Growth and diarrhoeagenic enterotoxin formation by strains of Bacillus cereus in vitro in controlled fermentations and in situ in food products and a model food system

Abstract

Growth and enterotoxin formation by diarrhoeagenic Bacillus cereus strain 1230-88 in vitro in controlled continuous and batch fermentations occurred over a wide range of conditions. Enterotoxin formation was not affected by growth rate ( T D 2·3–13·8 h), but was influenced by the nature of the nitrogen source, and at extremes of pH. The presence of 0·1–1·0% glucose or starch did not enhance or suppress toxin formation in controlled pH continuous cultures. Enterotoxin was not formed under anaerobic conditions in the defined medium used. Mesophilic and psychrotrophic strains of B. cereus were able to grow and form toxin in situ in several different proprietary dairy dessert products and also in a starch-based custard-like model food system. Growth and toxin formation were suppressed in low pH non-dessert food products. Specific compositional modifications to the sucrose or starch concentration, the type of protein used, or the initial pH (range pH 6–8) of the model food did not prevent either growth or toxinogenesis occurring. Compositional manipulation was not effective in preventing in situ proliferation and enterotoxin formation by B. cereus in food products. Lowering the incubation temperature, however, effectively restricted growth of both mesophilic and psychrotrophic strains of B. cereus in both the model food system and the dairy dessert products examined.