Molecular Approaches in the Diagnosis of Dermatophytosis

Diagnostic ability of Peptidase S8 gene in the Arthrodermataceae causing dermatophytoses: A metadata analysis

An unambiguous identification of dermatophytes causing dermatophytoses is necessary for accurate clinical diagnosis and epidemiological implications. In the current taxonomy of the Arthrodermataceae, the etiological agents of dermatophytoses consist of seven genera and members of the genera Trichophyton are the most prevalent etiological agents at present. The genera Trichophyton consists of 16 species that are grouped as clades, but the species borderlines are not clearly delimited. The aim of the present study was to determine the discriminative power of subtilisin gene variants (SUB1-SUB12) in family Arthrodermataceae, particularly in Trichophyton. Partial and complete reads from 288 subtilisin gene sequences of 12 species were retrieved and a stringent filtering following two different approaches for analysis (probability of correct identification (PCI) and gene gap analysis) conducted to determine the uniqueness of the subtilisin gene subtypes. SUB1 with mean PCI value of 60% was the most suitable subtilisin subtype for specific detection of T.rubrum complex, however this subtype is not reported in members of T. mentagrophytes complex which is one of the most prevalent etiological agent at present. Hence, SUB7 with 40% PCI value was selected for testing its discriminative power in Trichophyton species. SUB7 specific PCR based detection of dermatophytes was tested for sensitivity and specificity. Sequences of SUB7 from 42 isolates and comparison with the ITS region showed that differences within the subtilisin gene can further be used to differentiate members of the T. mentagrophytes complex. Further, subtilisin cannot be used for the differentiation of T. benhamiae complex since all SUB subtypes show low PCI scores. Studies on the efficiency and limitations of the subtilisin gene as a diagnostic tool are currently limited. Our study provides information that will guide researchers in considering this gene for identifying dermatophytes causing dermatophytoses in human and animals.

A Comparative Description of Dermatophyte Genomes: A State-of-the-Art Review

The nomenclature and phylogeny of dermatophytes is currently based on the nucleotide sequence polymorphisms of a few genomic regions. However, the limitations of this multilocus sequence-based approach makes dermatophyte species identification difficult. Variation and adaptation are key to the persistence of species. Nevertheless, this heterogeneity poses a genuine problem for the classification and nomenclature of dermatophytes. The relatively high intra-species and low inter-species polymorphisms of this keratinophilic group of fungi hampers both species delineation and identification. Establishing the taxonomic boundaries of dermatophyte species complexes remains controversial. Furthermore, until recently, knowledge of molecular biology, genetics and genomics remained limited. This systematic review highlights the added value of whole genome sequencing and analysis data in dermatophyte classification that might enhance identification and, consequently, the diagnosis and management of dermatophytoses. Our approach consisted in describing and comparing the dermatophyte mitochondrial genomes, secretomes (Adhesins, LysM domains, proteases) and metabolic pathways, with the aim to provide new insights and a better understanding of the phylogeny and evolution of dermatophytes.

Multiplex real-time PCR for skin fungal infections: The diagnostic reliability in a one-year non-interventional study

The skin fungal infection diagnostic workflow currently includes microscopic and culture-based methods as the gold standard. Recent published data described the possible limitations of these conventional techniques documenting the possibility of reducing response time intervals. The present study reports an evaluation of the DermaGenius® (DG) multiplex kit (PathoNostics) for rapid C. albicans and dermatophytes identification directly from skin samples. The investigations involved 90 specimens that underwent DNA extraction and amplification simultaneously to microscopic and culture methods. According to current guidelines, we defined a dermatophytic skin infection as the simultaneous presence of clinical evidence of skin lesions and positive results for dermatophyte elements from microscopy and/or cultures. The collected data remarked on the advantages of the molecular assay, especially in terms of sensitivity and rapidity. A statistical evaluation analysed a comparison between conventional and innovative diagnostic methods. The sensitivity, specificity, positive predictive value, and negative predictive value of DG-PCR in the cutaneous dermatophytosis were, respectively, 94.7%, 78.8%, 88.5%, and 89.6%. Based on our experience, the molecular technique could represent a diagnostic confirmation in the case of previous antifungal treatment, little biological material available, or urgent clinical conditions.

Advances of liposomal mediated nanocarriers for the treatment of dermatophyte infections

Due to the adverse effects associated with long-term administration of antifungal drugs used for treating dermatophytic lesions like tinea unguium, there is a critical need for novel antifungal therapies that exhibit improved absorption and minimal adverse effects. Nanoformulations offer a promising solution in this regard. Topical formulations may penetrate the upper layers of the skin, such as the stratum corneum, and release an appropriate amount of drugs in therapeutic quantities. Liposomes, particularly nanosized ones, used as topical medication delivery systems for the skin, may have various roles depending on their size, lipid and cholesterol content, ingredient percentage, lamellarity, and surface charge. Liposomes can enhance permeability through the stratum corneum, minimize systemic effects due to their localizing properties, and overcome various challenges in cutaneous drug delivery. Antifungal medications encapsulated in liposomes, including fluconazole, ketoconazole, croconazole, econazole, terbinafine hydrochloride, tolnaftate, and miconazole, have demonstrated improved skin penetration and localization. This review discusses the traditional treatment of dermatophytes and liposomal formulations. Additionally, promising liposomal formulations that may soon be available in the market are introduced. The objective of this review is to provide a comprehensive understanding of dermatophyte infections and the role of liposomes in enhancing treatment.

Development, preparation, and evaluation of a novel dotted lateral flow immunochromatographic kit for rapid diagnosis of dermatophytosis

Dermatophytosis is a widely spread contagious zoonotic disease, affecting both man (tinea) and animals (ringworm). This disease is caused by a group of closely related keratinophilic fungi known collectively as the dermatophytes group. Although the wide distribution of dermatophytosis cases throughout the whole world and its adverse clinical effect on human health, economical effect on productive animals, and pet animal welfare, there is no rapid accurate diagnostic tool for such disease. The current conducted study tries to accomplish the difficult equation by achieving an accurate, sensitive, specific, user-friendly, rapid, robust, device-less, deliverable to end-users, and economic cost for the development and production of diagnostic kits. Through the development of a rapid diagnostic kit based on immunochromatographic assay with three major affordable reproducible production stages; preliminary stage, developmental and standardization stage, and evaluation stage. Obtaining dermatophytes-specific polyclonal antibodies against criteria-based selected dermatophytes strains associating proper gold nanoparticle preparation, characterization, and conjugation, with proper loading of the different bio-reactants on the efficiently laminated and fabricated lateral flow strips were the main challenge and control points through the whole process. Also, as a result of examining 100 animal samples using the new kit, the κ coefficients of the kit with the direct microscopy while the kit with the culture were 0.44 and 0.76, respectively. Therefore, the newly designated and developed kit showed a very promising competitive diagnostic result within 5-7 min through easy-to-be-performed three steps.

