents are available and some preparations are complex compositions of these compounds . Although it has been proven that several agents are suited to achieve a considerable reduction of oral microorganisms many questions concerning the clinical benefit are yet to be answered . This report summarises the evidence of the efficacy of oral antiseptics (especially chlorhexidine, pvp-iodine, and Listerine) depending on different indications, which is the basis for clinical and practical recommendations.

Annu Rev Cell Dev Biol, 2000, 16, 173 - 89
Gut feelings: enteropathogenic E . coli (EPEC) interactions with the host; Goosney DL et al.; Enteropathogenic Escherichia coli (EPEC) is a gram-negative bacterial pathogen that adheres to human intestinal epithelial cells, resulting in watery, persistent diarrhea . It subverts the host cell cytoskeleton, causing a rearrangement of cytoskeletal components into a characteristic pedestal structure underneath adherent bacteria . In contrast to other intracellular pathogens that affect the actin cytoskeleton from inside the host cytoplasm, EPEC remains extracellular and transmits signals through the host cell plasma membrane via direct injection of virulence factors by a "molecular syringe," the bacterial type III secretion system . One injected factor is Tir, which functions as the plasma membrane receptor for EPEC adherence . Tir directly links extracellular EPEC through the epithelial membrane and firmly anchors it to the host cell actin cytoskeleton, thereby initiating pedestal formation . In addition to stimulating actin nucleation and polymerization in the host cell, EPEC activates several other signaling pathways that lead to tight junction disruption, inhibition of phagocytosis, altered ion secretion, and immune responses . This review summarizes recent developments in our understanding of EPEC pathogenesis and discusses similarities and differences between EPEC pedestals, focal contacts, and Listeria monocytogenes actin tails.

J Bacteriol, 2000 Nov, 182(21), 6161 - 8
A sheep in wolf's clothing: Listeria innocua strains with teichoic acid-associated surface antigens and genes characteristic of Listeria monocytogenes serogroup 4; Lan Z et al.; Listeria monocytogenes serotype 4b has been implicated in numerous food-borne epidemics and in a substantial fraction of sporadic listeriosis . A unique lineage of the nonpathogenic species Listeria innocua was found to express teichoic acid-associated surface antigens that were otherwise expressed only by L . monocytogenes of serotype 4b and the rare serotypes 4d and 4e . These L . innocua strains were also found to harbor sequences homologous to the gene gtcA, which has been shown to be essential for teichoic acid glycosylation in L . monocytogenes serotype 4b . Transposon mutagenesis and genetic studies revealed that the gtcA gene identified in this lineage of L . innocua was functional in serotype 4b-like glycosylation of the teichoic acids of these organisms . The genomic organization of the gtcA region was conserved between this lineage of L . innocua and L . monocytogenes serotype 4b . Our data are in agreement with the hypothesis that, in this lineage of L . innocua, gtcA was acquired by lateral transfer from L . monocytogenes serogroup 4 . The high degree of nucleotide sequence conservation in the gtcA sequences suggests that such transfer was relatively recent . Transfer events of this type may alter the surface antigenic properties of L . innocua and may eventually lead to evolution of novel pathogenic lineages through additional acquisition of genes from virulent listeriae.

J Biol Chem, 2001 Feb 2, 276(5), 3468 - 75 Epub 2000 Oct 11.
Activation of the Arp2/3 complex by the Listeria acta protein . Acta binds two actin monomers and three subunits of the Arp2/3 complex; Zalevsky J et al.; ActA is a bacterially encoded protein that enables Listeria monocytogenes to hijack the host cell actin cytoskeleton . It promotes Arp2/3-dependent actin nucleation, but its interactions with cellular components of the nucleation machinery are not well understood . Here we show that two domains of ActA (residues 85-104 and 121-138) with sequence similarity to WASP homology 2 domains bind two actin monomers with submicromolar affinity . ActA binds Arp2/3 with a K(d) of 0.6 microm and competes for binding with the WASP family proteins N-WASP and Scar1 . By chemical cross-linking, ActA, N-WASP, and Scar1 contact the same three subunits of the Arp2/3 complex, p40, Arp2, and Arp3 . Interestingly, profilin competes with ActA for binding of Arp2/3, but actophorin (cofilin) does not . The minimal Arp2/3-binding site of ActA (residues 144-170) is C-terminal to both actin-binding sites and shares sequence homology with Arp2/3-binding regions of WASP family proteins . The maximal activity at saturating concentrations of ActA is identical to the most active domains of the WASP family proteins . We propose that ActA and endogenous WASP family proteins promote Arp2/3-dependent nucleation by similar mechanisms and require simultaneous binding of Arp2 and Arp3.

Int J Food Microbiol, 2000 Oct 1, 61(1), 63 - 72
Synergistic inhibition of Listeria monocytogenes on cold-smoked rainbow trout by nisin and sodium lactate; Nykanen A et al.; The inhibition of Listeria monocytogenes and mesophilic aerobic bacteria in cold-smoked rainbow trout by nisin, sodium lactate or their combination was studied . Nisin (4000-6000 IU/ml), sodium lactate (60%) or their combination (1:1) were injected into rainbow trout at an industrial scale before the smoking process, or injected into the finished smoked product . Both types of fish samples were smoked, sliced and vacuum-packed according to normal practice in the plant . Packages were opened and L . monocytogenes was inoculated (10(3)-10(4) log colony forming units (cfu)/g) onto the fish samples, which were then vacuum packed again . Samples were stored at 8 degrees C for 17 days or at 3 degrees C for 29 days . Listeria and mesophilic aerobic bacteria counts were measured once a week . The effects of treatments on sensory characteristics and storage stability were also analyzed . Both nisin and lactate inhibited the growth of L . monocytogenes in smoked fish, but the combination of the two compounds was even more effective . The combination of nisin and sodium lactate injected into smoked fish decreased the count of L . monocytogenes from 3.26 to 1.8 log cfu/g over 16 days of storage at 8 degrees C . The level of L . monocytogenes remained almost constant (4.66-4.92 log cfu/g) for 29 days at 3 degrees C in the samples injected before smoking and which contained both nisin and sodium lactate . The treatments did not affect the sensory characteristics of cold-smoked rainbow trout . Based on a triangle test, the sensory quality of all test samples remained unchanged for 23 days of storage at 3 degrees C, whereas the control fish prepared without additives or additional salt remained unchanged only for 16 days.

Int J Food Microbiol, 2000 Oct 1, 61(1), 41 - 9
Maillard reaction causes suppression of virulence gene expression in Listeria monocytogenes; Sheikh-Zeinoddin M et al.; Many environmental signals affect the expression of virulence genes of the food borne pathogen Listeria monocytogenes . In addition media composition has been shown to suppress levels of haemolytic activity . Using a Pr(plcA)::luxAB reporter gene fusion it was observed that the heat processing of media also reduces the level of virulence gene expression in L . monocytogenes without affecting its growth . Physicochemical factors that are considered to enhance the Maillard reaction were also found to increase the levels of suppression . The results indicate that heat treatment of a multicomponent matrix gives rise to specific inhibitors of the Listeria virulence gene operon.

Int J Food Microbiol, 2000 Oct 1, 61(1), 27 - 39
Application of polynomial models to predict growth of mixed cultures of Pseudomonas spp . and Listeria in meat; Lebert I et al.; Three models for one rapid and one slow growing strain of Pseudomonas fragi and one slow growing strain of P . fluorescens were developed in a meat broth; they were designed to take account of variations in growth and to provide a growth response interval . These models, and another for Listeria monocytogenes (Lm14 model), were used to predict the growth of spoilage Pseudomonas spp . and pathogenic Listeria in meat products . The Pseudomonas and Listeria models provided satisfactory predictions concerning inoculated strains grown in decontaminated beef meat . It was also possible to use the Pseudomonas models to predict the growth of the natural flora (mainly Pseudomonas spp.) of refrigerated meat stored under aerobic conditions . In experiments with mixed populations, three situations were observed: (1) in decontaminated meat, L . monocytogenes inoculated alone grew well at 6 degrees C, and this result was correctly predicted by the model; (2) in decontaminated meat inoculated with Listeria and Pseudomonas strains, L . innocua grew well and was not affected by the presence of Pseudomonas, and the growth of both organisms was correctly predicted by the models; (3) in naturally contaminated meat inoculated with Listeria, the strain did not grow until Pseudomonas had reached the stationary phase . The models satisfactorily predicted the growth of Pseudomonas spp . but not that of Listeria . In conclusion, the Lm14 model cannot be used for refrigerated meat stored aerobically as the results suggest a 'fail-safe' level which may be too high: meat had already reached a spoilage state even though no increase in the level of Listeria was observed . The Pseudomonas models accurately predicted the growth of naturally occurring Pseudomonas spp.

Ann Neurol, 2000 Oct, 48(4), 661 - 5
Neurolisteriosis presenting as recurrent transient ischemic attacks; Staudinger R et al.; An elderly man experienced recurrent transient episodes of right arm weakness and expressive aphasia . He was initially treated with aspirin and then with coumadin . Thirteen days after initial presentation, he became febrile and had signs of meningitis . The illness progressed relentlessly to death 9 weeks after admission to the hospital . Necropsy showed prominent meningitis with vasculitis extending into the left frontal lobe . Polymerase chain reaction identified the organism as Listeria monocytogenes.

J Virol, 2000 Nov, 74(21), 9987 - 93
Induction of human immunodeficiency virus (HIV)-specific CD8 T-cell responses by Listeria monocytogenes and a hyperattenuated Listeria strain engineered to express HIV antigens; Friedman RS et al.; Induction of cell-mediated immunity may be essential for an effective AIDS vaccine . Listeria monocytogenes is an attractive bacterial vector to elicit T-cell immunity to human immunodeficiency virus (HIV) because it specifically infects monocytes, key antigen-presenting cells, and because natural infection originates at the mucosa . Immunization with recombinant L . monocytogenes has been shown to protect mice from lymphocytic choriomeningitis virus, influenza virus, and tumor inoculation . L . monocytogenes expressing HIV gag elicits sustained high levels of Gag-specific cytotoxic T lymphocytes (CTLs) in mice . We have examined the ability of Listeria to infect human monocytes and present HIV antigens to CD8 T lymphocytes of HIV-infected donors to induce a secondary T-cell immune response . Using this in vitro vaccination protocol, we show that L . monocytogenes expressing the HIV-1 gag gene efficiently provides a strong stimulus for Gag-specific CTLs in HIV-infected donor peripheral blood mononuclear cells . Listeria expressing Nef also elicits a secondary in vitro anti-Nef CTL response . Since L . monocytogenes is a pathogen, before it can be seriously considered as a human vaccine vector, safety concerns must be addressed . We therefore have produced a highly attenuated strain of L . monocytogenes that requires D-alanine for viability . The recombinant bacteria are attenuated at least 10(5)-fold . We show that when these hyperattenuated bacteria are engineered to express HIV-1 Gag, they are at least as efficient at stimulating Gag-specific human CTLs in vitro as wild-type recombinants . These results suggest that attenuated Listeria is an attractive candidate vaccine vector to induce T-cell immunity to HIV in humans.

J Med Microbiol, 2000 Oct, 49(10), 887 - 96
Cloning, sequencing and characterisation of a Listeria monocytogenes gene encoding a fibronectin-binding protein; Gilot P et al.; Listeria monocytogenes is a gram-positive, non-sporulating food-borne pathogen of man and animals that is able to invade many eukaryotic cells . L . monocytogenes possesses several proteins that bind fibronectin . In this study, an L . monocytogenes DNA library in pUC19 was screened with fibronectin and a gene encoding a 24.6-kDa fibronectin-binding protein (Fbp) was isolated and sequenced . Transcripts of the fbp gene were found in wild-type, in deltaprfA, and PrfA-S183A strains, despite the presence of a 'PrfA-like' box around its ribosome-binding site . The fbp gene was found to be present in all tested isolates of the species L . monocytogenes and a homologous DNA fragment was amplified in L . welshimeri . No homologies between the fbp gene and its translation product with any other DNA or proteins deposited in databanks were found . Restriction endonuclease-PCR (RE-PCR) showed that the fbp gene displays a degree of allelic variation among isolates of L . monocytogenes, whereas the corresponding amplified fragment of L . welshimeri seems to be monomorphic among isolates of this species . RE-PCR with Hha I, Dde I or Taq I produced DNA banding profiles specific for each of these two species, allowing their identification.

Arq Neuropsiquiatr, 2000 Sep, 58(3B), 836 - 42
Polymerase chain reaction for the laboratory diagnosis of aseptic meningitis and encephalitis; Chesky M et al.; A protocol for testing cerebrospinal fluid specimens using a range of PCR assays for the diagnosis of central nervous system infection was developed and used to test prospectively 383 specimens . PCR assays were used for the detection of adenovirus, Borrelia burgdorferi, enteroviruses, Epstein Barr virus, cytomegalovirus, herpes simplex virus, human herpes virus type 6, JC virus, Leptospira interrogans, Listeria monocytogenes, lymphocytic choriomeningitis virus, measles virus, mumps virus, Mycobacterium sp . , Mycoplasma pneumoniae, Toxoplasma gondii and varicella zoster virus . Of the 383 specimens tested in this study, 46 (12.0%) were found to be positive . The microorganisms detected were CMV, enterovirus, Epstein Barr virus, herpes simplex virus, human herpes virus type 6, JC virus, L . monocytogenes, Mycobacterium genus, Toxoplasma gondii and varicella zoster virus . The introduction of the PCR protocol described has improved the diagnosis of a range of central nervous system infections in our laboratory . We believe however that further evaluation of these assays in immunocompromised patients is necessary to better determine the predictive value of positive PCR results in these patient groups.

Clin Infect Dis, 2000 Sep, 31(3), 770 - 5 Epub 2000 Sep 26.
Foodborne listeriosis; Schlech WF 3rd; Listeria monocytogenes emerged as an important foodborne pathogen in the latter part of the 20th century . Clinical syndromes caused by this microorganism include sepsis in the immunocompromised patient, meningoencephalitis in infants and adults, and febrile gastroenteritis . Focal infections at other sites are less frequent . Listeria species are commonly found in raw and unprocessed food products . Major outbreaks of listeriosis, with high morbidity and mortality, have been caused by a variety of foods, including soft cheeses, delicatessen meats, and vegetable products . Improved detection methods, dietary recommendations, and, in some cases, preemptive antibiotic treatment or prophylaxis have reduced the incidence of sporadic listeriosis infections in the United States . Microbial virulence factors distinguishing environmental strains of L . monocytogenes from invasive strains causing foodborne illness and host factors promoting human infection remain incompletely understood.

Int J Food Microbiol, 2000 Sep 25, 60(2-3), 261 - 8
Analysis of the role of betL in contributing to the growth and survival of Listeria monocytogenes LO28; Sleator RD et al.; Survival of the food-borne pathogen Listeria monocytogenes in environments of elevated osmolarity and reduced temperature is attributed, at least in part, to the accumulation of the trimethylammonium compound glycine betaine . Previously we identified betL, a gene encoding the secondary glycine betaine transporter BetL, which we linked to the salt tolerance of Listeria . In this report, we demonstrate that betL, preceded by a consensus sigmaB-dependent promoter, is regulated by osmotic up-shock, at least in part at the level of transcription . Using allelic exchange mutagenesis we constructed an in-frame deletion in betL, and used this mutant to determine the role of BetL in contributing to the growth and survival of L . monocytogenes, both in a high risk food (Camembert cheese) and animal model . Our results indicate that while BetL plays an important role in glycine betaine mediated osmoprotection, mutating the gene does not significantly effect either the cryotolerance or virulence of the organism.

Int J Food Microbiol, 2000 Sep 25, 60(2-3), 137 - 46
Analysis of the role of the Listeria monocytogenes F0F1 -AtPase operon in the acid tolerance response; Cotter PD et al.; As little is known about the genes involved in the induction of an acid tolerance response in Listeria monocytogenes, the role of the F0F1-ATPase was analyzed as a consequence of its role in the acid tolerance of a number of other bacteria and its conserved nature . It was found that acid adapted cells treated with N,N'-dicyclohexylcarbodiimide (DCCD) exhibited greatly enhanced sensitivity to low pH stress . Degenerate primers were designed to amplify and sequence a portion of the atpD gene . Subsequently, a PCR product from atpA to atpD was identified . While we were unable to create a deletion in the atpA gene, the plasmid pORI19 was inserted in a region between atpA and atpG to reduce, rather than eliminate, expression of the downstream genes . As expected this mutant displayed enhanced resistance to neomycin and exhibited slower growth than the wild type strain . This mutant could still induce an acid tolerance response and remained susceptible to DCCD treatment, but its relative acid sensitivity was difficult to assess as a consequence of its slow growth.

J Clin Microbiol, 2000 Oct, 38(10), 3856 - 9
Absence of serotype-specific surface antigen and altered teichoic acid glycosylation among epidemic-associated strains of Listeria monocytogenes; Clark EE et al.; Outbreaks of food-borne listeriosis have often involved strains of serotype 4b . Examination of multiple isolates from three different outbreaks revealed that ca . 11 to 29% of each epidemic population consisted of strains which were negative with the serotype-specific monoclonal antibody c74.22, lacked galactose from the teichoic acid of the cell wall, and were resistant to the serotype 4b-specific phage 2671.

Inhal Toxicol, 2000 Nov, 12(11), 1017 - 36
Subchronic silica exposure enhances respiratory defense mechanisms and the pulmonary clearance of Listeria monocytogenes in rats; Antonini JM et al.; Both Listeria monocytogenes infection and silica exposure have been shown to significantly alter immune responses . In this study, we evaluated the effect of preexposure to silica on lung defense mechanisms using a rat pulmonary L . monocytogenes infection model . Male Sprague-Dawley rats were instilled intratracheally with saline (vehicle control) or silica using either an acute treatment regimen (5 mg/kg; 3 days) or a subchronic treatment protocol (80 mg/kg; 35 days) . At 3 or 35 days after silica instillation, the rats were inoculated intratracheally with either approximately 5000 or 500,000 L . monocytogenes . At 3, 5, and 7 days postinfection, the left lung was removed, homogenized, and cultured on brain heart infusion agar at 37 degrees C . The numbers of viable L . monocytogenes were counted after an overnight incubation . Bronchoalveolar lavage (BAL) was performed on the right lungs, and BAL cell differentials, acellular lactate dehydrogenase (LDH) activity and albumin content were determined . Alveolar macrophage (AM) chemiluminescence (CL) and phagocytosis were assessed as a measure of macrophage function . Lung-associated lymph nodes were removed, and lymphocytes were recovered and differentiated . Preexposure to silica significantly increased the pulmonary clearance of L . monocytogenes as compared to saline controls . Exposure to silica caused significant increases in BAL neutrophils, LDH and albumin, and lymph-nodal T cells and natural killer (NK) cells in infected and noninfected rats . CL and phagocytosis were also elevated in silica-treated rats . In summary, the results demonstrated that exposure of rats to silica enhanced pulmonary immune responses, as evidenced by increases in neutrophils, NK cells, T lymphocytes, and macrophage activation . These elevations in pulmonary immune response are likely responsible for the increase in pulmonary clearance of L . monocytogenes observed with preexposure to silica.

Immunology, 2000 Sep, 101(1), 83 - 9
The contribution of both oxygen and nitrogen intermediates to the intracellular killing mechanisms of C1q-opsonized Listeria monocytogenes by the macrophage-like IC-21 cell line; Alvarez-Dominguez C et al.; Listeria monocytogenes is a facultative intracellular pathogen which is internalized by host mammalian cells upon binding to their surface . Further listerial growth occurs in the cytosol after escape from the phagosomal-endosomal compartment . We have previously reported that C1q is able to potentiate L . monocytogenes phagocytosis upon bacterial opsonization by ingestion through C1q-binding structures . In this report, we analysed the post-phagocytic events upon internalization of C1q-opsonized L . monocytogenes and found an induction of macrophage (Mphi)-like IC-21 cell bactericidal mechanisms displayed by the production of oxygen and nitrogen metabolites . Both types of molecules are effective in L . monocytogenes killing . Further analysis of the cellular responses promoted by interaction of C1q with its surface binding structures, leads us to consider C1q as a collaborative molecule involved in Mphi activation . Upon interaction with surface binding structures, C1q was able to trigger and/or amplify the production of reactive oxygen and nitrogen intermediates induced by stimuli such as interferon-gamma and L . monocytogenes phagocytosis.

Appl Environ Microbiol, 2000 Oct, 66(10), 4351 - 5
Cold shock and its effect on ribosomes and thermal tolerance in Listeria monocytogenes; Bayles DO et al.; Differential scanning calorimetry (DSC) and fatty acid analysis were used to determine how cold shocking reduces the thermal stability of Listeria monocytogenes . Additionally, antibiotics that can elicit production of cold or heat shock proteins were used to determine the effect of translation blockage on ribosome thermal stability . Fatty acid profiles showed no significant variations as a result of cold shock, indicating that changes in membrane fatty acids were not responsible for the cold shock-induced reduction in thermal tolerance . Following a 3-h cold shock from 37 to 0 degrees C, the maximum denaturation temperature of the 50S ribosomal subunit and 70S ribosomal particle peak was reduced from 73.4 +/- 0.1 degrees C (mean +/- standard deviation) to 72.1 +/- 0.5 degrees C (P < or = 0.05), indicating that cold shock induced instability in the associated ribosome structure . The maximum denaturation temperature of the 30S ribosomal subunit peak did not show a significant shift in temperature (from 67.5 +/- 0.4 degrees C to 66.8 +/- 0.5 degrees C) as a result of cold shock, suggesting that either 50S subunit or 70S particle sensitivity was responsible for the intact ribosome fragility . Antibiotics that elicited changes in maximum denaturation temperature in ribosomal components also elicited reductions in thermotolerance . Together, these data suggest that ribosomal changes resulting from cold shock may be responsible for the decrease in D value observed when L . monocytogenes is cold shocked.

