Biodiversity of mycobial communities in health and onychomycosis

Abstract

Onychomycosis (OM) is a common fungal nail infection. Based on the rich mycobial diversity in healthy toenails, we speculated that this is lost in OM due to the predominance of a single pathogen. We used next generation sequencing to obtain insights into the biodiversity of fungal communities in both healthy individuals and OM patients. By sequencing, a total of 338 operational-taxonomic units were found in OM patients and healthy controls. Interestingly, a classifier distinguished three distinct subsets: healthy controls and two groups within OM patients with either a low or high abundance of Trichophyton. Diversity per sample was decreased in controls compared to cases with low Trichophyton abundance (LTA), while cases with a high Trichophyton abundance (HTA) showed a lower diversity. Variation of mycobial communities between the samples showed shifts in the community structure between cases and controls—mainly driven by HTA cases. Indeed, LTA cases had a fungal β-diversity undistinguishable from that of healthy controls. Collectively, our data provides an in-depth characterization of fungal diversity in health and OM. Our findings also suggest that onychomycosis develops either through pathogen-driven mechanisms, i.e., in HTA cases, or through host and/or environmental factors, i.e., in cases with a low Trichophyton abundance.

Single-Point Nail Sampling to Diagnose Onychomycosis Caused by Non-Dermatophyte Molds: Utility of Polymerase Chain Reaction (PCR) and Histopathology

“…Though rates of NDM detection appear lower with PCR, this is likely due to the restrictions of PCR testing to seven NDM genera. NDMs here are underestimated; per other studies, a much wider variety of species is likely detectable in toenails [19][20][21][22]. Broader molecular detection of NDM species in correlation with histopathology would provide a better determination of the utility of single NDM detection for predicting the positive presence of NDMs in nail samples.…”

“…Instead, a wide variety of molecular tools are now providing information on the nail mycobiome and the relationship of fungi to other organisms in healthy and diseased states. There is evidence to suggest that fungi exist in conjunction with bacteria as a ‘balanced’ commensal microbiome in many areas of the body, with bacteria aiding the fungi in avoiding host immunity and pharmaceutical treatment through biofilms [ 18 , 19 , 23 , 24 , 25 ]. This study had limited NDM and bacterial detection and therefore cannot support any suggestion of bacterial co-existence with fungi.…”

“…However, based on medical literature, we may expect to detect a wider variety of fungi and bacterial species in nails than has been reported by culture methods. Wider investigation by molecular methods is necessary to improve the understanding of organismal presence/interactions in onychomycosis pathology and response to treatment [ 19 ].…”