The pathogenesis of dermatophyte infections in human skin sections

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.

Yeast cell microcarriers for delivery of a model bioactive compound in skin

This study aimed at developing a cell-based encapsulation carrier for topical delivery of bioactives to the skin. The overall objectives were to evaluate affinity of the yeast-cell based carrier to bind to the skin surface following topical application and to quantify controlled release of curcumin as a model bioactive in ex-vivo skin models using a combination of imaging, modeling and analytical measurements. Both porcine skin tissue and clinically obtained human skin biopsies were studied. The results demonstrated that upon incubation with the ex-vivo skin tissues, the cell carriers rapidly bound to the skin surface following topical delivery and provided sustained release of encapsulated curcumin. The microcarrier binding and penetration of curcumin in the dermal compartment also showed to increase with incubation time. The average flux of curcumin in human skin biopsies J_p was 0.89 ± 0.02 μg/cm²/h. These results illustrated the potential of a novel cell-based carrier for high affinity binding to skin surface, efficient encapsulation of a model bioactive and controlled release from the cell carrier to the skin with enhanced permeation to the dermis section. Overall, this study demonstrated a new class of cost-effective carriers for improving delivery of bioactives to the skin and potentially other epithelial tissues.

Immunopathogenesis of Dermatophytoses and Factors Leading to Recalcitrant Infections

The pathogenesis of dermatophytic infections involves the interplay of three major factors: the dermatophyte, the inherent host defense, and the adaptive host immune response. The fungal virulence factors determine the adhesion and invasion of the skin while the immune response depends on an interaction of the pathogen-associated molecular patterns (PAMPs) and damage-associated molecular patterns (DAMP) with pattern recognition receptors (PRRs) of the host, which lead to a differential Th (T helper) 1, Th2, Th17, and Treg response. While anthropophilic dermatophytes Trichophyton rubrum and now increasingly by T. interdigitale subvert the immune response via mannans, zoophilic species are eliminated due to a brisk immune response. Notably, delayed-type hypersensitivity (Th1) response of T lymphocytes causes the elimination of fungal infection, while chronic disease caused by anthropophilic species corresponds to toll-like receptor 2 mediated IL (interleukin)-10 release and generation of T-regulatory cells with immunosuppressive potential. Major steps that determine the ultimate clinical course and chronicity include genetic susceptibility factors, impaired epidermal and immunological barriers, variations in the composition of sebum and sweat, carbon dioxide tension, skin pH, and topical steroid abuse. It is important to understand these multifarious aspects to surmount the problem of recalcitrant dermatophytosis when the disorder fails conventional therapeutic agents.

The stuA gene controls development, adaptation, stress tolerance, and virulence of the dermatophyte Trichophyton rubrum

The APSES family, comprising of the transcriptional regulators Asm1p, Phd1p, Sok2p, Efg1p, and StuA, is found exclusively in fungi and has been reported to control several cellular processes in these organisms. However, its function in dermatophytes has not yet been completely understood. Here, we generated two null mutant strains by deleting the stuA gene in the dermatophyte Trichophyton rubrum, the most common clinical isolate obtained from human skin and nail mycoses. The functional characterization of the knocked-out strains revealed the involvement of stuA in germination, morphogenesis of conidia and hyphae, pigmentation, stress responses, and virulence. Although the mutant strains could grow under several nutritional conditions, growth on the keratin medium, human nails, and skin was impaired. The co-culture of stuA mutants with human keratinocytes revealed enhanced development. Moreover, a stuA mutant grown on the keratin substrate showed a marked decrease in the transcript numbers of the hydrophobin encoding gene (hypA), suggesting the involvement of stuA in the molecular mechanisms underlying mechanosensing during the fungi-host interaction. In addition, bioinformatics analyses revealed the potential involvement of StuA in different biological processes such as oxidation-reduction, phosphorylation, proteolysis, transcription/translation regulation, and carbohydrate metabolism. Cumulatively, the present study suggested that StuA is a crosstalk mediator of many pathways and is an integral component of the infection process, implying that it could be a potential target for antifungal therapy.

Visualising virulence factors: Trichophyton benhamiaes subtilisins demonstrated in a guinea pig skin ex vivo model

BACKGROUND

Dermatophytoses rank among the most frequent communicable diseases in humans, and the zoonotic transmission is increasing. The zoophilic dermatophyte Trichophyton (T.) benhamiae is nowadays one of the main causes of tinea faciei et corporis in children. However, scientific data on molecular pathomechanisms and specific virulence factors enabling this ubiquitous occurrence are scarce.

