Understanding the Dangers of Bacillus cereus in Food and How to Control It
Food that looks safe is not necessarily free from microorganisms that can be harmful to health. One of them is Bacillus cereus, a bacterium commonly found in the environment that can contaminate various types of food, especially through its spores, which can survive under unfavorable environmental conditions.
The presence of B. cereus needs to be taken seriously because this bacterium can survive certain food processing methods and may later grow and produce toxins when food is stored under suitable conditions. Understanding the sources of contamination, the risk of food poisoning, and ways to control B. cereus is important for maintaining food safety and quality.
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The Dangers of Bacillus cereus in Food
Bacillus cereus is a spore-forming bacterium commonly found in the environment. Soil, for example, may contain around 10³–10⁵ spores per gram. The problem is that these bacterial spores do not always disappear after food is cooked.
If food is then stored without proper refrigeration, exposed to temperature abuse, or contains raw ingredients that support bacterial growth, the spores can germinate and multiply again. Food preservation technologies such as high hydrostatic pressure, pulsed electric fields, and cook-chill systems also require attention because some of these processes do not completely destroy spores.
Under certain conditions, they may leave cells that are able to grow at temperatures around 10°C or even lower. This risk is particularly relevant to rice-based foods. B. cereus spores are often found in raw rice because the bacterium is widely distributed in nature.
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A study of 244 rice-based food samples found that 11.92% contained more than 10⁴ CFU/g of B. cereus, which was considered a high-risk level. Contamination can also occur after the rice has been cooked, for example through a spatula used to stir the rice.
Small restaurants may face a higher risk due to poor hygiene practices and rice being prepared too long before it is served. One type of illness caused by B. cereus is the diarrheal type, which is associated with the production of enterotoxins and generally requires more than 10⁵ bacterial cells per gram of food.
Symptoms may include abdominal pain, watery diarrhea, a persistent urge to have a bowel movement (rectal tenesmus), moderate nausea, and rarely vomiting, without fever. Symptoms usually appear 6–15 hours after consumption and may last for about 24 hours. This illness can be quite similar to food poisoning caused by Clostridium perfringens.
In contrast, the emetic type occurs because the toxin has already been produced in the food before it is consumed. Toxin production at levels that can cause illness is generally associated with bacterial concentrations of around 10⁵–10⁸ CFU/g.
However, the number of bacteria consumed is no longer the main measure of risk because the illness depends on the amount of toxin ingested. The emetic toxin, known as cereulide, is resistant to heat and stomach acid.
Therefore, heating food may kill vegetative cells of B. cereus, but it may not always destroy the toxin. Symptoms usually appear more quickly, within about 1–5 hours after eating, and may include nausea, vomiting, headache, abdominal cramps, and/or diarrhea, resembling food poisoning caused by Staphylococcus aureus.
How to Control Bacillus cereus in Food
Controlling Bacillus cereus in rice and rice-based products involves more than simply cooking the food. Three important factors need to be considered: maintaining cleanliness during food processing, using appropriate preservation methods, and preventing bacterial growth during storage.
The first thing to consider is equipment hygiene. B. cereus spores can attach to stainless steel surfaces and survive inside pipes or other hard-to-reach parts of food-processing equipment. Therefore, the use of cleaning agents such as sodium hypochlorite or mild acids, together with appropriate equipment design, can help reduce areas where spores can attach and survive.
Food processing is also important for controlling B. cereus, but cooking does not necessarily mean that all forms of the bacterium will be destroyed. Vegetative cells of B. cereus are relatively easier to destroy with heat. For example, heating at 70°C for 12 seconds can reduce their numbers.
In contrast, spores are much more heat-resistant and require more severe conditions to achieve a similar level of reduction. This is important because rice is generally cooked at temperatures of around 80–90°C.
These temperatures can kill many vegetative cells, but they may not be sufficient to destroy all B. cereus spores present in the food. Surviving spores can then become a problem if the rice is stored at temperatures and under conditions that allow the spores to germinate and the bacteria to grow again.
Therefore, storage temperature is one of the most important factors, particularly by keeping rice-based foods below 4°C. Temperature control can also be combined with modified atmosphere packaging containing more than 40% CO₂, adjustment of pH or water activity, and the use of certain antimicrobials such as nisin and enterocin AS-48, which have been studied for their ability to inhibit B. cereus.
Controlling B. cereus requires more than simply making sure that food is properly cooked. From clean raw materials and hygienic equipment to proper processing, cooling, and storage, every stage plays a role in preventing the bacterium from growing.
By keeping food properly chilled, especially below 4°C, the opportunity for B. cereus to grow and produce toxins can be reduced.
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Author: Dherika
Editor: Lina
References
Fernandez, A., Ocio, M.J., Fernandez, P.S., Rodrigo, M., & Martinez, A. (1999). Application of Non-linear Regression Analysis to the Estimation of Kinetic Parameters for Two Enterotoxigenic Strains of Bacillus cereus Spores. Food Microbiol, 16, 607–613.
Rodrigo, D., Rosell, C.M., & Martinez, A. (2021). Risk of Bacillus cereus in Relation to Rice and Derivatives. Foods, 10, 302. https://doi.org/10.3390/foods10020302.
