Bacillus cereus
Large, spore-forming Gram-positive bacilli
Identification & Growth
Identification
- Catalase-positive, motile, beta-hemolytic, lecithinase-positive
- Resistant to penicillin; differs from B. anthracis (non-motile, non-hemolytic)
Growth Conditions
- Blood agar and MYP agar, 35 °C, 24 h; large, matte colonies with irregular edges
Clinical Significance
- Food poisoning (rice-associated), post-traumatic eye infection
- Catheter-related bacteremia in neutropenic patients
Intrinsic Resistance
- Constitutive beta-lactamase: penicillins and cephalosporins should not be reported
Bench Alerts
- Vancomycin is the empirical option for invasive infection
- A single positive blood culture bottle is usually environmental contamination
Clinical Notes
Clinical presentations
- Causes two foodborne intoxication syndromes: emetic form (preformed toxin, nausea/vomiting) and diarrheal form (enterotoxins produced in vivo).
- Can cause fulminant post-traumatic or post-surgical endophthalmitis with rapid vision loss.
- Catheter-associated bacteremia, especially in cancer patients and intravenous drug users.
- Soft tissue infections and necrotizing pneumonia have been reported in trauma and immunosuppression settings.
Specimens and collection
- Suspect food items and stool should be collected within hours of symptom onset for outbreak investigation.
- Vitreous and aqueous humor should be collected with strict sterile technique when endophthalmitis is suspected.
- Serial blood cultures help confirm true bacteremia versus contamination by environmental spores.
Epidemiology and at-risk populations
- Widely distributed in soil and associated with foods such as improperly refrigerated cooked rice.
- Intravenous drug users and neonates in intensive care units have increased risk of invasive infection.
- Penetrating ocular trauma with soil-contaminated material is a key risk factor for endophthalmitis.
Resistance and therapeutic implications
- Produces beta-lactamases that confer intrinsic resistance to penicillin, ampicillin and cephalosporins.
- Vancomycin, clindamycin and fluoroquinolones are usually active and used for confirmed invasive infections.
- Endophthalmitis requires aggressive intravitreal therapy combined with systemic antibiotics due to rapid progression.
Bench and reporting notes
- Large spore-forming Gram-positive rods with beta-hemolysis on blood agar aid differentiation from Bacillus anthracis.
- Positive motility and absence of capsule distinguish B. cereus from B. anthracis, which is non-hemolytic and non-motile.
- Isolation in a single blood culture should be interpreted cautiously due to the organism's environmental ubiquity.
Sources
Educational decision-support content. It does not replace laboratory validation, current guidelines or review by the responsible professional.
FAQ: Frequently Asked Questions
How to identify Bacillus cereus in the lab?
Bacillus cereus is identified through catalase-positive, motile, beta-hemolytic, lecithinase-positive, resistant to penicillin; differs from b. anthracis (non-motile, non-hemolytic).
What are the intrinsic resistances of Bacillus cereus?
This organism is naturally resistant to constitutive beta-lactamase: penicillins and cephalosporins should not be reported. These drugs should not be reported as susceptible.
Where is Bacillus cereus commonly found?
It is typically associated with food poisoning (rice-associated), post-traumatic eye infection, catheter-related bacteremia in neutropenic patients.
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