Question

Which of the following does NOT feature preformed toxins?

• A. Staphylococcus aureus
• B. ETEC (Enterotoxigenic E. coli)
• C. Bacillus cereus
• D. Clostridium botulinum

Hint:

Preformed toxins act fast, 1 to 6 hours, because the toxin is already in the food. ETEC needs to colonise the gut first.

Answer 1

The Correct Option is B

This question tests where the toxin is actually made, in the food before eating, or inside the body after the bacteria have colonised the gut.

1. Staphylococcus aureus: Grows in food left at room temperature and releases its enterotoxin into that food. The toxin is already present when the food is eaten, so it is preformed.
2. ETEC: The bacteria have to be swallowed, attach to the small bowel wall, and only then start making enterotoxin. Since the toxin is made inside the patient, not in the food, this is not a preformed toxin case.
3. Bacillus cereus: The emetic strains form a heat stable toxin in cooked rice that has been left out and reheated. This toxin is present in the food before it is swallowed, so it is preformed.
4. Clostridium botulinum: Grows in poorly preserved or canned food under anaerobic conditions and releases botulinum toxin straight into that food, so the toxin is preformed even though nerve symptoms take time to show up.

Staph aureus, Bacillus cereus and Clostridium botulinum all make their toxin in the food itself, but ETEC only makes toxin after it has set up infection in the gut, so ETEC is the exception.

Let's summarize:

• Preformed toxin food poisoning has a short 1 to 6 hour onset because the toxin is ready made.
• Staph aureus, Bacillus cereus emetic toxin, and Clostridium botulinum toxin are all made in the food.
• ETEC toxin is made only after the bacteria colonise the gut, so it is not preformed.

The organism that does not feature a preformed toxin is ETEC.