Question

The heat stable toxin of Bacillus cereus is responsible for .............................

• A. Undulant fever
• B. Abortion
• C. Diarrhoeal syndrome
• D. Emetic syndrome

Hint:

To distinguish between the two Bacillus cereus syndromes, remember:
- Emetic = Heat-stable toxin (cereulide) preformed in food, causing rapid vomiting.
- Diarrheal = Heat-labile enterotoxin produced in the intestine, causing delayed diarrhea.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Bacillus cereus is a Gram-positive, facultatively anaerobic, endospore-forming rod-shaped bacterium commonly found in soil, dust, and dairy environments.
It is notorious for causing two distinct types of foodborne illnesses: the diarrheal syndrome and the emetic syndrome.
These two syndromes are mediated by entirely different types of toxins with contrasting chemical properties and thermal stabilities.

Step 2: Detailed Explanation:
The diarrheal syndrome is caused by high-molecular-weight, heat-labile enterotoxins.
These include the non-hemolytic enterotoxin (NHE) and hemolysin BL (HBL) complexes, which are produced by vegetative cells replicating inside the small intestine.
Because these enterotoxins are proteins, they are easily inactivated by heat treatment (e.g., pasteurization or cooking).
Conversely, the emetic syndrome is caused by a small, cyclic dodecadepsipeptide toxin called cereulide.
Cereulide is preformed in the food matrix during the growth phase of specific emetic strains of Bacillus cereus before consumption.
This toxin is highly hydrophobic and exceptionally stable due to its cyclic depsipeptide structure.
It can easily withstand autoclaving at 121°C for 30 minutes, exposure to a wide pH range (2 to 11), and proteolytic degradation by enzymes like pepsin and trypsin.
Consequently, normal heat processing of milk or dairy products does not inactivate the preformed emetic toxin, leading to rapid onset of nausea and vomiting upon ingestion.
Undulant fever is caused by Brucella species, and infectious abortion is also commonly linked to Brucella or other specific pathogens, not the toxins of Bacillus cereus.

Step 3: Final Answer:
The heat-stable toxin cereulide produced by Bacillus cereus is responsible for the emetic syndrome.