Evaluation of a Liquid Media MALDI-TOF MS Protocol for the Identification of Dermatophytes Isolated from Tinea capitis Infections

One of the most common types of tinea is the superficial infection of the hair and scalp area known as tinea capitis. It is responsible for frequent outbreaks in nurseries and schools and represents a global health problem. Correct identification of the infection agent is essential in the determination of the infection source, epidemiological course, and treatment initiation. The conventional identification methods (direct exam, culture, DNA sequencing) are time-consuming, require experienced staff, are time-consuming, and the latter is expensive for routine identifications. Matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) is gaining new ground for routine identification of filamentous fungi. The main advantages of MALDI-TOF MS are its rapid and accurate identification capability, relatively low cost, and easy integration into the laboratory routine. Its accuracy heavily depends on the quality of the reference spectra database. Identification of clinical isolates with MALDI-TOF MS protocol requires a sub-culturing step to ensure reliable identification. It can take days to weeks before fungal growth appears on solid medium. In this study, a unique MALDI-TOF MS protocol using liquid cultures of dermatophyte species was developed in order to shorten the turnaround time for the culture and identification of clinical isolates. Material and Method A standard MALDI-TOF MS protocol was adapted for liquid instead of solid cultures. Three different databases were tested. Results Using the liquid media MALDI-TOF MS protocol, a global rate of 62% correct identification (RCI) was obtained, compared with 87% for the protocol based on solid cultures. Trichophyton tonsurans was not correctly identified in all isolates using liquid cultures, with 88% of the isolates misidentified as Trichophyton interdigitale. The turnaround time for primary isolates for the solid and liquid protocols were respectively 11.7 and 11.6 days (no significant difference between both methods (p = 0.96)). Conclusions The newly designed liquid MALDI-TOF MS protocol did not lead to a significantly shorter turnaround time for the identification of dermatophytes isolated from tinea capitis infections. The turnaround time for the method with primary isolates was not significantly lower, and the rate of correct identification decreased remarkably, which emphasizes the need for a sub-culturing step. Using different database did not lead to improvement in turnaround time or rate of correct identification. This study highlights the importance of the medium and the reference database when performing MALDI-TOF MS.

The qualitative accuracy of clinical dermatophytes via matrix-assisted laser desorption ionization-time of flight mass spectrometry: a meta-analysis

Dermatophytes are an important part of superficial fungal infections, and accurate diagnosis is paramount for successful treatment. Recently, matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) has emerged as a powerful tool to identify clinical pathogens; its advantages are cost-effectiveness, rapid detection, and high accuracy. However, as the accurate identification of clinical dermatophytes via MALDI-TOF MS has still not been fully evaluated, we performed a meta-analysis for systematic evaluation it. Fifteen eligible studies were involved and showed high accuracy with an identification ratio of 0.96 (95%CI = 0.92─1.01) and 0.91 (95%CI = 0.86─0.96) at the genus and species levels, respectively. The results showed higher accuracy ratio of Vitek MS (91%) than MALDI Biotyper (85%). Dermatophytes such as Trichophyton interdigitale (0.99, 95%CI = 0.97─1.02), T. mentagrophytes var interdigitale (1.00, 95%CI = 0.98─1.02), and Microsporum canis (0.97, 95%CI = 0.89─1.04) showed high accuracy in detected clinical dermatophytes. Moreover, a library with self-built database set up by laboratories showed higher accuracy than commercial database, and 15-day cultivation for dermatophytes showed highest accuracy considering culture time. High heterogeneity was observed and decreased only with the subgroup analysis of species. The subgroup analysis of mass spectrometry, library database, and culture time also exhibited high heterogeneity. In summary, our results showed that MALDI-TOF MS could be used for highly accurate detection of clinically pathogenic dermatophytes, which could be an alternative diagnostic method in addition to morphological and molecular methods.

LAY ABSTRACT

This meta-analysis comprehensively investigated the qualitative accuracy of clinical dermatophytes through MALDI-TOF MS. Owing to the high accuracy observed at both genus and species levels, this approach could be an alternative diagnostic method in addition to morphological and molecular methods.

Matrix-assisted laser desorption/ionisation-time of flight mass spectrometry: Protocol standardisation, comparison and database expansion for faster and reliable identification of dermatophytes

BACKGROUND

Accurate and early identification of dermatophytes enables prompt antifungal therapy. However, phenotypic and molecular identification methods are time-consuming. MALDI-TOF MS-based identification is rapid, but an optimum protocol is not available.

OBJECTIVES

To develop and validate an optimum protein extraction protocol for the efficient and accurate identification of dermatophytes by MALDI-TOF MS.

MATERIALS/METHODS

Trichophyton mentagrophytes complex (n = 4), T. rubrum (n = 4) and Microsporum gypseum (n = 4) were used for the optimisation of protein extraction protocols. Thirteen different methods were evaluated. A total of 125 DNA sequence confirmed clinical isolates of dermatophytes were used to create and expand the existing database. The accuracy of the created database was checked by visual inspection of MALDI spectra, MSP dendrogram and composite correlation index matrix analysis. The protocol was validated further using 234 isolates.

RESULT

Among 13 protein extraction methods, six correctly identified dermatophytes but with a low log score (≤1.0). The modified extraction protocol developed provided an elevated log score of 1.6. Significant log score difference was observed between the modified protocol and other existing protocols (T. mentagrophytes complex: 1.6 vs. 0.2-1.0, p < .001; T. rubrum: 1.6 vs. 0.4-1.0, p < .001; M. gypseum:1.6 vs. 0.2-1.0, p < .001). Expansion of the database enabled the identification of all 234 isolates (73.5% with log score ≥2.0 and 26.4% with log scores range: 1.75-1.99). The results were comparable to DNA sequence-based identification.

