Bacillus species: Bacillus cereus.

Question 1

Bacillus cereus - Overview

Answer 1

🦠 Bacillus cereus is a large, Gram-positive, spore-forming, aerobic rod found in soil and food. It is motile and beta-hemolytic. It can produce enterotoxins causing food poisoning and other infections.

Question 2

Bacillus cereus - Virulence factors

Answer 2

⚙️ Virulence Factors:
1. Heat-labile enterotoxin – stimulates cAMP → watery diarrhea (like cholera toxin)
2. Heat-stable enterotoxin – acts like staphylococcal enterotoxin → vomiting
3. Tissue-destructive enzymes – lecithinase (phospholipase C), hemolysins

Question 3

Bacillus cereus - Pathogenesis

Answer 3

✅ Pathogenesis:
- Spores survive cooking and germinate in food
- Toxins released during bacterial growth cause either emetic or diarrheal food poisoning
- Can also cause eye infections after trauma (especially with contaminated soil)

Question 4

Bacillus cereus - Clinical findings

Answer 4

🏥 Clinical Forms:
1. Emetic type: Nausea and vomiting, 1–6 hours after eating reheated rice (heat-stable toxin)
2. Diarrheal type: Watery diarrhea, abdominal pain 8–16 hours after ingestion (heat-labile toxin)
3. Ocular infections: Rapidly progressive eye damage after trauma
4. Severe systemic infections in immunocompromised patients

Question 5

Bacillus cereus - Diagnostic laboratory tests

Answer 5

🧪 Lab Tests:
- Gram stain: Large Gram-positive rods
- Culture: Beta-hemolytic colonies on blood agar
- Spores visible without capsule
- Toxin assays (rarely used clinically)

Question 6

Bacillus cereus - Resistance and immunity

Answer 6

🧱 Resistance & Immunity:
- Spores resist heat and disinfection
- Toxins are stable (heat-stable or labile)
- No long-term immunity after food poisoning
- Natural infection does not confer protective immunity

Question 7

Bacillus cereus - Treatment

Answer 7

💊 Treatment:
- Food poisoning: Usually self-limited → supportive care (hydration)
- Eye/systemic infections: Vancomycin + clindamycin or ciprofloxacin
- Resistant to beta-lactams (produces beta-lactamase)

Question 8

Bacillus cereus - Epidemiology

Answer 8

🌍 Epidemiology:
- Found in soil, dust, and food (especially rice, pasta, meats)
- Reheated fried rice is classic source for emetic type
- Eye infections linked to trauma with soil-contaminated objects

Question 9

Bacillus cereus - Prevention and control

Answer 9

🛡️ Prevention & Control:
- Proper food handling, refrigeration, and reheating practices
- Avoid leaving cooked rice at room temperature
- Prompt wound care to prevent eye infections after trauma