Appl Environ Microbiol, 2000 Oct, 66(10), 4345 - 50
Cold shock induction of thermal sensitivity in Listeria monocytogenes; Miller AJ et al.; Cold shock at 0 to 15 degrees C for 1 to 3 h increased the thermal sensitivity of Listeria monocytogenes . In a model broth system, thermal death time at 60 degrees C was reduced by up to 45% after L . monocytogenes Scott A was cold shocked for 3 h . The duration of the cold shock affected thermal tolerance more than did the magnitude of the temperature downshift . The Z values were 8.8 degrees C for controls and 7.7 degrees C for cold-shocked cells . The D values of cold-shocked cells did not return to control levels after incubation for 3 h at 28 degrees C followed by heating at 60 degrees C . Nine L . monocytogenes strains that were cold shocked for 3 h exhibited D(60) values that were reduced by 13 to 37% . The D-value reduction was greatest in cold-shocked stationary-phase cells compared to cells from cultures in either the lag or exponential phases of growth . In addition, cold-shocked cells were more likely to be inactivated by a given heat treatment than nonshocked cells, which were more likely to experience sublethal injury . The D values of chloramphenicol-treated control cells and chloramphenicol-treated cold-shocked cells were no different from those of untreated cold-shocked cells, suggesting that cold shock suppresses synthesis of proteins responsible for heat protection . In related experiments, the D values of L . monocytogenes Scott A were decreased 25% on frankfurter skins and 15% in ultra-high temperature milk if the inoculated products were first cold shocked . Induction of increased thermal sensitivity in L . monocytogenes by thermal flux shows potential to become a practical and efficacious preventative control method.

Appl Environ Microbiol, 2000 Oct, 66(10), 4266 - 71
Application of 5'-nuclease PCR for quantitative detection of Listeria monocytogenes in pure cultures, water, skim milk, and unpasteurized whole milk; Nogva HK et al.; PCR techniques have significantly improved the detection and identification of bacterial pathogens . Countless adaptations and applications have been described, including quantitative PCR and the latest innovation, real-time PCR . In real-time PCR, e.g., the 5'-nuclease chemistry renders the automated and direct detection and quantification of PCR products possible (P . M . Holland et al., Proc . Natl . Acad . Sci . USA 88:7276-7280, 1991) . We present an assay for the quantitative detection of Listeria monocytogenes based on the 5'-nuclease PCR using a 113-bp amplicon from the listeriolysin O gene (hlyA) as the target . The assay was positive for all isolates of L . monocytogenes tested (65 isolates including the type strain) and negative for all other Listeria strains (16 isolates from five species tested) and several other bacteria (18 species tested) . The application of 5'-nuclease PCR in diagnostics requires a quantitative sample preparation step . Several magnetic bead-based strategies were evaluated, since these systems are simple and relatively easy to automate . The combination of nonspecific binding of bacteria to paramagnetic beads, with subsequent DNA purification by use of the same beads, gave the most satisfactory result . The detection limit was approximately 6 to 60 CFU, quantification was linear over at least 7 log units, and the method could be completed within 3 h . In conclusion, a complete quantitative method for L . monocytogenes in water and in skimmed and raw milk was developed.

Appl Environ Microbiol, 2000 Oct, 66(10), 4173 - 9
Inactivation of Escherichia coli and Listeria innocua in milk by combined treatment with high hydrostatic pressure and the lactoperoxidase system; Garcia-Graells C et al.; We have studied inactivation of four strains each of Escherichia coli and Listeria innocua in milk by the combined use of high hydrostatic pressure and the lactoperoxidase-thiocyanate-hydrogen peroxide system as a potential mild food preservation method . The lactoperoxidase system alone exerted a bacteriostatic effect on both species for at least 24 h at room temperature, but none of the strains was inactivated . Upon high-pressure treatment in the presence of the lactoperoxidase system, different results were obtained for E . coli and L . innocua . For none of the E . coli strains did the lactoperoxidase system increase the inactivation compared to a treatment with high pressure alone . However, a strong synergistic interaction of both treatments was observed for L . innocua . Inactivation exceeding 7 decades was achieved for all strains with a mild treatment (400 MPa, 15 min, 20 degrees C), which in the absence of the lactoperoxidase system caused only 2 to 5 decades of inactivation depending on the strain . Milk as a substrate was found to have a considerable effect protecting E . coli and L . innocua against pressure inactivation and reducing the effectiveness of the lactoperoxidase system under pressure on L . innocua . Time course experiments showed that L . innocua counts continued to decrease in the first hours after pressure treatment in the presence of the lactoperoxidase system . E . coli counts remained constant for at least 24 h, except after treatment at the highest pressure level (600 MPa, 15 min, 20 degrees C), in which case, in the presence of the lactoperoxidase system, a transient decrease was observed, indicating sublethal injury rather than true inactivation.

Schweiz Arch Tierheilkd, 2000 Jul, 142(7), 387 - 90
{Isolation of Listeria spp . and Aspergillus fumigatus--two case reports from mastitis diagnosis}; Stephan R et al.; Two rare cases of a bovine listeria mastitis and a mould mastitis are being described and discussed . The L . monocytogenes strains isolated from milk as well as silage samples were further genotyped by means of Pulsed-Field Gel Electrophoresis (PFGE) and macrorestriction analysis (ApaI) . Three strains from the silage and four strains from quarter milking showed an identical PFGE-pattern.

Mem Inst Oswaldo Cruz, 2000 Sep-Oct, 95(5), 615 - 20
Species and serovars of the genus Listeria isolated from different sources in Brazil from 1971 to 1997; Hofer E et al.; Using phenotype techniques, characterization was made to species and serovar of 3,112 strains of Listeria, isolated from different sources of infection such as human (247-7.9%) and animals (239-7.6%), as well as from various routes of infection, including food (2, 330-74.8%) and environmental constituents (296-9.5%), all coming from different regions of the country and collected during the period 1971-1997 . The following species were recovered in the cultures analysed: L . monocytogenes (774-24.8%), L . innocua (2, 269-72.9%), L . seeligeri (37-1.1%), L . welshimeri (22-0.7%), L . grayi (9-0.2%), and L . ivanovii (1-0.03%) . L . monocytogenes was represented by ten serovars, the most prevalent being 4b (352-11.3%), (1/2)a (162-5.2%), and (1/2)b (148-4.7%) . The predominant serovar in L . innocua was 6a (2,093-67.2%) . Considerations about laboratory methods for diagnosis and epidemiological aspects are presented on the basis of the results obtained.

J AOAC Int, 2000 Jul-Aug, 83(4), 903 - 18
VIDAS enzyme-linked immunoflourescent assay for detection of Listeria in foods: collaborative study; Gangar V et al.; The VIDAS LIS method and the traditional culture methods for detection of Listeria species in food were evaluated in a multilaboratory comparative study . The 6 foods tested were either naturally contaminated or inoculated with 3 different concentrations of Listeria . Results for each food and each contamination level with the VIDAS LIS method were as good as or better than those obtained with the traditional culture method . Of 1558 samples tested, 935 were positive: 839 by the VIDAS method and 809 by standard culture methods . Overall false negative rates were 10.3 and 13.5% for the VIDAS LIS and culture methods, respectively . The false positive rate for the VIDAS LIS assay was 1.4% based on 9 VIDAS LIS positive assays that did not confirm positive by isolation of Listeria . The agreement between the VIDAS LIS and culture methods for all samples tested was 86%.

Infect Immun, 2000 Oct, 68(10), 5735 - 41
Activation of host phospholipases C and D in macrophages after infection with Listeria monocytogenes; Goldfine H et al.; Infection of the J774 murine macrophage-derived cell line with Listeria monocytogenes results in several elevations of intracellular calcium during the first 15 min of infection . These appear to result from the actions of secreted bacterial proteins, including phosphatidylinositol-specific phospholipase C (PI-PLC), a broad-range phospholipase C, and listeriolysin O (LLO) (S . J . Wadsworth and H . Goldfine, Infect . Immun . 67:1770-1778, 1999) . We have measured hydrolysis of host PI and the activation of host polyphosphoinositide-specific PLC and host phospholipase D (PLD) during infection with wild-type and mutant L . monocytogenes . Elevated hydrolysis of host PI occurred within the first 10 min of infection and was dependent on both bacterial PI-PLC and LLO, both of which were required for the earliest elevations of intracellular calcium in the host cell . A more rapid hydrolysis of host PI was observed at 30 min after infection, at the time when wild-type bacteria have been internalized . Activation of host PLC, also occurred in the first 10 min of infection but was not dependent on the presence of bacterial PI-PLC . Similar observations were made in murine bone marrow-derived macrophages . In J774 cells, activation of host PLD was observed after 20 min of infection and was dependent on bacterial LLO . Mutants in the bacterial phospholipases produced levels of PLD activation similar to those produced by the wild type . Phorbol myristate acetate (PMA) also activated host PLD, while long-term treatment with PMA resulted in loss of the ability of L . monocytogenes to activate host PLD, suggesting an involvement of protein kinase C (PKC) in the activation of PLD . Rottlerin, an inhibitor of PKC delta in J774 cells, also inhibited the activation of PLD, but hispidin, an inhibitor of PKC betaI and betaII, did not . Pretreatment of J774 cells with the PLD inhibitor, 2, 3-diphosphoglycerate partially inhibited escape of the bacteria from the primary phagocytic vacuole.

EMBO J, 2000 Sep 15, 19(18), 4903 - 14
Dual epitope recognition by the VASP EVH1 domain modulates polyproline ligand specificity and binding affinity; Ball LJ et al.; The Ena-VASP family of proteins act as molecular adaptors linking the cytoskeletal system to signal transduction pathways . Their N-terminal EVH1 domains use groups of exposed aromatic residues to specifically recognize 'FPPPP' motifs found in the mammalian zyxin and vinculin proteins, and ActA protein of the intracellular bacterium Listeria monocytogenes . Here, evidence is provided that the affinities of these EVH1-peptide interactions are strongly dependent on the recognition of residues flanking the core FPPPP motifs . Determination of the VASP EVH1 domain solution structure, together with peptide library screening, measurement of individual K(d)s by fluorescence titration, and NMR chemical shift mapping, revealed a second affinity-determining epitope present in all four ActA EVH1-binding motifs . The epitope was shown to interact with a complementary hydrophobic site on the EVH1 surface and to increase strongly the affinity of ActA for EVH1 domains . We propose that this epitope, which is absent in the sequences of the native EVH1-interaction partners zyxin and vinculin, may provide the pathogen with an advantage when competing for the recruitment of the host VASP and Mena proteins in the infected cell.

Bull Acad Natl Med, 2000, 184(2), 295 - 302; discussion 302-3
{Prevention of Listeria infections}; Pierre V et al.; Listeriosis is a rare but very serious foodborne disease . The non-contamination of food products is the best prevention of listeriosis . In spite of notable efforts to improve the microbiologic quality of food products through surveillance and control of food contaminations, the prevention has still to be based upon the information of consumers . This information can take different forms . When a food product is found to be contaminated with Listeria monocytogenes, if the withdrawal of this product does not occur as early as to prevent its commercialisation, a consumers alert is necessary to avoid any subsequent human case and to allow a rapid medical care of exposed persons in case of occurrence of symptoms of the disease . A specific information from health professionals to persons with risk factors of contracting listeriosis is a point of debate . Immunocompromised persons, for instance do not represent an easily defined group . On the other hand, pregnant women that are specially at risk of developing listeriosis, with potentially life threatening consequences for their foetus, represent a well identified population . They are medically monitored, and, because they feel concerned, most of them accept, during their pregnancy, to follow some simple rules that, sometimes, change their habits . At present, information is given to pregnant women by different ways: documents, leaflets, posters . The health authorities have decided to reinforce this information . They are also working on a special advisory meeting, specially targeted at foodborne diseases (including listeriosis), that could take place, for pregnant women, during the first months of their pregnancy.

Bull Acad Natl Med, 2000, 184(2), 287 - 93; discussion 294
{Prevention of Listeria infections}; Gaudot C; The prophylaxis of listeriosis needs the implementation of hygienic rules by the producers and controls by competent authorities and professionals . On this base, it is necessary to define a management method for emergencies and crises, depending on the complementarity of various intervening parties.

Bull Acad Natl Med, 2000, 184(2), 275 - 85; discussion 285-6
{Epidemiology of animal Listeria infections in France}; Vaissaire J; The animal listeriosis are sporadic diseases in the herds and flocks of herbivores generally in intensive farming with silage foods . The disease attacks other domestic or wild species . It's generally isolated cases or rare . The carrier animals are large in many species . 428 outbreaks have been detected in 1998-1999 of which 259 in cattle and 108 in sheep . The abortive forms are more important in the cattle and the meningoencephalitis in the sheep and goats . Cases are found in the poultry, birds, horse, dog, roe deer, rabbit, hare and wild boar.

Bull Acad Natl Med, 2000, 184(2), 267 - 74
{Epidemiology of human Listeria infections in France}; de Valk H et al.; Human listeriosis is a relatively rare but serious disease with case fatality rates between 20 and 30% . The majority of patients who have listeriosis present with meningitis or septicaemia . Listeriosis during pregnancy can lead to a congenital infection, neonatal sepsis and meningitis or foetal death . The main mode of transmission is through contaminated foods . The infection usually occurs sporadically but small outbreaks and even large epidemics have occurred in a large number of industrialised countries . During the last 10 years several Listeria monocytogenes control measures have been introduced and implemented at the retail level and in production for plants or foods potentially contaminated with Listeria monocytogenes . During this period the incidence of listeriosis decreased substantially and is at present estimated at 300-400 cases annually.

J Food Prot, 2000 Sep, 63(9), 1208 - 13
Incidence and seasonal variation of Listeria species in bulk tank goat's milk; Abou-Eleinin AA et al.; Four hundred and fifty raw goat's milk samples obtained from the bulk tanks of 39 goat farms were analyzed for Listeria spp . over a 1-year period . Modified versions of the U.S . Department of Agriculture Food Safety and Inspection Service (USDA-FSIS) and Food and Drug Administration (FDA) protocols were used for recovery of Listeria . Overall, 35 (7.8%) samples yielded Listeria spp . with Listeria monocytogenes identified in 17 of the 35 (3.8%) Listeria-positive samples . Listeria innocua was detected in 26 (5.8%) samples . Eight milk samples contained both L . monocytogenes and L . innocua . Milk samples from 18 of the 39 (46.2%) farms were positive for Listeria at least once during this 1-year study . The modified USDA-FSIS method, which used Listeria repair broth rather than University of Vermont (UVM) broth for primary enrichment followed by a 4-h nonselective incubation period, yielded more Listeria-positive samples (77.1%) than the FDA method (51.4%) . All L . monocytogenes isolates belonged to serotypes 1 (62.6%) or 4 (37.4%) . Moreover, five different Listeria ribotypes were identified from 34 selected L . monocytogenes isolates, 2 of which were deemed to be of clinical importance . Listeria isolation rates were markedly higher during winter (14.3%) and spring (10.4%) as compared to autumn (5.3%) and summer (0.9%) with these trends similar to those previously reported for cow's milk.

J Food Prot, 2000 Sep, 63(9), 1204 - 7
Persistent Listeria monocytogenes strains show enhanced adherence to food contact surface after short contact times; Lunden JM et al.; Adherence of 3 persistent and 14 nonpersistent Listeria monocytogenes strains to stainless steel surfaces after short and long contact times was investigated . L . monocytogenes strains were obtained from poultry plants and an ice cream plant throughout several years . Adherence tests were performed in tryptic soy broth at 25 degrees C for 1, 2, and 72 h . Test surfaces were rinsed after the contact time, and attached cells were stained with acridine orange and enumerated with an epifluorescence microscope . The persistent poultry plant strains showed adherence 2- to 11-fold higher than the nonpersistent strains following 1- and 2-h contact times . The adherence of the persistent ice cream plant strain after 1- and 2-h contact times was higher than most of the nonpersistent strains . Seven of 12 nonpersistent ice cream strains showed an adherence of less than half that of the persistent strain . After 72 h, the differences in adherence were not as marked, since half the nonpersistent strains had reached adherence levels comparable with the persistent strains . In fact, three nonpersistent strains showed even higher adherence than the persistent strains . Thus, results of this study reveal that persistent L . monocytogenes strains show enhanced adherence at short contact times, promoting their survival in food processing facilities and possibly having an effect on initiation of persistent plant contamination.

FEMS Microbiol Lett, 2000 Sep 1, 190(1), 29 - 34
The main cold shock protein of Listeria monocytogenes belongs to the family of ferritin-like proteins; Hebraud M et al.; The transfer of the food-borne pathogen Listeria monocytogenes from 30 to 5 degrees C was characterized by the sharp induction of a low molecular mass protein . This major cold shock protein has an isoelectric point at pH 5.1 and a molecular mass of about 18 kDa, as observed on two-dimensional gel electrophoresis (2-DE) pattern . Its N-terminal sequence, obtained from the 2-DE spot, shared a complete sequence identity with a Listeria innocua non-heme iron-binding ferritin . The purification of these ferritin-like proteins (Flp) revealed a native molecular mass of about 100-110 kDa which indicates a polypeptide composed of six 18 kDa-subunits . Northern analysis indicated the presence of a 0.8-kb monocistronic mRNA in exponential growing cells and an important increase inflp mRNA amount after a downshift but also an upshift in temperature.

Rev Latinoam Microbiol, 1999 Jul-Sep, 41(3), 133 - 8
{Enterocin-35, a bacteriocin with activity against Listeria monocytogenes . Possible use in the food industry}; Concha R et al.; The in vitro inhibitory activity of enterocin-35 produced by Enterococcus faecium CRL 35, was studied against Listeria monocytogenes, isolated from seafoods . Optimal growth conditions of the enterocin-35 producing strain, for higher bacteriocin production and improve the extraction and purification of these peptides, were applied . A crude extract of enterocin-35 was assayed in a frozen seafood artificially contaminated with Listeria monocytogenes isolate, simulating at laboratory scale an eventual application of this biopreservant in a routine production process at factory level . The feasibility of biopreservation of seafoods by means of bacteriocins is proposed and discussed.

Lett Appl Microbiol, 2000 Aug, 31(2), 100 - 4
A small outbreak of listeriosis potentially linked to the consumption of imitation crab meat; Farber JM et al.; A small outbreak of listeriosis involving two previously healthy adults occurred in Ontario . Food samples obtained from the refrigerator of the patients included imitation crab meat, canned black olives, macaroni and vegetable salad, spaghetti sauce with meatballs, mayonnaise and water . All of the samples except the water contained Listeria monocytogenes . The three most heavily contaminated samples were the imitation crab meat, the olives and the salad which contained 2.1 x 109, 1.1 x 107 and 1.3 x 106 cfu g-1, respectively . L . monocytogenes serotype 1/2b was isolated from the patients, as well as from the opened and unopened imitation crab meat . Molecular typing of the isolates by both randomly amplified polymorphic DNA (RAPD) and pulsed-field gel electrophoresis (PFGE) typing demonstrated the imitation crab meat and clinical strains to be indistinguishable . Challenge studies performed with a pool of L . monocytogenes strains showed that imitation crab meat, but not olives, supported growth of the organism . In this study we have shown for the first time the potential involvement of imitation crab meat in a small outbreak of listeriosis . In terms of disease prevention, temperature control is critical to prevent or reduce the growth of this foodborne pathogen . In addition, with refrigerated products having a long (> 30 d) shelf life, additional safety factors must be used to prevent the growth of foodborne pathogens such as L . monocytogenes.

J Appl Microbiol, 2000 Aug, 89(2), 296 - 301
Combined action of S-carvone and mild heat treatment on Listeria monocytogenes Scott A; Karatzas AK et al.; The combined action of the plant-derived volatile, S-carvone, and mild heat treatment on the food-borne pathogen, Listeria monocytogenes, was evaluated . The viability of exponential phase cultures grown at 8 degrees C could be reduced by 1.3 log units after exposure to S-carvone (5 mmol l-1) for 30 min at 45 degrees C, while individual treatment with S-carvone or exposure to 45 degrees C for 30 min did not result in a loss in viability . Other plant-derived volatiles, namely carvacrol, cinnamaldehyde, thymol and decanal, were also found to reduce the viability of L . monocytogenes in combination with the same mild heat treatment at concentrations of 1.75 mmol l-1, 2.5 mmol l-1, 1.5 mmol l-1 and 2 mmol l-1, respectively . These findings show that essential oil compounds can play an important role in minimally processed foods, and can be used in the concept of Hurdle Technology to reduce the intensity of heat treatment or other individual hurdles.

Eur J Biochem, 2000 Sep, 267(18), 5733 - 41
The unusual dodecameric ferritin from Listeria innocua dissociates below pH 2.0; Chiaraluce R et al.; The stability of the dodecameric Listeria innocua ferritin at low pH values has been investigated by spectroscopic methods and size-exclusion chromatography . The dodecamer is extremely stable in comparison to the classic ferritin tetracosamer and preserves its quaternary assembly at pH 2.0, despite an altered tertiary structure . Below pH 2.0, dissociation into dimers occurs and is paralleled by the complete loss of tertiary structure and a significant decrease in secondary structure elements . Dissociation of dimers into monomers occurs only at pH 1.0 . Addition of NaCl to the protein at pH 2.0 induces structural changes similar to those observed upon increasing the proton concentration, although dissociation proceeds only to the dimer stage . Addition of sulfate at pH values >/= 1.5 prevents the dissociation of the dodecamer . The role played by hydrophilic and hydrophobic interactions in determining the resistance to dissociation of L . innocua ferritin at low pH is discussed in the light of its three-dimensional structure.

