|
Résumé :
|
Three haemolytic, pathogenic strains of Listeria monocytogenes (a reference strain NCTC 7973, a food-derived strain L70 and a human strain L94) and a control strain of Listeria innocua L27 were held in phosphate-buffered saline (PBS) of pH 7.0 or 5.5 at 4 degrees C for 4 weeks. The number of viable cells did not change significantly during this storage (the cells were non-growing). Titers of Listeria listeriolysin O (LLO) activity against washed human erythrocytes and the pathogenicity of non-growing bacterial cells for 14-day-old chick embryos were determined before storage and after 1, 2, 3 and 4 weeks of storage. Prolonged storage at 4 degrees C affected both LLO production and pathogenicity of the non-growing cells, but effects were strain- and pH-dependent. At pH 7.0, all three L. Monocytogenes strains had lost LLO activity after 2 weeks of storage. At pH 5.5, the reference and the food strains lost LLO activity 1 week later than when stored at neutral pH, and the human strain maintained LLO activity throughout the 4-week period. Pathogenicity of the reference strain stored at pH 7.0 and 5.5 and that of the food strain stored at pH 7.0 decreased during storage at 4 degrees C.
|
