This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Systemic Bacteriology (Gram Positive Bacilli, Gram Negative Bacilli), Subject name: Microbiology
[{'content': 'All of the following statements about El-Tor vibrios are true, except: \nSelect and explain. \nA. Humans are the only reservoir, B. Resist high alkalinity, C. Killed by boiling for 15 minutes, D. Enterotoxin can have direct effects on other tissues besides intestinal epithelial cells.', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Enterotoxin can have direct effects on other tissues besides intestinal epithelial cells is not true. Option 1 - Reservoir: Humans are the only reservoir. Option 2 - Vibrios are resistant to high alkalinity. Option 3 - Cholera toxin: exotoxin, heat-labile protein- destroyed by heating at 56degC for 15 minutes. Option 4 - V. cholera enterotoxin do not have any affects on extra-intestinal tissues (lack of receptors of toxin).', 'role': 'assistant'}]