[Survey of Trichophyton tonsurans infection in Japan. Molecular epidemiology and factors affecting adequate hairbrush sampling]

Detection and identification of Trichophyton tonsurans from clinical isolates and hairbrush samples by loop-mediated isothermal amplification system

Since the 1990s, there have been reports of the spread of dermatophytosis caused by Trichophyton tonsurans among contact sports athletes in several countries, including Japan. This study was performed to develop a loop-mediated isothermal amplification (LAMP) system for rapid and accurate detection and identification of T. tonsurans from clinical isolates or hairbrush samples for diagnosis and to prevent the spread of infection. A specific primer set was prepared by comparing the whole genome sequence of T. tonsurans with those of six other closely related dermatophytes. After confirming the sensitivity and specificity of this system, LAMP assay was performed using 37 clinical samples obtained from three healthy volunteers and 24 judo athletes. A total of 155 fungal isolates (56 strains of various standard fungi, 96 identified T. tonsurans isolates, three hairbrush-cultured isolates from judo athletes) and 37 hairbrush samples (34 samples from 24 judo athletes, and three samples from three healthy volunteers) were used for culture and LAMP assay, respectively. The assay showed no cross-reactivity to standard strains other than T. tonsurans. The detection limit was 100 copies of DNA template per tube. All of the 96 T. tonsurans isolates were amplified, and all samples from healthy volunteers showed negative results. Four of the 34 hairbrush samples obtained from judo athletes showed positive results in LAMP assay, and two of the four were positive in both culture and LAMP assay. We developed a rapid LAMP system with high specificity and sensitivity for diagnosis of T. tonsurans infection.

Skin Infection due to Trichophyton tonsurans Still Occurs in People in Korea but not as Outbreaks

Since 1995, Trichophyton tonsurans has been one of the causative agents of dermatophytosis in Korea. Herein we evaluate 77 patients infected with T. tonsurans who visited an outpatient clinic between 2004 and 2014. Infections due to T. tonsurans were diagnosed by mycological examination, which included direct microscopic examination using 15% KOH and culture in potato dextrose agar complemented with 0.5% chloramphenicol. The annual prevalence of infection due to T. tonsurans was the highest in 2014 (15 cases) but remained constant in non-gladiators between 2004 and 2014. The ratio of male to female patients was 1:0.3. The spring season presented the highest incidence compared with other seasons, with 27 cases. The incidence of infections due to T. tonsurans among gladiators was highest in spring compared with the other seasons whereas the incidence in non-gladiators was the highest in the winter. The body site most commonly affected was the face. Tinea corporis was the most common subtype of dermatophytosis caused by T. tonsurans. Herein, we demonstrate that the prevalence of infection with T. tonsurans remain constant throughout the study period in Korea.