Bacillus species are gram-positive, aerobic, ubiquitous bacteria characterized by their ability to form resistant spore coats. About 48 known species exist in the genus Bacillus, but only B. anthracis and B. cereus are associated with human disease. Bacillus species produce heat-resistant endosopores and have a growth range of 10 degrees C to 48 degrees C, with optimal growth at 28 degrees C to 35 degrees C. They can grow in a broad pH range of 4.9 to 9.3.
Bacillus cereus is a spore-forming, Gram-positive, anaerobic bacterium associated with food poisoning in humans. Food poisoning is a result of ingesting heat-stable toxins produced by the bacteria: either a toxin that causes vomiting or one that causes diarrhea. B. cereus is widespread in the soil and in the food industry in such foods as rice, herbs, spices, milk and vegetables. The disease is transmitted from contaminated foods, improper food handling/storage, and improper cooling of cooked foods.
Two types of illness are associated with B. cereus. The most common is a diarrheal illness accompanied with abdominal pain. An incubation period of 4 to 16 hours is followed by symptoms lasting 12 to 24 hours.
The second type involves vomiting, often associated with ingestion of rice that is not properly refrigerated after cooking. This illness is characterized by vomiting and nausea that usually occur within 1 to 5 hours upon ingestion of the contaminated food. This is sometimes referred to as an intoxication.
B. cereus can infect anyone because illness may result from ingesting contaminated food. However, the immuno-compromised, the very young and older adults may suffer from more serious side effects. B. cereus may pose a higher risk for those working in food preparation areas and in slaughterhouses. Intact tissues and meat from animals are sterile, but, after the animals are slaughtered, they may become contaminated from the processing plant or from bacteria that grow on the hide or in the gut.
Generally, gastroenteritis symptoms from B. cereus resolve by themselves but may require medical intervention.
Bacillus cereus gastroenteritis is best prevented by controlling time and temperature. Proper cooking will kill vegetative cells; however, spores may survive. To prevent the bacteria from having an opportunity to grow, hot foods should be cooled as quickly as possible for storage and should not be allowed to remain at rooom temperature for more than two hours. Foods held on a food service line or hot bar should be maintained at a temperature of 135 degrees F or higher.