Usefulness of techniques based on real time PCR for the identification of onychomycosis-causing species

Onychomycosis (OM) is a nail infection caused mainly by dermatophyte species but other species of yeast and moulds are frequently involved as well. Classical diagnosis has limitations thus empirical treatment is common. The usefulness of different real time PCR (RT-PCR) assays for identifying species causing OM was assessed in samples from seventy patients and fifteen controls. Conventional methods and four different RT-PCR assays were used: a panfungal, a pandermatophyte and two specific assays for detecting Candida spp. and Aspergillus spp. Fungal elements were visualised in 58% of the samples, and 54% of cultures were positive. Panfungal and pandermatophyte RT-PCR were positive in 28% and 60%, respectively, and the sensitivity relative to positive cultures was 47% and 90%. Candida spp. were detected in 76% of samples analysed and Aspergillus spp. in 60%. These species were also present in 80% of control cases. In conclusion, molecular techniques were useful but showed limitations. The panfungal assay showed a low sensitivity, the pandermatophyte assay was sensitive and specific but did not allow for differentiation among species of dermatophytes. Finally, the role of non-dermatophyte species detected by using specific RT-PCR techniques should be carefully analysed as these species were also present in healthy nails.