This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Staphylococci, Subject name: Microbiology
Most common cause of artificial heart valve infection- 
Select and explain. 
A. Staphylococcus aureus, B. Streptococcus mutans, C. Staph epidermidis, D. Pneumococcus
C: Staph epidermidis
Answer: C: Staph epidermidis 
Explanation: Ans. is 'c' i.e., Staph epidermidis o Most common cause of prosthetic valve endocarditis upto 12 months is coagulase - negative staphylococci (staph, epidermidis).Most common causes of infective endocarditiso In native wall - Staphylococcus aureus.o In early prosthetic valve (up to 12 months after valve surgery) - Staphylococcus epidermidis (coagulase negative staphylococcus).o In late prosthetic valve (more than 12 months after valve surgery) - streptococcus viridans.o In IV drug abusers - Staphylococcus aureus.o In patients writh intravenous catheter - coagulase negative staphylococci,o After dental procedure (tooth extraction) - streptococcus mutans.