This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Infective Endocarditis, Subject name: Medicine
Organism leading to infective endocarditis? 
Select and explain. 
A. Staph aureus, B. Klebsiella, C. Streptococcus Pneumoniae, D. Meningococcus
A: Staph aureus
Answer: A: Staph aureus 
Explanation: Ans. (a) Staphylococcus aureusRef: Harrison 19th ed. / 816* Overall S.Aureus infection is the most common cause of IE, including Prosthetic Valve Endocarditis, acute Infective Endocarditis, and IVDA( Intravenous drug Abuse) Infective Endocarditis.* Approximately 35-60.5% of staphylococcal bacteremias are complicated by IE.* More than half the cases are not associated with underlying valvular disease.* The mortality rate of S aureus IE is 40-50%.* The incidence of MRSA infections, both the hospital- and community-acquired varieties, has dramatically increased (50% of isolates). Sixty percent of individuals are intermittent carriers of MRSA or MSSA.