Staphylococcus aureus is a gram-positive coccal bacterium that is a member of the Firmicutes, and is frequently found in the respiratory tract and on the skin forms where perspiration is present. It is often positive for catalase and nitrate reduction.he emergence of antibiotic-resistant forms of S. aureus such as MRSA is a worldwide problem in clinical medicine. Staphylococcus was first identified in 1880 in Aberdeen, Scotland, by the surgeon Sir Alexander Ogston in pus from a surgical abscess in a knee joint.