Bacillus cereus What you should know!

Bacillus cereus 

Bacillus cereus is a spore-forming, motile, aerobic, rod-shaped and gram-positive bacteria that can also grow well in anaerobic conditions. The bacteria is a common soil saprophyte and can easily spread to different types of food especially plant-based. It is also frequently found in meat, egg and dairy products. There are also psychrotrophic strains which have become an increasing problem for the dairy industry.

B.cereus produces 2 types of toxins, the first being an emetic toxin and the second being an enterotoxin. The bacteria causes two types of food poisoning, the first being the diarrhoeal type and the second being an emetic type. The diarrhoeal type (infection) is caused by the enterotoxins which are produced during vegetative growth of the bacteria in the small intestine. The emetic type (intoxication) is caused by toxins produced by the growing cells in the food. In both cases, the causing factor of the food poisoning comes from the spores the bacteria produce which may survive after food has been heat-treated. This heat treatment will cause the spores to germinate and start producing either of the toxins depending on where the spore is found in the food.

Bacillus cereus 

Sources of contamination

Bacillus cereus
Bacillus cereus What you should know!
Bacillus cereus What you should know!
Bacillus cereus What you should know!

Bacillus cereus is one of the most common causes of food poisoning and there is an estimated 63 000 cases reported each year within the U.S. The vast majority of the cases are unreported as the symptoms are generally mild and subside on their own within 24 hours.

Rice is one of the most common culprits as B.cereus can naturally colonise on uncooked rice and the spores produced by the bacteria can easily survive the cooking process. B.cereus bacteria grow best at room temperature.

The reheating or freezing of foods that have been left out for more than 2 hours may not prevent food poisoning from happening as the spores produced from the bacteria are very resilient. The reheating of foods to temperatures above 74 degrees Celsius for 15 seconds will kill the bacteria but will not deactivate the toxins if they have already formed.

Some other examples of typical foods where B.cereus may be found are:

  • Meat products
  • Soups
  • Vegetables
  • Puddings/Sauces
  • Milk/Milk products
  • Rice (cooked and raw)/ pasta, pastries and noodles

Bacillus cereus

How we test for B.cereus  in our SANAS accredited laboratory

At FCS we test powdered, solid or liquid samples. The sample is first completely homogenised in a peptone buffered water. 1ml of this homogenised sample is then put onto the surface of Mannitol-Egg-Yolk-Poymyxine agar plate (MYP agar) and spread evenly over the surface. Once the plate is dry it is incubated at ±30 degrees Celsius for 18-24 hours. Presumptive colonies are large, pink and surrounded by a zone of precipitation. These presumptive colonies are then further streaked onto sheep blood agar and then incubated at ± 30 degrees Celsius for ± 24hours. A Haemolysis reaction on the sheep blood agar indicates positive B.cereus colonies.

Symptoms of food poisoning

Common symptoms of Diarrheal type B.cereus food poisoning are:

  • Abdominal pain/cramping
  • Diarrhoea
  • Nausea (rarely)

Common symptoms of Emetic type B.cereus food poisoning are:

  • Nausea
  • Vomiting
  • Malaise
  •  Diarrhoea (rarely)

Bacillus cereus

Preventing Bacillus cereus food poisoning

Some of the basic principles in reducing the risk of B.cereus food poisoning are:

  • Ensuring all hot foods are kept hot and above 60 degree Celsius and cold food below 4 degrees Celsius.
  • Temperature control of foods that have been cooked/heated and left out to cool is of vital importance.
  • Personal hygiene practices by workers and food handlers.
  • Proper handling and processing in order to prevent cross-contamination.
  • Adequate cleaning and disinfecting of equipment.
  • Following guidelines such as :
  • Hazard Analysis and Critical Control Points (HACCP)
  • Good Manufacturing Practice (GMPs)
  • Good Hygienic Practices (GHPs)
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LEIGHTON BROWN

Chief Consultant

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