CONCLUSION

MALDI-TOF MS with an updated database and efficient protein extraction protocol developed in this study can identify dermatophytes accurately and also reduce the time for identifying them.

Prevalence of dermatophytosis in animals and antifungal susceptibility testing of isolated Trichophyton and Microsporum species

Dermatophytosis is a frequently encountered dermatological problem in domestic and pet animals which negatively affects animal health and production. This study investigated the prevalence of dermatophytosis in different animals and carried antifungal susceptibility testing in the northern Indian state of Uttarakhand. A total of 157 clinical samples were collected from the animals irrespective of sex and age during a time period of 3 years from December 2016 to December 2019. Direct microscopy, fungal culture, isolation, identification, and antifungal susceptibility testing were carried out. Direct microscopy and in vitro culture were equally efficient in diagnosis of dermatophytosis. The prevalence of dermatophytes ranged between 45 and 53.3% and Trichophyton mentagrophytes was the most abundant species (38%) followed by Microsporum canis (21.5%). All the species observed were isolated from goats and dogs except T. tonsurans and M. nanum, respectively. All the isolated dermatophytes were urease test positive except T. rubrum and T. verrucosum. The hair perforation test was negative for M. audouinii, along with T. rubrum and T. verrucosum, whereas only M. canis was positive for rice grain test. Only T. mentagrophytes, T. rubrum, T. verrucosum, and T. tonsurans were able to show optimum growth at 37 °C. Maximum inhibition of fungal growth was exhibited by clotrimazole and least by fluconazole.

Variations in ribosomal DNA copy numbers in a genome of Trichophyton interdigitale

Background

Ribosomal DNA (rDNA) reportedly has multiple copies in the fungal genome. The internal transcribed spacer (ITS) region in rDNA is useful for investigating relationships between close taxonomic relatives. Thus, ITS has been widely used as a target gene in medical mycology for the detection of pathogenic fungi and identification of fungal species. However, the rDNA copy number in a genome of Trichophyton interdigitale, the pathogen causing dermatophytosis, currently remains unknown.

Objective

Clarification of the rDNA copy number in a genome of T. interdigitale.

Methods

rDNA copy numbers in 64 clinical isolates of T. interdigitale were examined using quantitative real‐time PCR (qPCR) with the absolute quantitative method targeting TruMDR2, a single‐copy control gene and the ITS region in rDNA.

Results

The copy numbers of the rDNA subunit varied among the 64 strains tested, from 24 to 116 copies per genome. The average rDNA copy number ± standard deviation was 59 ± 16. No correlations were observed between the rDNA copy number and colony colour, colony morphology or molecular type of the non‐transcribed spacer region in rDNA. Experiments on rDNA copy numbers obtained from independent colonies of each strain in single‐spore cultures revealed that the copy number was homogeneous within each strain.

Conclusion

This is the first study to estimate copy numbers of the rDNA subunit in a genome of T. interdigitale. The rDNA copy number of T. interdigitale varied among the strains tested and was homogeneous within each strain.

Recent advances in the diagnosis of dermatophytosis

Dermatophytosis is a disease of global significance caused by pathogenic keratinolytic fungi called dermatophytes in both animals and humans. The recent taxonomy of dermatophytes classifies them into six pathogenic genera, namely Microsporum, Trichophyton, Epidermophyton, Nannizzia, Lophophyton and Arthroderma. It is because of the delayed diagnostic nature and low accuracy of dermatophyte detection by conventional methods that paved the path for the evolution of molecular diagnostic techniques, which provide the accurate and rapid diagnosis of dermatophytosis for an appropriate, timely antifungal therapy that prevents the nonspecific over-the-counter self-medication. This review focuses on the importance of rapid and accurate diagnosis of dermatophytosis, limitations of conventional methods, selection of targets in diagnosis, and factors affecting sensitivity and specificity of various molecular diagnostic technologies in the diagnosis of dermatophytosis. Generally, all the molecular techniques have a significant edge over the conventional methods of culture and microscopy in the dermatophytosis diagnosis. However, in mycology laboratory, the suitability of any molecular diagnostic technique in the diagnosis of dermatophytosis is driven by the requirement of time, economy, complexity, the range of species spectrum detected and the scale of diagnostic output required. Thus, various choices involved in the pursuit of a diagnosis of dermatophytosis are determined by the available conditions and the facilities in the laboratory.

Epidermophyton floccosum: nucleotide sequence analysis and antifungal susceptibility testing of 40 clinical isolates

Purpose. Epidermophyton floccosum is an anthropophilic dermatophyte species, which is one of the common causative agents of dermatophytosis in different parts of the world. The aim of the present investigation was to evaluate the genetic diversity of E. floccosum strains isolated from different parts of Iran and to define the in vitro susceptibility profiles of seven antifungal drugs against these clinical isolates.Methodology. Forty clinical strains of E. floccosum isolated from 40 patients with dermatophytosis were subjected to DNA extraction and PCR amplification of the ITS rDNA region using universal primers ITS1 and ITS4. The in vitro activities of griseofulvin, itraconazole, voriconazole, posaconazole, caspofungin, ketoconazole and terbinafine were determined using a broth microdilution method according to the CLSI-M-38A2 protocol.Results. A mean genetic similarity of 99.5 % was found between E. floccosum strains, with intraspecies differences ranging from 0 to 3 nt. The geometric mean (GM) MICs and minimum effective concentrations (MECs) across all isolates were, in increasing order, as follows: terbinafine (GM=0.018 mg l^-1), posaconazole (GM=0.022 mg l^-1), itraconazole (GM=0.034 mg l^-1) and voriconazole (GM=0.045 mg l^-1), which had low MICs against all tested strains, whereas caspofungin (GM=0.22 mg l^-1), ketoconazole (GM=0.41 mg l^-1) and griseofulvin (GM=0.62 mg l^-1) demonstrated higher MICs.Conclusion. Our study showed low intraspecies variation within strains of E. floccosum. Furthermore, terbinafine, posaconazole, itraconazole and voriconazole were shown to be the most potent antifungal drugs against E. floccosum strains.

