Opinion of the Scientific Panel on Biological Hazards on Bacillus cereus and other Bacillus spp in foodstuffs

Bacillus cereus is the cause of two kinds of foodborne 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. Other Bacillus spp., B. subtilis, B. licheniformis, B. pumilus have more rarely beeen identified as agents of foodborne diseases characterized by diarrhoea and/or vomiting. Emetic intoxication is caused by a very homogeneous group of strains of B. cereus identified by their ability to produce cereulide. In contrast, B. cereus strains able to cause diarrhoea are not easy to identify because the mechanisms leading to infection are complex and diverse. 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 foodborne poisoning. In most instances, foodborne diseases caused by B. 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 foodborne poisoning, can be found in a wide range of foodstuffs. Spores can germinate and multiply in humid, low acid foods, from 4-5 degrees C to 55 degrees C. However, strains able to multiply below 7 degrees C, and strains able to multiply above 45 degrees C, are not the most common. Emetic B. cereus are presumably unable to grow and produce their toxin cereulide below 10 degrees C, or in the absence of oxygen. Other Bacillus spp. involved in foodborne poisoning cases are also frequent causes of food spoilage. Almost all kind of foods have been implicated in B. cereus foodborne poisoning. However, a majority of reported outbreaks were linked to the consumption of heat treated foods and frequently occurred in restaurant and catering establishments. Failure in refrigeration was frequently suspected. Cooked dishes containing pasta or rice were the main, but not the only, foods implicated in emetic intoxications. The major control measures are to control temperature and to establish HACCP system. Only heat treatments used for canning of low acid foods will ensure a complete destruction of spores of B. cereus. The number of spores in other processed foods must be kept as low as possible by proper cleaning and disinfection of equipments. Rapid cooling is necessary to prevent germination and growth of B. cereus spores. Low pH (below 4.5), reduction in aw (below 0.92) would inhibit B. cereus. In other cases, refrigeration below 4 degrees C is necessary to prevent growth of all types of B. cereus, including psychrotrophic strains. However, below 10 degrees C, lag time and generation times are very significantly increased, particularly whenever other factors (i. e. pH, aw, nutrient content of the food) are not optimum for B. cereus. This should be verified by microbiological testing. Control measures for B. cereus would contribute to control other Bacillus spp.