Identification and subtyping of Trichophyton mentagrophytes by random amplified polymorphic DNA

Current Topics in Dermatophyte Classification and Clinical Diagnosis

Dermatophytes are highly infectious fungi that cause superficial infections in keratinized tissues in humans and animals. This group of fungi is defined by their ability to digest keratin and encompasses a wide range of species. Classification of many of these species has recently changed due to genetic analysis, potentially affecting clinical diagnosis and disease management. In this review, we discuss dermatophyte classification including name changes for medically important species, current and potential diagnostic techniques for detecting dermatophytes, and an in-depth review of Microsporum canis, a prevalent zoonotic dermatophyte. Fungal culture is still considered the “gold standard” for diagnosing dermatophytosis; however, modern molecular assays have overcome the main disadvantages of culture, allowing for tandem use with cultures. Further investigation into novel molecular assays for dermatophytosis is critical, especially for high-density populations where rapid diagnosis is essential for outbreak prevention. A frequently encountered dermatophyte in clinical settings is M. canis, which causes dermatophytosis in humans and cats. M. canis is adapting to its primary host (cats) as one of its mating types (MAT1-2) appears to be going extinct, leading to a loss of sexual reproduction. Investigating M. canis strains around the world can help elucidate the evolutionary trajectory of this fungi.

Mating analyses of Trichophyton benhamiae offspring reveals linkage of genetic markers used in taxonomy

Mating experiments were conducted with four clinical Trichophyton benhamiae isolates, genetically similar to the Trichophyton benhamiae CBS 112371, featuring the plus mating type and with two minus type strains. One minus type strain belonged to the white subgroup, and the other minus type strain, DSM 6916, showed genetic kinship to the yellow subgroup. Only two plus type strains were able to form mature, pigmented gymnothecia with DSM 6916. These two plus type strains demonstrated dark pigmentation and powdery mycelium on Takashio agar, whereas the other three strains exhibited a low degree of pigmentation on the same medium. All five plus strains were able to mate with the minus type strain of their own white subgroup. Cultures from single ascospore isolates showed highly variable morphology and pigmentation. Three genetic markers (ITS, mating type, EF1 alpha) were analyzed in polymerase chain reaction (PCR) experiments with optimized primers and PCR conditions to discriminate between subgroups. Furthermore, RAPD-PCR was used to generate a DSM 6916-specific DNA-fragment which served as an additional genetic marker. Assessing the isolates with recombinant genotypes, it was found that three genetic markers behave like linked genes. The recombination of plus mating type went together with ITS, EF1 alpha and RAPD marker of the DSM 6916 parental strain and was most frequently isolated, whereas plus types recombinants in this case were completely missing. This shows a high imbalance in mating type distribution of recombinants.

Distribution of Species of Dermatophyte Among Patients at a Dermatology Centre of Nghean Province, Vietnam, 2015-2016

INTRODUCTION

Vietnam is a tropical country so fungal diseases including dermatophytosis may be prevalent, but epidemiological profiles of agents responsible for the infection have rarely been reported.

OBJECTIVE

To find out the distribution of dermatophytes among patients living in a central province of Vietnam.

METHODS

We examined dermatophyte infections in patients with lesions suspected of dermatophytosis referred to the Nghean provincial leprosy and dermatology centre from August 2015 to August 2016. The speciation of dermatophyte was performed by conventional and molecular approaches.

RESULTS

One hundred and thirty-six patients (90 males and 46 females) were included. Those aged from 11 to 30 contribute 59.1%. The most common agent found was Trichophyton rubrum (66.9%), followed by T. interdigitale (12.5%), T. tonsurans (9.6%), Microsporum incurvatum (8.1%), and the less frequent species were M. canis (2.2%) and T. violaceum (0.7%). Epidermophyton floccosum was not reported. T. rubrum were more common in men (74.4%) than in women (52.2%), while T. interdigitale and M. incurvatum were more common in women (21.7 and 15.2%) than in men (7.8 and 4.4%). Patients infected with Microsporum spp. had small-sized lesions for only 3 months, while those affected by Trichophyton spp. had large-sized lesions with longer duration.