Genus- and species-level identification of dermatophyte fungi by surface-enhanced Raman spectroscopy

This paper demonstrates that surface-enhanced Raman spectroscopy (SERS) coupled with principal component analysis (PCA) can serve as a fast and reliable technique for detection and identification of dermatophyte fungi at both genus and species level. Dermatophyte infections are the most common mycotic diseases worldwide, affecting a quarter of the human population. Currently, there is no optimal method for detection and identification of fungal diseases, as each has certain limitations. Here, for the first time, we have achieved with a high accuracy, differentiation of dermatophytes representing three major genera, i.e. Trichophyton, Microsporum, and Epidermophyton. Two first principal components (PC), namely PC-1 and PC-2, gave together 97% of total variance. Additionally, species-level identification within the Trichophyton genus has been performed. PC-1 and PC-2, which are the most diagnostically significant, explain 98% of the variance in the data obtained from spectra of: Trichophyton rubrum, Trichophyton menatgrophytes, Trichophyton interdigitale and Trichophyton tonsurans. This study offers a new diagnostic approach for the identification of dermatophytes. Being fast, reliable and cost-effective, it has the potential to be incorporated in the clinical practice to improve diagnostics of medically important fungi.

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.

MALDI-TOF-Based Dermatophyte Identification

MALDI-TOF MS has become increasingly popular for microorganism identification in the routine laboratory. Compared with conventional morphology-based techniques, MALDI-TOF is relatively inexpensive (per-unit identification), involves a rapid result turnaround time and yields more accurate results without the need for highly qualified staff. However, this technology has been technically difficult to implement for filamentous fungi identification. Identification of dermatophytes, a type of filamentous fungi, remains particularly challenging, partly due to the lack of clear species definition for some taxa or within some species complexes. Review of the ten studies published between 2008 and 2015 shows that the accuracy of MALDI-TOF MS-based identification varied between 13.5 and 100 % for dermatophytes. This variability was partly due to inconsistencies concerning critical steps of the routine clinical laboratory process. Use of both a complete formic acid-acetonitrile protein extraction step and a manufacturer library supplemented with homemade reference spectra is essential for an accurate species identification. This technique is conversely unaffected by variations in other routine clinical laboratory conditions such as culture medium type, incubation time and type of mass spectrometry instrument. Provided that a reference spectra library is adequate for dermatophyte identification, MALDI-TOF MS identification is more economical and offers an accuracy comparable to that of DNA sequencing. The technique also represents an advantageous alternative to the protracted and labor-intensive dermatophyte identification via macroscopic and microscopic morphology in the routine clinical laboratory.

Diagnostic performance of molecular and conventional methods for identification of dermatophyte species from clinically infected Arabian horses in Egypt

BACKGROUND

Rapid and accurate identification of dermatophytes is crucial for the effective control of disease outbreaks. Current methods based on culture and microscopic characteristics may require weeks before positive identification is made.

OBJECTIVES

To (i) identify the most common pathogenic dermatophytes affecting Arabian horses; (ii) compare the performance of direct microscopy (DM), culture, PCR using hair samples (PCRhair ) and PCR based on culture isolates (PCRculture ) for the diagnosis of dermatophytosis.

METHODS

Samples of hair and crusts of skin lesions from Arabian horses were collected on a monthly basis by scraping skin of affected horses. Samples were divided into three portions: the first portion was used for microscopic examination, the second for culture and the third portion for PCR amplification of intergenic spacer (ITS) regions.

RESULTS

Out of 200 horses examined, 70 (35%) showed cutaneous lesions characteristic of dermatophytosis. DM revealed that 70.4% were positive for fungal elements and 85.7% were culture positive. The identified species were Microsporum canis, Trichophyton verrucosum, T. mentagrophytes var. mentagrophytes and M. equinum. Among 25 selected samples, 64, 92, 91.3 and 52% were positive for dermatophytes, as determined by DM, culture, PCRculture and PCRhair , respectively.

CONCLUSIONS

The dermatophytes M. canis, T. verrucosum, T. mentagrophytes var. mentagrophytes and M. equinum were the most common cause of dermatophytosis in Arabian horses. Although the number of samples was small, the ITS-based PCR may be a useful diagnostic tool when combined with culture.

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.

Are the classic diagnostic methods in mycology still state of the art?

The diagnostic workup of cutaneous fungal infections is traditionally based on microscopic KOH preparations as well as culturing of the causative organism from sample material. Another possible option is the detection of fungal elements by dermatohistology. If performed correctly, these methods are generally suitable for the diagnosis of mycoses. However, the advent of personalized medicine and the tasks arising therefrom require new procedures marked by simplicity, specificity, and swiftness. The additional use of DNA-based molecular techniques further enhances sensitivity and diagnostic specificity, and reduces the diagnostic interval to 24-48 hours, compared to weeks required for conventional mycological methods. Given the steady evolution in the field of personalized medicine, simple analytical PCR-based systems are conceivable, which allow for instant diagnosis of dermatophytes in the dermatology office (point-of-care tests).

Development a diagnostic pan-dermatophyte TaqMan probe real-time PCR assay based on beta tubulin gene

Early differentiation of dermatophytosis from other cutaneous mycoses is essential to avoid inaccurate therapy. DNA-based techniques including real-time PCR have increasingly been considered for detection of fungal elements in clinical specimens. In this study, after partial sequence analysis of beta tubulin (BT2) gene in 13 common and rare pathogenic dermatophyte species, a pan-dermatophyte primer and probe set was designed in a TaqMan probe-based PCR format. The sensitivity and specificity of the system was tested with 22 reference strains of dermatophytes, 234 positive clinical specimens, 32 DNA samples extracted from normal nails, several fungi other than dermatophytes and human DNAs. Analytical detection limit of the designed PCR on serially diluted DNAs of prepared recombinant plasmid indicated that only five molecules per sample are the minimum number for reliable detection by the assay. A total of 226 out of 234 (96.5%) DNAs extracted from clinical samples, but none of the 32 nail samples, from healthy volunteers were positive in PCR. The real-time PCR targeted beta tubulin gene established in this study could be a sensitive diagnostic tool which is significantly faster than the conventional culture method and should be useful in the clinical settings, in large-scale epidemiological studies and in clinical trials of antifungal therapy.

