Antifungal Susceptibility Testing of Dermatophytes

Moon, Seok Ki; Shin, Dong Hoon; Choi, Jong Soo; Kim, Ki Hong; Kim, Keuk Jun

Abstract

BACKGROUND: A standardized reference method for dermatophytes in vitro susceptibility testing is lacking. However, with increasing variety of drugs available to treat dermatophytosis, the need for a reference method for dermatophytes testing has become apparent.
OBJECTIVE
To evaluate a method of quantifying dermatophytes, the standards for broth microdilution method and evaluation of the availability of disk diffusion method in antifungal susceptibility testing for dermatophytes.
METHODS
14 Candida species (sp.), 30 Trichophyton(T.) mentagrophytes, 9 T. raubitschekii and 11 T. rubrum were tested for fluconazole susceptibility by the broth microdilution method and disc diffusion method. Candida sp. was tested according to National Committee for Clinical Laboratory Standards (NCCLS) M27-A and M44-A. Broth microdilution method for T. mentagrophytes, T. raubitschekii and T. rubrum was operated according to NCCLS M38-A. Disk diffusion method for T. mentagrophytes, T. raubitschekii and T. rubrum was tested refer to NCCLS M44-A.
RESULTS
The disk diffusion method showed 50% correlation rate with the broth microdilution method for antifungal susceptibility testing for Candida species. The MIC reading point and incubation time of the broth microdilution method for T. mentagrophytes, T. raubitschekii and T. rubrum are Spec-50 and from 7, 6 and 9 days. Relation between the broth microdilution method and disk diffusion method for dermatophytes is poor.
CONCLUSIONS
The good method for quantifying dermatophytes is using vortexing only or liquid nitrogen and homogenizer. Standards of MIC reading point and incubation time of microdilution method for dermatophytes are Spec-50 and from 6 to 9 days. It appears that the disk diffusion method is not recommended method for the antifungal susceptibility testing of dermatophytes.