Comparative Analysis of In vitro Susceptibility Profile of Dermatophytes Against 8 Antifungal Agents: A Cross-Sectional Study.

Abstract

Background: The currently reported prevalence of dermatophytosis (superficial mycoses) in India ranges from 6.09%-61.5%. Due to the rising cases of treatment failure, chronic recalcitrant disease, and frequent relapses, standardization of antifungal susceptibility testing of dermatophytes has become important.

Aims and objectives: To determine the in vitro susceptibility profile of different isolates of dermatophytes to eight antifungal drugs by broth microdilution method.

Materials and methods: In total, 236 consecutive patients who were clinically suspected of suffering from dermatophytosis were included in this cross-sectional descriptive study. Nails, hair clippings, and skin scrapings were tested by the KOH mount and cultured on Sabouraud's agar medium (incubated at 25°C and 37°C) and dermatophyte test media. The dermatophytes isolated were identified based on the morphology of the colony growth as observed in the lacto phenol cotton blue (LPCB) mount, temperature tolerance, urease production, and in vitro hair perforation test. Antifungal susceptibility test was performed for dermatophytes against eight antifungal agents (terbinafine, griseofulvin, itraconazole, fluconazole, voriconazole, ketoconazole, luliconazole, and posaconazole) using the Clinical and Laboratory Standards Institute broth microdilution method (M38-3^rd edition).

Results: Trichophyton rubrum was the most common dermatophyte species isolated in the study. Triazoles were found to have low minimum inhibitory concentration (MIC), except fluconazole, which showed very high MIC values with 55.2% isolates showing resistance (MIC ≥ 32 μg/mL). Luliconazole had the lowest MIC90 (0.003 μg/mL). There was a wide variation in the MIC values for terbinafine (0.06-16 μg/mL) and griseofulvin (0.125-8 μg/mL) with 13.1% and 52.6% of isolates showing resistance (MIC ≥ 4 μg/mL) to terbinafine and griseofulvin respectively.

Conclusion: The present study showcases the MIC values of eight anti-fungal drugs used for the treatment of different species of dermatophytes. It was observed that the commonly used antifungals such as fluconazole, griseofulvin, and terbinafine showed high MIC values compared to newer drugs such as luliconazole, posaconazole and voriconazole. More studies based on species distribution and antifungal susceptibility testing (AFST) should be performed to understand the changing epidemiology of dermatophytosis.