Most common organism for causing infective endocarditis in naive valve-: (A) Streptococcus Viridans, (B) Entero cocci, (C) Staphylo cocci, (D) Gram negative bacilli
Answer is C. Etiology of infective endocarditis The causative organisms differ depending on the underlying risk factors. Fifty percent to 60% of cases of endocarditis occurring on damaged or deformed valves are caused by Streptococcus viridans, a relatively banal group of normal oral flora. By contrast, the more virulent S. aureus (common to skin) can attack deformed as well as healthy valves and is responsible for 10% to 20% of cases overall; it also is the major offender in infections occurring in intravenous drug abusers. Additional bacterial agents include enterococci and the so-called HACEK group (Haemophilus, Actinobacillus, Cardiobacterium, Eikenella, and Kingella), all commensals in the oral cavity. Ref : Harrisons 20,th edition pg 1443