Disk diffusion test and E-test with enriched Mueller-Hinton agar for determining susceptibility of Candida species to...

A simplified antifungal disk diffusion test using Mueller-Hinton agar containing 2% glucose and methylene blue 5 microg/mL (GM-MH, Clinical and Laboratory Standards Institute [CLSI] M44-A) has proved to correlate well with the standard reference test. A new azole, voriconazole, has recently been approved for clinical therapy in Taiwan. This study investigated the reliability of the disk diffusion test with GM-MH agar and compared the results with those of the E-test using GM-MH agar to determine the voriconazole and fluconazole susceptibility of Candida isolates.

The antimicrobial susceptibility of Candida isolates were evaluated by E-test and disk diffusion test in accordance with the guidelines of the CLSI, and compared with the reference antifungal macrodilution susceptibility test (CLSI M27-A).

The antifungal disk diffusion test and the E-test using GM-MH agar plate provided a sufficiently accurate, time-efficient, and cost-effective way to determine the susceptibility of 182 Candida spp. to voriconazole and fluconazole. There was a high correlation between the test results of the E-test using the GM-MH agar plate and those obtained by the reference antifungal macrodilution susceptibility test (CLSI M27-A). The results of the E-test and those of the 1-microg voriconazole disk diffusion test on the GM-MH agar plate at 24 h had a high correlation. All the minimal inhibitory concentrations of voriconazole for all Candida spp. were <8 microg/mL. The positive predictive value of the susceptible disk test of voriconazole on the GM-MH agar plate was 100% at 24 h for C. albicans and other Candida spp.

The disk diffusion test and the E-test using the GM-MH agar plate can be performed quickly, simply, and cost-effectively, and are practicable methods for the initial testing of the susceptibility of Candida spp. to voriconazole and fluconazole.