Microb Pathog, 2000 Sep, 29(3), 137 - 44
Acid tolerance in Listeria monocytogenes influences invasiveness of enterocyte-like cells and macrophage-like cells; Conte MP et al.; Clinical and food Listeria monocytogenes isolates, pre-exposed to mild acidic conditions, were able to readily develop acid tolerance, irrespective of their origin . We attempted to investigate the influence of acid tolerance mechanisms, either constitutive or induced, on the invasive behaviour of this facultative food-borne pathogen . Entry efficiency and intracellular growth of acid-tolerant strains were evaluated in in vitro cell models capable to mimic in vivo target cells, such as enterocytes and macrophages . An acid-adapted L . monocytogenes wild-type strain and a constitutively acid-tolerant mutant were able to enter enterocyte-like (Caco-2) cells as well as to survive and proliferate intracellularly in lipopolysaccharide-treated macrophage-like (J774.A1) cells, at a significant increased extent by respect of the non acid-adapted wild-type strain . These findings add new information about the influence of the acid tolerance response on L . monocytogenes virulence, suggesting that in acid-adapted bacteria the early events of pathogenesis which allow the colonization and the spread of bacteria in the host may be highly promoted .

Proc Natl Acad Sci U S A, 2000 Aug 29, 97(18), 10008 - 13
A role for alpha-and beta-catenins in bacterial uptake; Lecuit M et al.; Interaction of internalin with E-cadherin promotes entry of Listeria monocytogenes into human epithelial cells . This process requires actin cytoskeleton rearrangements . Here we show, by using a series of stably transfected cell lines expressing E-cadherin variants, that the ectodomain of E-cadherin is sufficient for bacterial adherence and that the intracytoplasmic domain is required for entry . The critical cytoplasmic region was further mapped to the beta-catenin binding domain . Because beta-catenin is known to interact with alpha-catenin, which binds to actin, we generated a fusion molecule consisting of the ectodomain of E-cadherin and the actin binding site of alpha-catenin . Cells expressing this chimera were as permissive as E-cadherin-expressing cells . In agreement with these data, alpha- and beta-catenins as well as E-cadherin clustered and colocalized at the entry site, where F-actin then accumulated . Taken together, these results reveal that E-cadherin, via beta- and alpha-catenins, can trigger dynamic events of actin polymerization and membrane extensions culminating in bacterial uptake.

J Pediatr Hematol Oncol, 2000 Jul-Aug, 22(4), 340 - 3
Trimethoprim-sulfamethoxazole salvage for refractory listeriosis during maintenance chemotherapy for acute lymphoblastic leukemia; Wacker P et al.; A 5-year-old boy with acute lymphoblastic leukemia (ALL) and intolerance to oral trimethoprim-sulfamethoxazole (TMP/SMX) had Listeria monocytogenes bacteremia and meningitis develop during maintenance chemotherapy . Despite prompt administration of IV amoxicillin/gentamicin and microbiologic clearance of the bloodstream, the patient had no response to therapy after a course of 7 days . Intravenous TMP/SMX (10 mg/kg per day of TMP) was added to the antibiotic regimen after desensitization . Fever and meningeal signs rapidly resolved, and the patient was ultimately cured . Amoxicillin and gentamicin, although highly active and synergistic in vitro against L . monocytogenes, have limited intracellular penetration and activity . In contrast, TMP/SMX has bactericidal extracellular and intracellular activity against Listeria and excellent central nervous system penetration, and thus may be effective for the treatment of refractory listeriosis.

Harefuah, 1999 Nov 15, 137(10), 436 - 40, 512
{Listeria monocytogenes infections--ten years' experience}; Rainis T et al.; 7 cases of listeriosis were diagnosed here between 1988-1997 (6 in last 3 years), or 2.94/100,000 admissions . 2 elderly patients suffered from meningitis and 2 pregnant women presented with premature contractions, 1 of whom delivered a premature, infected baby . 2 other patients had fever and gastroenteritis . Listeria monocytogenes was isolated from blood in 4, CSF in 2 and the placenta in 1 . It was isolated from those with bacterial meningitis . All patients recovered . Both increased awareness for prevention and better diagnosis are essential to reduce morbidity from this unusual pathogen.

J Microbiol Methods, 2000 Aug, 41(3), 267 - 71
Application of a chromogenic medium and the PCR method for the rapid confirmation of L . monocytogenes in foodstuffs; Karpiskova R et al.; Detection of Listeria monocytogenes in foodstuffs by conventional cultivation methods carried out according to EN ISO guidelines is rather time-consuming . Therefore, two alternative methods were applied for rapid confirmation of L . monocytogenes in foodstuffs . Inoculum from liquid selective broth was plated on PALCAM and OXFORD agar and on chromogenic agar medium RAPID L . mono . Suspect colonies from PALCAM were confirmed according to EN ISO standards and by the multiplex PCR method . In total, 990 samples of foodstuffs were investigated and 63 strains of L . monocytogenes were isolated . The chromogenic medium RAPID L . mono provided results comparable to PCR, it is easier to handle and provides considerable financial savings.

Microbes Infect, 2000 Jun, 2(7), 803 - 11
Interactions between Listeria monocytogenes and host mammalian cells; Braun L et al.; Bacterial pathogens have developed a variety of strategies to induce their own internalization into mammalian cells which are normally nonphagocytic . The Gram-positive bacterium Listeria monocytogenes enters into many cultured cell types using two bacterial surface proteins, InlA (internalin) and InlB . In both cases, entry takes place after engagement of a receptor and induction of a series of signaling events.

J Cell Sci, 2000 Sep, 113 ( Pt 18), 3277 - 87
Mutations of arginine residues within the 146-KKRRK-150 motif of the ActA protein of Listeria monocytogenes abolish intracellular motility by interfering with the recruitment of the Arp2/3 complex; Pistor S et al.; The recruitment of actin to the surface of intracellular Listeria monocytogenes and subsequent tail formation is dependent on the expression of the bacterial surface protein ActA . Of the different functional domains of ActA identified thus far, the N-terminal region is absolutely required for actin filament recruitment and intracellular motility . Mutational analysis of this domain which abolished actin recruitment by intracellular Listeria monocytogenes identified two arginine residues within the 146-KKRRK-150 motif that are essential for its activity . More specifically, recruitment of the Arp2/3 complex to the bacterial surface, as assessed by immunofluorescence staining with antibodies raised against the p21-Arc protein, was not obtained in these mutants . Consistently, treatment of infected cells with latrunculin B, which abrogated actin filament formation, did not affect association of ActA with p21-Arc at the bacterial surface . Thus, the initial recruitment of the Arp2/3 complex to the bacterial surface is independent of, and precedes, actin polymerisation . Our data suggest that binding of the Arp2/3 complex is mediated by specific interactions dependent on arginine residues within the 146-KKRRK-150 motif present in ActA.

Allergy Asthma Proc, 2000 Jul-Aug, 21(4), 209 - 14
An updated model of cell-mediated immunity--listeriosis: clinical and research aspects; Wing EJ et al.; Listeria monocytogenes causes sepsis and meningitis in immunocompromised hosts and a devastating maternal/fetal infection in pregnant women . In recent years a more benign gastroenteritis in normal hosts has been described . Listeria has been increasingly identified as a food-borne pathogen, and large-scale contamination of processed foods with resulting outbreaks has occurred in recent years, possibly as a result of consolidation of the food industry . Experimental listeriosis in mice has proven to be an extraordinarily useful model for analyzing cell-mediated immune host defenses . Contrary to original concepts, we found that neutrophils, not macrophages, are the prime effectors during early infection . CD8+ T cells are then responsible for lysing infected hepatocytes through perforin-related (early primary and secondary infection) or Fas-L/Fas mechanism (late primary) . Of interest, non-classical MHC class Ib restricted recognition mechanisms exist early, whereas MHC class Ia mechanisms can be detected throughout infection.

J Infect Dis, 2000 Sep, 182(3), 978 - 82 Epub 2000 Aug 17.
Antibodies to the junctional adhesion molecule cause disruption of endothelial cells and do not prevent leukocyte influx into the meninges after viral or bacterial infection; Lechner F et al.; A hallmark of infectious meningitis is the invasion of leukocytes into the subarachnoid space . In experimental meningitis triggered by tumor necrosis factor-alpha and interleukin-1beta, the interaction of leukocytes with endothelial cells and the subsequent migration of the cells through the vessel wall can be inhibited by an antibody to the junctional adhesion molecule (JAM) . In contrast to the cytokine-induced meningitis model, anti-JAM antibodies failed to prevent leukocyte influx into the central nervous system after infection of mice with Listeria monocytogenes or lymphocytic choriomeningitis virus . Furthermore, in bacterial meningitis, anti-JAM IgG antibodies, but not Fab fragments, caused disruption of the endothelium . Likewise complement-dependent antibody-mediated cytotoxicity was observed in cultured brain endothelial cells treated with anti-JAM IgG but not with its Fab fragment.

J Infect Dis, 2000 Sep, 182(3), 902 - 8 Epub 2000 Aug 17.
Interleukin-1 signaling is essential for host defense during murine pulmonary tuberculosis; Juffermans NP et al.; Interleukin (IL)-1 signaling is required for the containment of infections with intracellular microorganisms, such as Listeria monocytogenes and Leishmania major . To determine the role of IL-1 in the host response to tuberculosis, we infected IL-1 type I receptor-deficient (IL-1R(-/-)) mice, in which IL-1 does not exert effects, with Mycobacterium tuberculosis . IL-1R(-/-) mice were more susceptible to pulmonary tuberculosis, as reflected by an increased mortality and an enhanced mycobacterial outgrowth in lungs and distant organs, which was associated with defective granuloma formation, containing fewer macrophages and fewer lymphocytes, whereas granulocytes were abundant . Lymphocytes were predominantly confined to perivascular areas, suggesting a defective migration of cells into inflamed tissue in the absence of IL-1 signaling . Impaired host defense in IL-1R(-/-) mice was further characterized by a decrease in the ability of splenocytes to produce interferon-gamma . Analysis of these data suggests that IL-1 plays an important role in the immune response to M . tuberculosis.

Infect Immun, 2000 Sep, 68(9), 5234 - 40
Induction of interleukin-4 (IL-4) by legionella pneumophila infection in BALB/c mice and regulation of tumor necrosis factor alpha, IL-6, and IL-1beta; Newton C et al.; Infection of BALB/c mice with a sublethal concentration of Legionella pneumophila causes an acute disease that is resolved by innate immune responses . The infection also initiates the development of adaptive Th1 responses that protect the mice from challenge infections . To study the early responses, cytokines induced during the first 24 h after infection were examined . In the serum, interleukin-12 (IL-12) was detectable by 3 h and peaked at 10 h, while gamma interferon was discernible by 5 h and peaked at 8 h . Similar patterns were observed in ex vivo cultures of splenocytes . A transient IL-4 response was also detected by 3 h postinfection in ex vivo cultures . BALB/c IL-4-deficient mice were more susceptible to L . pneumophila infection than were wild-type mice . The infection induced higher serum levels of acute-phase cytokines (tumor necrosis factor alpha {TNF-alpha}, IL-1beta, and IL-6), and reducing TNF-alpha levels with antibodies protected the mice from death . Moreover, the addition of IL-4 to L . pneumophila-infected macrophage cultures suppressed the production of these cytokines . Thus, the lack of IL-4 in the deficient mice resulted in unchecked TNF-alpha production, which appeared to cause the mortality . Monocyte chemoattractant protein-1 (MCP-1), a chemokine that is induced by IL-4 during Listeria monocytogenes infection, was detected at between 2 and 30 h after infection . However, MCP-1 did not appear to be induced by IL-4 or to be required for the TNF-alpha regulation by IL-4 . The data suggest that the early increase in IL-4 serves to regulate the mobilization of acute phase cytokines and thus controls the potential harmful effects of these cytokines.

Int J Food Microbiol, 2000 Jul 25, 59(1-2), 73 - 7
Prevalence and contamination levels of Listeria monocytogenes in retail foods in Japan; Inoue S et al.; Retail foods in Japan were surveyed for the presence and contamination levels of L . monocytogenes . It was isolated from 12.2, 20.6, 37.0 and 25.0% of 41 minced beef, 34 minced pork, 46 minced chicken and 16 minced pork-beef mixture samples, respectively . MPN values were higher than 100/g in five (10.9%) minced chicken samples, but lower than 100/g in all minced beef, pork and pork-beef mixture samples . The organism was also isolated from 5.4% of the 92 smoked salmon samples at MPN values lower than 10/g, and from 3.3% of 213 ready-to-eat raw seafood samples at MPN values from lower than 0.3 to higher than 100/g . None of the 285 vegetable samples were contaminated with L . monocytogenes . These findings indicate that ready-to-eat raw seafoods are relatively high risk among the foods surveyed in this study.

Immunopharmacol Immunotoxicol, 2000 Aug, 22(3), 501 - 18
Cytokine profile and natural killer cell activity in Listeria monocytogenes infected mice treated orally with Petiveria alliacea extract; Queiroz ML et al.; In this work, we investigated the effects of Petiveria alliacea extract on the production of Th1-type and Th2-type cytokines and on NK cells activity in normal and Listeria monocytogenes infected mice . Our results demonstrated that in normal/non-infected mice P . alliacea administration led to increased levels of Interleukin-2 (IL-2) . The infection alone enhanced INF-gamma levels and NK cell activity at 48 and 72 hours of infection . The treatment with five consecutive doses of 1000 mg/kg/day of P . alliacea extract, given previously to infection, led to further increases in IL-2 levels, in relation to normal/non-infected/P . alliacea treated controls, and in INF-gamma levels at 72 h of infection, compared to infected mice . On the other hand, the production of IL-4 and IL-10 were not altered either by the infection or by the treatment with P . alliacea extract . NK cells activity increased at 48 h and 72 h following the inoculation of the bacteria . When mice were treated with P . alliacea previously to infection, NK activity was higher than that observed at 48 h, 72 h and 120 h of infection in the infected animal . Based on these findings we suggest that P . alliacea up-regulates anti-bacterial immune response by enhancing both Th1 function and the activity of NK cells.

J Appl Microbiol, 2000 Jul, 89(1), 56 - 62
Efficient method for the detection of microbially-produced antibacterial substances from food systems; Morgan SM et al.; A novel method for the isolation of microbially-derived inhibitory substances from food sources was developed . The method involves an enrichment step coupled to a killing assay which is initially carried out in multiwell plates . The technique has advantages in that large numbers of samples can be tested in parallel . The assay can be completed in less than 60 h and is more sensitive than direct plating due to the enrichment step . This novel screening approach was compared with the standard direct plating approach in an effort to identify the antimicrobial potential of a number of Kefir grains . Kefir grains were incubated in 10% reconstituted skim milk for 20 h at 32 degrees C to enable production of any potential biopreservatives . Following overnight incubation, fermentates were aliquoted into multi-well plates and a known number of indicator cells was added to each well . The fermentates were incubated for a further 20 h and counts were carried out to determine whether a reduction in indicator cell numbers had occurred . A reduction in cell-forming units indicated the presence of an inhibitory substance and these inhibitory fermentates were selected for further investigation . Using the protocol outlined, Kefir fermentates capable of inhibiting Listeria innocua DPC1770 and Escherichia coli O157:H45 were identified.

J Food Prot, 2000 Aug, 63(8), 1064 - 70
Feasibility of a defined microflora challenge method for evaluating the efficacy of foodborne Listeria monocytogenes selective enrichments; Hitchins AD et al.; Comparison of isolation methods for microbial pathogens is complicated by the variable interference caused by the competitive microflora present in test samples such as foods . In principle, using measured amounts of a standard competitor in a defined surrogate food matrix might control the effect of variable interference . This possibility was investigated using Listeria monocytogenes and enrichment broths belonging to the acriflavine-nalidixate selective agent class . Triplicate test sample sets were prepared . Each set consisted of suspensions of variable levels of the standard competitor, Enterococcus faecium strain 111 (approximately 10 to 10(9) CFU/25 g), mixed with a low constant level (10 to 100 CFU/25 g) of L . monocytogenes . These test samples were enriched at 30 degrees C for 48 h in different selective media and streaked onto selective isolation agars . The input CFU ratio (E . faecium/L . monocytogenes) that permitted a 50% end point L . monocytogenes recovery was 2.2 x 10(6) or higher for the Food and Drug Administration one-step enrichments and 0.8 x 10(6) for the International Standards Organization (ISO) two-step enrichment . These and other results show that this evaluation method is feasible with this class of enrichments . Interestingly, L . monocytogenes could be detected in enrichment cultures at high-input E . faecium/L . monocytogenes ratios even when the enriched samples were plated onto nonselective media . The pinpoint colonies of L . monocytogenes embedded in a confluent lawn of E . faecium 111 were detectable by their contrasting coloration in Henry obliquely transmitted illumination.

J Food Prot, 2000 Aug, 63(8), 1058 - 63
Comparison of different reducing agents for enhanced detection of heat-injured Listeria monocytogenes; Suh JH et al.; The effect of different reducing agents (L-cysteine, Oxyrase, and Enterococcus faecium) and their combinations on the detection of heat-injured (62.8 degrees C, 7.5 min or 10 min) Listeria monocytogenes was examined . The incorporation of L-Cysteine (0.5 g/liter) yielded higher percentage detection than any of the other reducing agents (P < 0.05) . The combination of Oxyrase (10 U/ml) and E . faecium (10(3) CFU/ml) synergistically enhanced the detection of L . monocytogenes heat-injured for 10 min at 62.8 degrees C (P < 0.05) . Simultaneous addition of L-cysteine (0.5 g/liter) and Oxyrase (10 U/ml) significantly lowered the recovery of heat-injured L . monocytogenes (P < 0.05) . Higher activities of Oxyrase (50 U/ml) inhibited the detection of heat-injured L . monocytogenes (P < 0.05) . The rates of depletion of relative percentage O2 were in the order: L-cysteine (0.5 g/liter; 6.63%/ min) > Oxyrase (10 U/ml; 5.00%/min) > E . faecium (10(8) CFU/ml; 1.66%/min) > E . faecium (10(3) CFU/ml; 0.20%/min) . The final levels of redox potential (Eh) achieved were -110.5 mV, -100 mV, -83.5 mV, and -25 mV for E . faecium (10(8) CFU/ml), L-cysteine, Oxyrase, and E . faecium (10(3) CFU/ml), respectively.

J Infect Dis, 2000 Sep, 182 Suppl 1, S54 - 61
Consumption of eicosapentaenoic acid and docosahexaenoic acid impair murine interleukin-12 and interferon-gamma production in vivo; Fritsche KL et al.; In mice, individual dietary omega-3 polyunsaturated fatty acids n-3 (PUFA) were found to be sufficient to effect the changes in circulating interleukin (IL)-12 and interferon (IFN)-gamma levels that were previously seen in fish oil-fed mice . Weanling female C3H mice were fed one of five experimental diets . All five diets met all known nutritional requirements for mice and differed only in the fat source . After 4 weeks, mice were challenged with live Listeria monocytogenes or sterile PBS . Twenty-four hours after infection, n-3 PUFA-fed mice had significantly lower circulating IL-12 p70 and IFN-gamma than mice fed the control diet (P<.01) . In addition, splenic cytokine mRNA for IL-12 p40, tumor necrosis factor-alpha, and IL-1beta were lower in infected mice fed n-3 PUFA-containing diets than in mice fed the olive oil ethyl esters control diet . The reduction of IL-12 and IFN-gamma production by n-3 PUFA may have important implications for host infectious disease resistance.

Microbiol Immunol, 2000, 44(6), 431 - 8
Dithiothreitol enhances Listeria monocytogenes mediated cell cytotoxicity; Westbrook DG et al.; The hybridoma Ped-2E9 based cytotoxicity assay was developed to distinguish virulent from avirulent Listeria species in 6 hr . The cytotoxicity effect on Ped-2E9 was reported to be primarily due the cytolytic action of listeriolysin O (LLO), produced by L . monocytogenes . In this study, the effect of a reducing agent, dithiothreitol (DTT, 0-2 mM) that is known to activate LLO was investigated to make the Ped-2E9 based cytotoxicity assay an even more sensitive and rapid . Also, we examined the effect of fetal bovine serum (FBS, 0-50%), a common ingredient of tissue culture media on cytotoxicity . A DTT concentration of 0.5 mM gave an optimum cytotoxicity effect, which could be measured by both alkaline phosphatase (AP) and lactate dehydrogenase (LDH) assays in just 1.5-2 hr . FBS, at levels between 10 to 50%, significantly inhibited Listeria-mediated cytotoxicity . Concentrated culture filtrates from L . monocytogenes or LLO producing recombinant L . innocua (prfA+ hlyA+) strain also caused cytotoxicity effects, which were observed by scanning electron microscopy or a cytotoxicity assay in 2-3 hr . Interestingly, addition of DTT to culture filtrates produced 100% cell cytotoxicity in just 15 min . This indicated that LLO activity, which is responsible for Ped-2E9 cytotoxicity, was augmented several folds with the addition of a reducing agent . Examination of Listeria isolates belonging to different serogroups from clinical sources or naturally contaminated meat products with DTT gave cytotoxicity results in 2 hr, which were comparable to the 5-hr assay analyzed concurrently without DTT . These results indicated that DTT, which activated the LLO, could be used in the cytotoxicity assay to enhance Listeria-mediated Ped-2E9 cell cytotoxicity . This knowledge will greatly assist us to develop a user-friendly rapid assay to screen cytopathogenic properties of Listeria species.

