Evaluation of Spectrophotometric Broth Microdilution Method to Determine the Fluconazole MIC of the Candida Species

Yi, Ji Yon; Shin, Jong Hee; Lee, Kyung Won; Yong, Dong Eun; Chae, Myoung Jong; Suh, Soon Pal; Ryang, Dong Wook

Abstract

BACKGROUND: Although the broth microdilution method has been recently established for antifungal susceptibility testing of the Candida species, there is still an argue in the interpretation of the trailing endpoint. We evaluated the spectrophotometric broth microdilution method (SBM) to determine the fluconazole MICs from five different Candida species.
METHODS
A total of 252 clinical isolates of five Candida species (144 C. albicans, 42 C. tropicalis, 32 C. glabrata, 28 C. parapsilosis, and 6 C. krusei) were tested for fluconazole susceptibility with the broth microdilution method. The MICs were spectrophotometrically determined at 80% (Spec-80%) and 50% (Spec-50%) decrease in absorbance as compared with growth control, respectively. The results were compared with the fluconazole MICs tested by the National Committee for the Clinical Laboratory Standards (NCCLS) macrodilution method.
RESULTS
When MICs were obtained by Spec-80%, the agreements of SBM and the NCCLS macro dilution method within two doubling dilutions were 92.4% (220/238) at 24 h and 78.6% (198/252) at 48 h for all Candida species. Using the Spec-50%, those were increased to 97.9% (233/238) at 24 h and 98.8% (249/252) at 48 h (P<0.01). Especially, for C. albicans and C. tropicalis, the agreement of the Spec-50% was significantly higher than those of the Spec-80% at 48 h; 97.9% vs. 75.0%, for C. albicans (P<0.01), and 100% vs. 57.1%, for C. tropicalis (P<0.01).
CONCLUSIONS
These data suggest that the SBM using Spec-50% can provide a more precise and objective mean for fluconazole susceptibility testing, especially for C. albicans and C. tropicalis.