Bacillus cereus (B. cereus) is a Gram-positive, rod-shaped, facultatively anaerobic, motile, beta-hemolytic, spore forming bacterium. These bacteria are usually present in soil and food.
Bacillus cereus is a foodborne pathogen that can produce toxins. These toxins cause two types of gastrointestinal illness: the emetic syndrome and the diarrhoeal syndrome. When the emetic toxin (cereulide) is produced in the food, vomiting occurs after ingestion of the contaminated food. The diarrhoeal syndrome occurs when enterotoxins are produced in the intestine, following ingestion of food contaminated with B. cereus.
Symptoms of food poisoning due to Bacillus cereus
Symptoms include:
Emetic syndrome
- vomiting
- nausea
- sometimes diarrhea
Symptoms usually start 0.5 to 5 hours after ingestion of contaminated food. Usually, symptoms disappear in 6 to 24 hours.
Diarrhoeal syndrome
- diarrhea, sometimes with blood and/or mucus
- nausea,
- may also include abdominal pain
Symptoms usually start 8 to 16 hours after ingestion of contaminated food. Usually, symptoms disappear in 12 to 24 hours.
In some cases, the disease may be more severe. If you have serious symptoms, you should see your doctor.
Causes
B. cereus is widespread in the environment and commonly found in the soil. Bacillus cereus is able to produce spores that are resistant to heat and desiccation, therefore researchers can isolate it from both raw and cooked foods. These spores will germinate into the vegetative form of B. cereus, and grow if the food is held under favorable conditions of pH (>4.8) and temperature (between 8°C and 55°C) for a sufficient time. Although the presence of vegetative forms of B. cereus in food is always necessary for the disease to occur, not all the B. cereus strains can produce the toxins that cause the emetic or diarrhoeal syndromes. In addition, the conditions leading to each of the syndromes differ slightly.
The emetic syndrome will affect consumers of food contaminated with the cereulide, therefore the food needs to be contaminated with B. cereus strains that are able produce this toxin and be handled in a way that allows bacterial growth and subsequent toxin formation. It is estimated that, in order to produce sufficient cereulide to induce vomiting, levels of B. cereus should be greater than 10,000 per gram of food. The toxin is produced in the food and is resistant to heat; therefore it will not be eliminated by most cooking methods, even when the vegetative cells are inactivated. This syndrome is frequently associated with starchy food, such as pasta or rice.
The diarrhoeal syndrome occurs when a large number of vegetative cells of B. cereus (at least 10,000 per gram of food) are ingested, and produce enterotoxin in the small intestine. A wider range of foods have been linked with the diarrhoeal syndrome, such as meat products, stews, soups, sauces, vegetables and milk products.
Diagnosis
Food poisoning caused by B. cereus can be confirmed by isolation of this bacterium in food, stool or vomit samples.
Treatment of food poisoning caused by Bacillus cereus
Most people recover from this disease without treatment. The administration of fluids is recommended if the diarrhea or vomiting is severe. Antibiotics are not recommended, because the symptoms are caused by the toxins and not the bacteria.
How to prevent food poisoning caused by Bacillus cereus
As B. cereus is ubiquitous in the environment, control measures should be focused on preventing growth of B. cereus and the formation of emetic toxin in the food.
- You should keep the food at a temperature above 60°C, or refrigerate the food at below 4°C.
- When reheating food, ensure that the temperature reaches at least 74°C.
