Genetic diversity of community-associated methicillin-resistant Staphylococcus aureus in southern Stockholm, 2000-2005

This study investigated the molecular epidemiology of 104 community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) isolates from southern Stockholm during the period 2000-2005. The isolates were analysed by pulsed-field gel electrophoresis (PFGE), multilocus sequence typing, staphylococcal chromosomal cassette (SCC) mec typing and detection of genes encoding Panton-Valentine leukocidin (PVL). Overall, 28 distinct PFGE patterns and 13 sequence types (STs) were identified. ST80, ST8, ST88 and ST150 were the major CA-MRSA clones in the area, and these accounted for 75% (78/104) of all CA-MRSA isolates. ST150 isolates, which have, to date, been found only in Sweden, were isolated exclusively from a group of homeless individuals. Eighty-six (83%) of the 104 isolates in the study possessed SCCmecIV, found in ten different STs, while 16 isolates possessed SCCmecV. The PVL genes were detected in 56% (58/104) of the isolates. Strain ST80-MRSA-IV carrying PVL genes predominated over the 6-year period and accounted for 38% of all isolates. However, a polyclonal tendency was observed among the CA-MRSA isolates recovered in recent years.