Analysis of different molecular methods for typing methicillin-resistant Staphylococcus aureus isolates belonging to the Brazilian epidemic clone

The extensive geographic spread of MRSA isolates belonging to the BI azilia n epidemic clone (BEC) limited the value of pulsed-field gel electrophoresi s (PFGE) in epidemiological studies of outbreaks caused by these strains. T hus, the discriminatory power of eight different molecular methods was eval uated in an attempt to establish a methodology for genotyping BEC isolates involved in intra-hospital outbreaks. BEC isolates from five hospitals in T eresina City, Piaui State were genotyped by conventional electrophoresis or PFGE of ClaI- or SmaI-digested genomic DIVA hybridised with specific label led MecA, Tn554, IS257 and IS256 probes. The combination of PFGE with ClaI/ mecA, ClaI/Tn554, ClaI/IS257, SmaI/mecA and SmaI/IS257 probe-fingerprinting techniques provided a very poor discriminatory power for BEC strains, Alth ough ClaI/IS256 fingerprinting discriminated 17 different polymorphisms amo ng the isolates displaying PFGE A(1) pattern, this strategy was not reprodu cible. In contrast, the combination of PFGE and SmaI/IS256 polymorphisms di fferentiated BEC isolates into nine stable polymorphisms. Thus combination of PFGE and hybridisation with IS256 probe may be recommended as a useful m eans of typing BEC strains involved in intrahospital infections.