Antimicrobial spectrum and potency of dalbavancin tested against clinical isolates from Europe and North America (2003): initial results from an international surveillance protocol.

Dalbavancin is a bactericidal dimethylaminopropyl amide glycopeptide derivative possessing an extended serum elimination half-life in humans that allows once-weekly dosing for the therapy of Gram-positive infections. Strains from this baseline surveillance protocol in North America (NA; USA and Canada) and Europe (EU, 14 countries) were sampled in 2003. A total of 7,765 Gram-positive isolates (3,695 from NA and 4,070 from EU) were tested by reference broth microdilution methods against dalbavancin and 10 comparator agents. Species were analyzed separately by resistance phenotypes such as methicillin- (oxacillin-) resistant Staphylococcus aureus (MRSA), vancomycin-resistant enterococci (VRE) and penicillin-resistant Streptococcus pneumoniae. Dalbavancin and other glycopeptides were very active against staphylococci (n=4648) with dalbavancin being 16- to 32-fold more potent than vancomycin (MIC90, 0.06 versus 2 mg/L). MRSA rates were greater (31.6%) in NA than in EU (26.1%). Quinupristin/dalfopristin resistance (MIC, > or = 2 mg/L; 0.1-0.5%) was documented more often in EU compared to NA. Dalbavancin (MIC50, 0.03-0.06 mg/L) was active against enterococci, except VanA resistance phenotypes. VRE rates were lower in EU (8.3%) then in NA (35.9%) from this resistance-enhanced enterococcal collection. Streptococci (dalbavancin MIC90, 0.016-0.03 mg/L) were generally most susceptible to glycopeptides (100.0%), quinupristin/dalfopristin (98.6-100.0%) and linezolid (100.0%); but dalbavancin was 16-fold more active than comparators. All vancomycin-susceptible enterococci and > 90% of vanB VRE had dalbavancin MIC values at < or = 1 mg/L,but vanA VRE strains had dalbavancin MIC results ranging from 0.06 to > 8 mg/L (median MIC, > or = 8 mg/L). Dalbavancin MIC values were not adversely influenced by geographic region or resistance phenotype (except vanA VRE). Infrequently isolated Gram-positive organisms such as Bacillus spp. (MIC90, 0.12 mg/L), Corynebacterium spp. (MIC90, 0.12 mg/L), Listeria monocytogenes (MIC90, 0.25 mg/L) and Micrococcus spp. (MIC90, 0.03 mg/L) were very susceptible to dalbavancin. In conclusion, these 2003 baseline resistance surveillance findings confirm the potent dalbavancin activity compared to several comparator agents against important Gram-positive pathogens. This high volume international survey indicates potential therapeutic roles for dalbavancin against many troublesome resistant Gram-positive phenotypes.