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Detachment Characteristics and Oxacillin Resistance of Staphyloccocus aureus Biofilm Emboli in an In Vitro Catheter Infection Model. C. A. Fux, 2004.Catheter-related bloodstream infections due to Staphylococcus aureus are of increasing clinical importance . The pathophysiological steps leading to colonization and infection, however, are still incompletely defined . We observed growth and detachment of S . aureus biofilms in an in vitro catheter-infection model by using time-lapse microscopy . Biofilm emboli were characterized by their size and their susceptibility for oxacillin . Biofilm dispersal was found to be a dynamic process in which clumps of a wide range of diameters detach . Large detached clumps were highly tolerant to oxacillin compared with exponential-phase planktonic cultures . Interestingly, the degree of antibiotic tolerance in stationary-phase planktonic cultures was equal to that in the large clumps . The mechanical disruption of large clumps reduced the minimal bactericidal concentration (MBC) by more than 1,000 times . The MBC for whole biofilm effluent, consisting of particles with an average number of 20 bacteria was 3.5 times higher than the MBC for planktonic cultures . We conclude that the antibiotic resistance of detached biofilm particles depends on the embolus size and could be attributed to nutrient-limited stationary-phase physiology of cells within the clumps . We hypothesize that the detachment of multicellular clumps may explain the high rate of symptomatic metastatic infections seen with S . aureus . Medium-Chain Fatty Acids Decrease Colonization and Invasion through hilA Suppression Shortly after Infection of Chickens with Salmonella enterica Serovar Enteritidis. F. Van Immerseel, 2004.The most common source of Salmonella infections in humans is food of poultry origin . Salmonella enterica serovar Enteritidis has a particular affinity for the contamination of the egg supply . In this study, the medium-chain fatty acids (MCFA), caproic, caprylic, and capric acid, were evaluated for the control of Salmonella serovar Enteritidis in chickens . All MCFA were growth inhibiting at low concentrations in vitro, with caproic acid being the most potent . Contact of Salmonella serovar Enteritidis with low concentrations of MCFA decreased invasion in the intestinal epithelial cell line T84 . By using transcriptional fusions between the promoter of the regulatory gene of the Salmonella pathogenicity island I, hilA, and luxCDABE genes, it was shown that all MCFA decreased the expression of hilA, a key regulator related to the invasive capacity of Salmonella . The addition of caproic acid (3 g/kg of feed) to the feed of chicks led to a significant decrease in the level of colonization of ceca and internal organs by Salmonella serovar Enteritidis at 3 days after infection of 5-day-old chicks . These results suggest that MCFA have a synergistic ability to suppress the expression of the genes required for invasion and to reduce the numbers of bacteria in vivo . Thus, MCFA are potentially useful products for reducing the level of colonization of chicks and could ultimately aid in the reduction of the number of contaminated eggs in the food supply . Agrobacterium tumefaciens VirB6 Protein Participates in Formation of VirB7 and VirB9 Complexes Required for Type IV Secretion. Simon J. Jakubowski, 2003.This study characterized the contribution of Agrobacterium tumefaciens VirB6, a polytopic inner membrane protein, to the formation of outer membrane VirB7 lipoprotein and VirB9 protein multimers required for type IV secretion . VirB7 assembles as a disulfide cross-linked homodimer that associates with the T pilus and a VirB7-VirB9 heterodimer that stabilizes other VirB proteins during biogenesis of the secretion machine . Two presumptive VirB protein complexes, composed of VirB6, VirB7, and VirB9 and of VirB7, VirB9, and VirB10, were isolated by immunoprecipitation or glutathione S-transferase pulldown assays from detergent-solubilized membrane extracts of wild-type A348 and a strain producing only VirB6 through VirB10 among the VirB proteins . To examine the biological importance of VirB6 complex formation for type IV secretion, we monitored the effects of nonstoichiometric VirB6 production and the synthesis of VirB6 derivatives with 4-residue insertions (VirB6.i4) on VirB7 and VirB9 multimerization, T-pilus assembly, and substrate transfer . A virB6 gene deletion mutant accumulated VirB7 dimers at diminished steady-state levels, whereas complementation with a plasmid bearing wild-type virB6 partially restored accumulation of the dimers . VirB6 overproduction was correlated with formation of higher-order VirB9 complexes or aggregates and also blocked substrate transfer without a detectable disruption of T-pilus production; these phenotypes were displayed by cells grown at 28°C, a temperature that favors VirB protein turnover, but not by cells grown at 20°C . Strains producing several VirB6.i4 mutant proteins assembled novel VirB7 and VirB9 complexes detectable by nonreducing sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and two strains producing the D60.i4 and L191.i4 mutant proteins translocated IncQ plasmid and VirE2 effector protein substrates in the absence of a detectable T pilus . Our findings support a model that VirB6 mediates formation of VirB7 and VirB9 complexes required for biogenesis of the T pilus and the secretion channel . Virus-Contaminated Oysters: a Three-Month Monitoring of Oysters Imported to Switzerland. Christian Beuret, 2003.Molluscan shellfish are known to be carriers of viral and bacterial pathogens . The consumption of raw oysters has been repeatedly linked to outbreaks of viral gastroenteritis and hepatitis A . Switzerland imports over 300 tons of oysters per year, 95% of which originate in France . To assess the level of viral contamination, a 3-month monitoring study was conducted . Therefore, the sensitivities of several previously described methods for virus concentration were compared, and one protocol was finally chosen by using dissected digestive tissues . Eighty-seven samples consisting of five oysters each were analyzed for Norwalk-like viruses (NLVs), enteroviruses, and hepatitis A viruses from November 2001 to February 2002 . The oysters were exported by 31 French, three Dutch, and two Irish suppliers . Eight oyster samples from six French suppliers were positive for NLVs, and four samples from four French suppliers were positive for enteroviruses; two of the latter samples were positive for both viral agents . No hepatitis A viruses were detected . The sequences of NLV and enterovirus amplicons showed a great variety of strains, especially for the NLVs (strains similar to Bristol, Hawaii, Mexico, and Melksham agent) . The data obtained indicated that imported oysters might be a source of NLV infection in Switzerland . However, further studies are needed to determine the quantitative significance of the risk factor within the overall epidemiology of NLVs .
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