Large colonies of Bacillus cereus on blood agar. Cultivation 24 hours, 37°C. Colonies are surroundend by a wide zone of beta-hemolysis.
Bacillus cereus is an endemic, soil-dwelling, Gram-positive, rod-shaped, beta hemolytic bacterium. Some strains are harmful to humans and cause foodborne illness, while other strains can be beneficial as probiotics for animals. It is the cause of "Fried Rice Syndrome". B. cereus bacteria are aerobes, and like other members of the genus Bacillus can produce protective endospores.
B. cereus is responsible for a minority of foodborne illnesses (2–5%), causing severe nausea, vomiting and diarrhea. Bacillus foodborne illnesses occur due to survival of the bacterial endospores when food is improperly cooked. Cooking temperatures less than or equal to 100 °C (212 °F) allows some B. cereus spores to survive. This problem is compounded when food is then improperly refrigerated,
allowing the endospores to germinate. Germination and growth generally occurs between 10–50 °C (50–122 °F), though some strains are psychrotrophic. Bacterial growth results in production of enterotoxins, one of which is highly resistant to heat and to pH between 2 and 11; ingestion leads to two types of illness, diarrheal and emetic (vomiting) syndrome.