Detecting intraspecies polymorphisms in fungi causing dermatophytoses is important in elucidating routes of infection and determining whether Tinea recurrence is caused by exacerbation or re-infection. In fungi, the non-transcribed spacer region (NTS) of the ribosomal RNA gene shows the greatest accumulation of base sequence mutations. We therefore assessed NTS sequences in 64 clinical isolates of Trichophyton mentagrophytes var. interdigitale, the second most common species of dermatophytes in Japan. These isolates were among the clinical isolates of dermatophytes in the Department of Dermatology, Kanazawa Medical University Hospital in 2006 and were obtained by morphological and molecular biological identification methods. DNA was extracted from each isolate, as well as from one isolate maintained in our department, to detect length polymorphisms at each of three variable loci, TmiS0, TmiS1 and TmiS2, of the NTS for subtyping. We observed seven patterns for TmiS0, six patterns for TmiS1 and three patterns for TmiS2. The combinations of these patterns enabled us to classify the 65 isolates into 15 types. The most prevalent, constituted 46% (30/65) of all isolates. Eleven types were new combinations, whereas the other four were previously described. These results suggest that this method may be used to determine the molecular epidemiology of T. mentagrophytes var. interdigitale in Japan, because it generated results rapidly and in a sensitive manner.

To determine the relationships among Trichophyton species we constructed three phylogenies, based on the nucleotide sequences of the actin, rRNA and DNA topoisomerase II genes. These phylogenies showed several conflicting branch points. For example, strains of T. verrucosum, T. concentricum and T. mentagrophytes var. erinacei were mingled with strains of Arthroderma benhamiae and could not be separated into their own phylogenic groups. In addition, strains of A. vanbreuseghemii, T. tonsurans, T. mentagrophytes var. interdigitale and T. mentagrophytes var. quinckeanum were mingled with strains of A. simii and could not be separated into their own phylogenic groups. T. rubrum and T. violaceum made up a clade, which was phylogenetically related to the A. benhamiae clade or A. simii clade, depending on the gene examined. These findings indicate the need to reevaluate the boundaries among Trichophyton species using an alternative to morphological or molecular biological methods.

Three genetically hybrid F1 progenies produced between a clinical isolate of Arthroderma simii (KMU4810)and a tester strain of A. vanbreuseghemii (RV27961)were crossed with two tester strains of A. vanbreuseghemii (RV27961 and RV27960) and a tester strain of A. benhamiae (RV30001) , respectively. Three crossings yielded hybrid second progenies. Another interspecies crossing between A. simii (KMU4810)and a tester strain of A. benhamiae(RV26680)yielded one hybrid F1 progeny(Asb57). The second crossings of F1 progeny(Asb57)with A. vanbreuseghemii(RV27961)and A. benhamiae (RV30001)yielded many hybrid second progenies. Some hybrid second progenies produced between F1 progeny and A. vanbreuseghemii were confirmed to have genes from three species. The gene exchangeability among three Arthroderma species was shown and the meaning of these events discussed.