Gene, 2000 Aug 8, 253(2), 281 - 91
Mycobacterium tuberculosis H37Rv comparative gene-expression analysis in synthetic medium and human macrophage; Mariani F et al.; Mycobacteria are intracellular pathogens that survive and grow in host macrophages . Following phagocytosis, sustained intracellular bacterial growth depends on its ability to avoid destruction by macrophage-mediated host defences such as lysosomal enzymes, reactive oxygen and the reactive nitrogen intermediates.This suggests that the interaction between host cell and microbe is delicately balanced, and can be tipped in favour of either organism . The identification of Mycobacterium tuberculosis H37Rv (MTB) genes expressed within host cells would contribute greatly to the development of new strategies to fight tuberculosis . In the present study, we compared MTB gene expression in the course of intra- (human macrophages) and extracellular growth (Sauton's medium) to ascertain whether differences might occur between gene-expression patterns in the two habitats of replication . Using reverse-transcriptase polymerase chain reaction (RT-PCR) on a group of 14 MTB-Complex-specific genes, we found that MT10Sa (a small stable RNA), 35 kDa (unknown), ahpC (alkyl hydroperoxide reductase, AhpC), sigF (alternative RNA Polymerase sigma factor), and katG (catalase-peroxidase, HPI) genes are expressed in both the environments, while Ag85B, Ag85C (members of the Antigen 85 Complex), rpoV (RNA Polymerase sigma factor) and ESAT6 (early secretory antigen, 6 kDa) are expressed only in the in vitro culture; on the other hand, Ag85A (Antigen 85 Complex), rpoB (RNA Polymerase beta sub-unit), pab (Protein antigen b), invA and invB genes (encoding proteins that show homologies with p60 of Listeria monocytogenes) are expressed only inside the macrophage . Positive RT-PCR products on cDNAs for these genomic regions were not obtained from approximately 1000-fold more bacteria grown in Laboratory Broth . Identification of M . tuberculosis genes expressed in response to phagocytosis by human macrophages increases our basic understanding of the host-pathogen interaction, and helps to identify bacterial factors necessary for in vivo survival and growth.

Int J Food Microbiol, 2000 Jul 15, 58(3), 181 - 96
Quantitative risk assessment for Listeria monocytogenes in smoked or gravad salmon and rainbow trout in Sweden; Lindqvist R et al.; The objective of the present work was to develop a quantitative risk assessment model in which the exposure and risk of acquiring listeriosis from consumption of packaged smoked or gravad salmon and rainbow trout were estimated . An Excel spreadsheet model was constructed in which variables were represented by distributions based on surveys of L . monocytogenes in these food products, and on demographic and consumption data . Growth or inactivation was not included in the model . The model was run through Monte Carlo simulations using the @Risk software (Palisade Corporation) . The probability of illness per serving was calculated using two dose-response models from the literature . The first was an exponential model in which the species specific constant R, that helps define the dose-response curve, previously has been estimated to be 1.18 x 10(-10) based on German data (GR) . In this study, R was estimated to 5.6 x 10(-10) based on Swedish data . The second model was a flexible Weibull-Gamma model (WG), with different coefficients for high- and low-risk groups . The exponential model (GR), although conservative and generally overestimating the risk, still predicted a lower probability of illness than the WG-model . The estimated mean risk per serving was 2.8 x 10(-5) (GR, high-risk group), 2.0 x 10(-3) (WG, low-risk group) and 0.016 (WG, high-risk group), respectively . The average number of reported listeriosis cases in Sweden is 37 per year . In comparison, the mean number of annual cases predicted by the risk assessment model was 168 (range 47 to 2800, GR, high-risk group), and 95 000 (range 34 000 to 1.6 x 10(6), WG high-risk group), respectively . If 1 to 10% (uniform distribution) of strains, instead of all, were considered virulent, the mean number of predicted cases would decrease to nine (GR) and 5200 (WG), respectively . The mean annual cumulative individual risk in the high-risk group based on a monthly exposure was estimated to be 4.0 x 10(-4) (range 8.0 x 10(-8) to 5.4 x 10(-3), GR) . This risk increased to 1.5 x 10(-3) (range 1.7 x 10(-5) to 9.2 x 10(-3), GR) based on a weekly exposure . The risk assessment model was most sensitive to the input distribution describing the level of contamination and to a lesser degree on the prevalence of L . monocytogenes, the proportion of virulent strains, and serving sizes . A lack of data on the prevalence and concentration of L . monocytogenes in these products, dose-response data and quantitative information on the proportion of virulent strains were identified.

New Microbiol, 2000 Jul, 23(3), 289 - 95
In vivo and in vitro assessment of the virulence of Listeria monocytogenes strains; Gattuso A et al.; To evaluate whether the in vitro model (invasion and intracellular growth in Caco-2 cells) for determining virulence is a suitable alternative to the in vivo model (50% lethal dose), we compared the levels of virulence obtained with the two models . We tested L . monocytogenes strains isolated from food and clinical samples during three episodes of listeriosis occurring in Italy in the period 1993-1995 . We also tested L . monocytogenes strains isolated from food during official control activities . The results obtained from the tested strains varied according to the experimental method adopted: the L . monocytogenes strains featuring the same genetic pattern showed a greater uniformity of response in vivo than in vitro . We can conclude that the in vitro model may be used as an alternative to the animal model to determine Listeria spp pathogenicity, though it cannot distinguish levels of virulence within the L . monocytogenes species.

J Med Microbiol, 2000 Aug, 49(8), 681 - 3
Modulation of actA gene expression in Listeria monocytogenes by iron; Conte MP et al.; This study analysed the invasiveness of Listeria monocytogenes into enterocyte-like Caco-2 cells in which iron depletion was achieved by picolinic acid treatment . Both entry and intracellular multiplication varied depending on the endogenous iron content of bacterial and eukaryotic cells . The behaviour within enterocytes was correlated with a 10-fold increased transcription of the actA gene observed in bacterial cells grown under conditions of iron stress.

Rev Latinoam Microbiol, 1997 Jul-Dec, 39(3-4), 153 - 8
A simple procedure for determining the presence and concentration of Listeria monocytogenes in dairy products; Teves SA et al.; This paper presents a simple method for determining both the presence and concentration of Listeria monocytogenes in dairy products . The method involves application of the Most Probable Number (MPN) technique and enrichment of a 25 g sample . Our tests showed that the MPN correlates with the Colony Forming Units (CFU), and estimated concentrations of as low as 1 bacterium/gr or less . We also studied the influence of Listeria innocua as an accompanying flora . We detected L . monocytogenes, even in the presence of concentrations of 4 times as much L . innocua . Nonetheless, L . monocytogenes could not be detected when the concentration of L . innocua surpassed 90%.

J Cell Biol, 2000 Aug 7, 150(3), 527 - 38
Three regions within ActA promote Arp2/3 complex-mediated actin nucleation and Listeria monocytogenes motility; Skoble J et al.; The Listeria monocytogenes ActA protein induces actin-based motility by enhancing the actin nucleating activity of the host Arp2/3 complex . Using systematic truncation analysis, we identified a 136-residue NH(2)-terminal fragment that was fully active in stimulating nucleation in vitro . Further deletion analysis demonstrated that this fragment contains three regions, which are important for nucleation and share functional and/or limited sequence similarity with host WASP family proteins: an acidic stretch, an actin monomer-binding region, and a cofilin homology sequence . To determine the contribution of each region to actin-based motility, we compared the biochemical activities of ActA derivatives with the phenotypes of corresponding mutant bacteria in cells . The acidic stretch functions to increase the efficiency of actin nucleation, the rate and frequency of motility, and the effectiveness of cell-cell spread . The monomer-binding region is required for actin nucleation in vitro, but not for actin polymerization or motility in infected cells, suggesting that redundant mechanisms may exist to recruit monomer in host cytosol . The cofilin homology sequence is critical for stimulating actin nucleation with the Arp2/3 complex in vitro, and is essential for actin polymerization and motility in cells . These data demonstrate that each region contributes to actin-based motility, and that the cofilin homology sequence plays a principal role in activation of the Arp2/3 complex, and is an essential determinant of L . monocytogenes pathogenesis.

J Toxicol Environ Health A, 2000 Jul 28, 60(6), 391 - 406
In vivo cytokine production and resistance to infection after acute exposure to 3,4-dichloropropionaniline; Watson VA et al.; 3,4-Dichloropropionaniline (propanil) is an extensively used postemergent herbicide that has been shown to produce toxic and immunotoxic effects . The present report examined if acute exposure to propanil altered in vitro or in vivo cytokine production in response to antigenic stimulation . Studies to determine resistance to infection by the intracellular bacterium Listeria monocytogenes after exposure to propanil were also conducted . Our experiments demonstrate that in vivo exposure to propanil during bacterial infection reduced the subsequent in vitro production of interferon-gamma (IFN-gamma) by splenocytes and liver nonparenchymal cells in response to antigenic and mitogenic stimulation . Additional experiments examined the production of cytokines in vivo after propanil exposure alone or combined propanil exposure and L . monocytogenes infection . It was found that the endogenous levels of cytokines in the liver, spleen, and blood were similar in control and propanil-treated mice . The levels of cytokines were also similar in control and exposed mice that were infected with L . monocytogenes . Initial resistance to the infection was not affected by exposure to propanil . These results demonstrate that in vivo exposure to propanil during a bacterial infection suppresses the subsequent in vitro production of cytokines but that the endogenous levels are not affected during the initial stages of infection.

Zh Mikrobiol Epidemiol Immunobiol, 2000 May-Jun, (3), 80 - 5
{The results of a 5-year study of listeriosis in Ukraine}; Krasovskii VV et al.; Data on the isolation of Listeria spp . cultures on the territory of Ukraine, the frequency of Listeria contamination of alimentary raw materials and foodstuffs, the level of listeriosis morbidity, the clinical forms of the manifestation of this disease, as well as the occurrence of asymptomatic carriership among clinically healthy persons of epidemiologically significant professions, are given . The results of the study of the biological properties of 73 strains of Listeria spp., their sensitivity to antibiotics and Chlorophyllipt are presented.

Zh Mikrobiol Epidemiol Immunobiol, 2000 May-Jun, (3), 18 - 20
{Listeria bacterial carriage: a method for sanative treatment}; Krasovskii VV et al.; 1.6% of clinically healthy women active in certain professions have been found to be carriers of pathogenic species of Listeria . The study of the sensitivity of 73 strains of Listeria spp . to the preparations of Chlorophyllipt has revealed that in usual therapeutic concentrations Chlorophyllipt produces a pronounced antibacterial effect on these organisms . The use of Chlorophyllipt for the sanitation of carriers of pathogenic Listeria is proposed.

Res Vet Sci, 2000 Aug, 69(1), 99 - 100
Rapid molecular typing of Listeria monocytogenes by pulsed-field gel electrophoresis; Katsuda K et al.; Pulsed-field gel electrophoresis (PFGE) is a highly discriminating tool for molecular typing, but the conventional PFGE protocol is time consuming . This paper describes a rapid method of PFGE for Listeria monocytogenes that yields results within 2 days.

Appl Environ Microbiol, 2000 Aug, 66(8), 3586 - 91
Real-time measurements of the interaction between single cells of Listeria monocytogenes and nisin on a solid surface; Budde BB et al.; A method to obtain real-time measurements of the interactions between nisin and single cells of Listeria monocytogenes on a solid surface was developed . This method was based on fluorescence ratio-imaging microscopy and measurements of changes in the intracellular pH (pH(i)) of carboxyfluorescein succinimidyl ester-stained cells during exposure to nisin . Immobilized cells were placed in a chamber mounted on a microscope and attached to a high-precision peristaltic pump which allowed rapid changes in the nisin concentration . In the absence of nisin, the pH(i) of L . monocytogenes was almost constant (approximately pH 8.0) and independent of the external pH in the pH range from 5.0 to 9.0 . In the presence of nisin, dissipation of the pH gradient (DeltapH) was observed, and this dissipation was both time and nisin concentration dependent . The dissipation of DeltapH resulted in cell death, as determined by the number of CFU . In the model system which we used the immobilized cells were significantly more resistant to nisin than the planktonic cells . The kinetics of DeltapH dissipation for single cells revealed a variable lag phase depending on the nisin concentration, which was followed by a very rapid decrease in pH(i) within 1 to 2 min . The differences in nisin sensitivity between single cells in a L . monocytogenes population were insignificant for cells grown to the stationary phase in a liquid laboratory substrate, but differences were observed for cells grown on an agar medium under similar conditions, which resulted in some cells having increased resistance to nisin.

Curr Microbiol, 2000 Jul, 41(1), 1 - 4
Natural variation in susceptibility of Listeria strains to class IIa bacteriocins; Ennahar S et al.; Thirty-one Listeria strains were tested for sensitivity to four class IIa bacteriocins, namely, enterocin A, mesentericin Y105, divercin V41, and pediocin AcH, and to nisin A . Class IIa bacteriocins displayed surprisingly similar antimicrobial patterns ranging from highly susceptible to fully resistant strains, whereas nisin A showed a different pattern in which all Listeria strains were inhibited . Particularly, it was observed that the strain Listeria monocytogenes V7 could not be inhibited by any of the class lIa bacteriocins tested . These observations suggest that Listeria strains resistant to the whole range of class IIa bacteriocins may occur in natural environments, which could be of great concern with regard to the use of these peptides as food preservatives.

Proc Natl Acad Sci U S A, 2000 Aug 1, 97(16), 8784 - 8
A framework for interpreting the leucine-rich repeats of the Listeria internalins; Marino M et al.; The surface protein InlB of the bacterial pathogen Listeria monocytogenes is required for inducing phagocytosis in various nonphagocytic mammalian cell types in vitro . InlB causes tyrosine phosphorylation of host cell adaptor proteins, activation of phosphoinositide 3-kinase, and rearrangements of the actin cytoskeleton . These events lead to phagocytic uptake of the bacterium by the host cell . InlB belongs to the internalin family of Listeria proteins, which also includes InlA, another surface protein involved in host cell invasion . The internalins are the largest class of bacterial proteins containing leucine-rich repeats (LRR), a motif associated with protein-protein interactions . The LRR motif is found in a functionally diverse array of proteins, including those involved in the plant immune system and in the mammalian innate immune response . Structural and functional interpretations of the sequences of internalin family members are presented in light of the recently determined x-ray crystal structure of the InlB LRR domain.

J Food Prot, 2000 Jul, 63(7), 921 - 5
Use of capillary tubes and plate heat exchanger to validate U.S . Department of Agriculture pasteurization protocols for elimination of Listeria monocytogenes in liquid egg products; Michalski CB et al.; D-values for a five-strain cocktail of Listeria monocytogenes in five different liquid egg products (whole egg, egg yolk, egg white, egg yolk + 5% sucrose + 5% NaCl, and egg yolk + 10% NaCl) were determined using 100-microl capillary tubes . The egg products were inoculated with approximately 1 x 10(10) organisms/ml and heated in capillary tubes to temperatures ranging from 53 to 69 degrees C for various time intervals . Using a pilot scale plate heat exchanger, the U.S . Department of Agriculture (USDA) protocols for pasteurization were also evaluated using egg products inoculated with approximately 1 x 10(7) L . monocytogenes/ml . Results of experiments with capillary tubes suggested that all processes would result in less than the 9D process recommended by USDA . Moreover, although pasteurization with a plate heat exchanger provided greater lethality than did capillary tubes, all products still received less than a 5.4D process . Hence, these results suggest that the current USDA protocol may not be adequate to assure a large margin of safety.

J Food Prot, 2000 Jul, 63(7), 907 - 11
Growth and survival of Escherichia coli O157:H7 and Listeria monocytogenes in egg products held at different temperatures; Yang SE et al.; Growth and survival of Escherichia coli O157:H7 and Listeria monocytogenes in steamed eggs and scrambled eggs held at different temperatures (5, 18, 22, 37, 55, and 60 degrees C) were investigated in the present study . Among the holding temperatures tested, both pathogens multiplied best at 37 degrees C followed by 22, 18, and 5 degrees C . In general, E . coli O157:H7 grew better in the egg products than L . monocytogenes did at all the storage temperatures tested except at 5 degrees C . E . coli O157:H7 did not grow in steamed eggs and scrambled eggs held at 5 degrees C . L . monocytogenes showed a slight population increase of approximately 0.6 to 0.9 log CFU/g in these egg products at the end of the 36-h storage period at 5 degrees C . The population of both pathogens detected in the egg products was affected by the initial population, holding temperature, and length of the holding period . It was also noted that L . monocytogenes was more susceptible than E . coli O157:H7 in steamed eggs held at 60 degrees C . After holding at 60 degrees C for 1 h, no detectable viable cells of L . monocytogenes with a population reduction of 5.4 log CFU/g was observed in steamed eggs, whereas a lower population reduction of only approximately 0.5 log CFU/ml was noted for E . coli O157:H7.

J Food Prot, 2000 Jul, 63(7), 894 - 9
Effectiveness of two cooking systems in destroying Escherichia coli O157:H7 and Listeria monocytogenes in ground beef patties; D'Sa EM et al.; A rapid, high-temperature double-sided grilling-broiling (DGB) system was compared to a single-sided broiling (SSB) system for cooking of foodservice ground beef patties to reduce microbial numbers and maintain textural quality . Patties (110 g) containing either Escherichia coli O157:H7 or Listeria monocytogenes (10(6-7) CFU/g) were cooked to target internal temperatures of 60 or 68 degrees C on each cooking system and immediately removed from the grills without the additional holding time at 60 or 68 degrees C that is recommended for foodservice cooking of ground beef patties . Actual final internal temperature attained, position on the grill, degree of doneness, cooking time, after-cook weight, texture characteristics, and bacterial counts of the patties were monitored . The DGB reduced E . coli O157:H7 and L . monocytogenes populations in ground beef patties by 5.7 log10 and 5.4 log10 CFU/g, respectively, when cooked to a target temperature of 60 degrees C (actual final internal temperature of 71.2 degrees C) and by 6.1 log10 and 5.6 log10 CFU/g, respectively, when cooked to a target temperature of 68 degrees C (actual final internal temperature of 75.8 degree C) . The SSB reduced E . coli O157:H7 and L . monocytogenes populations by 1.3 log10 and 1.8 log10 CFU/g, respectively, when cooked to a target temperature of 60 degrees C (actual final internal temperature of 62.7 degrees C) and by 2.9 log10 and 3.6 log10 CFU/g, respectively, when cooked to a target temperature of 68 degrees C (actual final internal temperature of 69.3 degrees C) . The DGB system effected a higher, more rapid temperature increase in patties cooked to either target temperature compared to the SSB system . This higher temperature was more effective in destroying pathogens in beef patties . Texture analyses determined that patties cooked on the DGB system had significantly higher values for springiness, adhesiveness, and product height as compared to the SSB system, and patties cooked on either system had significantly higher hardness, gumminess, chewiness, and product height values at the target temperature of 68 degrees C as compared to 60 degrees C.

Arch Immunol Ther Exp (Warsz), 2000, 48(3), 151 - 62
Listeria monocytogenes as an alternative vaccine vector for HIV; Mata M et al.; The necessity for an HIV vaccine and a brief review of current strategies towards this aim are given here to set into context contemporary studies towards exploiting the bacterium Listeria monocytogenes as an HIV vaccine vector . The cell biology and immunology of this unusual intracellular organism are also reviewed, in addition to its application to introducing viral antigens, including HIV antigens, to the immune system.

J Vet Med Sci, 2000 Jun, 62(6), 673 - 5
Incidence of Listeria monocytogenes in wild animals in Japan; Yoshida T et al.; Between 1991 and 1993, the intestinal contents and feces of wild animals in Japan were examined for the presence of Listeria . The wild animals examined included 623 mammals (11 species) and 996 birds (18 species) . Listeria species were isolated from 38 (6.1%) of the 623 mammalian samples and 133 (13.4%) of 996 bird samples . The highest incidence of Listeria in the mammals was found in Japanese monkeys (20.0%) and that in birds was found in crows (43.2%) . The incidence of Listeria in Japanese monkeys varied from 0 to 40.0% depending on the capture area . L . monocytogenes was isolated from II of these positive samples . Serovars 1/2a and 4b predominated in eight serotyped L . monocytogenes isolates.

J Vet Med Sci, 2000 Jun, 62(6), 639 - 41
Listeriosis in a raccoon dog (Nyctereutes procyonoides) associated with canine distemper; Aoyagi T et al.; A wild raccoon dog (Nyctereutes procyonoides) that manifested severe illness and died was examined . Necropsy revealed severe emaciation, systemic icterus and petechial hemorrhages on the mucous membranes . Histopathologically, necroses were seen in the liver and brain stem associated with meningitis . Eosinophilic intranuclear inclusion bodies were observed in the spleen and intestinal mucosa, and eosinophilic intracytoplasmic inclusion bodies were seen in transitional epithelium in the bladder . Listeria monocytogenes 4b was isolated from the liver, spleen, kidneys and lungs, and the pathogen was also detected in the liver and brain stem immunohistopathologically . The disease was diagnosed as listeriosis associated with canine distemper virus infection in a raccoon dog.

