Insights on the etiopathogenesis of onychomycosis by dermatophyte, yeast and non‐dermatophyte mould in ex vivo model

Fungal biofilms have been involved in the pathogenesis of onychomycosis, but the aspects contributing to this association need to be enlightened. This study aimed to investigate the ability of three different fungi to form biofilm on the nail. All evaluated fungi were able to grow on the nails, using them as the only nutritional source and formed a structure strongly suggestive of biofilms. However, their architecture and morphology were highly contrasting: Candida albicans showed dense growth, exhibited a well‐structured community and a large amount of extracellular matrix (ECM), and FTIR‐ATR spectroscopy reinforced these findings revealing components suggestive of the biofilm. For Fusarium oxysporum, these events were also observed, but in lower intensity. Furthermore, while Trichophyton rubrum presented a well‐organized architecture, the ECM was not visualized. We hypothesize that these findings are related to the symptomatology of onychomycosis. When it is caused by a non‐dermatophyte, it usually is accompanied with paronychia, pain, oedema, inflammation and few signals of keratolysis, while dermatophytes are more associated with intense onycholysis and absence of the inflammatory signals. Biofilm seems to be crucial for non‐dermatophytes to cause onychomycosis, but not for T. rubrum.