RELATIONSHIP BETWEEN VARIATIONS IN PATHOGENICITY AND LAG PHASE AT 37-DEGREES-C OF LISTERIA-MONOCYTOGENES PREVIOUSLY STORED AT 4-DEGREES-C

Three haemolytic, pathogenic strains of Listeria monocytogenes (a refe rence strain, a food-derived strain and a human strain) were held at 4 degrees C for 4 weeks in phosphate-buffered saline pH 5.5 or 7.0, wit h and without 0.2% potassium sorbate or 0.3% sodium acetate. The numbe r of viable cells did not change significant-ly during this storage. P athogenicity of non-growing L. monocytogenes cells for 14-d-old chick embryos was determined before and after storage. Storage at 4 degrees C resulted in decreased pathogenicity, but effects were strain-, pH- a nd substrate-dependent. After 4 weeks storage at 4 degrees C non-growi ng bacterial cells were transferred to Brain Heart Infusion broth and growth characteristics were determined during incubation at 37 degrees C. Strains that showed decreased pathogenicity had significantly long er lag phases at 37 degrees C than strains that maintained pathogenici ty. It is concluded that decreased pathogenicity of L. monocytogenes s tored without growth at 4 degrees C for 4 weeks and subsequent long la g phase at 37 degrees C are correlated.