Staphylococcus aureus:
Staphylococcus is a group of bacteria that can cause a multitude of diseases as a result of infection of various tissues of the body. Staphylococcus is more familiarly known as Staph (pronounced "staff"). Staph-related illness can range from mild and requiring no treatment to severe and potentially fatal.
The name Staphylococcus comes from the Greek staphyle, meaning a bunch of grapes, and kokkos, meaning berry, and that is what Staph look like under the microscope, like a bunch of grapes or little round berries. (In technical terms, these are gram-positive, facultative anaerobic, usually unencapsulated cocci.)
Over 30 different types of Staphylococci can infect humans, but most infections are caused by Staphylococcus aureus. Staphylococci can be found normally in the nose and on the skin (and less commonly in other locations) of 25%-30% of healthy adults. In the majority of cases, the bacteria do not cause disease. However, damage to the skin or other injury may allow the bacteria to overcome the natural protective mechanisms of the body, leading to infection.