NAME: Bacillus cereus
SYNONYM OR CROSS REFERENCE: Bacillus cereus food-poisoning.
CHARACTERISTICS: 1.4 µm gram-positive rods, usually appear as pairs and short chains Footnote 1, Footnote 2. B. cereus are facultative anaerobes that are motile and able to form endospores, have colonial morphology of about 2-7 mm in diameter, and have a white granular texture Footnote 3. B. cereus grows above 10-20°C and below 35-45°C with an optimum temperature of about 37°C Footnote 1, Footnote 2. The bacteria are able to produce six types of toxins: five enterotoxins and an emetic toxin, which can be heat-stable or heat-labile depending on the strain Footnote 2, Footnote 4.
PATHOGENICITY/TOXICITY: B. cereus causes self-limiting (24-48 hours) food-poisoning syndromes (a diarrheal type and an emetic type), opportunistic infections and is associated with clinical infections such as endophthalmitis and other ocular infections Footnote 2, Footnote 5-Footnote 7. The diarrheal form of B. cereus food poisoning is characterized by abdominal cramps, profuse watery diarrhea, and rectal tenesmus, and, occasionally, fever and vomiting. The emetic form of B. cereus food poisoning is characterized by nausea, vomiting, and malaise, occasionally with diarrhea Footnote 2. B. cereus can cause wound infections, bacteremia, septicaemia, meningitis, pneumonia, central nervous system infections, endocarditis, pericarditis, respiratory infections, and peripheral infections Footnote 2, Footnote 7, Footnote 8. Infection in immunocompromised individuals can be life-threatening Footnote 5. B. cereus strains which harbour a plasmid bearing B. anthracis-like virulence factors can cause severe pneumonia in immunocompetant people Footnote 9.
EPIDEMIOLOGY: Worldwide Footnote 2. Diseases cased by B. cereus are commonly found in places where there is improper food handling. Between 1973–1985, B. cereus caused 17.8% of the total bacterial food poisonings in Finland, 11.5% in the Netherlands, 0.8% in Scotland, 0.7% in England and Wales, 2.2% in Canada, 0.7% in Japan, and 15.0% (between 1960–1968) in Hungary Footnote 10. As of 2008, 103 confirmed outbreak cases have been reported in the US Footnote 11. In Norway, B. cereus was the most common microbe isolated from foodborne illnesses in 1990 Footnote 10.
INFECTIOUS DOSE: In diarrheal illness, the toxin responsible is produced by organisms in the small intestine and infective dose is 104-109 cells per gram of food. The emetic toxin is preformed and indigested in food (about 105-108 cells per gram in order to produce sufficient toxin) Footnote 2.
MODE OF TRANSMISSION: The primary mode of transmission is via the ingestion of B. cereus contaminated food Footnote 1, Footnote 2: emetic type of food poisoning has been largely associated with the consumption of rice and pasta, while the diarrheal type is transmitted mostly by milk products, vegetables and meat. It forms spores and spreads easily Footnote 10. In hospitals, B. cereus can be transmitted via contaminated linen Footnote 12.
COMMUNICABILITY: Not transmitted from person-to-person.
DRUG SUSCEPTIBILITY/RESISTANCE: B. cereus is susceptible to imipenem and vancomycin, and most strains are sensitive to chloramphenicol, aminoglycosides, ciprofloxacin, erythromycin, and gentamicin Footnote 1, Footnote 2, Footnote 7, Footnote 14. Some strains were moderately sensitive to clindamycin and tetracycline Footnote 1. Clindamycin with gentamicin, given early, is the best treatment for ophthalmic infections from B. cereus.
SUSCEPTIBILITY TO DISINFECTANTS: Gluteraldehyde is a chemical agent used to sterilize bacillus-contaminated material. Spores can be killed by 1% sodium hypochlorite, paracetic acid, activated hydrogen peroxide, chlorine dioxide Footnote 15, formaldehyde, iodine, acids, alkali Footnote 7, Footnote 16. These chemical agents should be highly concentrated and required greater time of contact to kill spores. Oazolidinones are also effective antibacterial agents for B. cereus Footnote 1.
