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
Microbiologic studies on a gram-positive coccus isolated from a skin abscess demonstrate a positive catalase test and a positive coagulase test. This is most consistent with which of the following organisms? 
Select and explain. 
A. S. aureus, B. S. epidermidis, C. S. pneumoniae, D. S. pyogenes
A: S. aureus
Answer: A: S. aureus 
Explanation: All of the organisms listed are gram-positive cocci. The positive catalase test excludes the Streptococci, S. pyogenes, and S. pneumoniae. Of the Staphylococci, only S. aureus has a positive coagulase test. S. epidermidis and S. saprophyticus are coagulase-negative Staphylococci. Ref: Ray C.G., Ryan K.J. (2010). Chapter 24. Staphylococci. In C.G. Ray, K.J. Ryan (Eds), Sherris Medical Microbiology, 5e.