Bacillus cereus- An Overview


Bacillus cereus (B. cereus) is a type of bacteria that can cause food poisoning and other infections in humans. It is widely distributed in nature and can be found in soil, water, plants, dust, and food products. B. cereus belongs to a group of closely related bacteria that also includes Bacillus anthracis (the cause of anthrax) and Bacillus thuringiensis (a biopesticide).

B. cereus is a gram-positive, rod-shaped, spore-forming bacterium that can grow in aerobic or anaerobic conditions. It can produce toxins that are either heat-stable or heat-labile, depending on the type of food poisoning it causes. B. cereus can also produce enzymes that degrade various biological molecules, such as phospholipase C, lecithinase, hemolysin, and protease.

B. cereus can cause two types of food poisoning: the emetic (vomiting) syndrome and the diarrheal syndrome. The emetic syndrome is caused by ingesting a preformed toxin called cereulide that is produced by B. cereus in certain foods, such as rice, pasta, and pastry. The symptoms include nausea, vomiting, and abdominal cramps within 1 to 6 hours after eating the contaminated food. The diarrheal syndrome is caused by ingesting B. cereus cells or spores that produce a heat-labile enterotoxin in the small intestine. The symptoms include watery diarrhea, abdominal pain, and sometimes fever within 6 to 15 hours after eating the contaminated food.

B. cereus can also cause non-intestinal infections, such as eye infections (especially after traumatic injuries), wound infections, respiratory infections, blood infections, endocarditis (infection of the heart valves), meningitis (infection of the brain and spinal cord), osteomyelitis (infection of the bone), and pneumonia. These infections are more common in people who have a weakened immune system or who have other risk factors, such as intravenous drug use, surgery, trauma, or medical devices.

B. cereus infections are diagnosed by isolating and identifying the bacterium from clinical specimens, such as stool, vomit, blood, eye swabs, or wound swabs. The presence of toxins or genes encoding toxins can also be detected by various methods, such as gel diffusion test or polymerase chain reaction (PCR).

B. cereus infections are usually self-limiting and do not require specific treatment. However, some cases may require supportive care, such as fluid and electrolyte replacement for dehydration or antibiotic therapy for severe or systemic infections. B. cereus is generally susceptible to antibiotics such as clindamycin, erythromycin, vancomycin, aminoglycosides, and tetracycline, but resistant to penicillin and trimethoprim.

B. cereus infections can be prevented by proper food handling and storage practices, such as cooking food thoroughly, refrigerating leftovers promptly, reheating food adequately before consumption, and avoiding cross-contamination between raw and cooked foods. Prevention of non-intestinal infections depends on good hygiene and wound care practices, as well as avoiding exposure to contaminated soil or dust.