Waves of resistance: Staphylococcus aureus in the antibiotic era

Abstract

Staphylococcus aureus is notorious for its ability to become resistant to antibiotics. Antibiotic resistance in this organism has occurred in epidemic waves, beginning with the emergence of strains that were resistant to penicillin and progressing to the present pandemic of community-associated methicillin-resistant S. aureus (CA-MRSA). This article reviews the recent evolutionary history of drug-resistant strains of S. aureus. We discuss the molecular epidemiology of the epidemics of penicillin- and methicillin-resistant strains of S. aureus that have occurred since 1940 and their common features. The evolution of the mobile chromosome cassette element SCCmec, which carries mecA, the gene that determines resistance to methicillin and the entire class of β-lactam antibiotics, is also reviewed. The clinical and molecular epidemiology of CA-MRSA is then discussed, along with the virulence determinants that are present in CA-MRSA strains and the possible genetic basis of the epidemicity and disease severity that is associated with these strains. Finally, we look at antimicrobial therapy in the era of CA-MRSA.