Antifungal Susceptibility of Candida Species Using the Clinical and Laboratory Standards Institute Disk Diffusion and Broth Microdilution Methods

Abstract

There are conflicting reports on the agreement between the Clinical and Laboratory Standards Institute disk diffusion (M44-A) and reference broth microdilution (M27-A) methods for determination of antifungal susceptibility of yeasts. The antifungal susceptibility of 541 yeasts, the majority of which were from the oral cavity, was determined using these two methods and the accuracy of the disk diffusion method assessed for clinical testing of various Candida species. Of the strains tested, Candida albicans predominated (390 out of 541). The classification of susceptibility determined by the disk diffusion method was largely in concordance with that obtained using the broth dilution method, regardless of species within Candida genus. The overall observed agreement between these two methods was 94.7% for fluconazole and 96.7% for voriconazole was with a ‘very major’ discrepancy level of 1.5% and 1.7% respectively. This study demonstrates a strong agreement of the simple disk diffusion method with the more labour intensive ‘gold standard’ broth microdilution method. These findings would support the use of the disk diffusion method in a routine mycology service.

Keywords:

• Disk diffusion
• antifungal susceptibility
• Candida