Prevalence, characterization and growth of Bacillus cereus in commercial cooked chilled foods containing vegetables

In cooked-chilled and pasteurized vegetable products, initial numbers of Ba cillus cereus were below 10 cfu g(-1). Before the appearance of spoilage, n umbers reached 6-8 log cfu g(-1) at 20 degrees C and 4-6 log cfu g(-1) at 1 0 degrees C. Bacillus cereus was not detected in samples stored at 4 degree s C. Ten percent of strains isolated from the products were able to grow at 5 degrees C and 63% at 10 degrees C. Bacillus cereus strains unable to deg rade starch, a feature linked to the production of emetic toxin, did not gr ow at 10 degrees C and had a higher heat resistance at 90 degrees C. Using immunochemical assays, enterotoxin was detected in the culture supernatant fluid of 97.5% of the strains. All culture supernatant fluids were cytotoxi c but important variations in the level of activity were found. Psychrotrop hic isolates of B. cereus were unable to grow in courgette broth at 7 degre es C whereas they grew in a rich laboratory medium. At 10 degrees C, these isolates grew in both media but lag time in courgette broth was 20-fold lon ger than in the rich laboratory medium.