CONCLUSION

Trichophyton species are the predominant agents of infection in Nghean province, while Epidermophyton species is absent. Additional investigations are required to clarify the epidemiological profile of dermatophytes in Vietnam.

Relationship Between Phenotypic and Genotypic Characteristics of Trichophyton mentagrophytes Strains Isolated from Patients with Dermatophytosis

According to epidemiological, clinical and mycological criteria, it has long been admitted that the Trichophyton mentagrophytes species includes two varieties: a zoophilic variety (var. mentagrophytes) and an anthropophilic variety (var. interdigitale) that involve the upper and the lower part of the body, respectively. The further application of molecular techniques to the characterization of dermatophyte strains showed that this classification is unreliable. The aim of our study was to assess the usefulness of PCR-RFLP (restriction fragment length polymorphism) and sequencing in the characterization of T. mentagrophytes strains taken from Tunisian patients. The study was carried out in 2008 in the laboratory of Parasitology-Mycology of Farhat Hached University Hospital, Sousse, Tunisia. A total of 133 strains were isolated from 133 patients addressed to the laboratory for dermatological lesions very evocative of dermatomycosis. Eighty strains were isolated from lesions located on the lower part of the body (onychomycosis, tinea pedis) and 53 strains from the upper part of the body (tinea capitis, tinea corporis). All strains were submitted to mycological examination (direct microscopic examination and culture on Sabouraud medium) and further investigated by using RFLP analysis of the PCR-amplified ITS1-5.8 s-ITS2 region of the ribosomal DNA and the MvaI restriction enzyme. In addition, 62 strains were further submitted to a sequencing of the ITS1-5.8 s-ITS2 region. On the basis of mycological criteria, all strains were diagnosed as T. mentagrophytes. All strains produced the same RFLP pattern and were identified as T. mentagrophytes interdigitale regardless of the location of lesions. Out of the 62 sequenced strains, 16 were found anthropophilic and 46 were zoophilic. In conclusion, all strains provisionally diagnosed as T. mentagrophytes on the basis of mycological criteria were shown to belong to T. interdigitale by using PCR-RFLP and sequencing irrespective of the site of lesions. The predominance of zoophilic strains needs further investigation.

Molecular Markers Useful for Intraspecies Subtyping and Strain Differentiation of Dermatophytes

Dermatophytosis is a very common skin disorder and the most frequent infection encountered by practicing dermatologists. The identification, pathogenicity, biology, and epidemiology of dermatophytes, the causative agents of dermatophytosis, are of interest for both dermatologists and medical mycologists. Recent advances in molecular methods have provided new techniques for identifying dermatophytes, including intraspecies variations. Intraspecies subtyping and strain differentiation have made possible the tracking of infections, the identification of common sources of infections, recurrence or reinfection after treatment, and analysis of strain virulence and drug resistance. This review describes molecular methods of intraspecies subtyping and strain differentiation, including analyses of mitochondrial DNA and non-transcribed spacer regions of ribosomal RNA genes, random amplification of polymorphic DNA, and microsatellite markers, along with their advantages and limitations.

Kerion and Tinea Corporis Caused by Rabbit-Derived Trichophyton interdigitale in Three Siblings and One Consulting Doctor Using β-Tubulin Gene to Identify the Pathogen

Trichophyton interdigitale is generally deemed as an anamorph of Arthroderma vanbreuseghemii based on internal transcribed spacer (ITS) sequencing, but recently their anamorph/teleomorph connection should be cautioned based on β-tubulin phylogeny. We report three siblings and one consulting doctor who developed kerion and tinea corporis after contact with domestic rabbits. Seven same strains were isolated from four patients and three regions of a sick rabbit. The ITS and D1/D2 sequences of our isolate were 99 % homologous to A. Vanbreuseghemii, while β-tubulin sequence was 100 % identical to T. interdigitale. Our isolate was identified as T. interdigitale based on maximum likelihood analysis of β-tubulin. Random amplified polymorphic DNA revealed that the band patterns of five isolated strains and another rabbit-derived strain WCH023 were identical for OPF-03 and OPF-12. Skin lesions of all patients resolved completely for 2- to 6-week therapy of oral terbinafine and topical 1 % bifonazole or 1 % terbinafine cream. This study demonstrates that T. interdigitale of rabbit origin can cause various types of human dermatophytosis by mild scratch. Terbinafine may be the first choice for dermatophytosis caused by T. interdigitale.

