A clarion call for preventing taxonomical errors of dermatophytes using the example of the novel Trichophyton mentagrophytes genotype VIII uniformly isolated in the Indian epidemic of superficial dermatophytosis

Abstract

An alarming pan Indian increase in the incidence of superficial dermatophytosis has been noticed over the past 5-6 years. Recent studies have demonstrated emerging predominance of Trichophyton (T.) mentagrophytes as the causative organism in such cases. Interestingly, a distinct Indian genotype of T. mentagrophytes has been identified and recognised with the help of sequencing of the ITS region of the rDNA. That has, however, led to a basic confusion owing to the newly introduced taxonomy of dermatophytes in 2017. According to this most recently suggested classification and new taxonomy of dermatophytes, the former "T. mentagrophytes complex" is differentiated into T. mentagrophytes (zoophilic strains) and T. interdigitale (anthropophilic strains). We have noticed that in some recent studies the causative agent of the chronic, relapsing dermatophytosis outbreak in India has been described as T. interdigitale. In our opinion, it is very likely that these T. interdigitale strains isolated in Delhi and Chennai in India are indeed strains more closely related to the neotype of T. mentagrophytes and not strains of T. interdigitale. We therefore want to underscore the importance of a common nomenclature of species in accordance with the new taxonomy of dermatophytes. This would most likely facilitate better understanding of the issue amongst dermatologists and microbiologists in general. Mistaken identification of Trichophyton isolates not limited to India is very likely to occur due to the lack of appropriate molecular diagnosis which in turn is based on the already published data that presumably wrongly identify one species instead of the other.

Trichophyton mentagrophytes and T interdigitale genotypes are associated with particular geographic areas and clinical manifestations

“…All of them belonged to Type VIII and harboured single‐point mutations in the squalene epoxidase ( SQLE ) gene . Singh et al reported a large series of 20 terbinafine resistant strains among 63 T mentagrophytes isolates that later were found to belong to genotype VIII by Nenoff et al The genotypic affiliation of remained 43 susceptible isolates remained obscure. Interestingly, all terbinafine resistant isolates in our study also had ITS region sequence Type VIII.…”

Trichophyton mentagrophytes – a new genotype of zoophilic dermatophyte causes sexually transmitted infections

“…Im Gegensatz zu den veröffentlichten Fallstudien werden hier 37 Patienten beschrieben, die innerhalb von 18 Monaten die Klinik für Dermatologie an der Charité Berlin besuchten und Tinea-Infektionen, meist Tinea genitalis, aufwiesen, die durch den neuen Genotyp T. mentagrophytes , verursacht wurden. In Anlehnung an die von Heidemann et al 2010 [ 5 ] festgelegten und von Nenoff et al [ 19 ]…”

“…In contrast to the published case studies, we describe 37 patients who suffered from tinea infections (mostly tinea genitalis) caused by the new T. mentagrophytes genotype, and who visited the dermatological outpatient clinic within a period of 18 months. Following the nomenclature scheme established by Heidemann et al 2010 and grouped into a series of additional T. mentagrophytes variants by Nenoff et al , this genotype will be named T. mentagrophytes VII throughout the rest of this study.…”

In vitro activities of 15 antifungal drugs against a large collection of clinical isolates of Microsporum canis

“…Previous studies have documented low in vitro susceptibility towards fluconazole, itraconazole, ketoconazole, terbinafine, naftifine, griseofulvin and ciclopirox ; clinical isolates of T rubrum and T interdigitale that are resistant to allylamines, particularly terbinafine, with point mutations in the squalene epoxidase‐encoding gene, have also been reported . Owing to problems with molecular identification, the distinction between the anthropophilic T interdigitale and zoophilic T mentagrophytes leads to some taxonomical confusion …”