Abstract
Background
VITEK-2 yeast susceptibility test (AST-YS01; bioMerieux, Hazelwood, MO, USA) has recently been introduced as a fully automated commercial antifungal susceptibility test system that determines MIC (minimum inhibitory concentrations) endpoints spectrophotometrically, thereby eliminating subjective errors. We compared the VITEK-2 system with the CLSI (the Clinical and Laboratory Standards Institute) M27 method for susceptibility testing of Candida isolates from Korea.
Methods
A total of 175 Candida bloodstream isolates were collected from two hospitals during a 18-month period. We compared the MIC results for amphotericin B, fluconazole and voriconazole obtained with the VITEK-2 system to those obtained by the CLSI M27 broth microdilution method after 24-hr and 48-hr incubation.
Results
VITEK-2 system MIC endpoints for 175 isolates were determined after 11.75 to 35.50 hr of incubation (mean, 16.3±4.8 hr). The essential agreement (within 2 dilutions) between amphotericin B, fluconazole and voriconazole MICs obtained by the VITEK-2 system and CLSI method was 98.3%, 90.9% and 96.0%, respectively, at 24-hr incubation and 100%, 92.6% and 94.9%, at 48-hr incubation. The categorical discrepancy for fluconazole was 6.3% (major error, 2.9% and minor error, 3.4%) at 24-hr and 6.3% (major error, 2.3% and minor error, 4.0%) at 48-hr. The categorical discrepancy for voriconazole was 1.7% (major error, 1.1% and minor error, 0.6%) at both 24-hr and 48-hr. There were no very major errors for fluconazole and voriconazole.
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Table 1.
In vitro susceptibilities of 175 isolates of Candida spp. to amphotericin B, fluconazole and voriconazole as determined with the VITEK-2 system and by CLSI BMD methods
Table 2.
Categorical agreement between the fluconazole and voriconazole MICs determined by VITEK-2 system and CLSI 24-hr and 48-hr BMD method for 175 isolates of Candida spp.
Table 3.
Testing results for 14 Candida isolates showing a categorical disagreement of antifungal MIC results between VITEK-2 AST-YS01 and CLSI BMD method