Two clones of methicillin-resistant Staphylococcus aureus in Poland

OBJECTIVE: To evaluate relatedness among methicillin-resistant Staphylococcus aureus (MRSA) strains isolated in Poland. METHODS: Ninety-three MRSA hospital isolates were collected from different regions in Poland from 1990 to 1992. Strains were analyzed with respect to heterogeneity of methicillin resistance, phage types, resistance patterns, crystal violet staining, chromosomal DNA SmaI restriction patterns by PFGE, ERIC1 and ERIC2 AP-PCR types and DNA repeat polymorphism within the protein A gene. Resistance to methicillin was confirmed by the detection of the mecA gene by PCR. RESULTS: The combined results of typing methods demonstrate that all MRSA strains analyzed could be easily divided into two distinct clones (clonally related strains). The first consisted of strains with clear heterogeneous expression of resistance to methicillin (34 isolates) and the second showed more homogeneous resistance (59 isolates). In this study the best method for epidemiologic analysis of MRSA was found to be PFGE. A good correlation between the epidemic behavior of MRSA and a high number of repetitive DNA units within the protein A gene was observed. CONCLUSIONS: Results show that in Poland two distinct clones of epidemic MRSA have circulated in the past, easily discriminated by pheno- and genotyping methods, and both could be found together in a single hospital.