Decreased susceptibility to glycopeptides in methicillin-resistant Staphylococcus aureus:: a 20 year study in a large French teaching hospital, 1983-2002

Objectives: To assess the evolution of glycopeptide susceptibility in methicillin-resistant Staphylococcus aureus (MRSA) strains isolated in a large French teaching hospital from 1983 to 2002. Methods: Determination of glycopeptide MICs by using the Etest method in Mueller-Hinton agar on a sample of randomly selected MRSA strains. Results: A total of 1445 MRSA strains were tested, and one vancomycin-intermediate MRSA (VISA) and 31 teicoplanin-intermediate MRSA (TISA) strains were detected. The first strains were detected in 1985, and all strains were gentamicin resistant (GR). None of the gentamicin-susceptible strains had a glycopeptide MIC > 3 mg/L. In addition, there was a significant increase in glycopeptide MIC geometric means over the years, and this increase was higher for teicoplanin than for vancomycin. Conclusions: The higher increase in teicoplanin MICs, and the good correlation between vancomycin and teicoplanin MICs, suggests systematic determination of teicoplanin MIC to screen for abnormal glycopeptide susceptibility among GR-MRSA.