Biochem J, 2000 Aug 1, 349 Pt 3, 783 - 6
Iron oxidation and hydrolysis reactions of a novel ferritin from Listeria innocua; Yang X et al.; Iron deposition in the unusual 12-subunit ferritin from thebacterium Listeria innocua proceeds in three phases: a rapidfirst phase in which Fe(2+) binds to the apoprotein, P(Z) of charge Z, according to the postulatedreaction 2Fe(2+)+P(Z)-->{Fe(2)-P}(Z+2)+2H(+), where{Fe(2)-P}(Z+2) represents adinuclear iron(II) complex formed at each of the 12 ferroxidase centresof the protein; a second phase corresponding to oxidation of thisputative complex, i.e . {Fe(2)-P}(Z+2)+1/2 O(2)-->{Fe(2)O-P}(Z)+2H(+);and a third phase of iron(II) oxidation/mineralization, i.e . 4Fe(2+)+O(2)+8H(2)O-->8FeOOH((s))+8H(+) {where FeOOH((s)) represents the hydrous ferric oxidemineral that precipitates from the solution}, which occurs when iron isadded in excess of 24Fe(2+)/protein . In contrast with otherferritins, the ferroxidation reaction in L . innocua ferritinproceeds more slowly than the oxidation/mineralization reaction . Wateris the final product of dioxygen reduction in the 12-subunit L.innocua ferritin (the present work) and in the 24-subunit Escherichia coli bacterioferritin, whereas H(2)O(2) is produced in 24-subunit mammalian ferritins . Possible reasonsfor this difference are discussed.

Klin Lab Diagn, 2000 Jun, (6), 37 - 41
{Development and approbation of polymerase chain reaction for detection of pathogen in Listeria infection}; Krasovskii VV et al.; A system of primers for detection of Listeria by polymerase chain reaction (PCR) has been developed . Specificity and sensitivity of the method was evaluated by analyses of reference clinical and abiotic samples . Clinical trials of PCR were carried by detecting latent (asymptomatic) carriers of Listeria among healthy women of epidemiologically significant professions . PCR is characterized by numerous advantages in comparison with the traditional bacteriological analysis.

Clin Immunol, 2000 Aug, 96(2), 140 - 9
Humoral and cell-mediated immunity in mice with genetic deficiencies of prolactin, growth hormone, insulin-like growth factor-I, and thyroid hormone; Foster MP et al.; Prolactin (PRL), growth hormone (GH), insulin-like growth factor-I (IGF-I), and thyroid hormones have been proposed as critical immunoregulatory mediators, and their clinical use is being considered . The precise role played by each of these hormones in the generation of humoral and cell-mediated immune responses was assessed in a panel of mice with mutations that result in a selective reduction of PRL, GH, IGF-I, and/or thyroid hormone production . A surprising result, in view of previous studies indicating an immunoregulatory role for these hormones, was that all mice generated normal humoral and cell-mediated immune responses following challenge with T-independent and T-dependent antigens and with Listeria monocytogenes . A review of these findings in the context of previous data has resulted in the formulation of a working hypothesis proposing that these hormones act as anabolic and/or stress modulating mediators with effects on most cells, including those of the immune system . When considered in this context, it is possible to reconcile the contradictory data .

Infect Immun, 2000 Aug, 68(8), 4789 - 91
Critical role of neutrophils in eliminating Listeria monocytogenes from the central nervous system during experimental murine listeriosis; Lopez S et al.; Neutrophils are the main inflammatory cell present in lesions involving the central nervous system (CNS) during human and murine listeriosis . In this study, administration of the neutrophil-depleting monoclonal antibody RB6-8C5 during experimental murine listeriosis facilitated the multiplication of Listeria monocytogenes in the CNS . These data suggest that neutrophils play a key role in eliminating bacteria that gain access to the CNS compartment . In addition, we provide evidence that their migration into the CNS may be necessary for the subsequent recruitment of macrophages and activated lymphocytes.

Infect Immun, 2000 Aug, 68(8), 4666 - 72
Interleukin-10 has different effects on proliferation of Listeria monocytogenes in livers and spleens of mice; Samsom JN et al.; The aim of this study was to investigate the effect of interleukin-10 (IL-10) on the course of Listeria monocytogenes infection in naive and immune mice . Treatment with IL-10 during the course of a primary infection significantly decreased the number of bacteria in the spleen and did not affect the number in the liver . During a secondary infection in immune mice treated with IL-10, the number of bacteria was significantly lower in the spleen but significantly higher in the liver in comparison to mock-treated immune mice . IL-10 treatment during a primary Listeria infection decreased the concentration of gamma interferon (IFN-gamma) in plasma and the toxoplasmastatic activity of macrophages, whereas it increased the percentage of mildly CD3-positive T cells in the spleen . During a secondary infection, the concentration of IFN-gamma in plasma was decreased on day 1 but remained unaffected during later days of infection . From these results, we conclude that IL-10 has different effects on the proliferation of L . monocytogenes in the spleen and liver during primary and secondary Listeria infections.

Infect Immun, 2000 Aug, 68(8), 4470 - 6
Adaptive immunity against Listeria monocytogenes in the absence of type I tumor necrosis factor receptor p55; White DW et al.; Tumor necrosis factor (TNF) and the type I TNF receptor (TNFRI), p55, are critical for resistance against primary infections with the intracellular bacterial pathogen Listeria monocytogenes . Importantly, however, susceptibility to primary listeriosis in cytokine-deficient mice does not preclude the development or expression of effective adaptive immunity against virulent L . monocytogenes . We used TNFRI(-/-) mice to study adaptive antilisterial immunity in the absence of interactions between TNF and TNFRI . Our experiments indicate that TNFRI(-/-) mice survive and clear high-dose challenges with an attenuated strain of L . monocytogenes that is incapable of cell-to-cell spread . Furthermore, TNFRI(-/-) mice immunized with attenuated L . monocytogenes go on to develop potent adaptive immunity to subsequent high-dose challenges with virulent L . monocytogenes . Interestingly, CD8(+) T-cell depletion in vivo inhibits immunity to L . monocytogenes in the spleen but not in the liver of TNFRI(-/-) mice . The adaptive immune response in these animals is characterized by activation of listeriolysin O-specific CD8(+) T cells, which are capable of transferring antilisterial immunity to naive wild-type C57BL/6 host mice . These experiments demonstrate the development and expression of potent CD8(+) T-cell-mediated antilisterial immunity in the absence of TNFRI.

Curr Opin Immunol, 2000 Aug, 12(4), 425 - 31
Immunity to Listeria infection; Edelson BT et al.; Infection with Listeria monocytogenes is a well studied model for understanding host resistance to intracellular bacteria . Recent advances in the study of Listeria have carefully quantitated the response of CD8(+) T cells to infection and analyzed the effector functions of these cells in vivo . A surprising role for antibody in mediating resistance to Listeria has also recently emerged, providing new insight into the mechanisms of host defense.

Int J Food Microbiol, 2000 Jun 30, 58(1-2), 113 - 6
Listeria spp . in broiler flocks: recovery rates and species distribution investigated by conventional culture and the EiaFoss method; Petersen L et al.; The occurrence of Listeria monocytogenes in samples from broiler houses and cloacal swabs taken at the abattoir was investigated . An automated immunobased method (EiaFoss) was used, and 42 samples were also analysed by conventional culture; both methods were based on a two-step selective enrichment using CHR.4.17; Fraser and Fraser broths . L . monocytogenes was isolated from two of 71 broiler flocks, yielding an estimated flock prevalence of 3% . The flock prevalence of L . inocua was estimated to 13%, and it was speculated that the potential of this apathogenic bacteria to grow faster than L . monocytogenes in enrichment broths may lead to an underestimation of the prevalence of L . monocytogenes . Furthermore, as L . inocua was also detected by the EiaFoss method, a significant amount of bacterial confirmation work had to be done . Of 42 samples analysed by conventional culture, four yielded L . inocua, of which two were not positive by EiaFoss.

Cell, 2000 Jun 23, 101(7), 717 - 28
Negative regulation of fibroblast motility by Ena/VASP proteins; Bear JE et al.; Ena/VASP proteins have been implicated in cell motility through regulation of the actin cytoskeleton and are found at focal adhesions and the leading edge . Using overexpression, loss-of-function, and inhibitory approaches, we find that Ena/VASP proteins negatively regulate fibroblast motility . A dose-dependent decrease in movement is observed when Ena/VASP proteins are overexpressed in fibroblasts . Neutralization or deletion of all Ena/VASP proteins results in increased cell movement . Selective depletion of Ena/VASP proteins from focal adhesions, but not the leading edge, has no effect on motility . Constitutive membrane targeting of Ena/VASP proteins inhibits motility . These results are in marked contrast to current models for Ena/VASP function derived mainly from their role in the actin-driven movement of Listeria monocytogenes.

FEMS Immunol Med Microbiol, 2000 Aug, 28(4), 335 - 41
Roles of endogenous cytokines in liver apoptosis of mice in lethal Listeria monocytogenes infection; Miura T et al.; Various bacterial pathogens have been identified as mediators of apoptosis . Apoptosis reportedly shows both detrimental and beneficial effects on biological functions . We studied the role of liver apoptosis in lethal Listeria monocytogenes infection and the regulation of apoptosis by endogenous cytokines during infection . Apoptosis was observed in the spleen but not in the liver of infected mice, whereas the induction of liver necrosis was evident by rising levels of serum aminotransferases in these animals . Apoptosis was detected in the liver of L . monocytogenes-infected mice which had been treated with monoclonal antibody (mAb) against tumor necrosis factor-alpha (TNF-alpha) or interleukin-6 (IL-6), or in TNF-alpha(-/-) mice, but not in gamma- interferon (IFN-gamma)(-/-) mice or mice which had been treated with mAb against IL-4 or IL-10 . Augmentation of liver apoptosis in mice treated with mAb against TNF-alpha or IL-6 or in TNF-alpha(-/-) mice correlated with the increase in bacterial numbers in the organ, while no augmentation of apoptosis was observed in the liver of IFN-gamma(-/-) mice irrespective of the marked increase in bacterial numbers in the organs, indicating that augmentation of liver apoptosis may not be merely due to the increase in bacterial growth in the organs . These results suggest that TNF-alpha and IL-6 may play an important role in protecting the liver from apoptosis in lethal L . monocytogenes infection.

J Microbiol Methods, 2000 Jul, 41(2), 145 - 53
A colony lift immunoassay for the specific identification and quantification of Listeria monocytogenes; Carroll SA et al.; A colony lift immunoassay (CLI) has been developed to detect Listeria monocytogenes after the organisms have been cultured on filter membranes or agar plates . Polyvinylidene fluoride membranes (PVDF) (Millipore, Bedford, MA), used in the CLI, were prewet with methanol and used to imprint colonies that were grown on the filter or agar plates . A positive control was applied to the edge of each membrane . The imprinted membranes were subsequently air dried, peroxidase neutralized, blocked, and reacted for 20 min with a 2-microg/ml unconjugated Mab EM-7G1 solution . The membranes were washed briefly and reacted for 30 min with a 1:2000 dilution of a commercially prepared peroxidase-labeled goat anti-mouse secondary antibody (Kirkegaard and Perry Laboratories (KPL), Gaithersburg, MD) . After a second wash step, the membranes were exposed to a 3,3',5, 5'-tetramethylbenzidine membrane substrate (KPL), rinsed in deionized water, and allowed to dry . Colonies of L . monocytogenes were identified by a blue color reaction on the membrane, which could be used to reference the colonies either on the filter membranes or agar plates . The CLI was tested against a wide range of Listeria species as well as several non-Listeria species and was shown to have a high degree of sensitivity (96%) and specificity (90%) . We have shown that it is useful as a simple and rapid method to detect and identify L . monocytogenes.

J Microbiol Methods, 2000 Jul, 41(2), 113 - 20
Rapid detection of low levels of Listeria in foods and next-day confirmation of L . monocytogenes; Peng H et al.; Outbreaks of foodborne listeriosis caused by Listeria monocytogenes in recent years, and the high mortality rate associated with listeriosis, have raised the need for reliable and rapid detection of the pathogen . A simple, automated method was developed for the detection of Listeria organisms in foods . It consists of a 6-h pre-enrichment step followed by overnight incubation in selective broth at 35 degrees C . Changes in light transmittance in the selective broth are registered continuously by an optical sensor of the BioSys instrument (MicroSys, Ann Arbor, MI), and recorded in the computer . Esculin hydrolysis by listeriae results in black coloration of the media that causes a sharp drop in light transmittance, whereas negative samples remain colorless . Confirmation of L . monocytogenes is carried out only on esculin-positive samples and is completed within 6 h . Detection of 10-50 cells of Listeria inoculated into 25 g of food was confirmed in shell eggs, milk and ground beef . Naturally contaminated raw and ready-to-eat foods were further screened to validate the procedure.

Lett Appl Microbiol, 2000 Jul, 31(1), 68 - 72
Growth condition-related response of Listeria monocytogenes 412 to bacteriocin inactivation; Jydegaard AM et al.; Bacteriocin inactivation of Listeria monocytogenes 412 was studied as a function of growth phase . Cells were treated with nisin (300 IU ml-1) or pediocin (320 or 2560 AU ml-1) for 20 min at 30 degrees C . Inactivation with nisin or the low concentration of pediocin was growth phase dependent, with exponentially growing cells being more susceptible than stationary cells . No effect of growth phase was observed for the high pediocin concentration . Pediocin inactivation (320 AU ml-1) of L . monocytogenes 412 exposed to osmotic (6.5% NaCl) or low-temperature (5 degrees C) stress was investigated . Pediocin failed to inactivate osmotically stressed cultures and was unable to inhibit cold-stressed cells to the same degree as unstressed cells.

Proc R Soc Lond B Biol Sci, 2000 Jun 7, 267(1448), 1107 - 13
Sperm precedence in a novel context: mating in a sessile marine invertebrate with dispersing sperm; Bishop JD et al.; The compound ascidian Diplosoma listerianum releases aquatic sperm which are dispersed passively to potential mates as individual gametes prior to storage of sperm, internal fertilization and brooding of embryos . The storage of exogenous sperm enables D . listerianum to produce a lengthy series of progeny following a brief period of mating . Molecular paternity analysis following sequential mating of colonies in laboratory culture revealed a consistent pattern with a clear initial bias in paternity towards the first of two acting males . The sites of sperm storage and fertilization and the morphology of the ovary in D . listerianum suggest that this bias reflects first-in-first-out use of individual stored gametes . The proportion of second-male paternity subsequently increased with time within the progeny arrays . This may have reflected the ageing or passive loss of first-male sperm . It is also possible that the modular nature of the organism contributed to this temporal trend: any recently budded colony modules maturing in the interval between matings would have been available exclusively to second-male sperm as virgin zooids . Two sets of mating trials were run . In the first, the collection of progeny suffered an interruption of 13 days and each male gained a larger proportion of recorded paternity within the progeny analysed when mating first rather than when mating second . In one mating combination, the first male obtained almost 100% of recorded paternity . In the second set of trials, with different clonal combinations, the complete sequence of progeny was collected and the estimated overall proportion of second-male paternity (P2) was consistently > 0.5 . Taken as a whole, the results suggest that the overall P2-value can vary widely within the population studied . Proposed mechanisms of mating-order effects in species with copulatory mating include several which can have no counterpart in indirect aquatic mating since they involve the active removal, sealing off, volumetric displacement or incapacitation of first-male ejaculates . It is nevertheless clear that mating-order effects can be pronounced during the type of non-copulatory mating examined here, which is widespread in marine invertebrates.

Arq Gastroenterol, 1999 Oct-Dec, 36(4), 185 - 94
{Prolonged neonatal cholestasis: prospective study}; Prado ET et al.; Due to the urgency in choosing either clinical treatment or immediate surgical intervention, the study of the prolonged neonatal cholestasis involves two basic aims: the differential diagnosis between biliary atresia and neonatal hepatitis and the research into the associated etiological agents . So, in a prospective trial carried out in the 70's, 77 children with prolonged neonatal cholestasis were studied in order to establish the differential diagnosis between biliary atresia and neonatal hepatitis, followed by the evaluation of 108 children towards a pathogenesis of the prolonged neonatal cholestasis . The results of the differential diagnosis showed that within 18 items examined only 8 proved to be good biliary atresia indicators . They are as follows (in decreasing order): ductular proliferation (portal tracts), fibrosis (portal tracts), cholestasis (portal tracts), stools colour--acholia, hepatomegaly, canalicular cholestasis (lobule), infiltrate (portal tracts), giant cells (lobule) . These eight items were then gathered in a sole indicator of great discriminative power, with a confidence level of 99% . The figures regarding the pathogenesis are: rubella virus 0%, herpes simplex virus 0%, listeriosis 0%, cytomegalovirus 2.2%, hepatitis B virus 2.4%, toxoplasmosis 2.8%, alpha-1-antitrypsin deficiency 13.1%, syphilis 21.1%, autoantibodies against the liver 58.4% . Such work thus revealed that those eight most important factors when differentiating biliary atresia from neonatal hepatitis remain as fundamental indicators and, when employed alongside other diagnostic methods, can help in the assembling of a multifactorial strategy less and less invasive and more precise . The pathogenic study, with its heavy dependency on time and place, has become more complete with the introduction of new diagnostic methods, evolving to the ideal progressive reduction of idiopathic processes.

Syst Appl Microbiol, 2000 Apr, 23(1), 132 - 6
Amplified fragment length polymorphism (AFLP) analysis of Listeria monocytogenes; Ripabelli G et al.; AFLP analysis using four selective primers was performed on a set of 33 Listeria monocytogenes including strains from patients and foods implicated in outbreaks, human sporadic cases or foods . Strains were tested belonging to serovars 1/2a, 1/2b, 1/2c, 3b, and 4b . Using one of the primers, the AFLP technique generated 20 different sized DNA fragments . The 33 cultures segregated into 14 different patterns, each comprising 7-12 different fragments . Although the method was not sufficiently discriminatory for epidemiological typing, AFLP analysis reconfirmed the observation that L . monocytogenes comprises two major genetic groups: group 1 includes strains of serovars 1/2a and 1/2c, while group 2 serovars 1/2b, 3b and 4b.

Nat Cell Biol, 2000 Jul, 2(7), 385 - 91
The Arp2/3 complex branches filament barbed ends: functional antagonism with capping proteins; Pantaloni D et al.; The Arp2/3 complex is an essential regulator of actin polymerization in response to signalling and generates a dendritic array of filaments in lamellipodia . Here we show that the activated Arp2/3 complex interacts with the barbed ends of filaments to initiate barbed-end branching . Barbed-end branching by Arp2/3 quantitatively accounts for polymerization kinetics and for the length correlation of the branches of filaments observed by electron microscopy . Filament branching is visualized at the surface of Listeria in a reconstituted motility assay . The functional antagonism between the Arp2/3 complex and capping proteins is essential in the maintenance of the steady state of actin assembly and actin-based motility.

J Clin Microbiol, 2000 Jul, 38(7), 2643 - 8
Virulent rough filaments of Listeria monocytogenes from clinical and food samples secreting wild-type levels of cell-free p60 protein; Rowan NJ et al.; Atypical rough cell filaments of Listeria monocytogenes (designated FR variants), isolated from clinical and food samples, form long filaments up to 96 microm in length and demonstrated wild-type levels of adherence, invasion, and cytotoxicity to human epithelial HEp-2, Caco-2, and HeLa cells . Unlike previously described avirulent rough mutants of L . monocytogenes that secrete diminished levels of the major extracellular protein p60 and that form long chains that consist of multiple cells of similar size (designated MCR variants), FR variants secreted wild-type or greater levels of p60 . This study shows that virulent filamentous forms of L . monocytogenes occur in clinical and food environments and have atypical morphological characteristics compared to those of the wild-type form.

Eur Biophys J, 2000, 29(2), 134 - 40
Measurement of the elasticity of the actin tail of Listeria monocytogenes; Gerbal F et al.; We report biophysical experiments performed on the bacterium Listeria monocytogenes, a model system to study actin-based motility . Using optical tweezers and electrophoresis experiments, we find that the bacterium is firmly attached to its tail, and we demonstrate that the tail responds as an elastic gel when deformed . We have measured its elastic modulus at a value of 10(3)-10(4) Pa, which is 10 times higher than the rigidity of the eukaryotic cytoplasm . These results demonstrate that the bacterium and its tail form a very robust system, consistent with the steadyness of the motion observed in vivo . We propose an elastic model for the propulsion mechanism which takes into account the connection and thus the interaction between the actin filaments . It provides a generic description of the various aspects of actin-tail based movements.

Zh Mikrobiol Epidemiol Immunobiol, 2000 Jan-Feb, (1), 45 - 7
{Nutrient media for the isolation and accumulation of Listeria}; Omarova SM et al.; Dried culture media for the isolation and accumulation of Listeria from pathological material and foodstuffs have been developed . The media are suitable for use in bacteriological and sanitary-hygienic practice . The optimum nutrient base has been selected: dried broth (from sprat hydrolysate), produced by the Research and Manufacturing Amalgamation "Culture Media" . The optimum concentrations of ingredients, stimulating the growth of Listeria and inhibiting the growth of associated microbes, have been experimentally established . The samples of died accumulation and isolation culture media ensuring the growth of L . monocytogenes, diluted 10(-6), after 24-hour incubation at 37 degrees C have been obtained . The possibility of using these media for the bacteriological diagnosis of listeriosis in pregnant women has been demonstrated.

J Clin Gastroenterol, 2000 Jun, 30(4), 436 - 7
Listeria monocytogenes peritonitis: an unusual presentation and review of the literature; Adeonigbagbe O et al.; Listeria monotogenes bacteria-ascites developed in a 73-year-old man who had cholangiocarcinoma and liver metastasis . Spontaneous bacterial peritonitis (SBP) is a frequent complication in patients with chronic liver disease and ascites . L . peritonitis has been reported in only <30 cases world-wide . Our patient represents a unique case of L . peritonitis without peritoneal fluid analysis consistent with spontaneous bacteria peritonitis . However, the culture of the ascitic fluid provided the final diagnosis in this case.