OBJECTIVES

To study tissue invasion and the expression of important virulence factors of T. benhamiae, isolates that were recovered from two groups of hosts (humans vs. guinea pigs (GP)) using an ex vivo skin model.

METHODS

After confirmation of species identity by ITS sequencing, CFU suspensions of dermatophyte isolates (n = 20) were applied to the skin infection model and cultured. Employing specific immunofluorescence staining techniques, the expression of subtilisin 3 and 6 and metallocarboxypeptidase A was analysed. The general mode of invasion was explored. Results were compared with biopsies of naturally infected GP.

RESULTS

All isolates were successfully recovered and proliferated well after application to the infection model. Progressive invasion of hyphae through all skin structures and destruction of explants were observed with early events being comparable to natural infection. An increasing expression of the examined virulence factors towards the end of culture was noticed but no difference between the two groups of isolates.

CONCLUSIONS

For the first time, important in vivo markers of dermatophytosis were visualised immunohistochemically in an ex vivo skin infection model and in skin biopsies of GP naturally infected with T. benhamiae. More research on the underlying pathomechanisms of dermatophyte infection is urgently needed.

Evaluation of an Explanted Porcine Skin Model to Investigate Infection with the Dermatophyte Trichophyton rubrum

Dermatophytosis is a fungal infection of skin, hair and nails, and the most frequently found causative agent is Trichophyton rubrum. The disease is very common and often recurring, and it is therefore difficult to eradicate. To develop and test novel treatments, infection models that are representative of the infection process are desirable. Several infection models have been developed, including the use of cultured cells, isolated corneocytes, explanted human skin or reconstituted human epidermis. However, these have various disadvantages, ranging from not being an accurate reflection of the site of infection, as is the case with, for example, cultured cells, to being difficult to scale up or having ethical issues (e.g., explanted human skin). We therefore sought to develop an infection model using explanted porcine skin, which is low cost and ethically neutral. We show that in our model, fungal growth is dependent on the presence of skin, and adherence of conidia is time-dependent with maximum adherence observed after ~ 2 h. Scanning electron microscopy suggested the production of fibril-like material that links conidia to each other and to skin. Prolonged incubation of infected skin leads to luxurious growth and invasion of the dermis, which is not surprising as the skin is not maintained in conditions to keep the tissue alive, and therefore is likely to lack an active immune system that would limit fungal growth. Therefore, the model developed seems useful to study the early stages of infection. Furthermore, we demonstrate that the model can be used to test novel treatment regimens for tinea infections.

In vitro models of dermatophyte infection to investigate epidermal barrier alterations

Fungal infections of the skin, known as dermatophytoses, are initiated at the epidermal barrier and lead to dysfunctions of the stratum corneum and cornified skin appendages. Dermatophytosis affects a significant part of the human population and, despite the availability of effective treatments, its prevalence is still increasing. Numerous dermatophyte species are able to induce lesions in both animals and humans, with different clinical pictures and host inflammatory responses. The understanding of the infectious process and of tissue responses has been impeded by discrepancies between observations in vivo or in research models. Indeed, cells cultured as monolayers do not undergo the keratinization process required to study the adherence and invasion of dermatophytes. Animal models lack relevance to study human dermatophytosis because of species-specific differences in the development of lesions and inflammatory responses. This review focuses on the recent development of cultured human skin equivalents, which partly overcomes those limitations and allows improved understanding of the pathogenesis of dermatophytosis in human being, especially the impacts of infection on epidermal barrier integrity.

Host- and pathogen-dependent susceptibility and predisposition to dermatophytosis

Dermatophytes are a highly specialized group of keratinophilic and keratinolytic filamentous fungi causing a ringworm disease called dermatophytosis or superficial mycoses. Although dermatophyte infections do not threaten the host's life, they lower its quality in humans by causing discomfort related to cosmetic problems and through their epidemiological significance, whereas in farm animals they are responsible for economic losses and constitute a source of the spread of spores. Evidence from countless observational studies that have been conducted over the last 90 years indicates that dermatophytes infect humans of every age, race, gender and socioeconomic status with strikingly high rates, as well as both farmed and wild animals in various health conditions and with various epidemiological statuses. However, the prevalence of superficial fungal infections is highly variable, since it depends on several parameters associated with the infected individual and the dermatophyte, their mutual interactions, and epidemiological and geographical factors. The curious disparity in dermatophyte infection patterns has prompted many investigators to search for a link between the host, the host's predispositions and susceptibility to the disease, and the dermatophyte species and virulence. Thus, the question arises as to whether, in addition to the generally recognized factors predisposing hosts to diseases, there are some other predispositions to dermatophyte infections in a species-specific host. In this review, we describe recent findings about the mechanism of dermatophyte infections, focusing on the adaptation of the fungi to the host and conditions predisposing each side to the disease.

