A comparative in-vitro evaluation of resistance selection after exposure to teicoplanin, vancomycin, linezolid and quinupristin-dalfopristin in Staphylococcus aureus and Enterococcus spp.

The ability of breakpoint and serum concentrations of teicoplanin, vancomycin, linezolid and quinupristin-dalfopristin to select resistance was compared for isolates of methicillin-susceptible Staphylococcus aureus (MSSA), methicillin-resistant S. aureus (MRSA), Enterococcus faecalis and Enterococcus faecium. Mutation frequencies were always <10(-10), except for two isolates grown in the presence of teicoplanin at the trough serum concentration. After multistep selection, linezolid selected for resistance in staphylococci and enterococci, and serial exposure to certain concentrations of linezolid was more likely to select for stable resistance in MRSA, MSSA and enterococci than was exposure to glycopeptides and quinupristin-dalfopristin.