[Molecular biological detection of dermatophytes in clinical samples when onychomycosis or tinea pedis is suspected. A prospective study comparing conventional dermatomycological diagnostics and polymerase chain reaction].

BACKGROUND

The prevalence of onychomycosis is rising worldwide. Before starting antifungal treatment, an exact mycological diagnosis should be obtained. The current laboratory diagnosis of dermatomycoses is based on the detection of the causative agent by microscopy and culture. These conventional diagnostic methods for fungal infections often are not the best solution because they are time-consuming, cultures are false-negative and direct examination identifies non-vital structures which cannot be used for speciation.

PATIENTS AND

METHODS

A total of 218 patients presenting in a surgical practice over 3 months with clinical signs of tinea pedis and/or onychomycosis were involved in the prospective study. All patients had predisposing factors for tinea pedis and tinea unguium, such as vascular insufficiency, diabetes mellitus, and leg ulcers. Nail specimens and skin scrapings were investigated for fungi using Blancophor® preparation, and cultured. In addition to conventional diagnostics, PCR (polymerase chain reaction) for detection of dermatophyte DNA was employed. This PCR-Elisa assay is based on the use of specific primers which target the topoisomerase II gene. This allows the highly specific molecular identification of Trichophyton (T.) rubrum, T. interdigitale, and Epidermophyton floccosum directly in clinical samples.

RESULTS

23.9 % of patients were culture-positive for dermatophytes (either T. rubrum, or T. interdigitale). With PCR, dermatophyte DNA either of T. rubrum or T. interdigitale could be detected in nail samples and skin scrapings from at least 29.9 % of all patients. Epidermophyton floccosum was not found in this study, neither by cultivation nor by PCR. The diagnostic sensitivity of the PCR-Elisa assay was calculated as 79.0% ; the diagnostic specificity as 85.5 %.

CONCLUSION

PCR-Elisa evaluation makes possible a rapid, specific and sensitive diagnosis of dermatophytosis of the nails and skin within 24 (maximal 48) hours with identification of the involved species.