This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Microbiology
Most common cause of aificial hea 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 Most common cause of prosthetic valve endocarditis upto 12 months is coagulase - negative staphylococci (staph. epidermidis). Most common causes of infective endocarditis In native wall - Staphylococcus aureus. In early prosthetic valve (up to 12 months after valve surgery) - Staphylococcus epidermidis (coagulase negative staphylococcus). In late prosthetic valve (more than 12 months after valve surgery) - streptococcus viridans. In IV drug abusers - Staphylococcus aureus. In patients with intravenous catheter - coagulase negative staphylococci. After dental procedure (tooth extraction) - streptococcus mutans.