Overview of Pathogenic Bacteria: Bacillus cereus

  Pathogenic Bacteria: Bacillus cereus

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Bacillus cereus (B. cereus) is a Gram-positive, facultatively anaerobic, endospore-forming, large rod and has colonial morphology of about 2-7 mm in diameter, with a white granular texture.

The optimal growth temperature is 28°C to 35°C, with a minimum growth temperature of 4°C and a maximum of 48°C. Growth can occur in pH ranges from 4.9 to 9.

Pathogenicity: It causes two kinds of food-borne disease:

1. Intoxication due to a toxin performed in the food
2. Infection is due to the ingestion of cells that produce enterotoxins in the small intestine.

Sources: Widespread in the environment being found in soil, water, air, and vegetable matter.

 Rice products, pasta, vegetables, herbs, spices, milk, and meat.

Illness, Symptoms, and Complications:

B. cereus food poisoning is caused by toxins produced during the growth of the bacteria (emetic toxin (ETE)) and three different enterotoxins: Hemolysin (HBL), Nhe, and EntK. These toxins cause two distinctly different forms of food poisoning – the emetic/vomiting type or diarrhoeal type. Symptoms usually last around 24 hours. EntK ( Not involved in food poisoning).

Emetic-type symptoms include nausea, vomiting, and abdominal cramps.

Diarrhoeal-type symptoms include watery diarrhea, abdominal cramps, and pain with occasional nausea and vomiting.

Although both forms are self-limiting more severe cases have been reported which included complications such as pyogenic infections, gangrene, septic meningitis, lung abscesses, and infant death.

Controls to reduce the risk:

Foods should be cooked to a core temperature of 75°C (167°F) e.g. 70°C (158°F) for 2 minutes which will destroy the cells however in order to prevent the spores from germinating it is essential that rapid cooling takes place. It may be beneficial to implement or install rapid chilling equipment to speed up the cooling process.

Hot food should be maintained at a temperature greater than or equal to 63°C (145.4°F) and chilled food should ideally be maintained at a temperature less than or equal to 4°C (39.2°F).

Testing Method

ISO 7932:2004/AMD 1:2020 Microbiology of food and animal feeding stuff — Horizontal method for the enumeration of presumptive Bacillus cereus — Colony-count technique at 30 degrees.

BAM Chapter 14: Bacillus cereus; Authors: Sandra M. Tallent, Ann Knolhoff, E. Jeffery Rhodehamel (ret.), Stanley M. Harmon (ret.), and Reginald W. Bennett (ret.)