Staphylococci (staph) are Gram-positive spherical bacteria that occur in microscopic clusters resembling grapes. Bacteriological culture of the nose and skin of normal humans invariably yields staphylococci. In 1884, Rosenbach described the two pigmented colony types of staphylococci and proposed the appropriate nomenclature: Staphylococcus aureus (yellow) and Staphylococcus albus (white). The latter species is now named Staphylococcus epidermidis. Although more than 20 species of Staphylococcus are described in Bergey's Manual (2001), only Staphylococcus aureus and Staphylococcus epidermidis are significant in their interactions with humans. S. aureus colonizes mainly the nasal passages, but it may be found regularly in most other anatomical locales, including the skin, oral cavity and gastrointestinal tract. S epidermidis is an inhabitant of the skin.