Comparison of the Sensititre YeastOne® Colorimetric Antifungal Panel with the Modified Clinical and Laboratory Standards Institute Broth Microdilution (M38-A) Method for Antifungal Susceptibility Testing of Dermatophytes

Background: To compare the susceptibility of different dermatophyte species to itraconazole (I), fluconazole (F) and voriconazole (V) by the modified reference (microdilution, CLSI M38-A) and the colorimetric method Sensititre YeastOne® . The microdilution method is not very practical for use in routine susceptibility testing in the clinical laboratory, thus necessitating the use of other methods. Methods: We studied a total of 46 dermatophyte strains isolated from clinical specimens. The microdilution reference susceptibility testing was performed following the CLSI M38-A document, using I, F and V drugs. The MIC were defined as the lowest drug concentration that produced 100% (I and V) and 50% inhibition (F) after 72 h incubation at 35°C. The Sensititre MIC were detected by a change in color from pink to blue or purple. Results: Agreement levels between the 2 methods (±2 dilutions) for I, F and V were 30, 53.3 and 83.3%, 0, 12.5 and 66.6% and 37.5, 44.4 and 75% for Trichophyton mentagrophytes, Trichophyton rubrum and Microsporumgypseum, respectively. The MIC50/90 (mg/l) of I, F and V for T. mentagrophytes were 0.25/0.5, 16/64 and 0.12/0.25 by the microdilution method and 0.016/0.06, 8/16 and 0.03/0.06 by the Sensititre method. The MIC for I, F and V for T. rubrum were 0.25/1, 8/64 and 0.25/0.5 by the microdilution and 0.008/0.03, 2/8, 0.016/0.03 by the Sensititre method. For M. gypseum, MIC were 0.5/1 (I), /256 (F) and 0.25/1 (V) as well as 0.016/0.25 (I), 16/256 (F) and 0.06/0.25 (V) by the microdilution and Sensititre methods, respectively. Conclusions: The MICs obtained were lower by the Sensititre than the microdilution method. The best correlation between both methods was obtained for V in T. mentagrophytes (>80%), but was low for T. rubrum. Although the Sensititre method is easy to use in a clinical laboratory, it shows poor agreement with the reference method for dermatophytes.