Bacillus cereus
Bacillus cereus ( flagella staining)
Bacillus cereus is a motile, gram-positive, rod-shaped, catalase - positive, spore -forming, facultative anaerobic bacterium of the genus Bacillus.
It comes naturally in normal soil at a concentration of up to one million per gram, making it one of the most common culturable soil bacteria. He, together with other species (eg, Bacillus anthracis, Bacillus thuringiensis and Bacillus cytotoxicus ), the Bacillus cereus group, whose members are related genetically close and share a core genome of about 3100 genes. Historically used as a distinguishing feature of the diseases that are caused by them. As genetic distinguishing feature of the set is from 400 to 800 individual genes ( accessory genome, Bacillus cereus at about 420 genes) of the species
Properties
Temperature range: Minimum 10 (-4 ) ° C optimum 28-35 ° C Maximum 45 ° C
B. cereus is acid sensitive.
The spores are resistant to heat damage, there is no killing by pasteurization.
A share of 80 % of all fatty acid chains of the bacterium is branched.
Relevance to humans
B. cereus is a food vergiftendes bacterium that occurs especially in rice. B. cereus spores, which occur in the raw rice, cooking survive and proliferate when the rice is kept warm below 65 ° C or warming up. By keeping warm and above this temperature the propagation of bacteria is prevented, which make rice cooker with its warm function advantage. It also can be transported via dust and soil particles into the food (spices, dried mushrooms, milk).
B. cereus is in counts of 10 million / g food two responsible for food poisoning toxins:
- Vomiting toxin ( emetic toxin, cereulide ): The recording of the toxin -containing food leads to 0.5 to 6 hours for nausea and vomiting, abdominal cramps and less frequently diarrhea. The toxin is not sensitive to heat and acid.
- A diarrhea - causing toxin 8 to 16 hours after ingestion of the toxin watery diarrhea, which subside after 12 to 24 hours. The toxin is heat-and acid- sensitive.
B. cereus into pasteurized, not fermented milk products with counts of more than 1 million / g to bitterness and Süßgerinnung ( coagulation by protein- degrading enzymes and not by acid formation). Because caused by this germ by Lecithinasewirkung taste changes the risk of intoxication is not very large.
Since B. cereus in dairy products is growing at a temperature in the refrigerator from 10 ° C, the declaration of the shelf life of fresh milk was " at 10 ° C best before " by " at 8 ° C best before " changed.