Bacterial endocarditis is most commonly caused by-

Ref: R Alagappan - Manual of Practical Medicine 4th Edition.pg no:161 Infective Endocarditis (IE) It is the colonisation of the hea valves with microbiologic organisms, leading to the formation of friable, infected vegetations and frequently valve injury. Types 1. Acute infective endocarditis: Caused by highly virulent organisms mainly S. aureus (20-30%), seeding a previously normal valve. 2. Subacute infective endocarditis: Caused by organisms of moderate or low virulence mainly Streptococci (60-70%), seeding an abnormal or previously injured valve. 3. Endocarditis occurring in IV drug abusers: Caused predominantly by organisms found on the skin (S. aureus, Candida) and affecting the valves on the right side of the hea. 4. Prosthetic valve endocarditis: This may be early (symptoms appearing within 60 days of valve inseion), due to intraoperative infection of the valve or inseion of an infected valve or late (symptoms appearing after 60 days of valve inseion), due to late bacteraemia or earlier infection with microorganisms having a long incubation period. Prosthetic aoic valve is more prone for infective endocarditis than the mitral valve. Right sided IE has a more ourable prognosis than the left sided IE. However, when right sided IE vegetation size exceeds 2 cm, the moality increases.