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: Medicine
Bacteria responsible for post-operative endocarditis is: 
Select and explain. 
A. Streptococcus viridans., B. Staphylococcus epidermidis., C. Streptococcus aureus., D. Streptococcus pneumoniae.
B: Staphylococcus epidermidis.
Answer: B: Staphylococcus epidermidis. 
Explanation: None