Comparative In Vitro Activity Profile of Oritavancin against Recent Gram-Positive Clinical Isolates

Abstract

ABSTRACT Oritavancin activity was tested against 15,764 gram-positive isolates collected from 246 hospital centers in 25 countries between 2005 and 2008. Organisms were Staphylococcus aureus ( n = 9,075), coagulase-negative staphylococci ( n = 1,664), Enterococcus faecalis ( n = 1,738), Enterococcus faecium ( n = 819), Streptococcus pyogenes ( n = 959), Streptococcus agalactiae ( n = 415), group C, G, and F streptococci ( n = 84), and Streptococcus pneumoniae ( n = 1,010). Among the evaluated staphylococci, 56.7% were resistant to oxacillin. The vancomycin resistance rate among enterococci was 21.2%. Penicillin-resistant and -intermediate rates were 14.7% and 21.4%, respectively, among S. pneumoniae isolates. Among nonpneumococcal streptococci, 18.5% were nonsusceptible to erythromycin. Oritavancin showed substantial in vitro activity against all organisms tested, regardless of resistance profile. The maximum oritavancin MIC against all staphylococci tested ( n = 10,739) was 4 μg/ml; the MIC 90 against S. aureus was 0.12 μg/ml. Against E. faecalis and E. faecium , oritavancin MIC 90 s were 0.06 and 0.12, respectively. Oritavancin was active against glycopeptide-resistant enterococci, including VanA strains ( n = 486), with MIC 90 s of 0.25 and 1 μg/ml against VanA E. faecium and E. faecalis , respectively. Oritavancin showed potent activity against streptococci ( n = 2,468); MIC 90 s for the different streptococcal species were between 0.008 and 1 μg/ml. These data are consistent with previous studies with respect to resistance rates of gram-positive isolates and demonstrate the spectrum and in vitro activity of oritavancin against a wide variety of contemporary gram-positive pathogens, regardless of resistance to currently used drugs. The data provide a foundation for interpreting oritavancin activity and potential changes in susceptibility over time once oritavancin enters into clinical use.