Distinct genotypic clusters of heterogeneously and homogeneously methicillin-resistant Staphylococcus aureus from a Greek hospital

Methicillin-resistant Staphylococcus aureus (MRSA) strains isolated over a one-year period from a Greek hospital were tested for their levels of resistance to methicillin by population analysis. Heterogeneously resistant strains belonged to classes I, II, and II/III, whereas homogeneously resistant ones belonged to class IV. Strains of all classes possessed the mecA gene. Pulsed-field gel electrophoresis (PFGE) of Smal-digested genomic DNA revealed that all heterogeneously resistant strains were related. Homogeneously resistant strains were also closely related, but in a cluster distinct from the heterogeneous one. The methicillin-sensitive strains displayed a greater variety of PFGE types compared to MRSA isolates.