Stability of Mueller-Hinton Agar Supplemented with Glucose and Methylene Blue for Disk Diffusion Testing of Fluconazole and Voriconazole

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Abstract
The shelf life of Mueller-Hinton agar supplemented with 2% glucose and methylene blue (0.5 μg/ml) (MH-GMB) prepared in the laboratory to test disk diffusion of voriconazole and fluconazole was assessed using quality control (QC) strains of Candida albicans ATCC 90028, Candida krusei ATCC 6258, and Candida parapsilosis ATCC 22019. MH-GMB agar plates were prepared as described in National Committee for Clinical Laboratory Standards document M44-P, and isolates were tested using 25-μg fluconazole disks and 1-μg voriconazole disks over a 36-day period. Zone diameters for fluconazole and voriconazole varied by no more than 4 mm over the study period, and 95 to 100% of results were within the established QC limits for the strains tested. Prepared MH-GMB agar plates provide acceptable performance for disk diffusion testing for at least 30 days when stored at 5°C.