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What is Bacillus cereus?

Bacillus cereus (B. cereus) is a bacterium that is commonly associated with large outbreaks of foodborne illness. A high number of bacteria (around one million bacteria per gram of food) must be consumed in order to cause illness. This can occur when food remains at temperatures ranging from above 4°C to 60°C  (Temperature Danger Zone) for extended periods, such as, with barbeques, picnics, cafeterias, buffets, and in the home.

There are two types of illnesses associated with B. cereus: emetic and diarrheal. The emetic illness (vomiting) is caused by a heat and acid stable toxin produced by B. cereus in food before the food is consumed.

The diarrheal illness is associated with a less stable toxin. This toxin is released when a large number of B. cereus cells are broken down by the stomach’s enzymes.

Where is Bacillus cereus Found?

B. cereus is widely distributed in the environment and is found almost everywhere including soil, dust, water, air, and decaying matters.

It is also found on animals.

What Kind of Environmental Conditions Can it Survive?

B. cereus grows best at temperatures between 30-37^○C but, it continues to grow in the Temperature Danger Zone. Although, this bacterium prefers an oxygen environment, it can also grow and produce toxins without it, such as in thick soups.  B. cereus cannot grow in highly acidic or alkaline environments (pH levels below 4.5 or above 9.3) and therefore cannot grow in yoghurt.

This bacterium is able to form spores (seed-like materials); this allows it to survive in harsh environments. The spores are resistant to heat; temperatures must reach 100^○C for 10 minutes in order to inactivate them.

The toxin produced by the emetic type of B. cereus is extremely heat resistant and can survive for 90 min at temperatures as high as 126^○C whereas, the toxin produced by the diarrheal type is sensitive to heat and is inactivated at 56^○C for 5 min.

What Foods are Involved?

B. cereus can be found in large variety of foods. Restaurant buffets are commonly implicated because of improper food holding temperatures.

The emetic type is most commonly associated with starchy foods such as rice, potato, cheese and pasta.

The diarrheal type is associated with a wide variety of foods such as vegetables, salads, meats, fish, casseroles, pastries, sauces and milk.

What are the Symptoms of Illness?

The symptoms associated with the emetic type of foodborne illness include:

1.       Nausea

2.       Vomiting

3.       Abdominal cramps.

Symptoms of the diarrheal type include:

1.       Watery diarrhea

2.       Abdominal cramps.

People with a weakened immune system may suffer from long-term effects, such as pneumonia, meningitis and endocarditis.

What is the Duration and Onset of Illness?

B.cereus produces two different types of foodborne illness.

The onset of the emetic type of illness occurs 1-6 hours (average 4 hours) after ingestion of contaminated food.

The onset of the diarrheal type of illness occurs 6-24 hours (average 17 hours) after ingestion of contaminated food.

Healthy individuals usually recover rapidly (within 12-24 hours) from an infection without requiring treatment. However, some individuals may suffer dehydration or more serious complications and require medical attention.

What Can You Do To Control Or Prevent Bacillus cereus Infections?

1.       Cook all foods thoroughly to recommended internal temperatures. Cook meat to an internal temperature of 71^○C (160°F) and poultry to an internal temperature of 74^○C (165°F) or 85^○C (185°F) for whole birds.

2.       Cool cooked foods quickly by placing them in the refrigerator in shallow containers.

3.       Do not leave food in the Temperature Danger Zone for more than 2 hours.

4.       Reheat leftovers to an internal temperature of 74^○C (165°F). Caution, microwaves heat foods inconsistently, insert thermometer in several locations when testing the temperature.

Information Sources

New Zealand Food Safety Authority. (2001). Microbial pathogen data sheet, Bacillus cereus.  Retrieved from, http://www.nzfsa.govt.nz/science/data-sheets/bacillus-cereus.pdf

Todar, Kenneth. (2003). Todar’s online text book of bacteriology: Bacillus cereus and Food Poisoning. Retrieved from, http://textbookofbacteriology.net/B.cereus.html

United States Food and Drug Administration. (2007). Bacillus cereus. Retrieved from,     http://www.cfsan.fda.gov/~mow/chap12.html

United States Department of Agriculture. (2008). Use a food thermometer. Retrieved from, http://www.fsis.usda.gov/Fact_Sheets/Use_a_Food_Thermometer/index.asp