Disk diffusion test and E-test with enriched Mueller-Hinton agar for determining susceptibility of Candida species to voriconazole and fluconazole
Sai-Cheong Lee, Hsiu-Jung Lo, Chang-Phone Fung, Ning Lee, Lai-Chu See
Division of Infectious Diseases, Chang Gung Memorial Hospital, Keelung; Nursing Department, Chang Gung Institute of Technology, Linkou; Division of Clinical Research, National Health Research Institutes, Miaoli; Division of Infectious Diseases, Veterans General Hospital, Taipei; College of Medicine, Yang Ming University, Taipei; Department of Pathology, Chang Gung Memorial Hospital, Keelung; and Department of Public Health, Chang Gung University, Linkou, Taiwan
Received: June 18, 2007 Revised: January 15, 2008 Accepted: April 4, 2008
Background and purpose:
A simplified antifungal disk diffusion test using Mueller-Hinton agar containing 2% glucose and methylene blue 5 μg/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 GMMH 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-μg 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 μg/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.
Candida; Drug resistance, bacterial; Fluconazole; Voriconazole
J Microbiol Immunol Infect. 2009;42:148-153.