Staphylococcus (Staph) species are a type of soil microorganism that normally colonizes human and animal skin and mucous membranes.  There are at least 40 species of Staph, some of which can cause human disease.  S. aureusis the most common cause of hospital-acquired infections and there are antibiotic-resistant strains of Staphyloccocus in many hospitals and health care facilities worldwide.  Skin infections caused by S. aureus result in boils, abscesses and infected lacerations.  If the bacteria travel to the blood they can cause major systemic infections or target specific organs such as the heart (endocarditis), bone (osteomyelitis), or lungs (pneumonia) and cause organ failure.  S. aureus produces a toxin called enterotoxin B (SEB) that causes food poisoning and results in severe diarrhea, nausea and intestinal cramping shortly after ingestion.  SEB is very stable (it can withstand boiling at 100C ) and the toxin remains in food and on surfaces long after the bacteria are killed.  Therefore, it is important to kill the bacteria before they begin producing large amounts of enterotoxin.  S. aureus produces other toxins (A, C-G), as well as TSST-1, which causes toxic shock syndrome. Several new toxin genes have been sequenced in recent years, and it is likely that there are many more serotypes than previously thought. S. aureus is the most pathogenic of all staphylococci for humans.

Staphyloccocus epidermis is most common on human skin and is harmless to healthy people but can cause severe infections in immune-suppressed patients and young infants.  S. saprophyticus is part of the normal vaginal flora and is often the cause of genitourinary tract infections in sexually-active young women.