CHAPTER ONE
1.0 INTRODUCTION
Bacillus cereus is the cause of two kinds of food borne diseases, an emetic (vomiting) intoxication due to the ingestion of a toxin (cereulide) pre-formed in the food and a diarrhoeal infection due to the ingestion of bacterial cells/spores which produce enterotoxins in the small intestine (Lubenau .C. 1906). Other Bacillus spp, Bacillus subtilis, Bacillus licheniformis, Bacillus pumilus have more rarely been identified as agents of food borne diseases characterized by diarrhoea and/or vomiting. Emetic intoxication is caused by a very homogeneous group of strains of Bacillus cereus identified by their ability to produce cereulide. In contrast, Bacillus cereus strains able to cause diarrhoea are not easy to identify because the mechanisms leading to infection are complex and diverse (Kramer, .J.M. and R.J. Gilbert 1989). Very little is known on the virulence mechanisms of other Bacillus spp and therefore it is not possible to identify the strains able to cause food borne poisoning. In most
instances, food borne diseases caused by Bacillus cereus were associated with 5 log to 8 log cells/spores per g of the food vehicle. However, in some outbreaks, lower numbers in the food (3 – 4 log per g) were reported.
Foodborne poisoning caused by other Bacillus spp. has always been linked to high numbers of cells/spores in the food vehicle (equal or more to 6 log per g). Bacillus cereus is ubiquitous and low numbers of its spores, too low to cause food borne poisoning, can be found in a wide range of foodstuffs. Spores can germinate and multiply in humid, low acid foods, from 45°C to 55°C (Notermans et al. 1997). However, strains able to multiply below 7°C, and strains able to multiply above 45°C, are not the most common. Emetic Bacillus cereus are presumably unable to grow and produce their toxin cereulide below 10°C, or in the absence of oxygen. Other Bacillus spp. involved in food borne poisoning cases are also frequent causes of food spoilage. Almost all kind of foods have been implicated in B.
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