Hospital-associated methicillin-resistant Staphylococcus aureus (HA-MRSA) in Italy

The aim of our study was to trace the dynamic changes of hospital-associated methicillin-resistant Staphylococcus aureus (HA-MRSA) lineages in Italy, comparing the genotypic backgrounds of contemporary isolates over a period of 17 years, with those of a sample of early MRSA strains from 1980. In total, 301 non-repetitive MRSA clinical isolates, recovered from 19 Italian hospitals between 1990 and 2007 were selected and analyzed for their antibiotic resistance, typed by PFGE and SCCmec, grouped into clonal-types and further characterized using Multi Locus Sequence Typing (MLST). A sample of fifteen early MRSA strains from 1980 was also used for comparison. The most interesting feature was the recent increase of ST228-MRSA-I (formerly the Italian clone; PFGE E) over the period 2000–2007 (57%), when compared to the period 1990–1999 (29%), and its stability to date, associated with a decrease of the highly epidemic ST247-MRSA-IA (formerly the Iberian clone; PFGE A), (23% from 1990 to 1999, 6% from 2000 to 2007). ST1-MRSA-I (1 out of 2 strains carrying ccrA(2)B(2)), ST8-MRSA-I (4 strains), ST15-MRSA-I (1 out of 4 carrying ccrA(2)B(2)) and ST30-MRSA-I (2 out of 5 carrying no ccrAB-types and ccrC) were the predominant earliest STs among the MRSA strains in 1980. A temporal shift in the susceptibility levels to glycopeptides was observed: strains with vancomycin MIC of ≥ 2 mg/L increased from 19.4% to 35.5%. In conclusion, we describe the alternation of MRSA clones that occurred in hospitals from 1990 to 2007 and the increase of the glycopeptide MIC levels, reflecting a worldwide trend. We document the detection of ST1, ST8, ST15 and ST30 in the 1980 isolates; we hypothesize their possible latency and their appearance as the current CA-MRSA clones.