MRSA Antibiotic Resistance
S. aureus antibiotic resistance mechanisms include enzymatic inactivation (β-lactamase), decreased affinity to altered drug targets (mutated penicillin-binding protein 2a in MRSA,
peptidoglycan D-Ala-D-Lac in vancomycin-resistant strains), and efflux pumps (fluoroquinolones and tetracycline). MRSA has acquired complex genetic loci (e.g. mec elements or the vanA operon) through horizontal gene transfer, while resistance to other drugs, including the newer antibiotics linezolid and daptomycin, have developed through spontaneous mutations and natural selection.