Interlaboratory evaluation of the Etest for antifungal susceptibility testing of dermatophytes

A three-site interlaboratory reproducibility evaluation of the Etest concentration gradient strip method for testing antifungal susceptibilities was conducted using 30 strains of dermatophytes exposed to strips loaded with ketoconazole (KTZ), itraconazole (ITZ), amphotericin B (AMB) and fluconazole (FCZ). Etest minimal inhibitory concentrations were compared with those obtained using a broth microdilution method. All isolates produced clearly detectable growth at 28 degrees C within 72-96 h for reading with the Etest method. The highest interlaboratory agreement between Etest and the microdilution method was shown with FCZ (94%), and the lowest was seen with KTZ (60%). Overall, agreement between the Etest and microdilution method was variable. It was excellent for AMB (97%), good for ITZ (80%) and KTZ (77%), and low for fluconazole (27%).