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': 'Eight months after prosthetic valve replacement, most common organism causing infective endocarditis is: \nSelect and explain. \nA. Staph. epidermidis, B. Strep. viridans, C. Staph. aureus, D. HACEK', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. (a) Staph. epidermidis Coagulase negative staphylococci is the most common cause of endocarditis in posthetic value recepients with in one year of surgery.', 'role': 'assistant'}]