Molecular epidemiology of Arthroderma benhamiae, an emerging pathogen of dermatophytoses in Japan, by polymorphisms of the non-transcribed spacer region of the ribosomal DNA

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Abstract

In Japan, several isolates of Arthroderma benhamiae, a teleomorphic member of Trichophyton mentagrophytes complex, which were not found by earlier mating studies, have recently been recovered from human and animal dermatophytoses. In the present study, intraspecies polymorphism of A. benhamiae isolated in Japan was investigated using restriction fragment length polymorphisms (RFLP) of the non-transcribed spacer (NTS) region of the ribosomal DNA (rDNA), a method introduced to detect intraspecies polymorphisms of other dermatophyte species, such as T. rubrum. Based on their restriction profiles, there were five DNA types out of eight strains of A. benhamiae isolated in Japan. None of the five DNA types were found among the registered tester strains of A. benhamiae. Therefore, several different strains of A. benhamiae may have been brought into Japan separately.

Introduction

Dermatophytes are a specialized group of fungi which infect keratinized tissues of humans and animals. Among these dermatophytes, Trichophyton mentagrophytes is found in many countries, and is considered to be one of the most important causative agents for both human and animal dermatophytoses. However, mating studies have revealed that T. mentagrophytes is biologically a species-complex composed of three teleomorphic species, Arthroderma benhamiae, A. vanbreuseghemii and A. simii, and several anamorphic varieties [1]. In early 1980, A. benhamiae isolates could not be found in Japan from a mating study [2], [3]. Recently, however, several isolates of A. benhamiae have been established from human and animal specimens in Japan. All the isolates were from pet rabbits and a pet guinea pig and from the animal owners’ family of the pet animal and from a pet shop worker [4], [5], [6]. Therefore, A. benhamiae was probably introduced into Japan through animals imported from abroad [4], [5].

Recent advances in molecular biology indicated that a very sensitive technique, the analysis of length variation of non-transcribed spacer (NTS) regions of the ribosomal (r)DNA, might be useful in sub-typing the isolates of T. rubrum [7]. In the present study, we attempted to evaluate the molecular typing of A. benhamiae isolated in Japan to try to determine the origin and source of the isolates.

Section snippets

A. benhamiae strains

By October 2000, in Japan, eight clinical isolates of A. benhamiae had been established (Table 1). All eight isolates were used in this study. All of the isolates have been identified by standard morphological and mating studies. Among them, VUT 00002 and VUT 00003 were isolated from different animals. KMU 4136 and 4137, KMU 4169 and 4170 had the same origins respectively. Four tester strains for the mating study, all of which were provided by Prince Leopold Institute for Tropical Medicine,

Preliminary screening using RFLP analysis of the ITS regions

The RFLP profiles of the eight isolates of A. benhamiae were observed and were compared with each other and with those of typical clinical isolates of T. mentagrophytes var. interdigitale, SM 8796, tester strains of A. benhamiae, A. simii and A. vanbreuseghemii (Fig. 2). All eight isolates and the A. benhamiae strains had the same RFLP profile, whereas T. mentagrophytes var. interdigitale, A. vanbreuseghemii and A. simii had profiles characteristic of each of the taxa.

DNA typing based on polymorphisms of the NTS regions

Three bands about 2.5, 3.2

Discussion

Among the three teleomorphic species of the T. mentagrophytes complex, the incidence of isolation of A. benhamiae as a causative agent for human and animal dermatophytoses varies very much from one report to another. The highest incidence among freshly isolated T. mentagrophytes from clinical specimens was recorded in Czechoslovakia with a rate of 26.4% (27 of 102 isolates) [11] compared with 22.5% (30 of 133 isolates) in culture collected in Belgium [1] and only 1.5% in France (three of 200

Acknowledgements

We are very grateful to Professor E.G.V. Evans, Dr C. Jackson and Dr R. Barton, University of Leeds, UK, for their useful advice and encouragement.

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