Arthrospore Production in Trichophyton rubrum and a New Ex-vivo Model of Onychomycosis

S.A. Yazdanparast, R.C. Barton, E.G.V. Evans

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Background: Here we examine systematically the environmental and iatrogenic factors which affect arthrosporulation in vitro in T.rubrum and describe a new ex vivo model for the study of arthrospore formation in nails. Material and methods: 50 strains of T.rubrum isolated from the skin and nails of patients were used. Arthrospore production was examined by 2 methods: adhesive tape (No. of arthrospores in 4 microscopic fields) and slide culture technique (% hyphal tips with arthrospores) in various media and under various conditions (varying pH, temperature, CO2 concentration) and in the presence of antifungals. Nail powder from the healthy toenails of volunteers was ground with liquid nitrogen and 20 μl of microconidial suspension (1x 107 units/ml) of T.rubrum were spread over the surface of 0.2 g nail powder then incubated at 37°C for 14 days under moist conditions. The powder was then examined microscopically. Results: Arthrospore formation occurred in vitro in all 5 isolates of T.rubrum used in preliminary studies. The following were found as optimal for arthrospore formation in T.rubrum N250. Maximal production of arthrospores occurred after 10 days. CO2: 10 % was critical for arthrospore formation. Media: Sabouraud dextrose agar (SDA). Temperature: 37°C, and above 37°C no growth was seen. PH: 7.5. Subinhibitory levels of Amphotericin B, Griseofulvin and Clotrimazole, also steroid, betamethasone 17-valerate stimulated the level of arthrosporulation but Itraconazole and particularly Terbinafine suppressed the level of arthrospore formation. Of a total of 50 clinical isolates from 10 patients, obtained before, during and after treatment with Itraconazole and Terbinafine, only 2 strains failed to produced arthrospores under the previously defined optimal conditions (SDA, 37°C, 10 % CO2, 10 days. Arthroconidial production in ex vivo ground nails, occurred under the same optimal conditions but took longer (14 days) to reach maximal levels. Key word: Arthrospore, Trichophyton rubrum, New Ex-vivo Model of Onychomycosis

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Full conference title: 

Iranian Congress on Medical Mycology
    • ICMM 2011