Abstract: 【Abstract】 Objective To investigate differences in bacterial and fungal microbiome between infected nails and healthy nails among patients with onychomycosis. Methods Nail scraping samples were collected from infected nails and healthy nails of 31 patients with onychomycosis, who visited Dalian Dermatosis Hospital from August 2020 to July 2021. The total DNA of nail microbiota was extracted, and the V3-V4 regions of the bacterial 16S rDNA gene and the fungal internal transcribed spacer （ITS） region were amplified and sequenced using Illumina technology. The USEARCH and mothur softwares were used for data cluster analysis to obtain the operational taxonomic units （OTUs）, Wilcoxon rank sum test was used to analyze α diversity, analysis of similarities （ANOSIM） was performed to analyze β diversity, linear discriminant analysis of effect size（LEfSe）was performed to evaluate the species difference. Results Among the 31 patients with onychomycosis, 16 were males and 15 were females. According to the age, they were divided into young group （18 - 35 years old, 10 cases）, middle-aged group （36 - 60 years old, 11 cases）, and elderly group （over 60 years old, 10 cases）. As the α-diversity analysis revealed, the infected nail group showed significantly decreased Shannon index （W = 290, P = 0.007）, but significantly increased Simpson index （W = 663, P = 0.010） compared with the healthy nail group, suggesting that the diversity and evenness of bacterial communities were lower in the infected nail group than in the healthy nail group; however, there was no significant difference in the diversity of fungal communities between the infected nail group and healthy nail group. The β-diversity analysis based on the unweighted-UniFrac distance matrix showed no significant difference in the fungal or bacterial community composition between the infected nail group and healthy nail group （bacterial communities: R = 0.0052, P = 0.331; fungal communities: R = 0.0036, P = 0.337）; the β-diversity analysis based on the weighted-UniFrac distance matrix showed significant differences in the abundance of bacterial and fungal communities between the two groups （both P = 0.001）. In terms of the species composition, the bacterial flora with significantly decreased abundance in the infected nail group compared with the healthy nail group included Bacteroidetes, Proteobacteria, Betaproteobacteria, Burkholderiales, Ralstonia, Sphingomonas and Streptococcus, while the abundance of Bacilli, Bacillales and Staphylococcus was significantly higher in the infected nail group than in the healthy nail group. Compared with the healthy nail group, the fungal flora with significantly increased abundance in the infected nail group included Eurotiomycetes, Onygenales, Leotiomycetes-ord-incertae-sedis, Arthrodermataceae, Periconia, Erysiphe, Tilletiopsis, Trichophyton, Erysiphe cruciferarum, Trichophyton rubrum, Malassezia sympodialis, while the abundance of Saccharomycetes, Saccharomycetales, Saccharomycetaceae, Dothioraceae, Candida and Alternaria was significantly lower in the infected nail group than in the healthy nail group. Conclusion The diversity and abundance of bacterial communities significantly differed between infected nails and healthy nails among patients with onychomycosis, while only the abundance of fungal communities differed between the two groups, and perhaps there was correlations between some bacterial and fungal communities.

Key words: Onychomycosis, Microbial consortia, RNA, ribosomal, 16S, High-throughput nucleotide sequencing, ITS