Modeling dermatophytosis in reconstructed human epidermis: A new tool to study infection mechanisms and to test antifungal agents

Dermatophytosis is a superficial fungal infection of keratinized structures that exhibits an increasing prevalence in humans and is thus requesting novel prophylactic strategies and therapies. However, precise mechanisms used by dermatophytes to adhere at the surface of the human epidermis and invade its stratum corneum are still incompletely identified, as well as the responses provided by the underlying living keratinocytes during the infection. We hereby report development of an in vitro model of human dermatophytosis through infection of reconstructed human epidermis (RHE) by arthroconidia of the anthropophilic Trichophyton rubrum species or of the zoophilic Microsporum canis and Arthroderma benhamiae species. By modulating density of arthroconidia in the inoculum and duration of exposure to such pathogens, fungal infection limited to the stratum corneum was obtained, mimicking severe but typical in vivo situation. Fungal elements in infected RHE were monitored over time by histochemical analysis using periodic-acid Schiff-staining or quantified by qPCR-detection of fungal genes inside RHE lysates. This model brings improvements to available ones, dedicated to better understand how dermatophytes and epidermis interact, as well as to evaluate preventive and therapeutic agents. Indeed, miconazole topically added to RHE was demonstrated to inhibit fungal infection in this model.

Host Sensing by Pathogenic Fungi

The ability to cause disease extends from the ability to grow within the host environment. The human host provides a dynamic environment to which fungal pathogens must adapt to in order to survive. The ability to grow under a particular condition (i.e., the ability to grow at mammalian body temperature) is considered a fitness attribute and is essential for growth within the human host. On the other hand, some environmental conditions activate signaling mechanisms resulting in the expression of virulence factors, which aid pathogenicity. Therefore, pathogenic fungi have evolved fitness and virulence attributes to enable them to colonize and infect humans. This review highlights how some of the major pathogenic fungi respond and adapt to key environmental signals within the human host.

An invertebrate infection model for evaluating anti-fungal agents against dermatophytosis

Animal models of pathogenic infection are needed to evaluate candidate compounds for the development of anti-infectious drugs. Dermatophytes are pathogenic fungi that cause several infectious diseases. We established a silkworm dermatophyte infection model to evaluate anti-fungal drugs. Injection of conidia of the dermatophyte Arthroderma vanbreuseghemii into silkworms was lethal. A. vanbreuseghemii conidia germinated in liquid culture were more potent against silkworms than non-germinated conidia. Germinated conidia of other dermatophytes, Arthroderma benhamiae, Trichophyton rubrum, and Microsporum canis, also killed silkworms. Injection of heat-treated germinated A. vanbreuseghemii conidia did not kill silkworms, suggesting that only viable fungi are virulent. Injecting terbinafine or itraconazole, oral drugs used clinically to treat dermatophytosis, into the silkworm midgut had therapeutic effects against infection with germinated A. vanbreuseghemii conidia. When silkworms were injected with A. vanbreuseghemii expressing enhanced green fluorescent protein (eGFP), mycelial growth of the fungus was observed in the fat body and midgut. Injection of terbinafine into the silkworm midgut, which corresponds to oral administration in humans, inhibited the growth of A. vanbreuseghemii expressing eGFP in the fat body. These findings suggest that the silkworm infection model with eGFP-expressing dermatophytes is useful for evaluating the therapeutic activity of orally administered anti-fungal agents against dermatophytes.

Diagnosis and treatment of dermatophytosis in dogs and cats.: Clinical Consensus Guidelines of the World Association for Veterinary Dermatology

BACKGROUND

Dermatophytosis is a superficial fungal skin disease of cats and dogs. The most common pathogens of small animals belong to the genera Microsporum and Trichophyton. It is an important skin disease because it is contagious, infectious and can be transmitted to people.

OBJECTIVES

The objective of this document is to review the existing literature and provide consensus recommendations for veterinary clinicians and lay people on the diagnosis and treatment of dermatophytosis in cats and dogs.

METHODS

The authors served as a Guideline Panel (GP) and reviewed the literature available prior to September 2016. The GP prepared a detailed literature review and made recommendations on selected topics. The World Association of Veterinary Dermatology (WAVD) provided guidance and oversight for this process. A draft of the document was presented at the 8th World Congress of Veterinary Dermatology (May 2016) and was then made available via the World Wide Web to the member organizations of the WAVD for a period of three months. Comments were solicited and posted to the GP electronically. Responses were incorporated by the GP into the final document.

