Oritavancin Activity against Vancomycin-Susceptible and Vancomycin-Resistant Enterococci with Molecularly Characterized Glycopeptide Resistance Genes Recovered from Bacteremic Patients, 2009-2010

Oritavancin exhibited potent activity against vancomycin-susceptible (MIC50 and MIC90, 0.015/0.03 mu g/ml) and vanB-carrying E. faecalis isolates (MIC50 and MIC90, 0.015 and 0.015 mu g/ml). Higher (16- to 32-fold) MIC(50)s and MIC(90)s for vanA-harboring E. faecalis were noted (MIC50 and MIC90, 0.25 and 0.5 mu g/ml), although oritavancin inhibited all strains at <= 0.5 mu g/ml. Vancomycin-susceptible and vanB-carrying E. faecium strains (MIC50 and MIC90, <= 0.008 and <= 0.008 mu g/ml for both) were very susceptible to oritavancin, as were VanA-producing isolates (MIC50 and MIC90, 0.03 and 0.06 mu g/ml). Oritavancin exhibited good in vitro potency against this collection of organisms, including vancomycin-resistant enterococci.