Heat-resistance of psychrotolerant Bacillus cereus vegetative cells

Abstract

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 log10 reduction, of the vegetative cells of the three psychrotolerant phylogenetic groups of B. cereus varied between 3.02 °C and 4.84 °C. The temperature at which a 3 log10 reduction was achieved in 10 min varied between 47.6 °C and 49.2 °C for psychrotolerant vegetative cells and it was around 54.8 °C for thermotolerant vegetative cells. Moreover, 0.4 min at 60 °C would be sufficient for a 6 log10 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.