Comparison of gradient concentration strip and EUCAST methods for itraconazole and posaconazole MICs in Trichophyton indotineae

ABSTRACT The increasing spread of antifungal-resistant dermatophytosis caused by Trichophyton indotineae has become a major public health and therapeutic concern. Consequently, antifungal susceptibility testing in routine clinical laboratories is essential for effective patient management. Itraconazole is currently the recommended treatment for these infections. However, few molecular or phenotypic tools are available to assess susceptibility to azoles. In this context, we evaluated the itraconazole and posaconazole MICs obtained using gradient concentration strips (GCS), in comparison with the EUCAST reference method. A total of 73 clinical isolates belonging to the Trichophyton mentagrophytes complex, including 64 T. indotineae isolates, were analyzed. MIC readings for both methods were performed on days 5 and 7 at partial (80%) and complete (100%) inhibition. We found that the optimal reading frame is on day 5 at 100% growth inhibition. Essential agreement within ±1 dilution (and ±2 dilutions) for the GCS method versus the EUCAST method was 65.8% (89%) for itraconazole and 57.5% (83.6%) for posaconazole. The GCS test appears to be a valuable method for susceptibility screening of T. indotineae clinical isolates, providing a practical option for routine laboratories despite essential agreement values below the ideal 90% threshold for method validation.