Bacillus cereus (B. cereus) is a microscopic organism that releases harmful toxins. It can cause food poisoning (intestinal B. cereus) or more serious health issues (non-intestinal B. cereus). Most people with food poisoning recover within 24 hours. But you’re at higher risk of complications if you have a weak or compromised immune system.
Bacillus cereus (B. cereus) is a spore-forming bacteria that is so small you can only see it through a microscope. B. cereus commonly exists in the environment. This bacterium produces a harmful substance (toxin) that can make you sick.
There are two types of Bacillus cereus. They either affect:
Intestinal B. cereus causes food poisoning. This illness tends to go away on its own quickly. But you’re at risk of a more serious case if you have a weak or compromised immune system.
Bacillus cereus not related to food poisoning (non-intestinal B. cereus) can cause more severe infections. You’re at higher risk of more serious illness if you have non-intestinal B. cereus along with:
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In the enterotoxin form of the disease, you produce the toxin in your small intestine. This happens after you eat food with the bacteria or the cells they produce (spores). This is the most common type of B. cereus in the U.S. and Europe.
You usually get food poisoning six to 15 hours after eating contaminated food. Foods that can cause this illness include:
In the emetic form of this disease, the toxin forms in the food before you eat it. You usually get sick within one to six hours after eating contaminated food.
Rice is most commonly associated with this type of Bacillus cereus. Not all rice contains B. cereus, but this bacterium can form when cooked rice sits too long unrefrigerated. Other foods that can cause this illness include cheese as well as starchy foods such as:
Non-intestinal B. cereus affects your body outside of your gastrointestinal tract. It most commonly shows up in your:
This bacterium can be in:
People of every age and race can have intestinal or non-intestinal Bacillus cereus.
Your risk of non-intestinal Bacillus cereus increases if you:
Intestinal Bacillus cereus infections are very common. There are an estimated 63,400 instances of B. cereus outbreaks each year in the U.S.
Non-intestinal Bacillus cereus infections are rarer.
Intestinal Bacillus cereus commonly occurs from eating foods left at room temperature. Food poisoning can occur even if you reheat the food.
Intestinal B. cereus forms spores that give off toxins. At room temperature, these spores can increase in number. When you eat these spores, these toxins cause vomiting or diarrhea.
Symptoms of enterotoxins include:
Symptoms of emetic syndrome include nausea and vomiting.
Bacillus cereus can cause non-intestinal illnesses when the spores enter a person’s body and give off toxins. You can get the spores from:
Non-intestinal illnesses caused by B. cereus include:
Symptoms vary based on the type of illness. Endophthalmitis causes the highest amount of severe illness. Symptoms of this life-threatening eye infection may include:
Some people with endophthalmitis may end up losing their eye.
The diagnosis of B. cereus food poisoning can be confirmed by the isolation of greater than or equal to 100,000 B. cereus organisms per gram from epidemiologically implicated food.
If your provider suspects intestinal Bacillus cereus, they will ask about your symptoms and the last meal you had. They’ll also do a physical exam. To confirm B. cereus, they will need to test a sample of the food you ate as well as a sample of your stool (poop) or vomit. For diarrheal syndrome, they can also do a blood test to look for the toxin.
If your provider suspects non-intestinal Bacillus cereus, blood cultures are the most common method to detect bacteria in your bloodstream. Routine cultures and a Gram stain to look for bacteria can also be done on a sample of your body fluids. For instance, to test for endophthalmitis, they can sample fluid from your eye (vitreous fluid). They apply a stain to the sample on a glass microscope slide to check for bacteria.
Food poisoning related to Bacillus cereus usually goes away on its own within 24 hours. Your provider may suggest:
If you have severe diarrhea or vomiting, your provider may recommend getting IV fluids.
Treatment for non-intestinal B. cereus depends on your specific condition. Your provider will usually start you on antibiotics to fight the bacteria. However, B. cereus has shown resistance to certain types of antibiotics.
You can lower your risk of intestinal Bacillus cereus by storing your food safely. Steps you can take include:
Proper and frequent hand washing can reduce your risk of non-intestinal B. cereus. You can also reduce your risk by:
Intestinal Bacillus cereus complications are very uncommon — unless you have a compromised immune system. Most people with this form of B. cereus get better quickly.
However, non-intestinal Bacillus cereus may lead to death or other complications including:
If you have intestinal Bacillus cereus, the outlook is usually excellent. Most people recover fully.
If you have non-intestinal Bacillus cereus, the outlook depends on:
Overall, you’re at higher risk of complications from Bacillus cereus if you have a compromised immune system. You may also have a worse prognosis if you:
You can continue to take care of yourself during a bout with intestinal Bacillus cereus by:
If you have non-intestinal Bacillus cereus, you can take care of yourself by:
Call 911 immediately if you have a weak or compromised immune system and experience symptoms of food poisoning or Bacillus cereus infection.
A note from Cleveland Clinic
Being infected with Bacillus cereus can be upsetting. Food poisoning can be extremely unpleasant and make you feel quite ill. Luckily food poisoning caused by Bacillus cereus usually only lasts 24 hours and most people recover fully. B. cereus also causes illnesses outside of your gastrointestinal tract, but these are rarer. If you’re immunocompromised or have other underlying conditions, both intestinal and non-intestinal B. cereus infections can be more serious. Staying hydrated and resting can help you recover more quickly from intestinal infections. Antibiotics can help treat non-intestinal infections. Your chances of recovery are better if you’re treated promptly.
Last reviewed by a Cleveland Clinic medical professional on 07/27/2022.
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