Molecular epidemiology, phylogeny and evolution of dermatophytes

Dermatophytes are fungi that invade and propagate in the keratinized skin of mammals, including humans, often causing contagious infections. The species of medical concern belong to the genera Microsporum, Trichophyton, Epidermophyton (in their anamorphic state) and Arthroderma (in their telomorphic state), which were traditionally identified based on their morphology and biochemical characters. Nonetheless, limitations linked to the differentiation of closely related agents at species and strains level have been recently overcome by molecular studies. Indeed, an accurate identification of dermatophytes is pivotal for the establishment of effective control and prevention programs as well as for determining the most appropriate and effective antifungal therapies to be applied. This article reviews the DNA techniques and the molecular markers used to identify and to characterize dermatophyte species, as well as aspects of their phylogeny and evolution. The applications of typing molecular strain to both basic and applied research (e.g., taxonomy, ecology, typing of infection, antifungal susceptibility) have also been discussed.

Genetic variability in Microsporum canis isolated from cats, dogs and humans in Brazil

Dermatophytosis caused by Microsporum canis is a heterogeneous disease with variable clinical manifestations. M. canis is a zoophilic dermatophyte and the most frequent fungi isolated from dogs, cats and children in Brazil. The aim of this study was to investigate the genetic variability of M. canis isolates from different animal species using two microsatellite markers, namely, McGT(13) and McGT(17), and to correlate the results with the clinical and epidemiological patient data in Brazil. The study included a global set of 102 M. canis strains, including 37 symptomatic cats, 35 asymptomatic cats, 19 human patients with tinea, 9 asymptomatic dogs and 2 symptomatic dogs. A total of 14 genotypes were identified, and 6 large populations were distinguished. There was no correlation between these multilocus genotypes and the clinical and epidemiological data, including the source, symptomatology, clinical picture, breed, age, sex, living conditions and geographic location. These results demonstrate that the use of microsatellite polymorphisms is a reliable method for the differentiation of M. canis strains. However, we were unable to demonstrate a shared clinical and epidemiological pattern among the same genotype samples.

Direct detection of five common dermatophyte species in clinical samples using a rapid and sensitive 24-h PCR-ELISA technique open to protocol transfer

Identification of dermatophytes is usually based on morphological characteristics determined by time-consuming microscopic and cultural examinations. An effective PCR-ELISA method has been developed for rapid detection of dermatophyte species directly from clinical specimens within 24 h. Isolated genomic DNA of skin scrapings and nail samples from patients with suspected dermatophyte infections is amplified with species-specific digoxigenin-labelled primers targeting the topoisomerase II gene. The subsequent ELISA procedure with biotin-labelled probes allows a sensitive and specific identification of the five common dermatophytes -Trichophyton rubrum, T. interdigitale, T. violaceum, Microsporum canis and Epidermophyton floccosum. PCR-ELISA, based on the new polyphasic species concept, was assessed using 204 microscopy-positive samples in two university mycological laboratories in Munich and Tübingen, and 316 consecutive specimens - regardless of mycological findings - in a dermatological practice laboratory in Neu-Ulm. One of the five dermatophytes was confirmed by PCR-ELISA in 163 of 204 (79.9%) of the clinical samples from the university hospitals found positive using microscopy. Culture was positive for dermatophytes in 59.8% of the same cases. A significant difference between these two methods could be demonstrated using the McNemar test (P < 0.005). Analysis of specimens from Neu-Ulm confirmed the results in a dermatological practice laboratory as 25.0% of the specimens had positive PCR results, whereas only 7.3% were positive according to culture. Direct DNA isolation from clinical specimens and the PCR-ELISA method employed in this study provide a rapid, reproducible and sensitive tool for detection and discrimination of five major dermatophytes at species level, independent of morphological and biochemical characteristics.

