Production of an Emetic Toxin, Cereulide, Is Associated with a Specific Class of Bacillus cereus

Nagoya University, Nagoya, Aichi, Japan
Current Microbiology (Impact Factor: 1.36). 06/1996; 33(1):67-69. DOI: 10.1007/s002849900076

ABSTRACT The emetic toxin (cereulide) of Bacillus cereus was quantified in several isolates of B. cereus and in various food sources. When the emetic toxin was produced, vomiting-type food poisoning was observed in humans. We
also found that the H-1 serovar phenotype was strongly associated with the production of cereulide and that none of the isolates
that hydrolyzed starch or expressed diarrheal enterotoxin activity produced cereulide.

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    ABSTRACT: Factors influencing the production of cereulide, the emetic toxin of Bacillus cereus in food and laboratory media were investigated, using liquid chromatography–ion trap mass spectrometry and sperm motility inhibition bioassay for detection and quantitation. Oxygen was essential for production of the emetic toxin by B. cereus. When beans, rice or tryptic soy broth were inoculated with cereulide producing strains B203, B116 (recent food isolates) or the strain F-4810/72, high amounts (2 to 7 μg ml−1 or g−1 wet wt) of cereulide accumulated during 4-day storage at room temperature. In parallel cultures and foods, stored under nitrogen atmosphere (>99.5% N2), less than 0.05 μg of cereulide ml−1 or g−1 wet wt accumulated. The outcome of the bioassay matched that of the chemical assay, with no indication of interference by substances in the rice or beans. Boiling for 20 to 30 min did not inactivate cereulide or cereulide producing strains in rice or the beans. Adding l-leucine and l-valine (0.3 g l−1) stimulated cereulide production 10- to 20-fold in R2A and in rice water agar. When the B. cereus strains were grown on agar media under permissive conditions (air, room temperature), cereulide was produced overnight with little or no increase when the incubation was extended to 4 days. In broth culture, the production of cereulide started later than 16–24 h. Anoxic storage prevented cereulide production also when the amino acids had been supplied. Packaging with modified atmosphere low in oxygen may thus be used to reduce the risk of cereulide formation during storage of food.
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    ABSTRACT: Bacterial contamination of cooked rice was analyzed to evaluate the microbial safety. Thirty raw rice samples were collected in Korea and cooked in an electric rice cooker. Mesophilic aerobe, food-poisoning Bacillus cereus group, and their toxin genes were determined on cooked rice. The percentage of total mesophilic aerobe based on 1-3 log CFU/g was 27% among the samples. Bacillus spp. in MYP selective medium was similar to the number of mesophilic aerobe, whileas Bacillus spp. was detected in most samples after enrichment. Thirty-seven isolates from 30 cooked rices were identified as B. thuringiensis, B. cereus, B. valismortis, B. pumilus, B. coagulans, B. licheniformis, Geobacillus stearothermophilus, and Brevibacillus laterosporus. Twenty isolates (54%), more than half of the isolates, were B. thuringiensis while nine (27%) were identified as B. cereus. All B. thuringiensis isolates possessed non-hemolytic toxin genes and interestingly, seven B. cereus among nine isolates possessed emetic toxin genes. More B. thuringiensis was present on the cooked rice than B. cereus and most B. cereus possessed emetic toxin genes rather than diarrheal toxin genes. Therefore, food-borne outbreak due to B.cereus on the cooked rice kept at room temperature might be examples of emetic food-poisoning.
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