This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Cardiovascular system, Subject name: Pathology
[{'content': 'The most common etiology of native valve endocarditis is \nSelect and explain. \nA. Streptococcus viridians, B. Staphylococcus aureus, C. Enterococcus faecalis, D. Gram -ye bacilli', 'role': 'user'}, {'content': 'Answer: A \nExplanation: The causative organanism differ depending on the underlying risk factors. 50-60% of cases of endocarditis occurring on damaged or deformed valves are caused by Streptococcus viridans, a relative banal group of normal oral flora By contrast more virulent S. aureus can attack deformed as well as healthy valves and is responsible for 10%-20% of cases overall Robbins 9 th edition page no. 393', 'role': 'assistant'}]