Daptomycin non-susceptibility in vancomycin-intermediate Staphylococcus aureus (VISA) and heterogeneous-VISA (hVISA): Implications for therapy after vancomycin treatment failure

Abstract

Objectives: The aim of this study was to establish the relationship between reduced vancomycin and daptomycin susceptibility among Australasian vancomycin-intermediate Staphylococcus aureus (VISA) and heterogeneous-VISA (hVISA) isolates from patients never exposed to daptomycin. Methods: Forty-seven stored clinical isolates of hVISA/VISAcollected beforeNovember 2008 fromaroundAustralia andNewZealandwere selected. Daptomycinand vancomycinMICtestingwas performed using broth microdilution (BMD) and Etest methods. Daptomycin population analysis was performed on a subset of isolates. Results: The percentage of daptomycin non-susceptible isolates was 0% for vancomycin-susceptible S. aureus (VSSA) (Etest and BMD), for hVISA it was 26% by Etest and 15% by BMD, and for VISA 62% by Etest and 38% by BMD. Population analysis profile testing demonstrated daptomycin heteroresistance among the hVISA and VISA strains tested. Conclusions: This is the highest rate of daptomycin non-susceptibility reported among hVISA isolates to date. Clinicians should exhibit caution when using daptomycin in situations where serious hVISA or VISA infection is a possibility. © The Author 2011. Published by Oxford University Press on behalf of the British Society for Antimicrobial Chemotherapy. All rights reserved.