Ex Vivo Fungal Nail Penetration Study: Effects of Causative Organisms, Nail Polish and Age.

Background: Few ex vivo studies have investigated the virulence factors of fungi causing onychomycosis. The effect of nail polish in predisposing or protecting against onychomycosis remains debatable.

Objectives: This ex vivo study aimed to identify the nail invasion ability of dermatophytes, non-dermatophytes and yeast, with and without nail polishing, in the nails of young and elderly individuals.

Methods: Six fungal species were tested: dermatophytes (Trichophyton rubrum, T. mentagrophytes, Microsporum canis), non-dermatophytes (Neoscytalidium dimidiatum, Fusarium spp.) and Candida albicans. Nail plates from eight volunteers (four aged ≥ 70 years; four aged < 70 years) were divided into polished and non-polished groups, incubated with each fungus and evaluated at 2, 4 and 8 weeks. Positive results were determined the presence of fungal hyphae or pseudohyphae penetrating the nail plate, with the enlargement of invasive fungal elements confirmed by histology.

Results: At 2 weeks, N. dimidiatum exhibited the highest nail invasion rate (15/16, 93.75%), whereas C. albicans showed the lowest (1/16, 6.25%). Fungal penetration into nail plates increased with longer incubation durations. At 8 weeks, C. albicans did not invade any polished nail plates; however, the difference in invasion rates between polished and unpolished nail plates was not statistically significant. Additionally, age did not significantly affect the invasion of most fungi in this ex vivo study.

Conclusions: This ex vivo study supported the concept that fungal virulence is the main determining factor for nail invasion. N. dimidiatum caused the most and fastest nail plate penetration. Nail polishing may slow the penetration of low-virulence organisms.