This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Bacteria, Subject name: Microbiology
A patient of RHD developed infective endocarditis after dental extraction. Most likely organism causing this is : 
Select and explain. 
A. Streptococcus viridans, B. Streptococcus Pneumoneae, C. Streptococcus Pyogenes, D. Staphylococcus aureus
A: Streptococcus viridans
Answer: A: Streptococcus viridans 
Explanation: Ans. is 'a' ie Streptococcus viridans Viridans streptococci consists of multiple species of alpha hemolytic streptococciVarious species of viridans streptococciS. salivariusS. mitisS. sanguisS.mutans are a part of normal flora of mouth. They can cause bacteremia through minor trauma such as while eating, tooth, brushing and flossing.This bacteremia is thought to be the cause of Endocarditis in these patients.Some frequently asked questions about etiology of endocarditis Most common cause of Acute Bacterial Endocarditis (Native valve) - S.aureus* Most common cause of Early prosthetic valve Endocarditis (< 2 months) - Coagulase negativeStaphylococci* Most common cause of prosthetic valve endocarditis (> 12 months) - Streptococci * (includes viridans, S.bovis, other non-group A) Most common cause of endocarditis in l.V drug abusers - Staphylococcus aureus*