The Toxins of Bacillus cereus: Cereulide

Bacillus cereus produces several clinically relevant toxins that fall into two main categories: emetic (vomiting-type) toxins and diarrheal toxins. These toxins differ in structure, mechanism of action, and clinical presentation.

1. Emetic Toxin

Cereulide

• Type: Heat-stable cyclic dodecadepsipeptide

• Disease association: Emetic (vomiting) syndrome

• Mechanism: Acts as a potassium ionophore → mitochondrial dysfunction → stimulation of the vagus nerve

• Key features:

  • Preformed in food (commonly rice and starchy foods)

  • Resistant to heat, acid, and proteolysis

  • Symptoms begin rapidly (1–5 hours)

• Clinical significance: Can cause severe toxicity, including acute liver failure in rare cases

2. Diarrheal Enterotoxins

These are heat-labile, protein-based toxins produced in the intestine after ingestion of spores or vegetative cells.

Hemolysin BL (HBL)

• Components: Three-part toxin (B, L1, L2)

• Mechanism: Pore formation in intestinal epithelial cell membranes

• Effects: Diarrhea, abdominal cramps, fluid secretion

Non-hemolytic Enterotoxin (NHE)

• Components: Three-part toxin (NheA, NheB, NheC)

• Mechanism: Pore formation → epithelial cell damage

• Effects: Diarrhea and abdominal pain

• Note: Most common diarrheal toxin produced by B. cereus

Cytotoxin K (CytK)

• Type: Single-protein toxin

• Mechanism: Pore-forming cytolysin

• Clinical relevance: Associated with severe and occasionally fatal diarrheal disease

3. Additional Virulence Factors (Less Central to Food Poisoning)

• Phospholipases (e.g., phosphatidylinositol-specific phospholipase C)

• Proteases

• Hemolysins

These contribute to tissue destruction and extraintestinal infections (e.g., endophthalmitis, wound infections).