Epidemiological Aspects of Dermatophytosis in Khuzestan, southwestern Iran, an Update

Dermatophytosis is among the most common superficial mycoses in Iran. The purpose of this report was to update the clinical and mycological features of human dermatophytosis in the Khuzestan, southwestern Iran. In the framework of a one-year survey, a total of 4120 skin, hair and nail samples obtained from the outpatients with symptoms suggestive of tinea were analyzed by using direct microscopy, culture and molecular identification methods. Strains isolated from cultures were subjected to amplification of the nuclear rDNA ITS regions in a PCR assay followed by an early established RFLP analysis. For confirmation of species identification, 100 isolates as representatives of all presumable species were subjected to ITS sequencing. Infection was confirmed in 1123 individuals (27.25 %) in the age range of 1-89 years by direct microscopy and/or culture including 603 males versus 520 females. Frequencies of infections were the highest and the lowest in age groups of 21-30 and 11-20 years, respectively. Tinea corporis was the most prevalent clinical manifestation followed by tinea cruris, tinea capitis, tinea manuum, tinea pedis, tinea unguium, tinea faciei and tinea barbae. Trichophyton interdigitale (58.7 %) was the most dominant isolate followed by Epidermophyton floccosum (35.4 %), Microsporum canis (3 %), T. rubrum (1.5 %), T. species of Arthroderma benhamiae (0.5 %), T. tonsurans (0.3 %) and T. violaceum (0.3 %). Other species included M. gypseum, M. fulvum and T. verrucosum (each one 0.1 %). Such a high occurrence of infection with T. interdigitale, which has not been reported from Iran, is due to the use of accurate molecular methods based on new species concept in dermatophytes. The prevalence of dermatophytoses caused by zoophilic species remarkably increased and Trichophyton species of A. benhamiae has emerged as a new agent of dermatophytosis in southwestern Iran, while infections due to anthropophilic species, except E. floccosum, took a decreasing trend.

Use of Padlock Probes and Rolling Circle Amplification (RCA) for Rapid Identification of Trichophyton Species, Related to Human and Animal Disorder

Background:

The high degree of phenotypic similarity among Trichophyton species makes their identification difficult.

Objectives:

The current study aims to establish the use of rolling circle amplification (RCA) based on internal transcribed spacer ribosomal DNA (ITS rDNA) as a powerful, simple, and rapid procedure for distinguishing closely related organisms, and specifically to identify Trichophyton species, which cause human and animal disorders.

Materials and Methods:

A total of sixty-one isolates belonging to three species of Trichophyton were identified to the species level based on microscopic and macroscopic examinations and their ITS rDNA regions were sequenced. Three specific circular oligonucleotide probes targeting the ITS1 and ITS2 regions were designed to differentiate Trichophyton rubrum, T. mentagrophytes, and T. tonsurans.

Results:

Of the 61 putative Trichophyton clinical isolates, 52 were identified to the species level. The most common species was T. mentagrophytes var. interdigitale (31 isolates), followed by T. rubrum (11 isolates), T. tonsurans (9 isolates), and T. violaceum (1 isolates); moreover, 9 isolates were identified as non-Trichophyton species. The RCA method correctly identified four Trichophyton species and was 100% specific for each species. Neither cross-reaction between the examined species of Trichophyton nor false positive or false negative results were observed.

Conclusions:

Species identification of Trichophyton is crucially important for epidemiological and phylogenetic purposes and for genotype delineation. RCA based on ITS polymorphisms can be used to generate identification barcodes and as an alternative to DNA sequencing; it is a very fast, specific, and economical tool for species identification.

Isolation of dermatophytes (and other fungi) from human nail and skin dust produced by podiatric medical treatments in Australia

BACKGROUND

Podiatric physicians routinely use electric drills for the treatment of nail and skin conditions. The grinding process produces human nail and skin dust that is generally vacuumed into bags in the grinding unit. Many of the nails are thought to be mycotic, particularly because they are obtained from patients with symptoms of dermatophyte infections. Currently, there is limited information available on the detection of fungi from nail dust samples. Herein, we attempt to address this situation and outline some of the difficulties that pathology laboratories face in isolating and identifying dermatophytes from nail samples.

METHODS

Fifty nail dust bags from podiatric medical clinics across all of the states and territories of Australia were collected and analyzed. Samples from the bags were inoculated onto primary isolation media. Fungal colonies that grew were then inoculated onto potato dextrose agar for identification using standard morphological (macroscopic and microscopic) features.

RESULTS

One hundred fifty-one colonies of dermatophytes were identified from 43 of the 50 samples. In addition 471 nondermatophyte molds were isolated, along with some yeasts and bacteria.

CONCLUSIONS

The most common dermatophytes isolated were from the Trichophyton mentagrophytes/interdigitale complexes. Trichophyton rubrum, Trichophyton tonsurans, Trichophyton soudanense, and Epidermophyton floccosum were also isolated. An unidentified group of dermatophytes was also present. The three most common genera of nondermatophyte molds were Aspergillus, Penicillium, and Scopulariopsis, all of which have been implicated in onychomycosis and more general disease. The presence of viable fungal pathogens in the dust could potentially pose a health problem to podiatric physicians.

Molecular identification and classification of Trichophyton mentagrophytes complex strains isolated from humans and selected animal species

Species differentiation within Trichophyton mentagrophytes complex group currently poses a major diagnostic challenge, with molecular methods increasingly supplementing classical identification based on the morphological and physiological properties of the fungi. Diagnostic and epidemiological research aimed at determining the source and means of transmission of dermatophytoses in both humans and animals requires not only species differentiation of isolates but also differentiation within species. The study was conducted on 24 isolates originating in humans and various animal species with clinical symptoms of dermatophytosis. The analysis included phenotypical identification methods and molecular methods: internal transcribed spacer sequencing and ITS-restriction fragment length polymorphism (RFLP) with multi-enzyme restriction. ITS sequence analysis identified the isolates to species - Trichophyton interdigitale, Arthroderma benhamiae and A. vanbreuseghemii, and ITS-RFLP detected six different genotypes. Genotypes I, II and III characterised strains belonging to A. benhamiae, genotype IV characterised the A. vanbreuseghemii strain, and genotypes V and VI occurred only within the species T. interdigitale. Strains isolated from guinea pigs were dominant within genotype I, while genotype II was found mainly in strains from foxes. Multi-enzyme restriction analysis of this region enables intraspecific differentiation, which may be useful in epidemiological research, particularly in determining the source of infections.

