Molecular analysis and susceptibility patterns of meticillin-resistant Staphylococcus aureus (MRSA) strains circulating in the community in the Ligurian area, a northern region of Italy: emergence of USA300 and EMRSA-15 clones

For many years meticillin-resistant Staphylococcus aureus (MRSA) has been considered a typical nosocomial pathogen. Recently, MRSA has emerged as a frequent cause of infections in the community. A multicentre surveillance study was carried out in the Ligurian area of Italy to evaluate the incidence, molecular nature and susceptibility patterns of MRSA strains circulating among outpatients. The genetic background of MRSA strains was analysed by pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST). Determination of antimicrobial susceptibility patterns, staphylococcal cassette chromosome mec (SCCmec) type, accessory gene regulator (agr) group and Panton-Valentine leukocidin (PVL) production was also performed. In total, 12 (6.4%) of 188 S. aureus isolates collected during 2006-2007 were found to be MRSA by phenotypic and genotypic methods. Analysis of isolates by PFGE showed that the majority of strains (11/12) belonged to two well-known international clones (EMRSA-15 and USA300) and their variations. High variability regarding SCCmec IV subtypes, susceptibility patterns and PVL toxin production were found among members of the USA300 clonal group, even when displaying the same PFGE profiles. The remaining MRSA strain belonged to sequence type (ST) 8, agr group I and carried SCCmec type I. Both community-associated MRSA and healthcare-associated MRSA epidemic international clones circulate among outpatients in our region. It is alarming that members of the most represented clonal group in our collection (USA300) can acquire multiresistance as well as PVL genes. Infection control measures in our area should be improved to avoid the selection of microorganisms displaying both traits simultaneously as well as the spread of these epidemic international clones.