Detection of 2-ethyl-1-hexanol and its modulating effect in biofilm of Fusarium oxysporum

In immunocompetent individuals, Fusarium spp. stands out as the causative agent of onychomycosis, among the non-dermatophyte molds. Despite evidence indicating that Fusarium oxysporum organizes itself in the form of a biofilm causing onychomycosis, there is little literature on the etiopathogenesis of the biofilm on the nail, specifically the signaling molecules present, known as quorum sensing (QS). Thus, this study detected the presence of a molecule related to QS from the ex vivo biofilm of F. oxysporum on human nail and investigated its effect on preformed biofilm in vitro. The detection and physicochemical characterization of a QS molecule, from the extracellular matrix (ECM), was carried out by Fourier transform infrared (FTIR) spectroscopy with an attenuated total reflectance (ATR) accessory and by headspace gas chromatography coupled to mass spectrometry (GC-MS) analyses. Determination of viable cells, cell activity, total biomass, ECM components and scanning electron microscopy (SEM) were performed to evaluate the influence of the QS molecule on the in vitro biofilm of F. oxysporum. The beginning, in the ex vivo biofilm of F. oxysporum on human nails, the volatile organic compound 2-ethyl-1-hexanol (2EH) was detected as a component of QS. Thereafter in vitro analyses, synthetic 2EH was able to modulate the biofilm by stimulating its filament, increasing total biomass and ECM production in terms of total carbohydrates, but with a reduction in total proteins and nucleic acids. We thus evidence, for the first time, the presence of 2EH in the biofilm of F. oxysporum, developed on the human nail, and the in vitro action of this compound as a QS molecule.

Insights on the etiopathogenesis of onychomycosis by dermatophyte, yeast and non dermatophyte mold 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, edema, 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.

Characterization of a biofilm formed by Fusarium oxysporum on the human nails

BACKGROUND

Fusarium spp. has been considered as an onychomycosis agent, but little is known about the etiopathogenesis of fusarial onychomycosis; thus, the objective of this study was to characterize the fungal-nail interaction and the consequences of the nail infection process by Fusarium oxysporum using the human nail, in an ex␣vivo model.

METHODS

The kinetic of biofilm production and infection by F. oxysporum using the nail as the only nutritional source were evaluated by scanning electron microscopy, number of culturable cells, metabolic activity, characterization of extracellular matrix, spectroscopy and histopathology analyses.

RESULTS

After evaluating the biofilm kinetic over 7 days using different parameters and techniques, it was possible to characterize the Fusarium-nail interaction.

CONCLUSIONS

This study is a part of a big project aiming to clarify the fusarial pathogenesis and contributes to proving F. oxysporum is able to adapt, grow, develop, and form a biofilm on healthy human nails, which are crucial steps for the invasion process.