Cell Immunol, 2000 May 25, 202(1), 31 - 40
Differences in interleukin-12 and -15 production by dendritic cells at the early stage of Listeria monocytogenes infection between BALB/c and C57 BL/6 mice; Liu T et al.; The mechanisms responsible for the resistance of C57BL/6 mice and for the susceptibility of BALB/c mice to infection with Listeria monocytogenes were studied by comparing early IL-12 and IL-15 production by dendritic cells (DC) after infection with L . monocytogenes . Splenic DC expressing CD11b(low) and CD11c(+) obtained from C57BL/6 mice at 3 and 6 h after L . monocytogenes infection expressed higher levels of IL-12 p40 mRNA and IL-12 p40 protein than did those from BALB/c mice . Concurrently, a larger amount of IFN-gamma was produced by the splenic T cells from C57BL/6 mice in response to immobilized anti-TCRalphabeta mAb than by those from BALB/c mice, while the splenic T cells from BALB/c mice produced a higher level of IL-4 upon TCR alphabeta stimulation than did those of C57BL/6 mice . IL-15 mRNA and intracellular IL-15 protein were detected more abundantly in the DC from C57BL/6 mice than in those from BALB/c mice on day 3 after infection . CD3(+) IL2Rbeta (+) cells in the spleen were increased in C57BL/6 mice but not in BALB/c mice at the early stage after infection . Furthermore, IL-12Rbeta2 gene expression was up-regulated in T cells from C57BL/6 mice but not in those from BALB/c mice at the early stage after listerial infection . These results suggest that the difference in early production of IL-12 and IL-15 by DC may at least partly underlie the difference in susceptibility to L . monocytogenes between C57BL/6 and BALB/c mice .

New Microbiol, 2000 Apr, 23(2), 159 - 65
Characterization of iap gene in Listeria monocytogenes strains isolated in Japan; Saito A et al.; Variation of the iap gene region (407bp) encoding an invasion-associated protein p60 was studied on 12 strains of Listeria monocytogenes of different origin in Japan . These 12 strains are known to have 2 types of serotype (1/2a and 4b) and have a diversity among the strains (Saito et al., 1998) . The dye-primer cycle sequencing method was employed to determine the genomic structure, and the nucleotide sequences obtained were compared with those of reference strain SV 1/2a EGD . Differences found in the nucleotides were as follows; point mutations of 33 variations in 32 places; an insertion and 3 deletions of 3 bases; AAT position (po.) 1282-1283, and GCA po . 1307-1309, ACA po . 1412-1414, AAT po . 1439-1444, respectively . Different repeating numbers by 6 base unit, ACA AAT, were also found in the tandem repeat region (po . 1394-1423) . Classification of 12 strains was attempted, then 8, 4 and 5 types were obtained from the point mutations, the insertions and deletions, and the repeating numbers, respectively . Consequently, 8 patterns were profiled regardless of each serotype . From these results, genomic structures were partially clarified in the iap gene 407bp of L . monocytogenes isolated in Japan . Then, the possibility of detailed epidemiology for L . monocytogenes infection using a combination of serotype and genome structure was suggested because of the previous polymorphism thought to be due to the nucleotide differences in the region.

Int J Food Microbiol, 2000 Jun 15, 57(3), 219 - 24
Evaluation of a monoclonal antibody able to detect live Listeria monocytogenes and Listeria innocua; Solve M et al.; A monoclonal Listeria antibody, designated B4, was evaluated . The ability of the antibody to bind to viable bacteria belonging to Listeria spp . compared to bacteria of the same species killed by heat treatment, acid or base treatment, sanitizers, and irradiation was examined . The antibody was found to react with viable L . monocytogenes and L . innocua, but not with heat-killed (72 degrees C, 5 min) strains of these organisms . When L . monocytogenes and L . innocua were killed by methods other than heat treatment, it was ambiguous whether the antibody detected the organism or not . It was concluded that the B4 antibody has potential to be used in an immuno capture step to capture live L . monocytogenes and L . innocua from foods prior to identification of L . monocytogenes by polymerase chain reaction (PCR).

Int J Food Microbiol, 2000 Jun 15, 57(3), 169 - 81
A model describing the effect of temperature history on lag time for Listeria monocytogenes; Augustin JC et al.; A model was built to describe the influence of the temperature and the duration of pre-incubation on the lag time for regrowth of Listeria monocytogenes at low temperature . This model is consistent with the usual procedure used to calculate lag times of cultures growing under fluctuating temperatures . It also describes the effect of prolonged starvation conditions on the regrowth lag time and takes into account the influence of the physiological state of inocula in predictive models.

J Immunol, 2000 Jul 1, 165(1), 5 - 9
Cutting edge: antilisterial activity of CD8+ T cells derived from TNF-deficient and TNF/perforin double-deficient mice; White DW et al.; The mechanisms by which CD8+ T cells mediate immunity against bacterial pathogens remain largely unknown . Perforin-dependent cytolysis plays a role, but is not required for CD8+ T cell-mediated immunity against Listeria monocytogenes . TNF is essential for CD8+ T cell immunity to L . monocytogenes, but the cellular source of TNF is undefined . TNF-deficient and TNF/perforin double-deficient mice were used to generate CD8+ T cells specific for an L . monocytogenes-derived Ag . Wild-type and TNF-deficient CD8+ T cells mediated antilisterial immunity in wild-type but not TNF-deficient host mice, revealing that CD8+ T cell-derived TNF is not required for CD8+ T cell-mediated antilisterial immunity, but demonstrating a role for TNF derived from other cell types . TNF/perforin double-deficient CD8+ T cells mediated antilisterial immunity in the liver, but not in the spleen, of wild-type recipient mice, suggesting that perforin-independent immunity in the spleen requires CD8+ T cell-derived TNF.

J Exp Med, 2000 Jun 19, 191(12), 2145 - 58
Downmodulation of the inflammatory response to bacterial infection by gammadelta T cells cytotoxic for activated macrophages; Egan PJ et al.; Although gammadelta T cells are involved in the regulation of inflammation after infection, their precise function is not known . Intraperitoneal infection of T cell receptor (TCR)-delta(-/-) mice with the intracellular bacterium Listeria monocytogenes resulted in the development of necrotic foci in the livers . In contrast, the peritoneal cavities of infected TCR-delta(-/-) mice contained an accumulation of low density activated macrophages and a reduced percentage of macrophages undergoing apoptosis . gammadelta T cell hybridomas derived from mice infected with Listeria were preferentially stimulated by low density macrophages from peritoneal exudates of infected mice . Furthermore, primary splenic gammadelta T cells isolated from Listeria-infected mice were cytotoxic for low density macrophages in vitro, and cytotoxicity was inhibited in the presence of antibodies to the gammadelta TCR . These results demonstrate a novel interaction between gammadelta T cells and activated macrophages in which gammadelta T cells are stimulated by terminally differentiated macrophages to acquire cytotoxic activity and which, in turn, induce macrophage cell death . This interaction suggests that gammadelta T cells regulate the inflammatory response to infection with intracellular pathogens by eliminating activated macrophages at the termination of the response.

Arch Mal Coeur Vaiss, 2000 May, 93(5), 553 - 7
{Therapy and prognosis of infectious complete atrioventricular block in children}; Batmaz G et al.; From 1983 to 1997, we have studied ten children with complete atrioventricular block likely due to myocarditis in order to assess its prognosis and to define a therapeutic strategy . Their age ranged from 6 days to 16 years (median: 4.1 years) . All were admitted for sudden complete block, with symptoms in seven: syncope or fainting, seizures, collapse . Three had an asymptomatic bradycardia which was detected on routine auscultation in children with fever or already hospitalized; fever was present in 5 . The disease was related to infection on biological data in 4 cases (1 listeriosis and 3 seroconversions for Epstein Barr or cytomegalic or Coxsackie B viruses), on a myocardial biposy in 1 case and on scintigraphic data in 1 case . In the remaining 4, indirect arguments were considered such as infectious context, normal recent ECG, favourable outcome . Five children were given intravenous isoprenalin with ventricular tachycardia in 3 . Five were treated with steroids and 3 with specific antiviral agents . Seven patients were paced temporarily . One child died, 6 recovered totally and 3 have a permanent block with a definitive pacemaker implanted in 2 . In conclusion, sudden acquired complete atrioventricular blocks are often ill-tolerated in children and have to be treated with transient pacing . Recovery occurs as a rule but some of these blocks may be definitive . Infective myocarditis is likely to be the cause of the disease even if the pathogen agent cannot always be identified.

Int J Food Microbiol, 2000 May 25, 56(1), 53 - 70
Modelling the growth rate of Listeria monocytogenes with a multiplicative type model including interactions between environmental factors; Augustin JC et al.; A multiplicative secondary model previously published to describe independently the effects of environmental factors on the growth rate of Listeria monocytogenes (Augustin and Carlier, 2000) was improved by taking into account interactions between these environmental factors . The proposed model allowed to decrease the rate of fail-safe growth predicted from 13.5% to 12.1% and the rate of fail-dangerous no growth predicted from 16.1% to 7.1%.

Int J Food Microbiol, 2000 May 25, 56(1), 29 - 51
Mathematical modelling of the growth rate and lag time for Listeria monocytogenes; Augustin JC et al.; Growth data for Listeria monocytogenes were collected from the literature and a global model built with existing secondary models describing independently the effects of environmental factors on the growth rate and lag time was based on these data . The growth rates calculated with this model were consistent with the published ones but the fit was poor near the limits of growth of the micro-organism . The model was also less accurate to describe the lag time . It seems then that reliable predictions of the growth rate of L . monocytogenes could be obtained in a wide range of growth conditions, but models should take into account interactions between environmental factors . Furthermore, it is necessary to better model the lag phase duration and particularly to model the effect of the history of the inoculum on the subsequent lag time.

Int J Food Microbiol, 2000 Jun 1, 56(2-3), 161 - 6
Survival of osmotic and acid stress by Listeria monocytogenes strains of clinical or meat origin; Dykes GA et al.; The ability of 30 Listeria monocytogenes strains, 15 of meat origin and 15 of clinical origin, to use carnitine as an osmoprotectant and to resist acid stress was determined . All strains examined were able to use carnitine as an osmoprotectant, indicating the importance of this characteristic to the survival of L . monocytogenes in natural environments . Clinical and meat strains, however, differed with respect to this characteristic . Specifically, 73% of meat strains reached a lower maximum cell density in the presence of carnitine with osmotic stress than in its absence with no stress . Only 33% of clinical strains displayed the same feature whereas the remaining clinical strains reached a higher maximum cell density in the presence of carnitine with osmotic stress than in its absence with no stress . The physiological reasons and advantage of this difference are unclear . When exposed to conditions of severe acid stress (pH 2.5) for 2 h, only two L . monocytogenes strains (L66 and L78), both of meat origin, displayed significant reductions (P < 0.05) in number (3.51 and 2.79 log cfu, respectively) . Acid-sensitive strains were not found among the clinical isolates examined, highlighting the importance of acid stress resistance in the infection process.

Int J Food Microbiol, 2000 Jun 1, 56(2-3), 123 - 32
Survival characteristics and the applicability of predictive mathematical modelling to Listeria monocytogenes growth in sous vide products; Nyati H; Survival and growth of Listeria monocytogenes isolates during sous vide processing and storage, and the applicability of predictive modelling in determining the potential for growth of L . monocytogenes in broth models and in sous vide products was investigated . L . monocytogenes grew in anaerobic tryptose phosphate broth and in chicken and beef samples by 2 log cycles in 8 days at 3 degrees C and 4-5 log cycles in 6 days at 8 degrees C . However, heating to an internal temperature of 70 degrees C resulted in a 4-5 log reduction and 70 degrees C/2 min resulted in a reduction greater than 7 log cycles . Lowering the product pH to 5.0 was effective in inhibiting L . monocytogenes growth, whereas a sodium chloride concentration of 2% had a negligible effect on growth rates . The square root model (Ratkowsky et al., 1983) predicted L . monocytogenes growth rates at 0-25 degrees C with a coefficient of determination (R2 value) of 98.36-99.63% and a bias factor of 1.08 to 1.21 in beef, chicken and broth substrates of unmodified pH . In addition, the Response Surface Polynomial Model (Version 3.1, Buchanan et al., 1989) predicted generation times at 5-25 degrees C with a 0-17.4% difference between observed and expected generation times in tryptose phosphate broth at pH 7.3 . There were however, large differences (25.5 vs . 5.3 h) between observed generation times at pH 5.6 (8 degrees C) and those predicted by the Pathogen Modelling Program in tryptose phosphate broth . A divergence from predicted values was also noted at lower temperatures (0-3.5 degrees C) in the square root model.

FEMS Microbiol Lett, 2000 Jun 15, 187(2), 185 - 8
A multidrug efflux transporter in Listeria monocytogenes; Mata MT et al.; A chromosomal gene (mdrL) was found in Listeria monocytogenes L028, showing a high degree of similarity with multidrug efflux transporters of the major facilitator superfamily (family 2) . An allele-substituted mutant of this gene failed to pump out ethidium bromide and presented lower minimal inhibitory concentrations of macrolides, cefotaxime and heavy metals . This is the first multidrug efflux pump described in Listeria.

J Food Prot, 2000 Jun, 63(6), 721 - 6
Application of enterocins as biopreservatives against Listeria innocua in meat products; Aymerich T et al.; The antilisterial effect of enterocins A and B in meat and meat products (cooked ham, minced pork meat, deboned chicken breasts, pate, and slightly fermented sausages {espetec}) have been shown . An infective dose of 5 to 10 most probable numbers (MPN)/g to simulate the counts of Listeria generally found in meat products was used . Enterocins at 4,800 AU/g reduced the numbers of Listeria innocua by 7.98 log cycles in cooked ham and by 9 log cycles in pate when stored at 7 degrees C for 37 days . In deboned chicken breasts stored at 70 degrees C for 7 days, 4,800 AU/cm2 of enterocins diminished the L . innocua counts in 5.26 log cycles when compared to the control batch . In minced pork meat held at 7 degrees C for up to 6 days, 1,600 AU/g kept L . innocua counts under 3 MPN/g, while the control batch reached 50 CFU/g . In espetec sausages, 648 AU/g diminished the number of L . innocua under 50 CFU/g from the fifth day until the end of the process (12 days) while the control batch kept the initial counts (3 x 104 CFU/g) . This is the first report on enterocins showing an antilisterial effect in different types of meat products.

J Food Prot, 2000 Jun, 63(6), 715 - 20
Survival of listeria innocua in salmon following cold-smoke application; Sabanadesan S et al.; The ability of Listeria innocua to survive on salmon fillets during cold smoking in a commercial processing plant was investigated using a central composite rotatable response surface design to examine smoking temperatures in the range of 18 to 30 degrees C and a smoke time from 2 to 14 h . Smoke temperature did not significantly (P < 0.05) reduce counts of L . innocua on the salmon . However, the smoking time had a significant effect on L . innocua . The smoking time was directly related to the reduction in count (R2 = 0.831), and a 3-log cycle reduction in count was observed when the smoking time was 12 h . The reduction in L . innocua levels on the fish was unaffected by the pH, water activity, and salt concentration of the fillet.

Ann Pharmacother, 2000 May, 34(5), 656 - 61
Treatment of listeriosis; Temple ME et al.; OBJECTIVE: To review the most currently accepted treatment options for the treatment of listeriosis . DATA SOURCES: Clinical literature was accessed through MEDLINE (1966-October 1999) . Key search terms included Listeria monocytogenes, food-borne illness, penicillins, fluoroquinolones, cephalosporins, and vancomycin . DATA SYNTHESIS: Listeriosis is mainly a food-borne illness caused by L . monocytogenes; people most prone to the disease are pregnant women, newborns, elderly, and those with HIV or other diseases compromising immunity . Listeria infections are associated with a high mortality rate, and thus effective antibiotic treatment is essential . Although a variety of antibiotics have activity against the organism, ampicillin alone or in combination with gentamicin remains the treatment of choice . Some patients may require alternative therapies due to allergies or certain disease states . Second-line agents for these cases include trimethoprim/sulfamethoxazole, erythromycin, vancomycin, and the fluoroquinolones . Cephalosporins are not active against Listeria . CONCLUSIONS: Ampicillin is currently the drug of choice for treating L . monocytogenes infections . Many antibiotics have been shown to be effective and are used as second-line agents . However, further study is required for some of the most recently introduced antibiotics, such as the fluoroquinolones, to determine their place in the treatment of Listeria infections.

Urol Res, 2000 Apr, 28(2), 93 - 6
Pulsed-field gel electrophoresis for the analysis of Listeria monocytogenes infection clusters after kidney transplantation; Reek C et al.; Listeria monocytogenes causes a rare, life-threatening infection in recipients of transplanted organs . We used cultures of blood and cerebrospinal fluid to characterize isolates and to distinguish cases in clusters from what might have been sporadic cases . From December 1994 to November 1995, six systemic L . monocytogenes infections occurred at our renal-transplantation unit . We confirmed the clinical diagnosis with blood and cerebrospinal fluid cultures and characterized the isolates retrospectively with pulsed-field gel electrophoresis (PFGE), phage-typing, and serotyping . We also performed an environmental investigation (food, drug, and stool) . We took samples after the first two L . monocytogenes infections and then after cases three and four occurred . All patients recovered completely, and no graft was lost . Four patients had identical or genetically related L . monocytogenes isolates in PFGE (type A) and serotyping (type 1/2b) . The other two had PFGE type B and G . L . monocytogenes was not detected in food or drug samples from patients on the renal-transplantation ward or in stool samples from the ward staff . It was concluded that PFGE allows sporadic cases and cluster cases of L . monocytogenes infection to be distinguished.

Lett Appl Microbiol, 2000 Jun, 30(6), 468 - 72
A comparison of the bioscreen method and microscopy for the determination of lag times of individual cells of listeria monocytogenes; Wu Y et al.; Lag phase durations (tLag) of individual Listeria monocytogenes cells were analysed using the NightOwl Molecular Imaging System, and results were compared with mean individual cell lag times (tL) obtained from the detection time (td) method using Bioscreen . With Bioscreen, an average tL of 6.39+/-0.89 h was obtained from five separate experiments . With the NightOwl method, an average tLag of 2.73+/-0.06 h was obtained from three experiments consisting of eight total replicates . Lag values from the NightOwl and Bioscreen are related by the equation: tLag = tL + DT, where DT is the doubling time . The equivalent tLag mean value for the Bioscreen method was 7.11+/-0.84 h . Individual lag times measured by both methods were normally distributed (r2 for Bioscreen and NightOwl ranged from 0.951 to 0.999 and from 0.884 to 0.982, respectively) . The results suggest that the NightOwl method can provide accurate estimates of individual cell lag times, which will facilitate the development of combined discrete continuous models for bacterial growth.

J Appl Microbiol, 2000 Jun, 88(6), 1049 - 55
Solubility and antimicrobial efficacy of protamine on Listeria monocytogenes and Escherichia coli as influenced by pH; Hansen LT et al.; The antimicrobial efficacy of protamine on Listeria monocytogenes and Escherichia coli was evaluated at concentrations from 50 to 10 000 microgram ml-1 and pH levels from 5.5 to 8.0 . The minimum inhibitory concentrations decreased with increasing pH . Protamine inhibited E . coli at all pH values while L . monocytogenes was inhibited at pH 6.5 and above . The antimicrobial efficacy of protamine decreased in the presence of negatively charged gelatine B but remained almost unchanged with addition of the positively charged gelatine A . Binding studies showed that the amount of protamine adsorbed to culture media components in tryptic soy broth and bacterial cells increased with increasing pH values . The increased efficacy of protamine at alkaline pH may be explained on the basis of an increase in electrostatic affinity for the cell surface of target cells . E . coli produced a protamine-degrading enzyme, however, was still susceptible to protamine.

J Appl Microbiol, 2000 Jun, 88(6), 992 - 1000
Physicochemical surface properties of five Listeria monocytogenes strains from a pork-processing environment in relation to serotypes, genotypes and growth temperature; Giovannacci I et al.; Physicochemical surface properties, related to electrostatic, van der Waals and Lewis acid-base interactions, of five Listeria monocytogenes strains isolated from pork-processing environments were determined after two subcultures at 37 degrees C and a final culture at three temperatures: 37, 10 and 4 degrees C . Three strains (Lm1, Lm114 and Lm191) were genetically related while two were unrelated (Lm25 and Lm74) according to ApaI-macrorestriction and pulsed-field gel electrophoresis (PFGE) typing . Listeria monocytogenes cell surfaces were generally negatively charged regardless of pH and tended to be hydrophilic due to a basic character . However, variable physicochemical surface properties of the five Listeria monocytogenes isolates were observed after growth at 37 degrees C . After growth at 10 degrees C, the three genetically related isolates exhibited similar surface properties and were slightly more hydrophilic and basic than the others . After growth at 4 degrees C, the five isolates displayed the same weak affinity for all kinds of solvents and low electrophoretic mobility values . A sharp decrease of temperature and subsequent growth of various Listeria monocytogenes strains resulted in loss of the physicochemical surface property variability, which may suggest the role of common chill adaptation mechanisms affecting surface properties.

