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Bacillus cereus

bacillus cereus 10000 mag BCCDC Labs.jpg 

10,000 x mag; source: BCCDC Labs, LM

Food poisoning caused by B. cereus is an acute intoxication that occurs when this microorganism produces toxins, causing two types of gastrointestinal illness: an emetic (vomiting) syndrome or a diarrhoeal syndrome. B. cereus is considered a relatively common cause of gastroenteritis worldwide. In Canada, over 36,000 cases of foodborne illness due to B. cereus were estimated to have occurred in 2006. B. cereus will grow in food that has been improperly stored, therefore proper food handling, especially after cooking, will help prevent illnesses caused by this microorganism.

Bacillus cereus is a foodborne pathogen that can produce toxins, causing two types of gastrointestinal illness: the emetic (vomiting) 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 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, and 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 illness may be more severe. If you have serious symptoms, you should see your doctor. 


B. cereus is widespread in the environment and commonly found in the soil. It is able to produce spores that are resistant to heat and desiccation, therefore it is not uncommon to 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 foodborne 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 emetic toxin 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, but several publications have documented illnesses, including hospitalizations with lower numbers. 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 dishes.

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.


Both the emetic and diarrhoeal syndromes are usually self-limiting, resolving within one or two days. In a small percentage of cases it can be more severe, and deaths have been reported in the literature. The elderly and patients with lower stomach acidity may be more susceptible to the diarrhoeal syndrome.


Food poisoning caused by B. cereus can be confirmed by isolation of this bacterium in food, stool or vomit samples. Different media are available to culture this pathogen. Commercial kits are also available to detect the diarrhoeal enterotoxin, but this is not the case for emetic toxin.


Most people recover without treatment. The administration of fluids is recommended if the diarrhoea or vomiting is severe. Antibiotics are not indicated as the symptoms are caused by the toxins and not the bacteria.


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.

  • Ensure food is maintained either at a temperature above 60°C or refrigerated below 4°C.
  • Cool cooked foods that will not be immediately consumed to below 4°C within 6 hours.
  • When reheating food, ensure that the temperature reaches at least 74°C.

SOURCE: Bacillus cereus ( )
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