Comparative evaluation of fluconazole susceptibility methods for Candida species: Broth microdilution test, E test and disk diffusion test

Kim, Yeong Sic; Lee, Hee Joo; Lee, Jung Rim; Kang, Byung Ki; Lee, Woo In; Kil, Young Chul; Suh, Jin Tae; Suh, Hwan Jo

Abstract

BACKGROUND: Currently fungal infections have been increasing in clinical aspect. Among them Candida albicans is considered as the most pathogenic. National Committee for Clinical Laboratory Standards(NCCLS) recommends broth macrodilution method for antifungal susceptibility test, but it is difficult to perform. E test is a relatively easy method to perform for the susceptibility testing. So in this study, antifungal susceptibility procedures were compared to determine MIC for fluconazole against 130 Candida strains isolated from clinical specimens. METHOD: The tests including were microdilution method, E test and disk diffusion method. The latter two tests were performed in casitone agar and the former test performed in RPMI 1640 media(Sigma Chemical co. St. Louis, USA). MIC was determined after 24 hrs of incubation. We used Candida albicans ATCC 90018 and Candida parapsilosis ATCC 90028 as controls. A total of 130 strains(93 C. albicans, 29 C. tropicalis, 5 C. parapsilosis and 3 C. glabrata) were tested.
RESULTS
The MIC50 and MIC90 of broth microdilution test for C. albicans was > OR =64 microgram/mL equivalently. Agreement of > OR = +/-2 dilution between broth microdilution test and E test was 54 %, and the concordance rate was 55%. The concordance rate between E test and disk diffusion was 90%.
CONCLUSIONS
From this study, we conclude that E test can be used as a alternative and convenient method to macrodilution method to determine MIC of fluconazole. But it is necessary for attention to microcolonies surrounding the E test strip. Disk diffusion method is rapid and also can be used as an alternative and convenient method.