Question

All of the following statements about El Tor vibrios are true, except:

• A. Humans are the only reservoir
• B. Can survive in ice cold water for 2 to 4 weeks
• C. Killed by boiling for 30 seconds
• D. Enterotoxin can have direct effects on tissues other than intestinal epithelial cells

Hint:

Cholera toxin binds GM1 on enterocytes only, not on other tissues.

Answer 1

The Correct Option is D

Step 1: The question asks for the FALSE statement about the El Tor biotype of Vibrio cholerae.
Step 2: Humans are the only known natural reservoir of Vibrio cholerae. There is no animal or environmental reservoir that maintains the organism long term, so option A is a true statement.
Step 3: Vibrio cholerae, especially the El Tor biotype, is hardy in water. It can survive in ice cold water for 2 to 4 weeks, which helps explain water borne spread, so option B is true.
Step 4: Vibrios are killed easily by heat. Boiling for about 30 seconds destroys them, which is why boiled water is safe in cholera areas. Option C is true.
Step 5: The action of cholera toxin is highly specific. It binds the GM1 ganglioside receptor on intestinal epithelial cells and raises cyclic AMP, causing massive secretion of water and electrolytes into the gut lumen. The toxin does NOT act directly on other tissues besides the intestinal epithelium. So the claim that the enterotoxin has direct effects on other tissues is false.
Conclusion: The exception is option D, the enterotoxin acting on tissues besides intestinal epithelium.