Evaluation of telavancin susceptibility in isolates of Staphylococcus aureus with reduced susceptibility to vancomycin

Historically, vancomycin has been considered a primary therapeutic option for treating infections with Staphylococcus aureus, but isolates with reduced vancomycin susceptibility (SA-RVS) (MIC ≥ 4 μg/mL) have emerged. Telavancin, a semisynthetic lipoglycopeptide, is an alternative treatment option for S. aureus, but data examining telavancin activity against SA-RVS are limited. In the present study, we characterize 300 isolates of S. aureus isolates (50 vancomycin-susceptible (VSSA) isolates and 250 SA-RVS isolates) from a large tertiary care, academic medical center, 51.8% of which were methicillin resistant (MRSA). Sixteen (6.4%) SA-RVS isolates were non-susceptible to telavancin, whereas all VSSA isolates were susceptible. Additionally, 3.6% of SA-RVS isolates were non-susceptible to daptomycin, with three (1.2%) isolates testing non-susceptible to both telavancin and daptomycin. When tested against other classes of antimicrobials, there were no statistical differences in susceptibility of VSSA and SA-RVS isolates, except for the fluoroquinolones (ciprofloxacin and moxifloxacin). Molecular characterization of the isolates showed that SCCmec types II and IV together represented over half of the SA-RVS isolates; 12.0% of the VSSA isolates were SCCmec type II. Using RepPCR, we detected 16 distinct strain types in this isolate collection, and tst-1 (gene encoding the Staphylococcus toxic shock syndrome super-antigen) carriage was low (5.4%). Overall, we show that in addition to reduced vancomycin susceptibility, a small, but clinically significant, proportion of SA-RVS isolates also demonstrate reduced susceptibility to both telavancin and daptomycin.