The fate of Bacillus cereus in the gastrointestinal tract

This report presents a mathematical dynamical model for the behaviour of Bacillus cereus in the gastro-intestinal tract. Biological processes and system dynamics are simultaneously incorporated in this mechanistic model. Variability in growth characteristics and physical traits of different B. cereus strains are expressed through the incorporation of a range of reasonable parameter values obtained from experiments. Different hypotheses concerning initial ingestion of B. cereus microbes and subsequent in vivo processes leading to a potential infection are tested. Model outputs show the course of (attached) vegetative cells and/or spores in the stomach and small intestine during the digestion of food containing B. cereus microbes. Results show the minor influence of the stomach on the ultimate number of vegetative cells in the small intestine. A "mild" exposure (10^3 cfu g^-1) still causes an increased probability on food intoxication when 100 g of food containing, at least, slightly mesophilic B. cereus strains is consumed. Exposure to levels just above the Dutch standard (set at < 10^5 cfu g^-1) will, according to this model, always form a food hazard problem. Furthermore, this model gives insight in the uncertainty of some parameter values that need elaborated experimental investigation to come to an improved hazard characterisation and, with that, to improved suggestions for food microbiological criteria