Virulence Factors

S. aureus exerts a range of species-specific factors for the invasion of host tissues and evasion of the immune defense. These factors comprise, for instance, staphy-locoagulase, protein A, clumping factors A and B, staphylokinase, and hyaluroni-dase. Moreover, S. aureus strains encode a great variety of exotoxins and enterotox-ins which are mostly located on pathogenicity islands. Apart from the d- and ยก-hemolysins, S. epidermidis ATCC 12228 and RP62A harbor no staphylococcal exotoxin genes, and the genomic islands identified in these strains also do not carry superantigen genes and should therefore not be regarded as pathogenicity islands. Nevertheless, homologous genes for other secreted exoenzymes such as lipases, esterases, serine protease, cysteine proteases, and other proteases as well as thermonuclease and exonuclease are present in both S. epidermidis genomes. These factors reflect the interference with host structures and the recruitment of nutrient sources by S. epidermidis. The lack of toxins and superantigens in S. epidermidis explains the more subacute and chronic course of S. epidermidis infections, whereas S. aureus has the capacity to cause acute and often life-threatening infections.

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