CONCLUSIONS

No one diagnostic test was identified as the gold standard. Successful treatment requires concurrent use of systemic oral antifungals and topical disinfection of the hair coat. Wood's lamp and direct examinations have good positive and negative predictability, systemic antifungal drugs have a wide margin of safety and physical cleaning is most important for decontamination of the exposed environments. Finally, serious complications of animal-human transmission are exceedingly rare.

Chemical Composition, Antibacterial and Antifungal Activities of Crude Dittrichia viscosa (L.) Greuter Leaf Extracts

The small amount of data regarding the antifungal activity of Dittrichia viscosa (L.) Greuter against dermatophytes, Malassezia spp. and Aspergillus spp., associated with the few comparative studies on the antimicrobial activity of methanolic, ethanolic, and butanolic extracts underpins the study herein presented. The total condensed tannin (TCT), phenol (TPC), flavonoid (TFC), and caffeoylquinic acid (CQC) content of methanol, butanol, and ethanol (80% and 100%) extracts of D. viscosa were assessed and their bactericidal and fungicidal activities were evaluated. The antibacterial, anti-Candida and anti-Malassezia activities were evaluated by using the disk diffusion method, whereas the anti-Microsporum canis and anti-Aspergillus fumigatus activities were assessed by studying the toxicity effect of the extracts on vegetative growth, sporulation and germination. The methanolic extract contained the highest TPC and CQC content. It contains several phytochemicals mainly caffeoylquinic acid derivatives as determined by liquid chromatography with photodiode array and electrospray ionisation mass spectrometric detection (LC/PDA/ESI-MS) analysis. All extracts showed an excellent inhibitory effect against bacteria and Candida spp., whereas methanolic extract exhibited the highest antifungal activities against Malassezia spp., M. canis and A. fumigatus strains. The results clearly showed that all extracts, in particular the methanolic extract, might be excellent antimicrobial drugs for treating infections that are life threatening (i.e., Malassezia) or infections that require mandatory treatments (i.e., M. canis or A. fumigatus).

Deep Dermatophytosis Caused by Zoophilic Strain of Trichophyton interdigitale with Successful Treatment of Itraconazole

We report a 66-year-old female patient with deep dermatophytosis caused by zoophilic strain of Trichophyton interdigitale, a rare granulomatous presentation of Trichophyton species infection in patients with underlying systemic diseases, and she was successfully cured by itraconazole. Since the identification of Trichophyton mentagrophytes complex had been misused for years, a brief discussion of molecular diagnosis and taxonomy of T. mentagrophytes complex is given. The pathogenesis and comparison with cases reported in the literature are also discussed.

A Trichophyton Rubrum Infection Model Based on the Reconstructed Human Epidermis - Episkin®

BACKGROUND

Trichophyton rubrum represents the most common infectious fungus responsible for dermatophytosis in human, but the mechanism involved is still not completely understood. An appropriate model constructed to simulate host infection is the prerequisite to study the pathogenesis of dermatophytosis caused by T. rubrum. In this study, we intended to develop a new T. rubrum infection model in vitro, using the three-dimensional reconstructed epidermis - EpiSkin ®, and to pave the way for further investigation of the mechanisms involved in T. rubrum infection.

METHODS

The reconstructed human epidermis (RHE) was infected by inoculating low-dose (400 conidia) and high-dose (4000 conidia) T. rubrum conidia to optimize the infection dose. During the various periods after infection, the samples were processed for pathological examination and scanning electron microscopy (SEM) observation.

RESULTS

The histological analysis of RHE revealed a fully differentiated epidermis with a functional stratum corneum, which was analogous to the normal human epidermis. The results of hematoxylin and eosin staining and the periodic acid-Schiff staining showed that the infection dose of 400 conidia was in accord with the pathological characteristics of host dermatophytosis caused by T. rubrum. SEM observations further exhibited the process of T. rubrum infection in an intuitionistic way.

CONCLUSIONS

We established the T. rubrum infection model on RHE in vitro successfully. It is a promising model for further investigation of the mechanisms involved in T. rubrum infection.

Genetic Predictors of Susceptibility to Dermatophytoses

Countless observational studies conducted over the last century reveal that dermatophytes infect humans of every age, race, gender, and socioeconomic status with strikingly high rates. The curious disparity in dermatophyte infection patterns observed within and between populations has led countless investigators to explore whether genetics underlie a susceptibility to, or confer protection against, dermatophyte infections. This paper examines the data that offer a link between genetics and dermatophytoses and discusses the underlying mechanisms that support these observations.

