Antimicrobial Resistance and Molecular Analysis of Methicillin-Resistant Staphylococcus aureus Collected in a Spanish Hospital

Clonal distribution of methicillin-resistant Staphylococcus aureus (MRSA) in hospitals may differ according to the geographic location and time period. Knowledge of MRSA clonal epidemiology in hospital settings involves much more than the study of healthcare-associated MRSA (HA-MRSA) clones. In recent years, investigators have documented the introduction of both community-associated MRSA (CA-MRSA) and livestock-associated MRSA (LA-MRSA) clones, the emergence of clones carrying Staphylococcal cassette chromosome mec (SCCmec) XI, and the genetic diversity among sporadic MRSA isolates. The allocation of certain antibiotypes to dominant MRSA clones in an institution allows their use as phenotypic markers for a preliminary search for new clones, early detection of clonal shift, and as a guide for better empirical therapy, infection control, and treatment within a particular institution. For these reasons, we identified 938 strains detected in a System of Universal Active Surveillance of MRSA in clinical samples during the period 2009-2010, obtaining the clonal distribution of MRSA at the Hospital Universitario de Canarias (Tenerife, Spain) and the relationship between antimicrobial susceptibility and three major clones present. The antibiotypes that best defined the ST5-MRSA-IV (Pediatric) clone showed resistance to tobramycin and susceptibility to clindamycin, erythromycin, gentamicin, rifampin, trimethoprim-sulfamethoxazole, vancomycin, quinupristin/dalfopristin, and linezolid, whereas the ST22-MRSA-IV clone (EMRSA-15) showed susceptibility to these antibiotics, and finally, the ST36-MRSA-II clone (EMRSA-16) was resistant to clindamycin, erythromycin, and tobramycin and susceptible to the remaining antimicrobials. Similar observations would allow the early detection of changes in clonal epidemiology by analysis of antimicrobial susceptibility of the isolates within a single institution.