Genotyping and In Vitro Antifungal Susceptibility Testing of Fusarium Isolates from Onychomycosis in India

Onychomycosis refers to fungal infection of the nail and is commonly caused by dermatophytes, while yeasts and non-dermatophytic molds (NDM) are increasingly recognized as pathogens in nail infections. The present study was done to delineate molecular epidemiology of Fusarium onychomycosis in India. Five hundred nail samples of Indian patients clinically suspected of onychomycosis were subjected to direct microscopy and fungal culture. Representative Fusarium isolates were further identified to species level by multi-locus sequencing for internal transcribed spacer, translation elongation factor 1 alpha (tef1-α) and RNA polymerase II subunit (rpb2) regions (primer pairs: ITS1/ITS4, EF1/EF2, 5f2/7cr, respectively). These representative strains were also tested for in vitro antifungal susceptibility by the broth microdilution method. Members of the genus Fusarium proved to be the most common NDM responsible for onychomycosis. The Fusarium spp. responsible for onychomycosis belonged to the Fusarium solani species complex (F. keratoplasticum and F. falciforme) and Fusarium fujikuroi species complex (F. proliferatum, F. acutatum and F. sacchari). Antifungal susceptibility results indicated that amphotericin B was the most effective antifungal across all isolates (MIC ranging 0.5–2 mg/L), followed by voriconazole (MIC ranging 1–8 µg/ml). However, a large variation was shown in susceptibility to posaconazole (MIC ranging 0.5 to >16 µg/ml). To conclude, we identified different Fusarium spp. responsible for onychomycosis in India with variation within species in susceptibility to antifungal agents, showing that fusariosis requires correct and prompt diagnosis as well as antifungal susceptibility testing.