Biology and Diseases of Rabbits

Beginning in 1931, an inbred rabbit colony was developed at the Phipps Institute for the Study, Treatment and Prevention of Tuberculosis at the University of Pennsylvania. This colony was used to study natural resistance to infection with tuberculosis (Robertson et al., 1966). Other inbred colonies or well-defined breeding colonies were also developed at the University of Illinois College of Medicine Center for Genetics, the Laboratories of the International Health Division of The Rockefeller Foundation, the University of Utrecht in the Netherlands, and Jackson Laboratories. These colonies were moved or closed in the years to follow. Since 1973, the U.S. Department of Agriculture has reported the total number of certain species of animals used by registered research facilities (1997). In 1973, 447,570 rabbits were used in research. There has been an overall decrease in numbers of rabbits used. This decreasing trend started in the mid-1990s. In 2010, 210,172 rabbits were used in research. Despite the overall drop in the number used in research, the rabbit is still a valuable model and tool for many disciplines.

Translation elongation factor 1-α gene as a potential taxonomic and identification marker in dermatophytes

Intra- and interspecies variations of the translation elongation factor 1-α (Tef-1α) gene were evaluated as a new identification marker in a wide range of dermatophytes, which included 167 strains of 30 species. An optimized pan-dermatophyte primer pair was designed, and the target was sequenced. Consensus sequences were used for multiple alignment and phylogenetic tree analysis and the levels of intra- and interspecific nucleotide polymorphism were assessed. Between species, the analyzed part of the Tef-1α gene varied in length from 709 to 769 nucleotides. Significant numbers of species including Trichophyton rubrum, T. tonsurans, T. schoenleinii, T. concentricum, T. violaceum, Epidermophyton floccosum, Microsporum ferrugineum, M. canis, M. audouinii, T. equinum, T. eriotrephon, and T. erinacei were invariant in Tef-1α and had sufficient barcoding distance with neighboring species. Although overall consistency was found between ITS phylogeny as the current molecular marker of dermatophytes and Tef-1α, a higher discriminatory power of Tef-1α appeared particularly useful in some clades of closely related species such as the A. vanbreuseghemii, T. rubrum, A. benhamiae, and A. otae complexes. Nevertheless, we stress that a single gene can not specify species borderlines among dermatophytes and multiple lines of evidence based on a multilocus inquiry may ascertain an incontrovertible evaluation of kinship.

A comparative study on morphological versus molecular identification of dermatophyte isolates

OBJECTIVE

Dermatophytes are taxonomically classified in the genera Trichophyton, Microsporum, and Epidermophyton. Pleomorphism, cultural variability, slow growth and sporulation, and the need for additional physiological tests make dermatophytes notoriously difficult to identify. The present study aimed to compare the results of morphological and molecular identification of certain groups of clinical isolates of dermatophytes with a view to evaluating the accuracy of molecular methods.

PATIENTS AND METHODS

For each sample, the ITS1-5.8S-ITS2 rDNA region was amplified using the primers ITS1 and ITS4. PCR products were subjected to restriction fragment length polymorphism (RFLP) analysis using the enzyme MvaI and isolate identification was performed by comparing the electrophoretic RFLP patterns with reference profiles obtained previously. Finally, paired comparative analyses of molecular and conventional methods were performed.

RESULTS

While morphology results from routine daily reports of the laboratories indicated that 18 (6.8%) and 136 (52.10%) of the isolates were T. rubrum and T. interdigitale, respectively, PCR-RFLP results suggested that T. rubrum was the most common etiological agent of ringworm accounting for 94 (36.01%), followed by T. interdigitale accounting for 71 (27.20%). Interestingly, 80.8% out of the 94 isolates identified as T. rubrum by molecular testing had been identified by morphological examination as belonging to different species, such as T. interdigitale (75.5%), E. floccosum (2.1%) and M. canis, T. verrucosum, and T. tonsurans (each 1.06%). Ten strains out of 261 (T. interdigitale, n=8; E. floccosum, n=2) had been defined as unknown species by morphological tests.

CONCLUSION

An unexpected high percent of isolates identified as T. interdigitale by conventional methods were in effect T. rubrum shown by PCR-RFLP, and regarding the necessity of correct identification of dermatophytes recovered from different clinical forms of the infection, we highly recommend ITS-sequencing or ITS-RFLP of the isolates, particularly for epidemiological research studies.

Nucleotide sequence analysis of beta tubulin gene in a wide range of dermatophytes

We investigated the resolving power of the beta tubulin protein-coding gene (BT2) for systematic study of dermatophyte fungi. Initially, 144 standard and clinical strains belonging to 26 species in the genera Trichophyton, Microsporum, and Epidermophyton were identified by internal transcribe spacer (ITS) sequencing. Subsequently, BT2 was partially amplified in all strains, and sequence analysis performed after construction of a BT2 database that showed length ranged from approximately 723 (T. ajelloi) to 808 nucleotides (M. persicolor) in different species. Intraspecific sequence variation was found in some species, but T. tonsurans, T. equinum, T. concentricum, T. verrucosum, T. rubrum, T. violaceum, T. eriotrephon, E. floccosum, M. canis, M. ferrugineum, and M. audouinii were invariant. The sequences were found to be relatively conserved among different strains of the same species. The species with the closest resemblance were Arthroderma benhamiae and T. concentricum and T. tonsurans and T. equinum with 100% and 99.8% identity, respectively; the most distant species were M. persicolor and M. amazonicum. The dendrogram obtained from BT2 topology was almost compatible with the species concept based on ITS sequencing, and similar clades and species were distinguished in the BT2 tree. Here, beta tubulin was characterized in a wide range of dermatophytes in order to assess intra- and interspecies variation and resolution and was found to be a taxonomically valuable gene.

