Staphylococcus spp.: an update on the molecular epidemiology and mechanisms of antimicrobial resistance

Staphylococcus aureus and Coagulase-Negative Staphylococci (CoNS) represent harmful pathogenic agents responsible for human and animal infections. The Community-Acquired Methicillin Resistant S. aureus (CA-MRSA) is now considered a worldwide health issue. Methicillin resistance is attributed to the acquisition of the Staphylococcal Cassette Chromosome mec (SCCmec), a resistance island that contains the structural mecA gene. Recent studies have found a homologue gene to mecA denominated MECC, which is located in a cassette chromosome mec, designated SCCmec type XI. Some new treatment alternatives for methicillin and for vancomycin, a high toxic glycopeptide drug to which some resistant strains, include the lipoglycopeptides televancin and dalbavancin, the lipopeptides daptomycin and tripopeptin C, the oxazolidones linezolid and torezolid, the fluoroquinolones delafloxacin and moxifloxacin, the estreptogramines quinupristin/dalfopristin, the new cephalosporine ceftaroline, the glycylcycline tigecyclin and the DHFR inhibitor iclaprim. Despite their recent introduction, reduced susceptibility to these drugs has been identified in staphylococcal strains. The high spread of resistant strains among individuals lacking classic risk factors for these infections emphasizes the importance of epidemiological surveillance of S. aureus and CoNS, and the molecular characterization of resistant strains. The distinction between hospital and community isolates is becoming unclear, which raises the need for the investigation of the dynamics and epidemiology of resistance among these agents.