Trichophyton rubrum and Trichophyton interdigitale: genetic diversity among species and strains by random amplified polymorphic DNA method

Onychomycosis is a common condition that represents up to 50% of all nail problems and 30% of all cases of dermatophytoses. Trichophyton rubrum and Trichophyton interdigitale are the most common agents involved in this condition. In cases of recurrent post-treatment onychomycosis, strain fingerprinting could reveal whether the original isolate is responsible, a new strain has been acquired or if multiple strains are involved. The aim of this study was to evaluate the efficacy of the RAPD method for species and strain differentiation of T. rubrum and T. interdigitale obtained from patients with subungeal distal-lateral onychomycosis. A set of 86 strains of onychomycosis causative dermatophytes were submitted to species differentiation and strain typing by RAPD method with two previously described primers. Both primers proved capable of strain differentiation when tested for each species. Nineteen molecular profiles were configured for T. rubrum isolates with primers 1 and 6. For T. mentagrophytes, ten molecular profiles were configured with primer 1 and twenty-one with primer 6. We found that T. interdigitale and T. rubrum species were grouped in different clusters when both primers were analyzed together. This study shows that these primers are valuable tools for strain differentiation with T. rubrum and T. intedigitale.

Differentiation of Trichophyton rubrum clinical isolates from Japanese and Chinese patients by randomly amplified polymorphic DNA and DNA sequence analysis of the non-transcribed spacer region of the rRNA gene

BACKGROUND

Trichophyton rubrum is the most common pathogen causing dermatophytosis worldwide. Recent genetic investigations showed that the microorganism originated in Africa and then spread to Europe and North America via Asia.

OBJECTS

We investigated the intraspecific diversity of T. rubrum isolated from two closely located Asian countries, Japan and China.

METHODS

A total of 150 clinical isolates of T. rubrum obtained from Japanese and Chinese patients were analyzed by randomly amplified polymorphic DNA (RAPD) and DNA sequence analysis of the non-transcribed spacer (NTS) region in the rRNA gene.

RESULTS

RAPD analysis divided the 150 strains into two major clusters, A and B. Of the Japanese isolates, 30% belonged to cluster A and 70% belonged to cluster B, whereas 91% of the Chinese isolates were in cluster A. The NTS region of the rRNA gene was divided into four major groups (I-IV) based on DNA sequencing. The majority of Japanese isolates were type IV (51%), and the majority of Chinese isolates were type III (75%).

CONCLUSIONS

These results suggest that although Japan and China are neighboring countries, the origins of T. rubrum isolates from these countries may not be identical. These findings provide information useful for tracing the global transmission routes of T. rubrum.

Trichophyton mentagrophytes sive interdigitale? A dermatophyte in the course of time

Originally, the Trichophyton (T.) mentagrophytes complex distinguished between the anthropophilic subspecies T. mentagrophytes var. interdigitale, T. mentagrophytes var. nodulare (synonym T. krajdenii), and T. mentagrophytes var. goetzii and the zoophilic subspecies T. mentagrophytes var. granulosum (rodents), T. mentagrophytes var. erinacei (hedgehog), and T. mentagrophytes var. quinckeanum (mice). In addition, two sexual species (teleomorph) of this complex are known. These are Arthroderma (A.) benhamiae Ajello and Cheng 1967 and Arthroderma vanbreuseghemii Takashio 1973. According to recent molecular studies,the species T.mentagrophytes is synonymous with only the zoophilic subspecies T.mentagrophytes var. quinckeanum which is rare in Western Europe. The anthropophilic subspecies of T. mentagrophytes, as well as many of the zoophilic strains, formerly differentiated as var. mentagrophytes or var. granulosum, are indistinguishable and are now designated T.interdigitale. The morphological differentiation between anthropophilic and zoophilic T. interdigitale strains by classical microscopical and biochemical methods is often problematic. In particular, it is impossible to differentiate between the zoophilic strains of T. interdigitale, T. mentagrophytes, and the Trichophyton anamorph of A. benhamiae. In these cases, molecular identification methods may be applied to answer epidemiological, taxonomical and therapeutic questions.

