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': 'Commonest cause of nosocotnial infection ? \nSelect and explain. \nA. Pseudomonas, B. Staphylococci, C. Klebsiella, D. Enterobacteriacea', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Ans. is \'b\' i.e., Staphylococci "Overall, S. aureus is a leading cause of nosocomial infection"', 'role': 'assistant'}]