This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Microbiology
[{'content': 'The endotoxin of the following gram negative bacteria does not play any part in the pathogenesis of the natural disease. \nSelect and explain. \nA. E. coli, B. Klebsiella, C. Vibrio cholerae, D. Pseudomonas', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Cholera Vibrios also possess lipopolysaccharide O antigen (LPS, endotoxin) as in other gram-negative intestinal bacilli.\xa0But unlike other gram-negative bacilli like E.coli, Klebsiella and Pseudomonas, etc. (where endotoxin is the principle\xa0virulence factor), LPS apparently plays no role in pathogenesis of cholera but is responsible for the immunity induced\xa0by killed vaccine.\nFor Vibrio cholerae the principle virulence factor is the exotoxin, i.e. cholera toxin.', 'role': 'assistant'}]