Recognition of two groups of methicillin-resistant Staphylococcus aureus strains based on epidemiology, antimicrobial susceptibility, hypervariable-region type, and ribotype in Finland

Epidemiological evidence suggests that some methicillin-resistant Staphyloc occus aureus (MRSA) strains are more prone to dissemination than others. We studied 72 MRSA strains, collected through nationwide MRSA surveillance in 1992 through 1999 and known to be either (i) sporadic, (ii) local outbreak strains spread within one hospital, or (iii) epidemic strains spread among hospitals, by antimicrobial susceptibility testing, hybridization of the m ec hypervariable region (HVR), and ribotyping, Our results show that two ma in groups can be identified among these strains. The first group includes m ainly nonepidemic, nonmultiresistant MRSA strains showing a specific mec HV R hybridization pattern, A, in combination with a variety of ribotypes, The other group includes multiresistant strains with mec HVR hybridization pat tern B or C in association,vith closely related ribotype a or b, Sixty-four percent (9 of 14) of Finnish epidemic MRSA strains belong to the latter gr oup. These findings support the existence of differences in epidemic potent ial among MRSA strains.