Relationship between variations in pathogenicity and lag phase at 37°C of Listeria monocytogenes previously stored at 4°C

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

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