Early events in the invasion of the human nail plate by Trichophyton mentagrophytes

A new in vitro model for the study of nail invasion by dermatophyte fungi was developed. The dermatophyte Trichophyton mentagrophytes, and fragments of finger-nails and toe-nails were used. Arthroconidia were inoculated on the ventral surface of the nails. After 6 h, adherence and germination of arthroconidia was observed. By 16 h, small germ tubes with side branches were evident. At about 24 h, micro-colonies had become established. At 48 h, a mycelium had formed, and at about 72 h most of the nail fragment was covered with fungal growth. Nail penetration occurred from the ventral surface through the intercellular spaces, and with longer incubation all three layers were invaded by arthroconidia growing through channels. Nail invasion occurred in the absence of added nutrients. Dermatophyte fungi appeared to invade the nail by a combination of mechanical and chemical factors. The model provides a substrate to study the pharmacokinetics and bioavailability of new antifungal agents in situ.