This organism is a gram positive coccus organized into grape-like clusters. It produces a yellow pigment and the positive mannitol salt agar test showed that it could ferment mannitol and had a high salt tolerance. This organism is catalase positive and coagulase positive, two critical tests for the correct identification of Staphylococcus aureus. Bacteroides fragilis is a gram-negative rod that grows anaerobically. It does cause abscesses, but does not have the characteristics described for the organism in this case. Clostridium perfringens is a gram-positive spore forming organism that causes gangrene. It would not grow aerobically on blood agar. The organism can ceainly spread in the skin when introduced by trauma, but would not demonstrate the biochemical profile described. Escherichia coli is a gram-negative rod that would grow on the blood agar but would not produce yellow pigment. Growth on MacConkey's agar after it was gram-stained would indicate lactose fermentation, and other biochemical tests would be used to specifically identify the organism.