Question

'Emetic Syndrome' is associated with ________.

• A. Salmonella typhi
• B. Bacillus cereus
• C. Clostridium perfringens
• D. Escherichia coli O157: H7

Hint:

Remember the dual nature of Bacillus cereus food poisoning:
1. Emetic Type: Rapid onset (1–5 hours), caused by the heat-stable toxin cereulide in starchy foods like rice.
2. Diarrheal Type: Slower onset (8–16 hours), caused by heat-labile enterotoxins produced in the intestine after ingesting meat or vegetables.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Food poisoning caused by Bacillus cereus is unique because it manifests as two distinct clinical syndromes: the diarrheal syndrome and the emetic (vomiting) syndrome.
These two conditions are caused by different types of toxins produced by the bacterium under different environmental conditions.
Detailed Explanation:
The emetic syndrome is characterized by severe nausea, abdominal cramps, and vomiting that develop rapidly, typically 1 to 5 hours after consuming contaminated food.
This rapid onset occurs because the illness is caused by a pre-formed toxin consumed directly with the food.
The toxin responsible is cereulide, a small, cyclic dodecadepsipeptide ionophore.
Cereulide is synthesized by vegetative cells of Bacillus cereus growing in starch-rich foods, most notably cooked rice that has been stored at room temperature.
Cereulide is highly stable: it resists heat (surviving $121^\circ\text{C}$ for 90 minutes), is stable across a wide pH range, and is resistant to proteolytic enzymes like pepsin and trypsin.
As a result, reheating contaminated rice kills the bacteria but leaves the active toxin intact, which then triggers the emetic response by binding to 5-$\text{HT}_3$ receptors in the duodenum, stimulating the vagus nerve.
Let us review the other options:
- Salmonella typhi causes systemic enteric (typhoid) fever.
- Clostridium perfringens causes diarrheal food poisoning via enterotoxin production during intestinal sporulation.
- Escherichia coli O157:H7 causes hemorrhagic colitis and hemolytic uremic syndrome (HUS).

Step 2: Final Answer:
The emetic syndrome is uniquely associated with Bacillus cereus.