Microbiology All of the following statements about El-Tor vibrios are true, except: A 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. 💡 Explanation All of the following statements about El-Tor vibrios are true, except: ✓ Correct Answer: D. Enterotoxin can have direct effects on other tissues besides intestinal epithelial cells.