<prompt> 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?S. aureusS. epidermidisS. pneumoniaeS. pyogenes  <response>: 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. 