Transcription profile of Trichophyton rubrum conidia grown on keratin reveals the induction of an adhesin-like protein gene with a tandem repeat pattern

Background

Trichophyton rubrum is a cosmopolitan filamentous fungus that can infect human keratinized tissue (skin, nails and, rarely, hair) and is the major agent of all chronic and recurrent dermatophytoses. The dermatophyte infection process is initiated through the release of arthroconidial adhesin, which binds to the host stratum corneum. The conidia then germinate, and fungal hyphae invade keratinized skin structures through the secretion of proteases. Although arthroconidia play a central role in pathogenesis, little is known about the dormancy and germination of T. rubrum conidia and the initiation of infection. The objective of this study was to evaluate the transcriptional gene expression profile of T. rubrum conidia during growth on keratin- or elastin-containing medium, mimicking superficial and deep dermatophytosis, respectively.

Results

A transcriptional profiling analysis was conducted using a custom oligonucleotide-based microarray by comparing T. rubrum conidia grown on elastin and keratin substrates. This comparison shows differences according to protein source used, but consisted of a very small set of genes, which could be attributed to the quiescent status of conidia. The modulated genes were related to the dormancy, survival and germination of conidia, including genes involved in the respiratory chain, signal transduction and lipid metabolism. However, an induction of a great number of proteases occurred when T. rubrum was grown in the presence of keratin such as the subtilisin family of proteases (Sub 1 and Sub 3) and leucine aminopeptidase (Lap 1 and Lap 2). Interestingly, keratin also promoted the up-regulation of a gene encoding an adhesin-like protein with a tandem repeat sequence. In silico analysis showed that the protein contains a domain related to adhesin that may play a role in host-pathogen interactions. The expression of this adhesin-like gene was also induced during the co-culture of T. rubrum with a human keratinocyte cell line, confirming its role in fungal-host interactions.

Conclusion

These results contribute to the discovery of new targets involved in the adhesion of conidia and the maintenance of conidial dormancy, which are essential for triggering the process of infection and the chronicity of dermatophytosis.

In vitro and ex vivo infection models help assess the molecular aspects of the interaction of Trichophyton rubrum with the host milieu

Dermatophytes are fungal pathogens that cause cutaneous infections such as onychomycosis and athlete's foot in both healthy and immunocompromised patients.Trichophyton rubrum is the most prevalent dermatophyte causing human nail and skin infections worldwide, and because of its anthropophilic nature, animal infection models are limited. The purpose of this work was to compare the expression profile of T. rubrum genes encoding putative virulence factors during growth in ex vivo and in vitro infection models. The efficiency of the ex vivo skin infection model was confirmed by scanning electron microscopy (SEM), which showed that the conidia had produced hyphae that penetrated into the epidermis. Quantitative RT-PCR (qRT-PCR) analysis showed that the expression of some genes is modulated in response to the infection model used, as compared to that observed in cells grown in glucose-containing media. We concluded that ex vivo infection models help assess the molecular aspects of the interaction of T. rubrum with the host milieu, and thus provide insights into the modulation of genes during infection.

Heat Shock Protein 90 (Hsp90) as a Molecular Target for the Development of Novel Drugs Against the Dermatophyte Trichophyton rubrum

Treatment of fungal infections is difficult due to several reasons, such as side effects of drugs, emergence of resistant strains, and limited number of molecular targets for the drug compounds. In fungi, heat shock proteins (Hsps) have been implicated in several processes with the conserved molecular chaperone Hsp90 emerging as a potential target for antifungal therapy. It plays key cellular roles by eliciting molecular response to environmental changes, morphogenesis, antifungal resistance, and fungal pathogenicity. Here, we evaluated the transcription profiles of hsp genes of the most prevalent dermatophyte Trichophyton rubrum in response to different environmental challenges including nutrient availability, interaction with cells and molecules of the host tissue, and drug exposure. The results suggest that each Hsp responds to a specific stress condition and that the cohort of Hsps facilitates fungal survival under various environmental challenges. Chemical inhibition of Hsp90 resulted in increased susceptibility of the fungus to itraconazole and micafungin, and decreased its growth in human nails in vitro. Moreover, some hsp and related genes were modulated by Hsp90 at the transcriptional level. We are suggesting a role of Hsp90 in the pathogenicity and drug susceptibility of T. rubrum as well as the regulation of other Hsps. The synergism observed between the inhibition of Hsp90 and the effect of itraconazole or micafungin in reducing the fungal growth is of great interest as a novel and potential strategy to treat dermatophytoses.