J Immunol, 2000 Jun 15, 164(12), 6444 - 52
Adaptive immunity and enhanced CD8+ T cell response to Listeria monocytogenes in the absence of perforin and IFN-gamma; Badovinac VP et al.; Single Ag-specific CD8+ T cells from IFN-gamma-deficient (GKO) or perforin-deficient (PKO) mice provide substantial immunity against murine infection with Listeria monocytogenes . To address the potential for redundancy between perforin and IFN-gamma as CD8+ T cell effector mechanisms, we generated perforin/IFN-gamma (PKO/GKO) double-deficient mice . PKO/GKO-derived CD8+ T cells specific for the immunodominant listeriolysin O (LLO91-99) epitope provide immunity to LM infection similar to that provided by Ag-matched wild-type (WT) CD8+ T cells in the liver but reduced in the spleen . Strikingly, polyclonal CD8+ T cells from immunized PKO/GKO mice were approximately 100-fold more potent in reducing bacterial numbers than the same number of polyclonal CD8+ T cells from immunized WT mice . This result is probably quantitative, because the frequency of the CD8+ T cell response against the immunodominant LLO91-99 epitope is >4.5-fold higher in PKO/GKO mice than WT mice at 7 days after identical immunizations . Moreover, PKO/GKO mice can be immunized by a single infection with attenuated Listeria to resist >80,000-fold higher challenges with virulent organisms than naive PKO/GKO mice . These data demonstrate that neither perforin nor IFN-gamma is required for the development or expression of adaptive immunity to LM . In addition, the results suggest the potential for perforin and IFN-gamma to regulate the magnitude of the CD8+ T cell response to infection.

Int Immunol, 2000 Jun, 12(6), 887 - 97
In vitro and in vivo macrophage function can occur independently of SLP-76; Myung PS et al.; Expression of SH2 domain-containing leukocyte-specific phosphoprotein of 76 kDa (SLP-76), a hematopoietic cell-specific adapter protein, is required to couple Syk family tyrosine kinase activation to downstream mediators such as phospholipase C (PLC)-gamma following TCR, platelet collagen receptor and mast cell Fc epsilon R stimulation . In addition to T cells, mast cells and platelets, SLP-76 is expressed in monocytes and macrophages . To determine the role of SLP-76 in Fc gamma R-stimulated signaling pathways in macrophages, we examined cultured bone marrow-derived macrophages (BMM) from SLP-76(-/-) and wild-type mice . In this study, we show that Fc gamma R cross-linking rapidly induces tyrosine phosphorylation of SLP-76 in wild-type BMM . Surprisingly, however, BMM from SLP-76(-/-) mice activate ERK2 and phosphorylate PLC-gamma 2 following Fc gamma R ligation . Furthermore, SLP-76(-/-) BMM display normal Fc gamma R-dependent phagocytic function and reactive oxygen intermediate production . SLP-76(-/-) and SLP-76(+/+) BMM secrete comparable levels of IL-12 in response to lipopolysaccharide and IFN-gamma . To examine macrophage function in vivo, SLP-76(-/-) mice were challenged i.v . with Listeria monocytogenes . SLP-76(-/-) mice survive and efficiently contain the acute phase of infection similar to wild-type mice but exhibit a stable chronic infection attributed to the lack of mature T cells . These data show that, although SLP-76 is required to couple Syk family PTK activity to downstream mediators and effector functions in Fc gamma R-induced pathways in some cell types, activation of Fc gamma R-dependent pathways occurs independently of SLP-76 in BM

Indian J Pediatr, 1995 Jan-Feb, 62(1), 33 - 9
Listeria Monocytogenes infections; Gordon RC; This article reviews current information regarding human infection with Listeria monocytogenes . Significant advances have occurred in regard to our knowledge of the epidemiology, pathogenesis, immunology, and treatment of this disease which was formerly believed to be of importance mainly to veterinarians . It remains a cause of high mortality in the many different groups of compromised hosts it infects unless diagnosis and treatment are rapidly established.

J Food Prot, 2000 May, 63(5), 662 - 4
Inactivation of Listeria monocytogenes Scott A on artificially contaminated frankfurters by high-pressure processing; Lucore LA et al.; Vacuum-packaged frankfurters, inoculated with 24-h cultures of Listeria monocytogenes Scott A (approximately 10(9) CFU/ml) by injection into the packages, were held at pressures of 300, 500, and 700 MPa for up to 9 min . L . monocytogenes were washed from the surface of the frankfurter and plated onto brain heart infusion agar . During the time to achieve 300, 500, and 700 MPa (come-up time), L . monocytogenes populations decreased by 1, >3, and >5 logs, respectively . Additional inactivation of L . monocytogenes occurred while the samples were held at 300 and 500 MPa . A 5-log reduction in bacterial population was possible at all pressure treatments; however, pressurization at 700 MPa showed the fastest inactivation with L . monocytogenes reduced from 10(8) to 10(2) CFU/package during the come-up time . These results show that high-pressure processing may be a viable method for controlling foodborne pathogens in postprocessed, packaged frankfurters.

J Food Prot, 2000 May, 63(5), 659 - 61
Temperature gradient gel electrophoresis of the amplified product of a small 16S rRNA gene fragment for the identification of Listeria species isolated from food; Manzano M et al.; The development of a rapid method for the identification of Listeria spp . is described . It is based on the polymerase chain reaction amplification of a small fragment from the 16S rRNA gene followed by temperature gradient gel electrophoresis . Forty-five strains of Listeria spp . (Listeria monocytogenes, Listeria innocua, Listeria ivanovii, Listeria seeligeri, and Listeria welshimeri) were used for the optimization of the protocol . No differences were observed between the results of the identification of the strains tested using traditional methods and those obtained by polymerase chain reaction-temperature gradient gel electrophoresis analysis.

J Food Prot, 2000 May, 63(5), 613 - 9
Pathogenicity and production of virulence factors by Listeria monocytogenes isolates from channel catfish; Erdenlig S et al.; Pathogenicity of four channel catfish Listeria monocytogenes isolates (CCF1, CCF4, HCC7, and HCC23) was examined in a comparative manner with virulent type strains L . monocytogenes ATCC 19115 and EGD and avirulent type strain ATCC 15313 in BDF and A/J mice . Isolates HCC7 and CCF1 (both serovar 1) caused similar percent mortalities and 50% lethal concentration values when compared with virulent type strains and were therefore considered pathogenic . The presence of the virulence factors listeriolysin (LLO), phosphotidylcholine-phospholipase (PC-PLC), and phosphotidylinositol-phospholipase (PI-PLC) was determined using specific activity tests . The virulent catfish isolates were positive for production of LLO, PC-PLC, and PI-PLC . However, catfish isolate HCC23 was not virulent in mice despite being hemolytic, suggesting that not every hemolytic L . monocytogenes strain is virulent . With the exception of HCC7, all virulent strains displayed enhanced LLO production in a special stress medium, whereas almost undetectable LLO activity was present when catfish isolates and virulent type strain L . monocytogenes were grown in a rich medium such as brain heart infusion . Avirulent strains were found to lack or have decreased expression of LLO, PC-PLC, or PI-PLC.

Immunopharmacology, 2000 Jun, 48(1), 35 - 42
Protective effect of a traditional Japanese medicine, Bu-zhong-yi-qi-tang (Japanese name: Hochu-ekki-to), on the restraint stress-induced susceptibility against Listeria monocytogenes; Yamaoka Y et al.; In this study, the effect of traditional Japanese (Chinese) medicine, Bu-zhong-yi-qi-tang (Japanese name: Hochu-ekki-to, HOT), on the restraint stress treatment (RST)-induced susceptibility against Listeria monocytogenes (L . monocytogenes) was examined . When RST was performed every day for 10 h from the day of infection, the bacterial numbers were increased at 3 and 5 days after the infection . Oral pretreatment with HOT for 7 days prevented such increases . Pretreatment with HOT prevented the suppression of antigen-specific IFN-gamma production by RST . HOT also prevented suppression of macrophage accumulation, including MHC-class II positives, in the peritoneal cavity and their bactericidal activity by RST . HOT suppressed the serum corticosterone level elevated by RST in infected mice . Taken together, the suppression of corticosterone using HOT participates in the prevention of suppressions of the bactericidal activity of macrophages, migration of macrophages and antigen-specific IFN-gamma production of Th1 cells by RST . Our findings suggest that HOT is a useful drug for patients suffering from stress disease to reduce the susceptibility to bacterial infection.

Br J Pharmacol, 2000 Jun, 130(3), 581 - 6
Retinoid-mediated inhibition of interleukin-12 production in mouse macrophages suppresses Th1 cytokine profile in CD4(+) T cells; Kang BY et al.; Interleukin-12 (IL-12) plays a central role in the immune system by driving the immune response towards T helper 1 (Th1) type responses characterized by high IFN-gamma and low IL-4 production . In this study we investigated whether retinoid-mediated inhibition of interleukin-12 production in mouse macrophages could regulate cytokine profile of antigen (Ag)-primed CD4(+) Th cells . Pretreatment with retinoids (9-cis-RA, all-trans-RA, TTNPB) significantly inhibited IL-12 production by mouse macrophages stimulated with lipopolysaccharide (LPS) or heated-killed Listeria monocytogenes (HKL) . Retinoid-pretreated macrophages reduced their ability to induce IFN-gamma and increased the ability to induce IL-4 in Ag-primed CD4(+) T cells . Addition of recombinant IL-12 to cultures of retinoid-pretreated macrophages and CD4(+) T cells restored IFN-gamma production in CD4(+) T cells . The in vivo administration of 9-cis-RA resulted in the inhibition of IL-12 production by macrophages stimulated in vitro with either LPS or HKL, leading to the inhibition of Th1 cytokine profile (decreased IFN-gamma and increased IL-4 production) in CD4(+) T cells . These findings may explain some known effects of retinoids including the inhibition of encephalitogenicity, and point to a possible therapeutic use of retinoids in the Th1-mediated immune diseases such as autoimmune diseases.

J Infect Dis, 2000 May, 181(5), 1838 - 41 Epub 2000 May 09.
An outbreak of Listeria monocytogenes serotype 3a infections from butter in Finland; Lyytikainen O et al.; In February 1999, an outbreak of listeriosis caused by Listeria monocytogenes serotype 3a occurred in Finland . All isolates were identical . The outbreak strain was first isolated in 1997 in dairy butter . This dairy began delivery to a tertiary care hospital (TCH) in June 1998 . From June 1998 to April 1999, 25 case patients were identified (20 with sepsis, 4 with meningitis, and 1 with abscess; 6 patients died) . Patients with the outbreak strain were more likely to have been admitted to the TCH than were patients with other strains of L . monocytogenes (60% vs . 8%; odds ratio, 17.3; 95% confidence interval, 2.8-136.8) . Case patients admitted to the TCH had been hospitalized longer before cultures tested positive than had matched controls (median, 31 vs . 10 days; P=.008) . An investigation found the outbreak strain in packaged butter served at the TCH and at the source dairy . Recall of the product ended the outbreak.

Infect Immun, 2000 Jun, 68(6), 3680 - 8
Listeria monocytogenes-infected human dendritic cells: uptake and host cell response; Kolb-Maurer A et al.; Dendritic cells (DCs) are potent antigen-presenting cells and play a crucial role in initiation and modulation of specific immune responses . Various pathogens are able to persist inside DCs . However, internalization of the gram-positive bacterium Listeria monocytogenes into human DCs has not yet been shown . In the present study, we demonstrate that human monocyte-derived immature DCs can efficiently phagocytose L . monocytogenes . This uptake is independent of listerial adhesion factors internalin A and internalin B but requires cytoskeletal motion and factors present in human plasma . A major portion of internalized bacteria is found in membrane-bound phagosomes and is rarely free in the cytosol, as shown by transmission electron microscopy and by using an L . monocytogenes strain expressing green fluorescent protein when in the host cell cytosol . The infection caused maturation of the immature DCs into mature DCs displaying high levels of CD83, CD25, major histocompatibility complex class II, and the CD86 costimulator molecule . This effect appeared to be largely mediated by listerial lipoteichoic acid . Although L . monocytogenes infection is known to induce death in other cell types, infection of human DCs was found to induce necrotic but not apoptotic death in fewer than 20% of DCs . Therefore, the ability of DCs to act as effective antigen-presenting cells for listerial immunity is probably enhanced by their resistance to cell death, as well as their ability to rapidly differentiate into mature, immunostimulatory DCs upon encountering bacteria.

Infect Immun, 2000 Jun, 68(6), 3275 - 9
Interaction of Listeria monocytogenes with human brain microvascular endothelial cells: an electron microscopic study; Greiffenberg L et al.; Internalization of Listeria monocytogenes into human brain microvascular endothelial cells (HBMEC) has recently been demonstrated to be dependent upon the inlB gene . In the present scanning electron microscopic study we show that L . monocytogenes efficiently interacts with the surface of HBMEC in an inlB-independent manner which is also different from invasion . The inlB-dependent invasion of HBMEC by L . monocytogenes is accompanied by intracellular multiplication, movement, and production of bacterium-containing protrusions . These protrusions extend from the cell surface without perturbation of any adjacent cellular membrane.

Infect Immun, 2000 Jun, 68(6), 3242 - 50
Listeriolysin O as a reporter to identify constitutive and in vivo-inducible promoters in the pathogen Listeria monocytogenes; Dubail I et al.; Listeria monocytogenes is a facultative intracellular gram-positive bacterium capable of growing in the cytoplasm of infected host cells . Bacterial escape from the phagosomal vacuole of infected cells is mainly mediated by the pore-forming hemolysin listeriolysin O (LLO) encoded by hly . LLO-negative mutants of L . monocytogenes are avirulent in the mouse model . We have developed a genetic system with hly as a reporter gene allowing the identification of both constitutive and in vivo-inducible promoters of this pathogen . Genomic libraries were created by randomly inserting L . monocytogenes chromosomal fragments upstream of the promoterless hly gene cloned into gram-positive and gram-negative shuttle vectors and expressed in an LLO-negative mutant strain . With this hly-based promoter trap system, combined with access to the L . monocytogenes genome database, we identified 20 in vitro-transcribed genes, including genes encoding (i) p60, a previously known virulence gene, (ii) a putative new hemolysin, and (iii) two proteins of the general protein secretion pathway . By using the hly-based system as an in vivo expression technology tool, nine in vivo-induced loci of L . monocytogenes were identified, including genes encoding (i) the previously known in vivo-inducible phosphatidylinositol phospholipase C and (ii) a putative N-acetylglucosamine epimerase, possibly involved in teichoic acid biosynthesis . The use of hly as a reporter is a simple and powerful alternative to classical methods for transcriptional analysis to monitor promoter activity in L . monocytogenes.

Microbes Infect, 1999 Aug, 1(10), 753 - 64
Cytolytic T-cell responses to human dendritic cells and macrophages infected with Mycobacterium bovis BCG and recombinant BCG secreting listeriolysin; Conradt P et al.; Cytolytic T-cell responses from 63 normal blood donors were monitored in a Mycobacterium bovis BCG infection system in vitro . We wanted to know whether cultured dendritic cells were capable of potentiating the cytolytic T-cell responses to M . bovis BCG . Infected cultured dendritic cells were up to ten times more effective antigen-presenting cells than macrophages in proliferative assays, while cytolytic T-cell induction did not differ significantly between dendritic cells and macrophages . Separated CD4+ and CD8+ T-cell subsets contributed equally to lysis of infected targets . Experiments comparing wild-type M . bovis BCG strain with two new recombinant M . bovis BCG strains secreting listeriolysin revealed statistically significant higher maximal lysis values for recombinant M . bovis BCG . We conclude from our in vitro infection system with mycobacteria that dendritic cells are superior to macrophages in proliferative assays but equal to macrophages in their ability to induce cytolytic T-cell responses . Moreover, our data suggest that recombinant M . bovis BCG vaccine strains secreting listeriolysin improve cytolytic T-cell responses.

Zh Mikrobiol Epidemiol Immunobiol, 2000 Mar-Apr, (2), 32 - 6
{The laboratory diagnosis of an outbreak of hemorrhagic fever at Oblivskaya village, Rostov Province: proof of the etiological role of the Crimean-Congo hemorrhagic fever virus}; Onishchenko GG et al.; The results of the molecular biological detection of the etiologic agent of hemorrhagic fever in Rostov Province are presented . The role of the causative agents of Astrakhan rickettsial fever, hemorrhagic fever with the renal syndrome, Q fever, leptospirosis and listeriosis has been excluded by means of such immunochemical reactions as the direct and indirect immunofluorescent tests, the solid-phase immunoenzyme assay, the complement fixation test and the agglutination test . The relationship between the cases of hemorrhagic fever in the focus of the outbreak and Crimean-Congo hemorrhagic fever virus has been demonstrated due to the use of the polymerase chain reaction with preliminary reverse transcription.

Immunol Rev, 2000 Apr, 174, 150 - 9
Innate defenses in the liver during Listeria infection; Cousens LP et al.; The majority of pathogens entering the bloodstream are cleared by the liver . Listeria monocytogenes, an important natural pathogen of humans, is a useful tool for examining protective immune responses during systemic infections of mice . Innate immunity contributes to blood clearance and eventual sterilization of the liver subsequent to Listeria infections . Effector mechanisms expressed in the liver early after infections are orchestrated by complex interactions between resident populations, i.e . hepatocytes and Kupffer cells, with infiltrating monocytes, neutrophils, and natural killer cells . These interactions include cell to cell contact through adhesion molecules, as well as communication through secretion of cytokines and chemokines . The liver environment, as the interface between blood-borne pathogens and innate host defenses, is reviewed here.

Immunol Rev, 2000 Apr, 174, 112 - 22
CD8+ T-cell-mediated response to Listeria monocytogenes taken up in the liver and replicating within hepatocytes; Gregory SH et al.; Like most other organisms that enter the bloodstream, the bulk of Listeria monocytogenes injected i.v . into mice is taken up by the liver . Listeriae not killed rapidly by infiltrating neutrophils are internalized by hepatocytes which constitute the principal site of intracellular replication in the liver . CD8+ T cells play a critical role in eliminating infected hepatocytes and resolving listerial infections of the liver; the specific mechanisms involved are not understood fully . Here, we review recent data implicating the cytolytic activities expressed by MHC class Ia- and class Ib-restricted CD8+ T cells in host resistance to Listeria . Evidence demonstrating the perforin- and/or Fas ligand-dependent induction of caspase activity and the resultant apoptosis of Listeria-infected hepatocytes is discussed.

Med Dosw Mikrobiol, 1999, 51(3-4), 413 - 9
{The effect of selected antibacterial antibiotics on production of interferon gamma (IFN-G) by mouse T lymphocytes stimulated by Listeria monocytogenes}; Sacha PT et al.; The aim of the study was to determine the influence of certain antibiotics on the production of IFN-gamma by mouse lymphocytes T after four days incubation with Listeria monocytogenes . The level of mouse IFN-gamma was determined by ELISA method (Inter Test-gamma Mouse IFN-gamma Kit, Genzyme) . The strongest immunosuppression effect was demonstrated using rifampicin (39 ng/ml IFN-gamma) (Control: 123 +/- 29 ng/ml IFN-gamma, p < 0.05) . Lower immunosuppression effects were observed also with cephradine (54 ng/ml IFN-gamma), amikacin (56 ng/ml IFN-gamma) and ticarcillin (83 ng/ml) . The obtained results show that all tested cephalosporins (cephamandole, cefotaxime, cephradine) and aminogllycosides (gentamicin, streptomycin, amicacin) inhibit production of IFN-gamma by mouse lymphocytes T . The influence of penicillin G and ampicillin, as well as, erythromycin and lincomycin on the production IFN-gamma was not observed . Our results suggest that rifampicin, ticarcillin, cephalosporins and aminoglycosides act as inhibitors of production IFN-gamma.

Med Dosw Mikrobiol, 1999, 51(3-4), 399 - 412
{The influence of antibiotics on phagocytic and bacteriocidal activity of rabbit peritoneal macrophages stimulated by filtrates of cultured t-lymphocytes}; Sacha PT et al.; The aim of the study was to determine the influence of twelve antibacterial antibiotics (various concentrations) on the activation of rabbit peritoneal macrophages . Macrophages were stimulated by filtrates of culture of lymphocytes T obtained from OVA immunized rabbits . Phagocytic activity and intracellular killing against Listeria monocytogenes were tested by fluorescence method . Penicillin G (0.4-50 mg/l), erythromycin and lincomycin (2.5-40 mg/l) used at all concentrations, were not exerting significant effects on activation of peritoneal macrophages . Cephalosporins, aminoglycosides, and rifampicin at low concentrations (0.4-5.0 mg/l) had no influence on phagocytosis and intracellular killing, also . Cephalosporins at concentration 10 mg/l (cephradine and cefamandole) and 50 mg/l (cefotaxime) inhibited intracellular killing and phagocytic activity . The same results were observed with ampicillin and ticarcillin (50 mg/l) . The highest suppression effect was demonstrated using rifampicin at concentration 10 mg/l or more . Gentamicin, streptomycin and amicacin at concentrations 40 mg/l or more significantly inhibited macrophage activation in response to filtrates lymphocytes of culture . These inhibitions were more marked with gentamicin (10 mg/l) than amicacin (20 mg/l) or streptomycin (40 mg/l) . All antibiotics did not stimulated the activity of peritoneal macrophages . The suppression activity of peritoneal macrophages by some antibiotics probably acts at the level of specific immune system by interfering with cytokine production.

