DNA Sequencing to Evaluate Nail Pathogens: An Investigation into Bacteria and Fungi

It is well established and accepted that fungi are a major contributing factor in nail dystrophy. It has also been recognized that bacteria play a crucial role in onycholysis. However, the bacteria and fungi that can be grown on culture media in the laboratory are only a small fraction of the total diversity that exists in nature. Contemporary studies have revealed that fungi and bacteria often form physically and metabolically interdependent consortia that harbor properties and pathogenicity distinct from those of their individual components. Metagenomic DNA "shotgun" sequencing has proved useful in determining microbial etiology in clinical samples, effective for not only bacteria but also fungi, archaea, and viruses.

Thirty-nine consecutive nail and subungual debris samples with suspected onychomycosis were sent for laboratory analysis using three examination techniques: DNA sequencing, polymerase chain reaction analysis, and standard fungal culture. The nail plate and surrounding areas were disinfected with an ethyl alcohol swab before nail sampling. Samples from 16 patients were analyzed for suspected onychomycosis with DNA sequencing, searching a database of 25,000 known pathogens. These results were compared with 15 real-time polymerase chain reaction screening assays and eight fungal cultures sampled with the same methods.

The DNA sequencing detected 32 species of bacteria and 28 species of fungi: 50% were solely bacterial, 6.3% were solely fungal, and 43.7% were mixed communities of bacteria and fungi.

Toenails tested with DNA sequencing demonstrated the presence of both bacteria and fungi in many samples. Further work is required to fully investigate its relevance to nail pathology and treatment.