Rapid identification of Trichophyton tonsurans by specific PCR based on DNA sequences of nuclear ribosomal internal transcribed spacer (ITS) 1 region.

Background: Trichophyton tonsurans, a dermatophyte implicated in an international epidemic of tinea capitis, was also found to be responsible for infecting wrestling and Judo athletes nationwide in Japan since 2001.

Objective: A rapid and highly accurate means of identifying this pathogen has been required to control the infection. We have developed a T. tonsurans-specific PCR method based on the DNA sequences of the nuclear ribosomal internal transcribed spacer 1 region.

Subjects: Eighteen species of six genera of standard strains and 75 strains of clinically isolated Trichophyton species were used in this study.

Methods: A T. tonsurans-specific PCR primer pair (tonsF1 and tonsR1) was designed on the nuclear ribosomal internal transcribed spacer 1 region, located between 18S and 5.8S rDNA. Fungal DNA was extracted from the colonies grown on culture plates, and the specificity of the PCR primers was tested.

Results: The specific PCR product was amplified from the standard strain of T. tonsurans and from five strains isolated from black dot ringworms, but there was no band from the 70 clinical isolates of other Trichophyton species. This T. tonsurans-specific PCR method was able to detect 10 pg of T. tonsurans genomic DNA with ethidium bromide staining.

Conclusions: A PCR identification system specific for T. tonsurans is rapid, sensitive, and specific.