Methicillin-resistant Staphylococcus aureus isolates recovered from a New York City hospital: analysis by molecular fingerprinting techniques.

Fifty-five methicillin-resistant Staphylococcus aureus (MRSA) isolates collected at New York Hospital Medical Center of Queens in 1989 were analyzed by molecular fingerprinting techniques. Close to 70% of these isolates (38 of 55) shared a common pulsed-field gel electrophoretic pattern, carried the same mecA gene polymorph type II, were free of the transposon Tn554, and would not react with a mecI-specific gene probe. An additional five isolates shared all properties of the major MRSA clone except that they carried mecA gene polymorph type III. All these isolates had an extremely heterogeneous methicillin resistance phenotype that belonged to population analysis profile class 1 or 2. The rest of the 12 MRSA isolates showed a variety of chromosomal pulsed-field gel electrophoretic patterns that carried different mecA polymorphs and that also gave positive reactions with DNA probes for Tn554 and for the mecI gene. The molecular features of the majority MRSA clone suggest that it is an archaic MRSA isolate similar in features to early MRSA isolates recovered in the 1960s.