Chapter 253. Bacillus Cereus

Bacillus cereus is a gram-positive, spore-forming, motile aerobic rod that also grows well anaerobically.1 It is ubiquitous in the environment, frequently isolated from plants, meat, eggs, and dairy products.

Clinical Manifestations

Food poisoning due to B cereus occurs after eating food contaminated with spores (diarrheal form) or preformed toxin (emetic form) as spores are heat resistant, often surviving heating or cooking.2 Both forms are usually mild and self-limited, lasting 6 to 24 hours. The diarrhea syndrome includes profuse, watery diarrhea, abdominal cramps, and vomiting. Nausea, vomiting, and abdominal cramps within hours of ingesting contaminated foods characterize the emetic form.

Bacillus cereus is a significant cause of virulent posttraumatic endophthalmitis, typically following a penetrating injury or intravenous drug use.3 Severe pain, reduced visual acuity, chemosis, swelling, and proptosis, often with systemic symptoms, are noted. Surgical management with parenteral, intraocular, and topical antimicrobial treatment is indicated. Full vision recovery is rare.

Clinically significant B cereus bacteremia is reported among neonates, intravenous drug users, immunocompromised patients, and those with indwelling devices.4-9Bacillus cereus endocarditis is associated with intravenous drug use or valvular disease.10-12 Pneumonia is reported in immunosuppressed patients and neonates.13-14 Meningitis and brain abscess due to B cereus occurred in children with ventricular shunts or neonates.1,11,15-18 Postsurgical, traumatic, or burn wounds due to B cereus and severe deep infections such as necrotizing fasciitis and gangrene have occurred.19-21

Diagnosis

Bacillus species are commonly considered contaminants. Among at-risk populations noted above, B cereus should be considered a potential pathogen.1Bacillus cereus grows readily on nutrient agar or peptone media at 25°C to 37°C (77–98.6°F) and may require the addition of certain amino acids.

Treatment and Prevention

Bacillus cereus food poisoning is self-limited, requiring no antimicrobial therapy. Antibiotic therapy is indicated in invasive B cereus infections. Empiric therapy with vancomycin or clindamycin, with or without an aminoglycoside, is most commonly cited in the literature. Bacillus cereus is resistant to β-lactam antibiotics but is usually susceptible in vitro to aminoglycosides, chloramphenicol, ciprofloxacin, clindamycin, erythromycin, imipenem, and vancomycin.5 Surgical intervention is usually necessary in ophthalmic or skin infections due to B cereus. Removal of prosthetic devices is typically necessary for cure.

Food-borne B cereus disease is prevented by appropriate storage and preparation of food. Bacterial growth may be prevented if hot food is kept above 60°C (140°F) or rapidly cooled to less than 10°C (50°F). Careful attention to aseptic technique and handwashing prevents B cereus infections among immunocompromised patients and those with indwelling devices.