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Identification
S. aureus is a Gram-positive coccus 0,5 - 1 µm in diameter portrayed by a typical grape-like cluster organisation. The colonies appear large, round and golden-yellow, in blood agar culture mediums _-haemolysis is often evident. It differentiates from most others species of its genus resulting positive in the coagulase test, as well it's also positive in catalase test and this fact permits the distinction between S. aureus and S. faecalis.
Pathogenesis
Molecular biology recently took a relevant role in the comprehension of the diseases imputable to S. aureus infections. The singling out of genes encoding for potential virulence factors and their consequent cloning and sequencing lead to purified proteins better enforceable to reproduced molecular model. Furthermore these encoding genes had been inactivated and the virulence of mutant strains had been compared with the wild-type one in animal models, verifying this way the mutual relation between the missing factor and the virulence fall. ItÕs a multifactorial origin in most of diseases because of the presence of multiple virulence mechanisms :