Bacillus cereus

The Bacillus cereus group currently consists of nine Bacillus species, i.e., B. anthracis, B. cereus, B. mycoides, B. pseudomycoides, B. thuringiensis, B. weihenstephanensis, B. cytotoxicus, B. bombysepticus, and the most recent member of the group, B. toyonensis. The species within the B. cereus group are very closely related, and their toxicity ranges from avirulent strains used as probiotics to highly toxic strains responsible for severe illness and fatalities. B. cereus causes two different types of foodborne illness: the diarrheal type caused by enterotoxins and the emetic type caused by a small heat-stable emetic toxin. For both these types of foodborne illness, the food involved has usually been heat treated, and surviving spores are the source of the food poisoning. The members of the B. cereus group are common soil saprophytes and are easily spread to many types of foods, especially those of plant origin (rice and pasta), but are also frequently isolated from dairy products. Some strains of the B. cereus group are able to grow at refrigeration temperature. These variants raise concerns regarding the safety of cooked, refrigerated foods with extended shelf lives. Foodborne B. cereus illness is probably greatly underreported, as both types of illness are usually mild and last for less than 24 hours. However, more severe forms of B. cereus foodborne illness, including fatalities, are reported occasionally.