[Taxonomic study of clinic isolates of Trichophyton in Rosario, Argentina]

Due to the pleomorphism and cultural variability displayed by species of the genus Trichophyton, the identification methods based solely on morphological features are usually insufficient for their classification. The goal of the present work was to test a set of phenotypic methods in order to identify fungal isolates that belong to the aforementioned genus. These methods were based on a molecular taxonomic technique used as standard. Clinical isolates (56) were used as samples along with 6 reference strains. Macro and micromorphological studies were performed as well as biochemical and physiological tests such as in vitro hair perforation, nutritional requirements in Trichophyton agar media, urease production and growth on bromocresol purple-milk. solids-glucose (BCP-MS-G) agar. Additionally, PCR fingerprinting using the (GACA)4 primer was employed. As a result of the PCR method, specific profiles were observed for Microsporum canis, Epidermophyton floccosum, Trichophyton rubrum and Trichophyton interdigitale. Identical profiles were obtained for Arthroderma benhamiae y Trichophyton erinacei. Of the total number of clinical isolates, 39 matched the T. rubrum profile while 13 corresponded to A. benhamiae and 4 to T. interdigitale. The most useful phenotypic test to differentiate between T. rubrum and T. mentagrophytes complex strains was alkalinization of the BCP-MS-G medium. Phenotypic tests did not allow differentiation among the T. mentagrophytes complex species. On the other hand, the molecular technique allowed characterization of T. rubrum isolates as well as of those observed in our study and included in the T. mentagrophytes complex: T. interdigitale and Trichophyton sp., the anamorph of A. benhamiae.

Tinea pedis: the etiology and global epidemiology of a common fungal infection

Tinea pedis, which is a dermatophytic infection of the feet, can involve the interdigital web spaces or the sides of the feet and may be a chronic or recurring condition. The most common etiological agents are anthropophiles, including Trichophyton rubrum sensu stricto, which is the most common, followed by Trichophyton interdigitale and Epidermophyton floccosum. There has been a change in this research arena, necessitating a re-evaluation of our knowledge on the topic from a multidisciplinary perspective. Thus, this review aimed to provide a solid overview of the current status and changing patterns of tinea pedis. The second half of the twentieth century witnessed a global increase in tinea pedis and a clonal spread of one major etiologic agent, T. rubrum. This phenomenon is likely due to increases in urbanization and the use of sports and fitness facilities, the growing prevalence of obesity and the aging population. For optimal patient care and management, the diagnosis of tinea pedis should be verified by microbiological analysis. In this review, we discuss the epidemiology, clinical forms, complications and mycological characteristics of tinea pedis and we highlight the pathogenesis, prevention and control parameters of this infection.

Restriction analysis of β-tubulin gene for differentiation of the common pathogenic dermatophytes

BACKGROUND

Identification of dermatophytes at the species level, relying on macro- and microscopic properties of the colonies is time-consuming, questioned in many circumstances, and requires considerable expertise. In this study, we examined the potency of a new genetic marker, β-tubulin (BT2) gene, for differentiation of dermatophytes in an in silico and experimental restriction fragment length polymorphism (RFLP) profile.

METHODS

The BT2 sequences of dermatophyte species were retrieved from GenBank and analyzed using bioinformatics softwares to choose suitable restriction enzyme(s). Forty reference culture collections and 100 clinical isolates were PCR-amplified using the primers T1 and Bt2b and consequently subjected to virtual RFLP analysis. The dermatophytes were identified according to specific lengths of bands in agarose gel electrophoresis.

RESULTS

After digestion of partially amplified β-tubulin gene with the restriction enzyme FatI, three dermatophyte species, that is, Microsporum gypseum, M. canis, and Trichophyton verrucosum yielded unique restriction maps while the remaining species including T. interdigitale, T. rubrum, T. tonsurans, T. schoenleinii, and T. violaceum, were identified by further restriction digestion by Alw21I, MwoI, and HpyCH4V endonucleases. The length of RFLP products was same as of those expected by computer analysis.

CONCLUSION

The two-step BT2 restriction mapping used in this study is an effective tool for reliable differentiation of the clinically relevant species of dermatophytes.

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.

A MALDI-TOF MS procedure for clinical dermatophyte species identification in the routine laboratory

The conventional identification of dermatophytes requires a long turnaround time and highly skilled mycologists. We have recently developed a tandardized matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) assay to routinely identify molds of potential clinical significance. This study objective was to determine if this same assay could also be employed to identify clinical dermatophytes in the routine laboratory setting. The effects of the inclusion of cycloheximide in the culture medium and incubation time were tested after building a reference spectra library that included 48 well-characterized isolates of 17 dermatophyte species. Then these same isolates were prospectively identified using this library. MALDI-TOF MS-based identification was effective regardless of the presence of cycloheximide or incubation time as 130/133 (97.8%) of the clinical isolates were appropriately identified. Two Microsporum canis isolates yielded uninformative spectra and one M. audouinii isolate was misidentified. Since one only requires a small colony for MALDI-TOF MS analysis, accurate identifications were obtained in 3-6 days and, specifically, before the appearance of their characteristic morphological features. Consequently, identification turnaround time was dramatically reduced as compared to that needed for conventional morphological identification. In conclusion, this standardized MALDI-TOF MS-based identification procedure for filamentous fungi effectively identifies clinical dermatophyte isolates and drastically reduces the response times in the routine clinical laboratory.

