Surrogate analysis of vancomycin to predict susceptible categorization of dalbavancin

Dalbavancin (DAL) represents a recently approved addition for the treatment of acute bacterial skin and skin structure infections (ABSSSIs). Newly released antimicrobial agents are rarely found on commercial susceptibility testing devices, and surrogate testing may be an option for clinical microbiology laboratories. A total of 33,688 Staphylococcus aureus, 2800 viridans group streptococci (VGS), and 5722 β-hemolytic streptococci (BHS) were included in this cross-susceptibility (DAL versus vancomycin [VAN]) analysis as well as 4576 coagulase-negative staphylococci and 6515 enterococci (nonindicated species groups). Isolates were collected as part of the SENTRY Antimicrobial Surveillance Program for the United States (USA) and Europe (2011-2013). Susceptibility testing followed CLSI (M07-A9 and M100-S24) methods. USA Food and Drug Administration (DAL) and CLSI (VAN) breakpoint criteria were used for correlations between DAL and VAN susceptibility results. A categorical agreement (CA; susceptible) rate of 99.9% was observed between DAL and VAN when testing S. aureus. Only 48 (0.14%) very major (false-susceptible) errors were noted against VAN-susceptible isolates that displayed a DAL-nonsusceptible (MIC, 0.25 or 0.5 μg/mL) phenotype. When susceptible MIC correlations were analyzed against indicated BHS species (Streptococcus agalactiae and Streptococcus pyogenes), an overall CA rate of 97.7-100.0% was obtained. Complete (100.0%) CA was documented for S. pyogenes, as well as against all VGS isolates, including the indicated Streptococcus anginosus group (758 strains). In conclusion, high susceptible CA rates between DAL and VAN were observed when testing a contemporary collection of indicated clinical isolates found in ABSSSI. VAN-susceptible isolates can be inferred to be inhibited by DAL (97.7-100.0%) at the regulatory agency-approved susceptible interpretive breakpoint of ≤0.12 μg/mL.