Fast and sensitive detection of Trichophyton rubrum in superficial tinea and onychomycosis by use of a direct polymerase chain reaction assay

Detection of Trichophyton rubrum in superficial skin infections by conventional methods is time consuming and not always successful. However, with modern molecular methods, an alternative is in sight. The aim of this study was to compare the detection of T. rubrum by conventional methods and by a direct specific PCR assay under routine conditions. Skin scrapings (n = 464) and nail samples (n = 230) collected from suspected tinea lesions were equally divided for KOH-mounts, cultures and PCR-analysis. For the latter, DNA was extracted and PCR was performed with T. rubrum-specific primers. Of the scale samples, 16% were positive for T. rubrum in the culture and PCR as well, 9% were positive in the PCR only and 3% in the culture only, whereas 5% were only KOH-positive. The corresponding results for nail samples were 17%, 20%, 3% and 7%. PCR results were available after 2-5 days, culture results after 2-3 weeks. Our results show that a specific PCR assay can successfully be used to detect T. rubrum directly in samples collected from superficial skin lesions and nails under routine conditions. Compared with conventional methods, it is faster and more sensitive. We recommend its complementary use.