Antifungal Effect of Non-Woven Textiles Containing Polyhexamethylene Biguanide with Sophorolipid: A Potential Method for Tinea Pedis Prevention

Tinea pedis is a preventable skin disease common in elderly or diabetic patients. Daily foot washing is effective for prevention, but can be difficult for many patients. Additionally, conventional methods cannot eliminate fungi within the stratum corneum, a common site for fungal invasion. This study investigates the antifungal effects, cytotoxicity, permeability, and efficacy of non-woven textiles containing polyhexamethylene biguanide (PHMB) mixed with sophorolipid. Permeability of PHMB with varying concentrations of sophorolipid was assessed via a cultured skin model. Stratum corneum PHMB concentration was quantified by polyvinylsulphuric acid potassium salt titration and cytotoxicity was assayed via 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide. Antifungal effects were evaluated via a new cultured skin/Trichophytonmentagrophytes model, with varying PHMB exposure duration. Clinically-isolated Trichophyton were applied to the feet of four healthy volunteers and then immediately treated with the following methods: washing with soap, a non-woven textile with PHMB, the textile without PHMB, or without washing. Fungal colony forming units (CFUs) were evaluated after one of these treatments were performed. Sophorolipid with various concentrations significantly facilitated PHMB permeation into the stratum corneum, which was not in a dose-dependent manner. Significant PHMB antifungal effects were achieved at 30 min, with low cytotoxicity. Textiles containing PHMB significantly reduced CFU of fungi in healthy volunteers to levels comparable to soap washing. Our results indicate the utility of this product for tinea pedis prevention in clinical settings.

Histological skin morphology enhancement base on molecular hyperspectral imaging technology

BACKGROUND

Most traditional skin histological analysis methods are based on the light microscopy images, which can only provide limited information and low contrast results for pathology evaluation. Molecular hyperspectral imaging technology can provide both spatial and spectral information of skin sections, which is a new method for histological skin analysis.

METHODS

The molecular hyperspectral imaging system was developed by coupling an acousto-optic tunable filters adapter to microscopy and the molecular hyperspectral images were analyzed by home-written software with image processing algorithms. Then, the histological structures in skin sections were investigated in several locations to evaluate the potential application of the molecular hyperspectral imaging technique to dermatology.

RESULTS

Molecular hyperspectral images of skin sections were obtained. Single-band images, false color images, virtual 3D surface view images, and color-coded spectral clustering results were produced to highlight the skin structures for histological evaluation.

CONCLUSION

Unlike traditional histological analysis with light microscopy, the molecular hyperspectral imaging technology can enhance the visualization of skin structures using their spectral signatures and their gray values. This technology has potential for the diagnosis and histopathologic characterization of different kind of skin cells.

Dermatophytosis diagnosed at the Evandro Chagas Institute, Pará, Brazil

Dermatophytosis is caused by a dermatophyte fungus that affects the stratum corneum and keratinized tissue. Dermatophyte fungus has been reported worldwide as the causative agent of dermatophytosis, but the etio-epidemiological aspects of these mycoses in the state of Pará remain unknown. The purpose of this study was to describe the etio-epidemiological profile of dermatophytosis diagnosed in patients at the Evandro Chagas Institute from May 2005 to June 2006. A total of 494 patients were admitted, and their samples were collected, submitted for direct microscopic examination using 20% KOH and cultured in Sabouraud and Mycosel medium. The identification was based in macro and microscopic characteristics. Direct examinations were positive in 13% (66/494) of the patients, and agent isolation by cultivation of the biological sample was successful in 4% (20/494), with a high prevalence of T. mentagrophytes (40%; 8/20). Dermatophytosis was more frequent in women (58%; 38/66). Fifty-two percent (21/38) of the cases were children with an average age of 8 years. The most frequent clinical presentation was Tinea corporis (55%, 36/66). For the cases in which the dermatophyte agent was not isolated, we discuss the factors that may be interfering with isolation. Tinea corporis occurred more frequently observed when T. mentagrophytes and T. rubrum were the major etiologic agents.

