Comparison of the Vitek 2 yeast susceptibility system with CLSI microdilution for antifungal susceptibility testing of fluconazole and voriconazole against Candida spp., using new clinical breakpoints and epidemiological cutoff values

A commercially available, fully automated yeast susceptibility test system (Vitek 2; bioMerieux, Marcy d'Etoile, France) was compared in 3 different laboratories with the Clinical and Laboratory Standards Institute (CLSI) reference microdilution (BMD) method by testing 2 quality control strains, 10 reproducibility strains, and 425 isolates of Candida spp. against fluconazole and voriconazole. Reference CLSI BMD MIC endpoints and Vitek 2 MIC endpoints were read after 24 hours and 9.1-27.1 hours incubation, respectively. Excellent essential agreement (within 2 dilutions) between the reference and Vitek 2 MICs was observed for fluconazole (97.9%) and voriconazole (96.7%). Categorical agreement (CA) between the 2 methods was assessed using the new species-specific clinical breakpoints (CBPs): susceptible (S) <= 2 mu g/mL, susceptible dose-dependent (SDD) 4 mu g/mL, and resistant (R) >= 8 mu g/mL for fluconazole and Candida albicans, Candida tropicalis, and Candida parapsilosis and <= 32 mu g/mL (SDD), >= 64 mu g/mL (R) for Candida glabrata; S <= 0.12 mu g/mL, SDD 0.25-0.5 mu g/mL, R >= 1 mu g/mL for voriconazole and C. albicans, C. tropicalis, and C. parapsilosis, and <= 0.5 mu g/mL (S), 1 mu g/mL (SDD), >= 2 mu g/mL (R) for Candida krusei. The epidemiological cutoff value (ECV) of 0.5 mu g/mL for voriconazole and C. glabrata was used to differentiate wild-type (WT; MIC <= ECV) from non-WT (MIC > ECV) strains of this species. Due to the lack of CBPs for the less common species, the ECVs for fluconazole and voriconazole, respectively, were used for Candida lusitaniae (2 mu g/mL and 0.03 mu g/mL), Candida dubliniensis (0.5 mu g/mL and 0.03 mu g/mL), Candida guilliermondii (8 mu g/mL and 0.25 mu g/mL), and Candida pelliculosa (4 mu g/mL and 0.25 mu g/mL) to categorize isolates of these species as WT and non-WT. CA between the 2 methods was 96.8% for fluconazole and 96.5% for voriconazole with less than 1% very major errors and 1.3-3.0% major errors. The Vitek 2 yeast susceptibility system remains comparable to the CLSI BMD reference method for testing the susceptibility of Candida spp. when using the new (lower) CBPs and ECVs. (c) 2013 Elsevier Inc. All rights reserved.