The most common etiology of native valve endocarditis is

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