Nat Med, 2000 May, 6(5), 589 - 93
The trophoblast is a component of the innate immune system during pregnancy; Guleria I et al.; Systemic infection with Listeria monocytogenes, a Gram-positive intracellular bacterium, has been used extensively to analyze the innate immune response . Macrophages are central to this response, acting as both the host for and principal defense against this bacterium . During pregnancy L . monocytogenes has a predilection for replication at the maternal-placental interface and consequently is an important cause of fetal morbidity and mortality . However, macrophages are mostly excluded from the murine placenta with neutrophils acting as the main immune effector cell against this bacterium . Colony stimulating factor (CSF)-1, a macrophage growth factor, is synthesized in high concentrations by the uterine epithelium during pregnancy, where it is targeted to trophoblast bearing CSF-1-receptors . To define the involvement of CSF-1 in placental immunity, we infected pregnant mice either homozygous or heterozygous for an inactivating recessive mutation in the gene for CSF-1 (osteopetrotic; Csfmop) with L . monocytogenes . CSF-1 was required to recruit neutrophils to the site of listerial infection in the decidua basalis, and infection by Listeria remained unrestrained in its absence . CSF-1 acted by inducing the trophoblast to synthesize the neutrophil chemoattractants (KC) and macrophage inflammatory protein (MIP)-2 . Thus, during pregnancy, trophoblast responsive to CSF-1 acts to organize the maternal immune response to bacterial infection at the utero-placental interface . This previously unknown function indicates that the trophoblast acts as a pregnancy-specific component of the innate immune system.

Nat Med, 2000 May, 6(5), 573 - 7
High susceptibility to bacterial infection, but no liver dysfunction, in mice compromised for hepatocyte NF-kappaB activation; Lavon I et al.; Based on the essential involvement of NF-kappaB in immune and inflammatory responses and its apoptosis-rescue function in normal and malignant cells, inhibitors of this transcription factor are potential therapeutics for the treatment of a wide range of diseases, from bronchial asthma to cancer . Yet, given the essential function of NF-kappaB in the embryonic liver, it is important to determine its necessity in the liver beyond embryogenesis . NF-kappaB is normally retained in the cytoplasm by its inhibitor IkappaB, which is eliminated upon cell stimulation through phosphorylation-dependent ubiquitin degradation . Here, we directed a degradation-resistant IkappaBalpha transgene to mouse hepatocytes in an inducible manner and showed substantial tissue specificity using various means, including a new method for live-animal imaging . Transgene expression resulted in obstruction of NF-kappaB activation, yet produced no signs of liver dysfunction, even when implemented over 15 months . However, the transgene-expressing mice were very vulnerable both to a severe immune challenge and to a systemic bacterial infection . Despite having intact immunocytes and inflammatory cells, these mice were unable to clear Listeria monocytogenes from the liver and succumbed to sepsis . These findings indicate the essential function of the hepatocyte through NF-kappaB activation in certain systemic infections, possibly by coordinating innate immunity in the liver.

J Biol Chem, 2000 Jul 21, 275(29), 22503 - 11
Characterization of the interaction between zyxin and members of the Ena/vasodilator-stimulated phosphoprotein family of proteins; Drees B et al.; Zyxin contains a proline-rich N-terminal domain that is similar to the C-terminal domain in the ActA protein of the bacteria, Listeria monocytogenes . We screened the entire amino acid sequence of human zyxin for Mena-interacting peptides and found that, as with ActA, proline-rich sequences were the sole zyxin sequences capable of binding to Ena/vasodilator-stimulated phosphoprotein (VASP) family members in vitro . From this information, we tested zyxin mutants in which the proline-rich sequences were altered . The reduction in Mena/VASP binding was confirmed by peptide tests, immunoprecipitation, and ectopic expression of zyxin variants at the surface of mitochondria . By transfection assays we showed that zyxin interaction with Mena/VASP in vivo enhances the production of actin-rich structures at the apical surface of cells . Microinjection into cells of peptides corresponding to the first proline-rich sequence of zyxin caused the loss of Mena/VASP from focal contacts . Furthermore, these peptides reduced the degree of spreading of cells replated after trypsinization . We conclude that zyxin and proteins that harbor similar proline-rich repeats contribute to the positioning of Mena/VASP proteins . The positioning of Ena/VASP family members appears to be important when the actin cytoskeleton is reorganized, such as during spreading.

Mol Microbiol, 2000 Apr, 36(2), 487 - 97
PrfA mediates specific binding of RNA polymerase of Listeria monocytogenes to PrfA-dependent virulence gene promoters resulting in a transcriptionally active complex; Bockmann R et al.; There is accumulating evidence that the coordinate transcription of the virulence genes in Listeria monocytogenes constitutes a very complex regulation mechanism which might require other factors in addition to PrfA . We previously described an unknown proteinaceous component from crude bacterial cell extracts, which, together with PrfA, formed a specific complex (CI) in electrophoretic mobility shift assays (EMSA) with an hly promoter probe . Here we identify the RNA polymerase (RNAP) of L . monocytogenes as an essential component of the CI complex . Addition of purified RNAP plus PrfA to the hly promoter probe allowed reconstitution of a complex migrating at the same height as CI . By using EMSA and DNaseI footprint experiments it could be shown that PrfA leads to an enhanced and specific binding of RNAP . Transcriptional activity of RNAP in vitro, using the actA promoter, was strictly dependent on PrfA.

J Appl Microbiol, 2000 May, 88(5), 870 - 6
Improved detection of Listeria monocytogenes in soft mould-ripened cheese; Johansson T et al.; In comparison with standard methods, enrichment in half-Fraser broth for 24 h at 30 degrees C, followed by plating out onto Listeria monocytogenes blood agar (LMBA) and PALCAM medium combined with an additional streak proved to be the most rapid and specific method for the detection of indigenous L . monocytogenes populations from soft mould-ripened cheese . This procedure, with a high sensitivity (93%) and a low detection limit (1-10 cfu 25 g-1), provided negative and presumptive positive results within 2-3 d . Differences between LMBA, PALCAM and Oxford medium turned out to be highly significant (at 99% significance level); plating on LMBA after standard enrichment protocols giving the best overall results . An improvement in detection was also obtained by modifying the confirmation procedure . A loopful of culture (an additional streak) from PALCAM or Oxford medium was streaked on non-selective medium in addition to streaking only separate colonies as specified in the standards.

J Appl Microbiol, 2000 Apr, 88(4), 686 - 94
Effect of sausage ingredients and additives on the production of enterocin A and B by Enterococcus faecium CTC492 . Optimization of in vitro production and anti-listerial effect in dry fermented sausages; Aymerich T et al.; Enterocin A and B in Enterococcus faecium CTC492 were co-induced by the different factors assayed in this study (r = 0.93) and followed primary metabolic kinetics . Enterocin production was significantly inhibited by sausage ingredients and additives, with the exception of nitrate . The addition of sodium chloride and pepper decreased production 16-fold . The temperature and pH influenced enterocin production, with optima between 25 and 35 degrees C, and from 6.0 to 7.5 of initial pH . The maximum activity was achieved, under favourable growth conditions, with MRS supplemented with sucrose (2%) plus glucose (0.25%) and Tween-80 (1%) . MRS concentration, NaCl plus pepper addition, absence of Tween-80 in the growth medium, incubation at 45 degrees C and an initial pH under 5.5 were detrimental to bacteriocin production . Stress conditions did not favour enterocin production . Desadsorption was Tween-dependent . Enterocin A activity in the crude extracts stored at -80 degrees C was better preserved than enterocin B (when tested against their specific indicator strain), but anti-listerial activity remained intact . Applied as anti-listerial additives in dry fermented sausages, enterocins significantly diminished Listeria counts by 1 . 13 log (P < 0.001), while Enterococcus faecium CTC492 added as starter culture did not significantly reduce Listeria counts (P > 0 . 1) compared with the standard starter culture (Bac-) . Enterocins A and B could be considered as extra biopreservative hurdles for listeria prevention in dry fermented sausages.

Int J Food Microbiol, 2000 Apr 10, 55(1-3), 201 - 7
Modelling the growth of Listeria monocytogenes in dynamic conditions; Cheroutre-Vialette M et al.; A recurrent neural network for the prediction of Listeria monocytogenes growth under pH and a(w) variable conditions was developed . The use of this model offered the possibility to take into account the consequences of the variations of the factors on L . monocytogenes growth . The effects of solutions, such as NaCl, acetic acid and NaOH, and their interactions on the response of L . monocytogenes cells were studied . Furthermore, the results showed the capacity of the recurrent neural network to predict growths carried out in different experimental conditions without using those used for its elaboration.

Int J Food Microbiol, 2000 Apr 10, 55(1-3), 151 - 5
Proteins variations in Listeria monocytogenes exposed to high salinities; Esvan H et al.; Listeria monocytogenes Scott A grown in the minimal chemically defined medium M6LT was challenged to a concentration of either 35 or 65 g l(-1) of NaCl for 1 h in the presence of a {35S}cysteine-{35S}methionine labelling mix . The protein patterns were analysed by 2D-electrophoresis in the two conditions and isoosmotic condition (5 g l(-1) of NaCl in M6LT) . A great number of proteins which were synthesized under isoosmotic conditions were either completely repressed or expressed at a reduced level, at 65 g l(-1) and to a lesser extent at 35 g l(-1) of NaCl . At 35 g l(-1) of NaCl, six proteins were up-regulated, five proteins showed no change in expression level and five were repressed . Among the proteins up-regulated at 35 g l(-1) of NaCl, a single one (18.7 kDa, pI 5.05) was up-regulated at 65 g l(-1) too . We observed 21 proteins which were repressed at 65 g l(-1) of NaCl, among which 11 completely disappeared . Some of the up-regulated proteins have characteristics of molecular weight and isoelectric point close to those of stress proteins reported elsewhere: the protein induced both at 35 and 65 g l(-1) might correspond to a previously proposed universal stress protein of Listeria . Some proteins which were repressed at 65 g l(-1) have molecular weights close to those of virulence proteins.

Int J Food Microbiol, 2000 Apr 10, 55(1-3), 121 - 6
Acid responses of Listeria monocytogenes; Phan-Thanh L et al.; The acid response and the correlated protein synthesis in Listeria monocytogenes were studied . The lowest pH value which L . monocytogenes could resist was dependent on the strain and the kind of acid used . Previous adaptation to an intermediary pH augmented bacterial resistance to a subsequent lethal acidic pH . The acid tolerance was also growth phase dependent . Organic volatile acids exerted a more deleterious effect on L . monocytogenes than inorganic acids, because weak acids infer a lower intracytoplasmic pH . The responses to acid adaptation (mildly acidic pH) and acid stress (lethal acidic pH) shared the majority of acid-induced proteins . The bacteria required more stress proteins to face severe acidic conditions . In order to obtain insights into the role these acid-induced proteins play in the mechanism of acid resistance, the proteins were analysed by two-dimensional electrophoresis and the most abundant were identified by peptide mass fingerprinting and MALDI-TOF mass spectrometry.

Rev Argent Microbiol, 2000 Jan-Mar, 32(1), 49 - 52
{Investigation of LIsteria monocytogenes in soft cheeses}; Copes J et al.; Listeria monocytogenes has been recognized as a bacteria that produces severe illness in animals and humans . Considering the importance of the presence of L . monocytogenes in soft paste cheeses, a study of diverse cheeses from supermarkets of direct sale to the public was carried out . From the 35 analyzed cheeses, 4 strains were isolated (11.4%) . The result of the serological study showed that all the strains corresponded to the serotype 4 . The proteic profiles of the isolated strains showed similarity with the used pattern (4b) . Several authors reported the importance of L . monocytogenes as contaminant in foods ready to eat like the soft paste cheeses . Thus, it must be remarked the importance of the good handling practices in the production, transport, refrigeration and exhibition of this product.

Infection, 2000 Mar-Apr, 28(2), 121 - 3
Listeria meningitis in children: report of two cases; Economou M et al.; We report two cases of meningitis caused by Listeria monocytogenes in children . The first patient was a healthy 14-month-old boy and the second patient a 3-year-old girl with Byler disease which, however, is not reported as a predisposing factor for listeriosis . We present these cases because Listeria infection, although common in neonates, is extremely infrequent during infancy and childhood.

N Engl J Med, 2000 Apr 27, 342(17), 1236 - 41
An outbreak of febrile gastroenteritis associated with corn contaminated by Listeria monocytogenes; Aureli P et al.; BACKGROUND: On May 21, 1997, numerous cases of febrile gastrointestinal illness were reported among the students and staff of two primary schools in northern Italy, all of whom had eaten at cafeterias served by the same caterer . METHODS: We interviewed people who ate at the cafeterias about symptoms and foods consumed on May 20 . There were no samples of foods left at the cafeterias, but we tested routine samples taken on May 20 by the caterer and environmental specimens at the catering plant . The hospitalized patients were tested for common enteropathogens and toxins . RESULTS: Of the 2189 persons interviewed (82 percent of those exposed), 1566 (72 percent) reported symptoms; of these, 292 (19 percent) were hospitalized . Among samples obtained from hospitalized patients, all but two of the stool specimens and all blood specimens were negative for common enteropathogens . Listeria monocytogenes was isolated from one blood specimen and from 123 of the 141 stool specimens . Consumption of a cold salad of corn and tuna was associated with the development of symptoms (relative risk, 6.19; 95 percent confidence interval, 4.81 to 7.98; P<0.001) . L . monocytogenes was isolated from the caterer's sample of the salad and from environmental specimens collected from the catering plant . All listeria isolates were serotype 4b and were found to be identical on DNA analysis . Experimental contamination of sterile samples of the implicated foods showed that L . monocytogenes grew on corn when kept for at least 10 hours at 25 degrees C . CONCLUSIONS: Food-borne infection with L . monocytogenes can cause febrile illness with gastroenteritis in immunocompetent persons.

Anesthesiology, 2000 May, 92(5), 1268 - 77
Smoking decreases alveolar macrophage function during anesthesia and surgery; Kotani N et al.; BACKGROUND: Smoking changes numerous alveolar macrophage functions and is one of the most important risk factors for postoperative pulmonary complications . The current study tested the hypothesis that smoking impairs antimicrobial and proinflammatory responses in alveolar macrophages during anesthesia and surgery . METHOD: The authors studied 30 smoking and 30 nonsmoking patients during propofol-fentanyl general anesthesia . Alveolar immune cells were harvested by bronchoalveolar lavage immediately and 2, 4, and 6 h after induction of anesthesia and at the end of surgery . The types of alveolar immune cell and macrophage aggregation were determined . The authors measured opsonized and unopsonized phagocytosis . Microbicidal activity was determined as the ability of the macrophages to kill Listeriamonocytogenes directly . Finally, RNA was extracted from harvested cells and cDNA was synthesized by reverse transcription . The expression of interleukin 1beta, 6, and 8, interferon gamma, and tumor necrosis factor alpha were measured by semiquantitative polymerase chain reaction using beta-actin as an internal standard . RESULTS: The fraction of aggregated macrophages increased significantly over time in both groups, whereas phagocytosis of opsonized and nonopsonized particles and microbicidal activity of alveolar macrophages decreased significantly . The changes, though, were nearly twice as great as in patients who smoked . Gene expression of all proinflammatory cytokines in alveolar immune cells except interleukin 6 increased 2- to 20-fold over time in both groups . The expression of interleukin 1beta, interferon gamma, and tumor necrosis factor alpha, however, increased only half as much in smokers as in nonsmokers . CONCLUSION: Smoking was associated with macrophage aggregation but markedly reduced phagocytic and microbicidal activity-possibly because expression of proinflammatory cytokines was reduced in these patients . Our data thus suggest that smokers may have a limited ability to mount an effective pulmonary immune defense after anesthesia and surgery.

FEMS Microbiol Lett, 2000 May 1, 186(1), 35 - 40
Specific binding of recombinant Listeria monocytogenes p60 protein to Caco-2 cells; Park JH et al.; The Listeria monocytogenes p60 is a major extracellular protein, which is believed to be involved in the invasion of these bacteria into their host cells . So far the mechanism by which p60 participates in the internalization or penetration of L . monocytogenes is still veiled . To determine the possibility of a direct interaction of p60 with the host cell surface, the iap gene was recombinantly expressed in Escherichia coli and used for binding studies with the enterocyte-like Caco-2 cells . Fluorescence activated flow cytometry and confocal laser scanning microscopy revealed a cell membrane specific staining with p60, which implications in Listeria virulence are discussed.

Int J Food Microbiol, 2000 Mar 25, 54(3), 205 - 12
The use of immuno-magnetic separation (IMS) as a tool in a sample preparation method for direct detection of L . monocytogenes in cheese; Uyttendaele M et al.; A sample preparation procedure was developed for direct detection of L . monocytogenes in cheese . The sample preparation protocol consisted of a 10-fold dilution and homogenization, a centrifugation step to precipitate large food particles, passage of the supernatant over a sieve and through a separatory funnel to further eliminate food particles and fat, a centrifugation step to recover the bacterial pellet and finally enzymatic digestion of the suspension to degrade the remaining small food particles . Recovery of L . monocytogenes was confirmed by plating on Oxford medium and confirmation of suspected colonies . This protocol enabled direct detection (without prior enrichment) of low numbers of L . monocytogenes (0.5-1.5 cfu/g cheese) from different types of cheese . The performance of Dynabeads Anti-Listeria (Dynal, Oslo, Norway) for selective recovery of L . monocytogenes and their applicability in the above mentioned procedure for direct detection of low numbers of L . monocytogenes from cheese was evaluated . IMS could not separate and recover L . monocytogenes from the food particles in the concentrated suspension . The use of IMS after a 24 h enrichment procedure (as recommended by the manufacturer) allowed for the detection of low numbers of L . monocytogenes (< 10 cfu/g) . However, experiments in broth cultures showed that although the detection limit of IMS with Dynabeads Anti-Listeria was 40-100 cfu/ml, the ratio of L . monocytogenes to non-Listeria flora was not increased . Thus, selective enrichment or concentration of L . monocytogenes was not obtained.

Int J Food Microbiol, 2000 Mar 25, 54(3), 171 - 80
A combined discrete-continuous model describing the lag phase of Listeria monocytogenes; McKellar RC et al.; Food microbiologists generally use continuous sigmoidal functions such as the empirical Gompertz equation to obtain the kinetic parameters specific growth rate (mu) and lag phase duration (lambda) from bacterial growth curves . This approach yields reliable information on mu; however, values for lambda are difficult to determine accurately due, in part, to our poor understanding of the physiological events taking place during adaptation of cells to new environments . Existing models also assume a homogeneous population of cells, thus there is a need to develop discrete event models which can account for the behavior of individual cells . Time to detection (t(d)) values were determined for Listeria monocytogenes using an automated turbidimetric instrument, and used to calculate mu . Mean individual cell lag times (tL) were calculated as the difference between the observed t(d) and the theoretical value estimated using mu . Variability in tL for individual cells in replicate wells was estimated using serial dilutions . A discrete stochastic model was applied to the individual cells, and combined with a deterministic population-level growth model . This discrete-continuous model incorporating tL and the variability in tL (expressed as standard deviation; S.D.(L)) predicted a reduced variability between wells with increased number of cells per well, in agreement with experimental findings . By combining the discrete adaptation step with a continuous growth function it was possible to generate a model which accurately described the transition from lag to exponential phase . This new model may serve as a useful tool for describing individual cell behavior, and thus increasing our knowledge of events occurring during the lag phase.

J Food Prot, 2000 Apr, 63(4), 457 - 61
Rapid hot dog surface pasteurization using cycles of vacuum and steam to kill Listeria innocua; Kozempel M et al.; The vacuum/steam/vacuum surface pasteurization process was applied to hot dogs inoculated on the surface with non-pathogenic Listeria innocua . Using the optimum conditions previously found for processing chicken carcasses as a starting point, optimum process conditions were determined for a hot dog treatment compatible with current process line speed . Cycling the treatment significantly improved the microbiological kill . At the optimum conditions of steam time of 0.3 s at 138 degrees C (two cycles), a bacteria kill >3 log CFU/ml was attained . Pasteurization, frequently considered to be a kill of >5 log CFU/ml, was reached by increasing the number of cycles to three . The surface pasteurization process should ensure that hot dogs reaching the consumer are free of Listeria.

J Bacteriol, 2000 May, 182(9), 2544 - 50
Osmotic and chill activation of glycine betaine porter II in Listeria monocytogenes membrane vesicles; Gerhardt PN et al.; Listeria monocytogenes is a foodborne pathogen known for its tolerance to conditions of osmotic and chill stress . Accumulation of glycine betaine has been found to be important in the organism's tolerance to both of these stresses . A procedure was developed for the purification of membranes from L . monocytogenes cells in which the putative ATP-driven glycine betaine permease glycine betaine porter II (Gbu) is functional . As is the case for the L . monocytogenes sodium-driven glycine betaine uptake system (glycine betaine porter I), uptake in this vesicle system was dependent on energization by ascorbate-phenazine methosulfate . Vesicles lacking the gbu gene product had no uptake activity . Transport by this porter did not require sodium ion and could be driven only weakly by artificial gradients . Uptake rates could be manipulated under conditions not affecting secondary transport but known to affect ATPase activity . The system was shown to be both osmotically activated and cryoactivated . Under conditions of osmotic activation, the system exhibited Arrhenius-type behavior although the uptake rates were profoundly affected by the physical state of the membrane, with breaks in Arrhenius curves at approximately 10 and 18 degrees C . In the absence of osmotic activation, the permease could be activated by decreasing temperature within the range of 15 to 4 degrees C . Kinetic analyses of the permease at 30 degrees C revealed K(m) values for glycine betaine of 1.2 and 2.9 microM with V(max) values of 2,200 and 3,700 pmol/min . mg of protein under conditions of optimal osmotic activation as mediated by KCl and sucrose, respectively.

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