Dermatophyte virulence factors: identifying and analyzing genes that may contribute to chronic or acute skin infections

Dermatophytes are prevalent causes of cutaneous mycoses and, unlike many other fungal pathogens, are able to cause disease in immunocompetent individuals. They infect keratinized tissue such as skin, hair, and nails, resulting in tinea infections, including ringworm. Little is known about the molecular mechanisms that underlie the ability of these organisms to establish and maintain infection. The recent availability of genome sequence information and improved genetic manipulation have enabled researchers to begin to identify and study the role of virulence factors of dermatophytes. This paper will summarize our current understanding of dermatophyte virulence factors and discuss future directions for identifying and testing virulence factors.

rpb2 is a reliable reference gene for quantitative gene expression analysis in the dermatophyte Trichophyton rubrum

The selection of reference genes used for data normalization to quantify gene expression by real-time PCR amplifications (qRT-PCR) is crucial for the accuracy of this technique. In spite of this, little information regarding such genes for qRT-PCR is available for gene expression analyses in pathogenic fungi. Thus, we investigated the suitability of eight candidate reference genes in isolates of the human dermatophyte Trichophyton rubrum subjected to several environmental challenges, such as drug exposure, interaction with human nail and skin, and heat stress. The stability of these genes was determined by geNorm, NormFinder and Best-Keeper programs. The gene with the most stable expression in the majority of the conditions tested was rpb2 (DNA-dependent RNA polymerase II), which was validated in three T. rubrum strains. Moreover, the combination of rpb2 and chs1 (chitin synthase) genes provided for the most reliable qRT-PCR data normalization in T. rubrum under a broad range of biological conditions. To the best of our knowledge this is the first report on the selection of reference genes for qRT-PCR data normalization in dermatophytes and the results of these studies should permit further analysis of gene expression under several experimental conditions, with improved accuracy and reliability.

The pathogenesis of Candida infections in a human skin model: scanning electron microscope observations

Cutaneous candidiasis is an opportunistic infection that arises, in most cases, from endogenous, saprophytic candidal blastospores that selectively colonize oral, gastrointestinal, vaginal, and cutaneous epithelium. Candida albicans has been regarded as the most common causative agent in human fungal infections. However, other Candida species have become a significant cause of infection. Scanning electron microscope (SEM) observations were used to analyze the capability of C. albicans, C. tropicalis, and C. parapsilosis to adhere to human skin model, used in this study, which was found to mimic the human skin in vivo. The skin sections were inoculated with low and high concentration of the yeasts and followed for 1 and 5 days; then they were viewed by SEM. The electron microscopy observations revealed that all three yeasts tested adhered to the skin but C. albicans covered the entire skin model to a higher extent than C. tropicalis or C. parapsilosis. Mucin-like material coated the blastoconidia mainly in C. albicans. All Candida species have shown characteristics resembling biofilm formation. The use of human skin sections for ex vivo evaluation of adherence of various yeasts may partially explain the predominance of C. albicans in cutaneous pathogenicity.

Analysis of the differentially expressed genes in Microsporum canis in inducing smooth skin and scalp tissue conditions

Microsporum canis is a common zoophilic dermatophyte, which causes a range of infections. To explore the pathogenic mechanism of tinea capitis, we used the suppression subtractive hybridization (SSH) technique to investigate the differences in gene expression between different cultures of Microsporum canis incubated on three different types of mineral media containing child glabrous skin, child scalp tissue and adult scalp tissue. Using dot-blot hybridization and real-time PCR technique, we successfully screened and identified a pair of genes that had expression levels 44.6 and 117 times higher in culture 1 (M. canis cultured in mineral medium with child scalp tissue) than in culture 2 (M. canis cultured in mineral medium with glabrous skin tissue), and another pair of genes with expression levels 78.2 and 9.8 times higher in culture 1 than in culture 3 (M. canis cultured in mineral medium with adult scalp tissue). These four genes were found to have 41%, 53%, 40% and 94% homology to those encoding a hypothetical protein [family of serine hydrolases 1; (FSH1)], PQ loop repeat protein (PQ-LRP), a predicted protein [porphyrin galactose 4; (P-GAL4)] and NADH dehydrogenase subunit (NADH)1, respectively. The upregulation of the FSH1, PQ-LRP, P-GAL4 and NADH1 genes in cultures of child scalp tissue indicates that they are essential in the pathogenesis of tinea capitis caused by M. canis.

Mechanisms of skin adherence and invasion by dermatophytes

Dermatophytes are keratinophilic fungi that can be pathogenic for humans and animals by infecting the stratum corneum, nails, claws or hair. The first infection step consists of adherence of arthroconidia to the stratum corneum. The mechanisms and the kinetics of adherence have been investigated using different in vitro and ex vivo experimental models, most notably showing the role of a secreted serine protease from Microsporum canis in fungal adherence to feline corneocytes. After germination of the arthroconidia, dermatophytes invade keratinised structures that have to be digested into short peptides and amino acids to be assimilated. Although many proteases, including keratinolytic ones, have been characterised, the understanding of dermatophyte invasion mechanisms remains speculative. To date, research on mechanisms of dermatophyte infection focused mainly on both secreted endoproteases and exoproteases, but their precise role in both fungal adherence and skin invasion should be further explored.

