Bacillus cereus and other Bacillus sp.
Name of the Organism:
Bacillus cereus is a Gram-positive, facultatively aerobic sporeformer whose cells are large rods and whose spores do not swell the sporangium. These and other characteristics, including biochemical features, are used to differentiate and confirm the presence of B. cereus, although these characteristics are shared with B. cereus var. mycoides, B. thuringiensis and B. anthracis. Differentiation of these organisms depends upon determination of motility (most B. cereus are motile), presence of toxin crystals (B. thuringiensis), hemolytic activity (B. cereus and others are beta hemolytic whereas B. anthracis is usually nonhemolytic), and rhizoid growth which is characteristic of B. cereus var. mycoides.
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Nature of Acute Disease:
B. cereus food poisoning is the general description, although two recognized types of illness are caused by two distinct metabolites. The diarrheal type of illness is caused by a large molecular weight protein, while the vomiting (emetic) type of illness is believed to be caused by a low molecular weight, heat-stable peptide.
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Nature of Disease:
The symptoms of B. cereus diarrheal type food poisoning mimic those of Clostridium perfringens food poisoning. The onset of watery diarrhea, abdominal cramps, and pain occurs 6-15 hours after consumption of contaminated food. Nausea may accompany diarrhea, but vomiting (emesis) rarely occurs. Symptoms persist for 24 hours in most instances.
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The emetic type of food poisoning is characterized by nausea and vomiting within 0.5 to 6 h after consumption of contaminated foods. Occasionally, abdominal cramps and/or diarrhea may also occur. Duration of symptoms is generally less than 24 h. The symptoms of this type of food poisoning parallel those caused by Staphylococcus aureus foodborne intoxication. Some strains of B. subtilis and B. licheniformis have been isolated from lamb and chicken incriminated in food poisoning episodes. These organisms demonstrate the production of a highly heat-stable toxin which may be similar to the vomiting type toxin produced by B. cereus.
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The presence of large numbers of B. cereus (greater than 10^6 organisms/g) in a food is indicative of active growth and proliferation of the organism and is consistent with a potential hazard to health.
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Diagnosis of Human Illness:
Confirmation of B. cereus as the etiologic agent in a foodborne outbreak requires either (1) isolation of strains of the same serotype from the suspect food and feces or vomitus of the patient, (2) isolation of large numbers of a B. cereus serotype known to cause foodborne illness from the suspect food or from the feces or vomitus of the patient, or (3) isolation of B. cereus from suspect foods and determining their enterotoxigenicity by serological (diarrheal toxin) or biological (diarrheal and emetic) tests. The rapid onset time to symptoms in the emetic form of disease, coupled with some food evidence, is often sufficient to diagnose this type of food poisoning.
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Associated Foods:
A wide variety of foods including meats, milk, vegetables, and fish have been associated with the diarrheal type food poisoning. The vomiting-type outbreaks have generally been associated with rice products; however, other starchy foods such as potato, pasta and cheese products have also been implicated. Food mixtures such as sauces, puddings, soups, casseroles, pastries, and salads have frequently been incriminated in food poisoning outbreaks.
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Relative Frequency of Disease:
In 1980, 9 outbreaks were reported to the Centers for Disease Control and included such foods as beef, turkey, and Mexican foods. In 1981, 8 outbreaks were reported which primarily involved rice and shellfish. Other outbreaks go unreported or are misdiagnosed because of symptomatic similarities to Staphylococcus aureus intoxication (B. cereus vomiting-type) or C. perfringens food poisoning (B. cereus diarrheal type).
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Course of Disease and Complications:
Although no specific complications have been associated with the diarrheal and vomiting toxins produced byB. cereus, other clinical manifestations of B. cereus invasion or contamination have been observed. They include bovine mastitis, severe systemic and pyogenic infections, gangrene, septic meningitis, cellulitis, panophthalmitis, lung abscesses, infant death, and endocarditis.
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Target Populations:
All people are believed to be susceptible to B. cereus food poisoning.
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Food Analysis:
A variety of methods have been recommended for the recovery, enumeration and confirmation of B. cereus in foods. More recently, a serological method has been developed for detecting the putative enterotoxin of B. cereus (diarrheal type) isolates from suspect foods. Recent investigations suggest that the vomiting type toxin can be detected by animal models (cats, monkeys) or possibly by cell culture.
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Selected Outbreaks:
For more information on recent outbreaks see the Morbidity and Mortality Weekly Reports from CDC.
Education and Background Resources:
Literature references can be found at the links below.
Loci index for genome Bacillus cereus available from the GenBank Taxonomy database, which contains the names of all organisms that are represented in the genetic databases with at least one nucleotide or protein sequence.
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“Produce Handling and Processing Practices” (1997) Emerging Infectious Diseases 3(4).
In the past decade, outbreaks of human illness associated with the consumption of raw vegetables and fruits (or unpasteurized products produced from them) have increased in the United States. Pathogens such as Listeria monocytogenes, Clostridium botulinum, and Bacillus cereus are naturally present in some soil, and their presence on fresh produce is not rare. Salmonella, Escherichia coli O157:H7, Campylobacter jejuni,Vibrio cholerae, parasites, and viruses are more likely to contaminate fresh produce through vehicles such as raw or improperly composted manure, irrigation water containing untreated sewage, or contaminated wash water. Treatment of produce with chlorinated water reduces populations of pathogenic and other microorganisms on fresh produce but cannot eliminate them. Reduction of risk for human illness associated with raw produce can be better achieved through controlling points of potential contamination in the field; during harvesting; during processing or distribution; or in retail markets, food-service facilities, or the home.