Rapid identification and differentiation of fungal DNA in dermatological specimens by LightCycler PCR

The aim was to develop a LightCycler PCR method for the rapid detection and differentiation of fungal DNA in dermatological specimens such as skin scales and skin swabs. LightCycler PCR assays were established for seven primer sets specific for fungal DNA. For each primer set LightCycler melting points were defined by amplification of DNA from 21 fungi and sensitivity was determined by amplification of serial dilutions of fungal DNA. A protocol was established that allows detection and differentiation of mould and yeast DNA with one highly sensitive PCR reaction by assessment of LightCycler melting points. Two subsequent LightCycler PCR reactions and one RFLP reaction allowed the differentiation of dermatophytes and non-dermatophyte moulds and the subclassification of yeasts. Analysis of clinical samples from 38 patients with fungal skin diseases provided conclusive new diagnostic information in 9/38 cases (23.7 %) by this PCR protocol that was not equally provided by direct microscopy and mycological culture. Thus the LightCycler PCR protocol established here represents a rapid diagnostic tool that aids in the diagnosis of fungal skin disease in a substantial number of patients.

PCR-based identification of common dermatophyte species using primer sets specific for the DNA topoisomerase II genes

BACKGROUND

We have determined nucleotide sequences of the DNA topoisomerase II genes of the dermatophyte species, and conducted a PCR-based identification system using species-specific primers for the nucleotide sequences.

OBJECTIVE

To identify the major dermatophytes, Trichophyton rubrum, T. mentagrophytes, T. violaceum, M. gypseum, M. canis and E. floccosum, by PCR amplifications at the species level, without determining the nucleotide sequence.

METHODS

For PCR-based identification of the major dermatophyte species, a common primer set (dPsD1) for these species and species-specific primer sets (PsT and PsME) for each species were designed based on the genomic sequences of the DNA topoisomerase II genes of the dermatophytes, and tested for their specificities in PCR amplifications. The method consisted of amplification of the genomic DNA topoisomerase II gene by the common primer set, followed by a second PCR with the primer sets consisting of species-specific primers for each dermatophyte species.

RESULTS

Using dPsD1, a DNA fragment of 3390 bp was amplified from the genomic DNA of all the dermatophyte species. In the subsequent nested PCR using species-specific primer sets (PsT and PsME), both sets amplified unique sizes of PCR products, all of which corresponded to a species of the dermatophytes even in the presence of other fungal DNA.

CONCLUSION

We demonstrate that the PCR-based identification targeting the DNA topoisomerase II gene is rapid and simple, and is available as a tool for the identification of the major dermatophyte species.

Species identification and strain differentiation of dermatophyte fungi using polymerase chain reaction amplification and restriction enzyme analysis

BACKGROUND

Standard biochemical tests, microscopy, colony characteristics, and mating tests have conventionally been used for the identification of dermatophytes species, but these methods of identification are costly, time-consuming, and require special skills.

OBJECTIVE

Our purpose was to identify a method that enables rapid species identification and strain differentiation of dermatophyte fungi.

METHODS

We chose 4 restriction enzymes (BsYiI, DdeI, HinfI, and MvaI) that could produce different fragment patterns after enzyme digestion according to species or strain. We performed enzyme digestions after polymerase chain reaction amplification of internal transcribed spacer region and identified different restriction fragment length polymorphisms (RFLP) according to species and strains.

RESULTS

All the species included in this study could be easily differentiated using any combination of 2 different restriction enzymes except Trichophyton rubrum and T raubitschekii, which produced identical digestion patterns after all 4 restriction enzyme digestions. In the case of T mentagrophytes, MvaI and DdeI each produced 2 distinct RFLP patterns.

CONCLUSION

This study showed that internal transcribed spacer region analysis using polymerase chain reaction-RFLP through DdeI and MvaI is useful for rapid identification of the majority of dermatophytes species. However, there were 2 different band patterns by DdeI and MvaI restriction enzyme digestion and no correlations between morphologic types and RFLP patterns in T mentagrophytes.