Comparative evaluation of E-test and CLSI methods for Itraconazole, Fluconazole and Ketoconazole susceptibilities of Microsporum canis strains.

The incidence of resistance to antifungal agents for dermatophytes is increasing, but most of the methods currently available to test the antifungal susceptibility of Microsporum canis still require standardization. The aims of this study were: (i) to evaluate the antifungal susceptibility of M. canis strains recovered from animals to ketoconazole (KTZ), fluconazole (FLZ) and itraconazole (ITZ) using a modified CLSI broth microdilution (CLSI M38-A2-BMD) and the E-test® protocols and (ii) to estimate the agreement between the methods. Tentative azole epidemiological cutoff values (ECVs) were also proposed in order to interpret the results of in vitro susceptibility tests and to establish the agreement between the E-test and CLSI BMD methods. A total of forty clinical M. canis strains from animals with skin lesions were tested, and the essential (EA) and categorical agreement (CA) between the two methods were determined. KTZ displayed the lowest MIC values, while ITZ and FLZ the highest. The ECV for KTZ and ITZ were 4 μg/ml, while those of FLZ was 64 μg/ml. Based on ECVs, about 88% of M. canis strains were susceptible to all azoles being a cross-resistance with ITZ-FLZ registered for one strain. A total of five M. canis strains showed MIC > ECV for FLZ using CLSI, while one strain showed MIC > ECV for ITZ using both tests. KTZ, ITZ and FLZ showed EA ranging from 92.5 to 95%, for all azoles and CA > 97% except for FLZ (87.5%). The good CA between the E-test and the CLSI BMD provides evidence of the reliability of the former method to test the antifungal susceptibility of M. canis for ITZ and KTZ and not for FLZ.