Strain variation in the MRSA population over a 10-year period in one Dublin hospital.

Between 1989 and 1998, the number of patients carrying methicillin-resistant Staphylococcus aureus in one Dublin hospital increased fourfold, and the antibiogram-resistogram (AR) type distribution changed. In 1989, the predominant AR types were AR01 and AR02; in 1993, AR14 predominated; and in 1994, AR14 and AR13 were predominant. By 1998, the prevalence of AR13 and AR14 had declined and AR06 and AR07 were observed more frequently. In 1989, 65% of isolates were nontypeable using the International Basic Set of Typing Phages. This percentage increased to 78% in 1998. Total cellular DNA macrorestriction analysis reflected the changing AR type distribution. No vancomycin-intermediate isolates were recovered, but possible heteroresistance was observed in 2.7% of isolates. High-level mupirocin resistance occurred in 4% of isolates, and 32% exhibited low-level resistance.