Staphylococci are non-motile, non-spore-forming, gram-positive organisms occurring singly, in pairs, tetrads, or clusters resembling grapes. The image on the right is an example of a staphylococci gram stain. More than 20 species have been identified; three species are significant in their interactions with humans—S. aureus, S. epidermidis, and S. saprophyticus.
The staphylococci are members of the normal flora of the skin and mucous membranes of humans and warm-blooded animals. Colonization of the nares (nostrils) and skin can provide large reservoirs of organisms for transmission.
Approximately 25–30% of the general population are colonized by S. aureus, mainly in the nasal passages, but the organism can be found in most anatomical sites including the skin, oral cavity, and GI tract.
Infections are frequently acquired when the colonizing strain gains access to a normally sterile site as a result of trauma or abrasion to the skin or mucosal surface. S. aureus infections range from superficial, localized skin infections, such as folliculitis, to deeper, more serious skin lesions and more serious toxin-mediated conditions like scalded skin syndrome and toxic shock syndrome.