Identification of dermatophytes by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

In this study we evaluated the suitability of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) for the identification of dermatophytes in diagnostic laboratories. First, a spectral database was built with 108 reference strains belonging to 18 species of the anamorphic genera Epidermophyton, Microsporum and Trichophyton. All strains were well characterized by morphological criteria and ITS sequencing (gold standard). The dendrogram resulting from MALDI-TOF mass spectra was almost identical with the phylogenetic tree based on ITS sequencing. Subsequently, MALDI-TOF MS SuperSpectra were created for the identification of Epidermophyton floccosum, Microsporium audouinii, M. canis, M. gypseum (teleomorph: Arthroderma gypseum), M. gypseum (teleomorph: A. incurvatum), M. persicolor, A. benhamiae (Tax. Entity 3 and Am-Eur. race), T. erinacei, T. interdigitale (anthropophilic and zoophilic populations), T. rubrum/T. violaceum, T. tonsurans and T. terrestre. Because T. rubrum and T. violaceum did not present enough mismatches, a SuperSpectrum covering both species was created, and differentiation between them was done by comparison of eight specific peptide masses. In the second part of this study, MALDI-TOF MS with the newly created SuperSpectra was tested using 141 clinical isolates representing nine species. Analyses were done with 3-day-old cultures. Results were compared to morphological identification and ITS sequencing; 135/141 (95.8%) strains were correctly identified by MALDI-TOF MS compared to 128/141 (90.8%) by morphology. Therefore, MALDI-TOF MS has proven to be a useful and rapid identification method for dermatophytes.

[New apects in the diagnosis and therapy of dermatomycoses]

Recent observations indicate that Arthroderma benhamiae can cause bullous tinea, that onychomycosis increasingly occurs in children and that molds can cause tinea-like lesions. If a mycotic infection is suspected, the pathogen needs to be identified. The first genetic assays for the detection of dermatophytes have successfully been tested under routine conditions. Using appropriate techniques, genetic diagnosis is faster and more sensitive than a culture. Laboratory standards that would facilitate widespread implementation of genetic identification of dermatophytes have not yet been established. For the identification of yeasts, MALDI-TOF has already been established in many laboratories. This method is being refined for the diagnosis of hyphomycetes too. Newer antimycotics that are approved for certain systemic mycoses such as the triazoles voriconazole and posaconazole and the echinocandines caspofungin, micafungin und anidulafungin may be considered for dermatomycoses that cannot be treated by other therapies. Thermotherapy and photodynamic therapy are additional options in particularly difficult cases.

An improved molecular diagnostic assay for canine and feline dermatophytosis

The few studies attempting to specifically characterize dermatophytes from hair samples of dogs and cats using PCR-based methodology relied on sequence-based analysis of selected genetic markers. The aim of the present investigation was to establish and evaluate a PCR-based approach employing genetic markers of nuclear DNA for the specific detection of dermatophytes on such specimens. Using 183 hair samples, we directly compared the test results of our one-step and nested-PCR assays with those based on conventional microscopy and in vitro culture techniques (using the latter as the reference method). The one step-PCR was highly accurate (AUC > 90) for the testing of samples from dogs, but only moderately accurate (AUC = 78.6) for cats. A nested-PCR was accurate (AUC = 93.6) for samples from cats, and achieved higher specificity (94.1 and 94.4%) and sensitivity (100 and 94.9%) for samples from dogs and cats, respectively. In addition, the nested-PCR allowed the differentiation of Microsporum canis from Trichophyton interdigitale (zoophilic) and geophilic dermatophytes (i.e., Microsporum gypseum or Trichophyton terrestre), which was not possible using the one step-assay. The PCRs evaluated here provide practical tools for diagnostic applications to support clinicians in initiating prompt and targeted chemotherapy of dermatophytoses.

Molecular diagnosis of dermatophyte infections

PURPOSE OF REVIEW

Recent advances in the molecular diagnostics of dermatophytosis may improve speed, specificities and sensitivities. This review provides an update on the current available molecular techniques for the diagnosis of dermatophytosis.

RECENT FINDINGS

Molecular diagnostics of dermatophytosis relate to the direct detection of dermatophyte DNA in clinical specimens. Important challenges have been associated with the DNA extraction procedures, which despite improvement still lack consensus, and the fact that phenotypic species classification not always translates into distinct molecular taxonomic entities. Molecular methods are divided into conventional PCR, real-time PCR and post-PCR techniques. The former benefits from simplicity and being less expensive to implement, real-time PCR is less laborious, may enable a broader spectrum of simultaneous species detections and the closed system reduces contamination risk, whereas post-PCR strategies may increase the number of species identified but prolong the turnaround time, and the processing of PCR products increases the laboratory contamination risk.

SUMMARY

Current molecular methods are on the verge of overcoming most of the early challenges regarding dermatophyte taxonomy, DNA extraction procedures and species specificity, and thus may lead to an increased adoption of such methods. This may point towards a novel consensus in which molecular methods supplement or even replace classical diagnosis of dermatophytosis.

Trichophyton bullosum: a new zoonotic dermatophyte species

We report the first human case of dermatophytosis caused by Trichophyton bullosum in a 21-year-old male who had a skin lesion located on his forearm. The dermatophyte was isolated in culture and further identified by sequence analysis of internal transcripted spacer regions. The species T. bullosum is a zoophilic dermatophyte rarely isolated from the coat of horses in Africa and Asia. In the present case, it was probably transmitted by contact with an infected donkey in a rural area in France. Antifungal therapy led to remission of the lesion in the patient after 2 months of treatment. T. bullosum ITS region sequences were closely related to those of the African species of Arthroderma benhamiae and grouped in a zoophilic cluster with Trichophyton verrucosum, T. erinacei and the Trichophyton anamorph of A. benhamiae (zoophilic species of the T. mentagrophytes complex). Systematic molecular identification could contribute to an accurate identification of this unusual species.

Histopathologic diagnosis of fungal infections in the 21st century

Fungal infections are becoming more frequent because of expansion of at-risk populations and the use of treatment modalities that permit longer survival of these patients. Because histopathologic examination of tissues detects fungal invasion of tissues and vessels as well as the host reaction to the fungus, it is and will remain an important tool to define the diagnostic significance of positive culture isolates or results from PCR testing. However, there are very few instances where the morphological characteristics of fungi are specific. Therefore, histopathologic diagnosis should be primarily descriptive of the fungus and should include the presence or absence of tissue invasion and the host reaction to the infection. The pathology report should also include a comment stating the most frequent fungi associated with that morphology as well as other possible fungi and parasites that should be considered in the differential diagnosis. Alternate techniques have been used to determine the specific agent present in the histopathologic specimen, including immunohistochemistry, in situ hybridization, and PCR. In addition, techniques such as laser microdissection will be useful to detect the now more frequently recognized dual fungal infections and the local environment in which this phenomenon occurs.