It’s best known for causing food poisoning linked to reheated rice or fried rice. It’s also recognized as a cause of several gastrointestinal and non-gastrointestinal diseases, some of which can resemble anthrax.
It’s a Gram-positive, non-capsulated, aerobic, spore-forming, rod-shaped bacterium with rounded ends. Cells are typically seen in pairs and short chains. It’s motile due to peritrichous flagella.
Some strains have an outer surface protein called the S layer, which helps with adhesion and has antiphagocytic effects.
It forms oval, centrally located endospores. Spores are not seen in clinical specimens, but they can be seen in culture.
Not relevant.
Pathogenicity is closely related to toxin production, including hemolysins, enterotoxins, and cytotoxins. It causes the following diseases in humans:
Food poisoning: It can occur in two forms: diarrhoeal type or emetic type.
Once ingested, vegetative bacterial cells multiply in the intestine and produce an enterotoxin, leading to watery diarrhoea. The onset is 8-16 hours after ingestion of foods such as meat, soups, vegetables, puddings, and dairy products.
Disease can also occur after ingestion of a preformed, heat-stable emetic toxin (cereulide) in food, which causes vomiting. The onset is 30 minutes to 5 hours after ingestion of foods such as fried rice, pasta, pastry, and noodles.
Non-gastrointestinal infections: B.cereus can cause both local and systemic infections, including endophthalmitis, meningitis, brain abscess, pneumonia, cutaneous infections, and bacteremia. These infections are more common in neonates, intravenous drug users, people with indwelling catheters, and after traumatic wounds or surgery.
Characteristic morphology may be seen in clinical specimens such as blood, vomit, stool samples, and anterior chamber eye aspirates. Endospores are seen in culture but not in host tissue.
On blood agar, colonies are beta-hemolytic, have a rough, matted surface, and may show swarming growth. In severe food poisoning cases, toxin assays can be performed using PCR or immunoassays.
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