Six cases of Trichophyton (T.) violaceum infection seen in a nursing home are reported. A 66-year-old female (case 1) was found with tinea corporis on her face, chest and shoulder, associated with black dot ringworm. A KOH examination of hair showed endothrix parasitism. Reddish purple colonies were isolated from the patient on Sabouraud's dextrose agar, and intercalary and terminal chlamydospores were observed on slide culture. PCR-RFLP analysis of the microorganism showed a pattern of T. violaceum type. Therefore, the isolated fungus was identified as T. violaceum, a typical anthropophilic dermatophyte which had spread among residents and staffs easily. Using a mycological method, we examined 59 persons (21 residents and 38 staff members) who had had contact with case 1. The results were as follows. An 85-year-old female (case 2) and an 83-year-old female (case 3) were carriers of T. violaceum. A 23-year-old male (case 4) had tinea corporis on his right forearm due to T. violaceum. A 24-year-old male (case 5) probably had tinea corporis on his right forearm due to T. violaceum. One year after case 1's first visit to our clinic, we observed an 88-year-old female (case 6) of tinea capitis by T. violaceum. It seems that the organism was preserved in surroundings and members of the nursing home. The contagion in our cases could either have been caused by directly touching the person or by sharing their comb. PCR-RFLP analysis was performed within a short time, so that we managed effectively to select a way of treatment and to prevent the infection from spreading.

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Two strains of T rubrum and one strain of T mentagrophytes were inoculated into human skin grafted onto BALBIc nude mice by the needle puncture method. Infection was established in 1 of the 10 animals inoculated with fluffy colony type T rubrum, 2 of the 10 animals inoculated with powdery colony type T rubrum, and 7 of the 10 animals inoculated with granular colony type T mentagrophytes, suggesting that the skin grafts are infectible by anthropophilic and zoophilic strains of dermatophytes. T. rubrum infection continued for a maximum of 9 weeks and T mentagrophytes infection for more than 11 weeks. In the animals inoculated with T. mentagrophytes, fungal elements were localized in the stratum corneum of the human skin grafts. In the acute stage, microabscesses consisting of neutrophils were observed under the stratum corneum in contact with fungal elements; in the chronic stage, epidermal thickening and infiltration, mainly consisting of histiocytes and a smaller number of lymphocytes, was noted in the upper and middle dermis. Ultrastructural findings from the parasites were similar to those of dermatophytosis in man. This experimental system should be useful as a model of chronic dermatophyte infection in the human skin.