Susceptibility patterns of coagulase-negative staphylococci to several newer antimicrobial agents in comparison with vancomycin and oxacillin

Coagulase-negative staphylococci (CoNS) have emerged as important nosocomial pathogens. CoNS resistance to meticillin and other semisynthetic penicillins is now common. Elevated vancomycin minimal inhibitory concentrations (MICs) have been reported and are associated with worse treatment outcomes. Several newer antibiotics have recently become available for the treatment of Gram-positive infections. The purpose of this study was to assess the in vitro activity of telavancin, daptomycin, linezolid and tigecycline in comparison with oxacillin and vancomycin against 653 non-duplicate clinical isolates of CoNS by the agar dilution method. The greatest variability in MIC was observed for oxacillin. Presence of the mecA gene conferred higher MICs for oxacillin but did not influence MICs to all other antibiotics tested. Telavancin tended to have MICs that were 1-2 dilutions lower than vancomycin. Daptomycin had good activity against all isolates. Staphylococcus haemolyticus, Staphylococcus hominis subsp. novobiosepticus, Staphylococcus saprophyticus, Staphylococcus schleiferi and Staphylococcus simulans were the most daptomycin-susceptible CoNS species tested. The validity of the agar dilution method for daptomycin was confirmed, with >90% isolates having MICs that were within 1 dilution of parallel Etest results. Within-species MIC variation was most restricted for linezolid and tigecycline, with the exception of Staphylococcus epidermidis and Staphylococcus haemolyticus that demonstrated higher overall MICs to tigecycline.