The production of Bacillus cereus enterotoxins is influenced by carbohydrate and growth rate.

ABSTRACT

Enterotoxin production is a key factor in Bacillus cereus food poisoning. Herein, the effect of the growth rate (mu) on B. cereus toxin production when grown on sucrose was studied and the Hemolytic BL enterotoxin (HBL) and nonhemolytic enterotoxin (Nhe) production by B. cereus was compared according to carbohydrate at mu = 0.2 h(-1). The anaerobic growth was carried out on continuous cultures in synthetic medium supplemented with glucose, fructose, sucrose, or an equimolar mixture of glucose and fructose. Concerning the HBL and Nhe enterotoxin production (1) the highest enterotoxin production has occurred at mu = 0.2 h(-1) when growing on sucrose; (2) HBL production was repressed when glucose was consumed and the presence of fructose (alone or in mixture) cancelled glucose catabolite repression; (3) the consumption of sucrose increased Nhe production, which was not affected by the catabolite repression. Furthermore, analysis of the fermentative metabolism showed that whatever the mu or the carbon source, B. cereus used the mixed acid fermentation to ferment the different carbohydrates. The enterotoxin productions by this strain at mu = 0.2 h(-1) are highly influenced by the carbohydrates that do not involve any fermentative metabolism changes.