The emergence of community-associated methicillin-resistant Staphylococcus aureus at a London teaching hospital, 2000-2006

We used ciprofloxacin susceptibility as a phenotypic marker of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) in a London hospital collection of MRSA isolates from inpatients, outpatients and primary-care clinics during 2000-2006. Four-hundred and fifty-eight ciprofloxacin-susceptible (Cip-S) MRSA isolates were reported; antimicrobial susceptibility, staphylococcal cassette chromosome mec (SCCmec) type, spa type and the presence of Panton-Valentine leukocidin (PVL) genes were determined for all 194 surviving Cip-S MRSA isolates. Multilocus sequence typing and pulsed-field gel electrophoresis were performed on representative isolates. Clinical and epidemiological features of Cip-S MRSA infections were consistent with CA-MRSA, the incidence of which increased markedly during the study period from 49 in 2000 to 102 in 2006. Most (82.0%) of the surviving Cip-S MRSA isolates were SCCmec IV and 25.3% were PVL-positive. Considerable clonal heterogeneity was noted among the recovered isolates, including the t044/ST80-IV European clone and the PVL-negative t127/ST1-IV clone; PVL-positive t008/ST8-IV (USA300) isolates were rare. Ciprofloxacin susceptibility is a useful screening marker of CA-MRSA strains in London, which are more frequent than previously thought and whose incidence is increasing.