What Is Bacillus cereus?

Medically Reviewed by Neha Pathak, MD on September 11, 2023
5 min read

Bacillus cereus (B. cereus) is a type of bacteria that creates a dangerous substance (called a toxin) that can cause you to get sick. This bacteria is common in the environment. It can cause food poisoning, or intestinal B. cereus, or a more severe condition, called non-intestinal B. cereus. Many people with the food poisoning form of the bacterium will get better within 24 hours. But the risk is higher if you have a weak immune system.

How common is Bacillus cereus?

In the United States, there are about 63,400 cases of B. cereus every year. Intestinal B. cereus infections are very common. But non-intestinal B. cereus infections are rarer.

There are two types of B. cereus. They affect different areas of your body:

Non-intestinal. This form affects other parts of your body. It can be found in plants, dust, soil, or water. Non-intestinal B. cereus can lead to even worse infections. Your risk continues to go up if you have this type alongside a weak immune system or other wounds or injuries from trauma or surgery.

Non-intestinal B. cereus tends to happen in your:

  • Respiratory system (the parts of the body that help you breathe)
  • Wounds
  • Eyes

Intestinal. This type affects your digestive system. It causes food poisoning. Usually, it can go away quickly on its own. But if you have a weak immune system, it can affect you more severely.

What are the different types of intestinal Bacillus cereus?

There are two forms of intestinal B. cereus:

Enterotoxins (diarrheal syndrome). This type is the most common in the United States and Europe. With this version, your body makes the toxin in your small intestine after you've eaten food with the bacteria or spores (the cells they make). Food poisoning will usually show up 6 to 15 hours after you've eaten the food with the bacteria.

You might get this form of B. cereus from fish, meat, dairy, sauces, vegetables, soups, or stews. 

Emetic (vomiting syndrome). With this form, the toxins are already in the food before you eat it. You'll usually get sick between 1 and 6 hours after you consumed the food with the bacteria.

The most common food for this to happen in is rice. Not all rice has B. cereus. But it can form in it when cooked rice is unrefrigerated for too long. This illness can also happen with cheese and starchy foods like pastries, pasta, sushi, and potatoes.

Intestinal B. cereus happens when you eat food left out at room temperature. B. cereus creates spores that let off toxins. If you leave your food at room temperature, the spores can multiply. If you eat the spores in the food, the toxins will cause diarrhea or vomiting. This type of food poisoning can still happen even after you heat up the food. 


In a similar way, B. cereus can cause issues in other parts of your body outside of your intestines. If the spores get into your body, they'll give off toxins. This can happen if you:

  • Have a wound that becomes infected
  • Inhale dust with the bacteria in it
  • Are in a hospital with an outbreak of this bacteria
  • Come in contact with infected hospital tools, like a catheter

The illnesses caused from non-intestinal B. cereus include:

  • Brain abscess
  • Cellulitis
  • Endophthalmitis (a bacterial or fungal infection in your eye)
  • Bacteremia (bacteria in your bloodstream)
  • Endocarditis
  • Meningitis
  • Pneumonia
  • Osteomyelitis

Anyone can get intestinal or non-intestinal B. cereus. 

But your risk of non-intestinal B. cereus goes up if you:

  • Use intravenous (IV) drugs
  • Have an indwelling catheter (one that empties urine from your body)
  • Have wounds from trauma or an operation
  • Have a weakened immune system

Newborn babies also have a higher risk of non-intestinal B. cereus.


The symptoms of food poisoning from B. cereus include:

  • Belly pain, watery diarrhea, and stomach cramping with enterotoxins
  • Nausea and vomiting with emetic syndrome

For non-intestinal B. cereus, the symptoms will be different based on the type of issue the bacteria creates in your body. The most severe complication is endophthalmitis, which is inflammation of the inner part of your eye. This creates the highest number of serious illnesses. You may even lose an eye with this complication. In some cases, it can be life-threatening. 

The symptoms of this issue include:

  • Fever
  • Fatigue
  • Eye pain
  • Leukocytosis, or a high white blood cell count
  • Low vision
  • Red vision
  • A ring-shaped corneal ulcer

To diagnose you with food poisoning from B. cereus, your doctor will ask about your symptoms after you ate your last meal. To confirm the diagnosis, they'll take a sample of the food you ate and a sample of your poop or vomit. In some cases, they can also do a blood test to look for the toxin.

For non-intestinal B. cereus, your doctor will give you a blood test that looks for bacteria in your bloodstream. They might also be able to do other tests on other body fluids to look for the bacteria. In this case, your doctor might test your eye fluid to look for signs of endophthalmitis.

Food poisoning from B. cereus will usually go away by itself in a day. Your doctor may tell you to get a lot of sleep and drink more water in the meantime. For extreme diarrhea or vomiting, they may have you take IV fluids.

For non-intestinal B. cereus, your doctor will tailor your treatment to your specific symptoms. They might start you on antibiotics to get rid of the bacteria. But in some cases, B. cereus can be resistant to antibiotics. This means the medication won't work to fight it off.

There are a few ways you can lower your risk of B. cereus:

  • Make sure you keep cold food in the refrigerator below 41 F.
  • Keep hot food at a temperature above 135 F.
  • Ensure that your reheated food gets to a temperature above 165 F.
  • Within 6 hours, cool down cooked food (that you're not going to eat right away) to below 41 F.
  • Toss out any food that might have bacteria.

You can steam, roast, grill, or fry food to destroy spores. But to get rid of the toxin created by those spores, food needs to be heated to 249 F for more than 80 minutes. So simply reheating foods to destroy harmful bacteria isn't usually enough to make it safe to eat.

It's also very important to wash your hands often to lower your risk of non-intestinal B. cereus. Other ways to lower your risk of non-intestinal B. cereus include not using IV drugs, taking proper care of any injuries, and getting treatment for any conditions that might weaken your immune system.