Diversity among community isolates of methicillin-resistant Staphylococcus aureus in Australia

Community methicillin-resistant Staphylococcus aureus (CMRSA) strains are being isolated with increasing frequency around the world. In Western Australia CMRSA are endemic in geographically remote communities and have been found to belong to five different contour-clamped homogeneous electric field (CHEF) electrophoretic patterns. Representatives of each of these CHEF patterns have been compared to CMRSA representative of CHEF patterns from other Australian states and New Zealand. With one exception, all of the isolates were nonmultiresistant and were not resistant to many antimicrobial agents other than the beta-lactams. With one exception, which is not believed to be a CMRSA, all of the isolates harbored a beta-lactamase plasmid. Erythromycin resistance was associated with a 2-kb plasmid. One of the beta-lactamase plasmids was found to be able to acquire additional resistance determinants to become a multiple resistance plasmid. There were 10 multilocus sequence types belonging to eight distantly related clonal complexes of S. aureus. One new sequence type was found. Although most of the CMRSA harbored the type IVa SCCmec, a type IV structural variant was found and two new SCCmec types were identified. Protein A gene (spa) typing revealed two new spa types and, with two exceptions, corresponded to multilocus sequence typing. In contrast to other reports on CMRSA, most of the CMRSA strains studied here did not contain the Panton-Valentine leukocidin genes. The results also demonstrate that nonmultiresistant hospital strains such as UK EMRSA-15 may be able to circulate in the community and could be mistaken for CMRSA based on their resistance profiles.