[5] Many species cannot cause disease and reside normally on the skin and mucous membranes of humans and other animals.

[12] Group A includes S. aureus, S. borealis, S. capitis, S. epidermidis, S. haemolyticus, S. hominis, S. lugdunensis, S. pettenkoferi, S. simiae and S. warneri.

Assignment of a strain to the genus Staphylococcus requires it to be a Gram-positive coccus[15] that forms clusters, has an appropriate cell wall structure (including peptidoglycan type and teichoic acid presence) and G + C content of DNA in a range of 30–40 mol%.

Staphylococcus species can be differentiated from other aerobic and facultative anaerobic, Gram-positive cocci by several simple tests.

One of the most important phenotypical features used in the classification of staphylococci is their ability to produce coagulase, an enzyme that causes blood clot formation.

Seven species are currently recognised as being coagulase-positive: S. aureus, S. delphini, S. hyicus, S. intermedius, S. lutrae, S. pseudintermedius, and S. schleiferi subsp.

S. epidermidis, a coagulase-negative species, is a commensal of the skin, but can cause severe infections in immunosuppressed patients and those with central venous catheters.

S. saprophyticus, another coagulase-negative species that is part of the normal vaginal flora, is predominantly implicated in genitourinary tract infections in sexually active young women.

In recent years, several other Staphylococcus species have been implicated in human infections, notably S. lugdunensis, S. schleiferi, and S. caprae.

Many more complete S. aureus genomes have been submitted to the public databases, making it one of the most extensively sequenced bacteria.

Whole genome technologies, such as sequencing projects and microarrays, have shown an enormous variety of S. aureus strains.

A greater understanding of how the staphylococci evolve, especially due to the acquisition of mobile genetic elements encoding resistance and virulence genes is helping to identify new outbreak strains and may even prevent their emergence.

Members of the genus Staphylococcus frequently colonize the skin and upper respiratory tracts of mammals and birds and also in marine sponge.

In healthcare facilities, the risk of more serious staph infection is higher because many patients have weakened immune systems or have undergone procedures.

In the bloodstream, these factors cause inflammation, impair immune cell function, alter coagulation, and compromise vascular integrity.

When left untreated, S. aureus triggers pathophysiologic disturbances that are further amplified by the host inflammatory response, culminating in the severe clinical manifestations of sepsis and septic shock.

[26] Staphylococcus can cause a wide variety of diseases in humans and animals through either toxin production or penetration.