What is Bacillus cereus and how to protect against it?

What are the sources of contamination and what are the health risks?

The main route of transmission of Bacillus cereus to humans is food.

When the conditions of temperature (between 4°C and 55°C) and nutrient availability are favourable, Bacillus cereus will multiply in food and, in the case of pathogenic strains, produce toxins that can make the consumers who ingest them sick.

Two types of food poisoning syndrome are observed:

• Emetic syndrome: characterised by nausea, vomiting, discomfort, sometimes diarrhoea and occasionally abdominal pain. It is caused by the cereulide toxin, which is produced directly in the food before consumption. Very stable and heat resistant, this toxin remains active even after (re)heating or cooking the food. Symptoms usually appear between 30 minutes and 5 hours after the meal;
• Diarrhoeal syndrome: characterised by diarrhoea, abdominal pain and sometimes nausea. It is caused by the production of enterotoxins, i.e. toxins produced in the gut by the pathogenic bacterium, and which manifests itself if the pathogenic bacterium is present in large numbers in the ingested food (above 10 5 cfu/g in food). Symptoms occur later, between 6 and 24 hours after the meal.

Several pathogenic strains of Bacillus cereus may coexist in the same food and be responsible for either or both syndromes. In the majority of cases, the prognosis is favourable with spontaneous recovery in less than 24 hours.

Which populations are most at risk?

In healthy people, symptoms are usually mild and develop rapidly. In contrast, more severe forms may occur in vulnerable populations, such as the immunocompromised, the elderly and young children, especially infants. 

Which foods should you be most wary of?

Almost all food categories may contain Bacillus cereus spores.

The foods most often involved in FBOs are:

• dry and dehydrated products: spices, dried herbs and aromatics, cereals, flours,
• certain vegetables bought fresh, in particular tomatoes and salad greens,
• dehydrated foods reconstituted by the addition of hot water (instant soups, instant mashed potatoes, powdered milk, etc.) or cooked with water (pasta, rice, couscous) when they are then stored at room temperature.

How to prevent risks?

To limit the contamination of marketed products, agri-food professionals can do the following:

• cleaning and disinfection of equipment and production environments;
• performing self-checks to monitor the presence of Bacillus cereus spores in ingredients, at the end of the manufacturing process and throughout the product’s shelf life.

In mass catering and at home, compliance with food hygiene and preservation rules is essential to prevent the multiplication of pathogenic bacteria and the production of toxins:

• Ensure strict hygiene  of surfaces and utensils;
• quickly cool the preparations after cooking and store in the refrigerator within 2 hours.

How is the Bacillus cereus group regulated?

As with any food, the five European regulations of the ‘Food Hygiene Package’ form the regulatory base. These regulations require, inter alia, the establishment of procedures based on the HACCP (Hazard Analysis Critical Control Point) principles as part of a health control plan, i.e. each producer or processor must analyse the risks of contamination and the means of controlling those risks. Specific requirements may be added.

For example, European Regulation (EC) No 2073/2005, as amended by Regulation (EC) No 1441/2007, requires specific analyses of Bacillus cereus for powdered infant formula and certain dietetic foods intended for infants under six months of age.

For other foods, there is no specific regulatory requirement. Risk control is therefore mainly based on the implementation of the health control plan: preventive measures (hygiene, temperature control, rapid cooling, etc.) and microbiological self-checks carried out regularly by companies to check the safety of their products.

In practice, a level of 10⁵ CFUs (colony forming units) per gram of feed is often used as an alert threshold by health authorities. Beyond that, and if they have not been triggered before, investigations and product withdrawals can be decided.

What is ANSES doing?

The ‘Staphylococcus, Bacillus and Clostridium’ unit of ANSES’s Food Safety Laboratory carries out work to improve knowledge of the Bacillus cereus group. In particular, the laboratory develops new approaches to detect and quantify the hazards associated with this toxin-producing bacterium. Its research also focuses on improving characterisation of its pathogenicity, with regard to its ability to produce emetic and diarrheal toxins.

In conjunction with the competent health authorities (DGAL, DGS), ANSES is also involved in the investigation into foodborne illnesses, whether individual or collective, involving Bacillus cereus.

Finally, the Agency conducts risk assessments throughout the food chain and identifies the most effective measures to reduce the risk of contamination. Together with its scientific expert groups, it issues recommendations for professionals, public authorities and consumers, which are detailed in a hazard data sheet.