Antimicrobial Resistance Properties of Staphylococcus aureus
Staphylococcus (S.) aureus isolates of human and animal origin harbor a wide variety of resistance genes. So far, at least 60 different resistance genes have been identified in S. aureus. This includes genes that confer resistance to virtually all classes of antimicrobial agents approved for use in humans and animals, such as β-lactam antibiotics, tetracyclines, macrolides, lincosamides, streptogramins, phenicols, aminoglycosides, aminocyclitols, pleuromutilins, oxazolidinones, diaminopyrimidines, sulphonamides, fusidic acid, mupirocin, and glycopeptides. The resistance mechanisms specified by the resistance genes fall into three major categories: (1) enzymatic inactivation and modification, (2) active efflux, or (3) protection/modification/replacement of the cellular target sites of the antimicrobial agents. Mobile genetic elements, in particular plasmids and transposons, play a major role as carriers of antimicrobial resistance genes in S. aureus. They facilitate the exchange of resistance genes not only among S. aureus isolates but also between S. aureus and other Gram-positive bacteria. In addition, mutations accounting for resistance to fluoroquinolones, fusidic acid, mupirocin, rifampicin, sulphonamides, and oxazolidinones have been identified in S. aureus.