Heat-resistance of psychrotolerant Bacillus cereus vegetative cells

Spores of psychrotolerant strains of the foodborne pathogen Bacillus cereus can multiply during storage of cooked or pasteurized, refrigerated foods and can represent a risk if these cells are not eliminated during reheating of food product before consumption. We determined the heat-resistance of psychrotolerant B. cereus vegetative cells at different heating temperatures in laboratory medium and compared it with that of thermotolerant B. cereus vegetative cells. The z values, based on times for a 3 logio reduction, of the vegetative cells of the three psychrotolerant phylogenetic groups of B. cereus varied between 3.02 degrees C and 4.84 degrees C. The temperature at which a 3 logio reduction was achieved in 10 min varied between 47.6 degrees C and 49.2 degrees C for psychrotolerant vegetative cells and it was around 54.8 degrees C for thermotolerant vegetative cells. Moreover, 0.4 min at 60 degrees C would be sufficient for a 6 logio CFU/ml reduction of the most heat resistant psychrotolerant B. cereus vegetative cells. These data clearly showed that psychrotolerant B. cereus vegetative cells can be rapidly eliminated by a mild heat treatment such as food reheating