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': 'An adolescent with valvular disease developed low grade fever and significant weight loss, diagnosed of having subacute bacterial endocarditis. It is most commonly caused by: \nSelect and explain. \nA. Staph, aureus, B. Str. viridans, C. Str. hemolyticus, D. Esch. coli', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Subacute endocarditis progresses to death over weeks to months with low-grade fever, night sweats, weight loss, and vague constitutional complaints. The clinical course is substantially related to the virulence of the infecting organism; Staphylococcus aureus, for example, usually produces acute disease, whereas infections by the less virulent viridans streptococci are more likely to be subacute. Ref: Ray C.G., Ryan K.J. (2010). Chapter 66. Intravascular Infections, Bacteremia, and Endotoxemia. In C.G. Ray, K.J. Ryan (Eds), Sherris Medical Microbiology, 5e.', 'role': 'assistant'}]