Molecular epidemiology of methicillin-resistant Staphylococcus aureus in a Spanish hospital over a 4-year period: clonal replacement, decreased antimicrobial resistance, and identification of community-acquired and livestock-associated clones

This study was carried out on 189 methicillin-resistant Staphylococcus aureus (MRSA) clinical isolates collected in a third-level hospital in Valladolid, Spain, between 2005 and 2008 in order to investigate the changes in molecular epidemiology and genetic backgrounds associated with the changes in resistance phenotypes produced over time. The MRSA isolates were classified as belonging to 10 different clones, including the identification of a novel MRSA clone, ST2422-MRSA-IV, belonging to CC121; 1 CA-MRSA strain from a USA300 clone; another from ST97-MRSA-IV, associated with clones adapted to livestock (LA-MRSA); and 2 strains belonging to a new spa type (t10258) related to the ST8-MRSA-IV clone. Sixty-two percent of the strains belonging to Spanish-prevalent MRSA sequence type ST125 harboured composite or multiple SCCmec elements including SCCmec type IV plus ccrA/B4 (ST125-SCCmec IV/VI). In the years studied, it was observed that ST125-SCCmec IV/VI replaced the multiresistant ST228-SCCmec I previously prevalent, and, as a consequence, decreased gentamicin and clindamycin resistance was further observed.