Multiplex PCR assay for the detection of common dermatophyte nail infections

Onychomycosis is one of the most prevalent dermatophytic diseases. Mycological methods used in the conventional diagnosis may not be optimal. Multiplex (MX) PCR was reported as a reliable alternative. Dermatophyte gene sequence records were used to design a MX PCR for detection and identification of dermatophytes in nail specimens. A MX PCR method based on the amplification of the chitin synthase 1 and internal transcribed spacer genes was developed. The study included 93 strains of dermatophytes and non-dermatophytic fungi, six dermatophytic reference strains and 201 nail specimens from patients with dermatophytic onyxis. DNA extraction directly from nail samples was carried out by using the QIAamp DNA extraction kit (Quiagen). A set of primers was designed and their specificity was assessed. MX PCR detected the causal agent in specimens from which Trichophyton rubrum and T. interdigitale grew in culture and also identified a dermatophyte species in an additional 32 specimens that were negative in microscopy and culture. None of the investigated non-dermatophytic strains was positive. Sensitivity of MX PCR was higher as compared to mycological examination (97% vs. 81.1%). MX PCR for direct detection of dermatophytes from nail samples yielded mixed flora in 32.8% of samples. MX PCR proved sensitive and adequate for the diagnosis of dermatophytic onychomycosis. It is much adapted to cases where culture is negative or contaminated by overgrowing moulds, which makes the identification of the causal agent problematic.