Characteristics of French methicillin-resistant Staphylococcus aureus isolates with decreased susceptibility or resistance to glycopeptides

According to the French Society of Microbiology, Staphylococcus aureus isolates are suspected to have decreased susceptibility to glycopeptide(s) when at least one colony is able to grow from an inoculum of 10 microL of 2 McFarland bacterial suspension plated on Mueller-Hinton agar containing 5 mg/L teicoplanin and incubated for 48 h at 35-37 degrees C. We analysed 89 methicillin-resistant S. aureus isolates (MRSA), collected in 2000-2001 from 24 hospitals located in 18 French cities, which were able to grow on this selective medium. These isolates were distributed into six groups on the basis of their glycopeptide resistance phenotypes: (A) glycopeptide susceptible (GSSA, 21 isolates); (B) heterogeneous teicoplanin intermediately resistant (hetero-TISA, 24 isolates); (C) heterogeneous and intermediately resistant to both glycopeptides, teicoplanin and vancomycin (hetero-GISA, six isolates); (D) heterogeneous vancomycin intermediately resistant/teicoplanin intermediately resistant (hetero-VISA/TISA, 30 isolates); (E) GISA (four isolates); (F) TISA (four isolates). Despite the persistent decrease in gentamicin-resistant MRSA isolates in French hospitals since 1993, their prevalence is very high in groups D, E and F. Moreover, most of the group C, D and E isolates exhibiting decreased susceptibility to both glycopeptides belong to the same major SmaI genotype, which has been detected in Europe since at least 1989.