Interlaboratory evaluation of the Etest® for antifungal susceptibility testing of dermatophytes

A three- site interlaboratory reproducibility evaluation of the Etest(R) 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(R) minimal inhibitory concentrations were compared with those obtained using a broth microdilution method. All isolates produced clearly detectable growth at 28 degreesC within 72 - 96 h for reading with the Etest(R) method. The highest interlaboratory agreement between Etest(R) and the microdilution method was shown with FCZ ( 94%), and the lowest was seen with KTZ ( 60%). Overall, agreement between the Etest(R) and microdilution method was variable. It was excellent for AMB ( 97%), good for ITZ ( 80%) and KTZ ( 77%), and low for fluconazole ( 27%).