PHYSICAL INACTIVATION: B. cereus can be inactivated by pulse electric field in 0.15 % NaCl solution Footnote 17. B. cereus spores can be resistant to heat and radiation, but heating at 100°C for 5 minutes results in cellular damage to the membranes and ribosomes Footnote 2, Footnote 18. Gamma irradiation at 2-5 kGy is required to inactivate B. cereus cells Footnote 19.
SURVIVAL OUTSIDE HOST: B. cereus survives in soil and on vegetation, and is generally heat-resistant and thus may survive thermal food processing with or without injury to cells Footnote 11, Footnote 20.
SURVEILLANCE: Monitor for symptoms. B. cereus strains can be isolated and grown in laboratory media at 37°C. Specimen isolated from contaminated human stool can be grown with tryptic soy broth with polymyxin Footnote 2. The organism can be isolated in B. cereus medium, i.e. in mannitol, egg yolk, polymyxin B agar (MEYP) or polymyxin B, egg yolk, mannitol, bromthymol blue agar (PEMBA). Immunological assays, polymerase chain reaction and biological tests, have been used to detect the enterotoxin activity of B. cereus Footnote 10. Isolation of greater than 105 organisms/g from contaminated food can confirm B. cereus contamination Footnote 1.
Note: All diagnostic methods are not necessarily available in all countries.
FIRST AID/TREATMENT: Administer appropriate drug therapy with supportive treatment Footnote 6. Oral rehydration therapy is the treatment for acute food poisoning syndromes, and antibiotics are seldom required Footnote 21. Patients are given corticosteroids and antibiotics as a first line treatment for eye infections from B. cereus Footnote 22. Whenever gram-positive rods are discovered in the blood or the cerebrospinal fluid of an immunocompromised patient with clinical signs of infection, the empiric antibiotic treatment should cover B. cereus (B. cereus is usually sensitive to clindamycin, aminoglycosides, vancomycin, chloramphenicol, and erythromycin) Footnote 1, Footnote 23.
PROPHYLAXIS: In cases of an acute non-inflammatory infectious diarrhea, a pharmacologic prophylaxis with bismuth subsalicylate in a dose of two tablets four times daily with meals and at bedtime may be useful. Duration of use should not exceed 3 weeks Footnote 21.
LABORATORY ACQUIRED INFECTIONS: No reported cases.
PRIMARY HAZARD: Ingestion of contaminated material. B. cereus produces toxins that can be present in food and soil Footnote 10.
SPECIAL HAZARD: None.
RISK GROUP CLASSIFICATION: Risk Group 2.
CONTAINMENT REQUIREMENTS: Containment Level 2 facilities, equipment, and operational practices for work involving infectious or potentially infectious materials, animals, or cultures Footnote 24.
PROTECTIVE CLOTHING: Lab coat. Gloves when direct skin contact with infected materials or animals is unavoidable. Eye protection must be used where there is a known or potential risk of exposure to splashes Footnote 24.
OTHER PRECAUTIONS: All procedures that may produce aerosols, or involve high concentrations or large volumes should be conducted in a biological safety cabinet (BSC). The use of needles, syringes, and other sharp objects should be strictly limited. Additional precautions should be considered with work involving animals or large scale activities Footnote 24.
SPILLS: Allow aerosols to settle and, wearing protective clothing, gently cover spill with paper towels and apply an appropriate disinfectant (1% sodium hypochlorite), starting at the perimeter and working towards the centre. Allow sufficient contact time before clean up.
DISPOSAL: Decontaminate all wastes that contain or have come in contact with the infectious organism before disposing by autoclave, chemical disinfection, gamma irradiation, or incineration Footnote 24.
STORAGE: The infectious agent should be stored in leak-proof containers that are appropriately labelled.
REGULATORY INFORMATION: The import, transport, and use of pathogens in Canada is regulated under many regulatory bodies, including the Public Health Agency of Canada, Health Canada, Canadian Food Inspection Agency, Environment Canada, and Transport Canada. Users are responsible for ensuring they are compliant with all relevant acts, regulations, guidelines, and standards.
UPDATED: December 2011
PREPARED BY: Pathogen Regulation Directorate, Public Health Agency of Canada
Although the information, opinions and recommendations contained in this Pathogen Safety Data Sheet are compiled from sources believed to be reliable, we accept no responsibility for the accuracy, sufficiency, or reliability or for any loss or injury resulting from the use of the information. Newly discovered hazards are frequent and this information may not be completely up to date.
Public Health Agency of Canada, 2011