Targeted gene deletion and in vivo analysis of putative virulence gene function in the pathogenic dermatophyte Arthroderma benhamiae

Dermatophytes cause the majority of superficial mycoses in humans and animals. However, little is known about the pathogenicity of this specialized group of filamentous fungi, for which molecular research has been limited thus far. During experimental infection of guinea pigs by the human pathogenic dermatophyte Arthroderma benhamiae, we recently detected the activation of the fungal gene encoding malate synthase AcuE, a key enzyme of the glyoxylate cycle. By the establishment of the first genetic system for A. benhamiae, specific ΔacuE mutants were constructed in a wild-type strain and, in addition, in a derivative in which we inactivated the nonhomologous end-joining pathway by deletion of the A. benhamiae KU70 gene. The absence of AbenKU70 resulted in an increased frequency of the targeted insertion of linear DNA by homologous recombination, without notably altering the monitored in vitro growth abilities of the fungus or its virulence in a guinea pig infection model. Phenotypic analyses of ΔacuE mutants and complemented strains depicted that malate synthase is required for the growth of A. benhamiae on lipids, major constituents of the skin. However, mutant analysis did not reveal a pathogenic role of the A. benhamiae enzyme in guinea pig dermatophytosis or during epidermal invasion of the fungus in an in vitro model of reconstituted human epidermis. The presented efficient system for targeted genetic manipulation in A. benhamiae, paired with the analyzed infection models, will advance the functional characterization of putative virulence determinants in medically important dermatophytes.

Dermatomycosis: Conditions that contribute to the disease development

Skin lesions caused by dermatophytes are classified depending on the infected skin structure: surface layer of cutis, fur layer, clutches or nails. Surface mycoses are caused by dermatophytes: Epidermophyton, Microsporum and Trichophyton species (also important are Malassezia spp., Candida spp., and Trichosporon). Skin is the target tissue for fungal infections if the epithelial layer is damaged and immune system cannot cope with the infection, or if the conditions are favorable for dermatophytes, which spread in the cutis due to the enzyme activities. Dermatophytes can be found on skin surface if they contaminate or colonize epidermis or hair follicles. However, clinical symptoms of lesion on the skin are sometimes absent. According to the literature data 6-9% of skin lesions are caused by dermatophyte in human medicine. Similar situation is in veterinary medicine. Fungus that cause dermatomycosis are widespread in the nature and could be divided into: zoophilic, geophilic and anthrophilic. The goal of this paper is to present the latest knowledge in pathogenesis on dermatomycosis, predisposing factors important for the outcome of the disease, and immunological reaction of organism to the fungal infection. Our intention is to summarize the subject and present the facts related to specific problems in dermatomycosis.

Pathogenesis of tinea

Dermatophytes are hyphomycetes that can degrade keratin. This puts them in a position to cause infections of the keratin-containing superficial skin. The resulting clinical picture is called tinea. The pathogenesis and course of tinea is decisively determined by pathogen-related factors and by the defense mechanisms of the host. An infection starts with an adherence of fungal propagules, followed by the formation of hyphae that can spread within the tissue. This process is accompanied by a release of fungal enzymes and other pathogenic factors. Next keratinocytes are activated, the epidermal barrier is destroyed, epidermal proliferation is enhanced and defensins are expressed within the epidermis. In addition, innate and specific immune responses are initiated, involving neutrophilic granulocytes, macrophages, antibodies and T cells. The cellular mechanisms are thought to be crucial for healing. Special conditions apply to nail infections, because within nail plates the fungi are not accessible to effective defense mechanisms, as well as to infections of hair follicles that contain specific concentrations of steroid hormones. Dermatophytes that penetrate into the dermis can cause granulomatous inflammatory reactions and systemic immune reactions are supposed to be a trigger of so-called id reactions.

Expression dynamics of secreted protease genes in Trichophyton rubrum induced by key host's proteinaceous components

Trichophyton rubrum is the most common agent of dermatophytosis, a disease that affects millions of individuals worldwide. Its molecular pathogenicity mechanisms are still not completely elucidated. It has been widely recognized that proteases secreted by T. rubrum are the key virulence factors during host infection. However, our knowledge about the expression of its secreted proteases in host infection is still obscure. This investigation provides the expression patterns and dynamics of secreted protease genes belonging to the subtilisins (SUB) and metalloproteases (MEP) gene families in T. rubrum. The data was obtained under simulated host infection conditions through relative quantification of real time PCR. Keratin, collagen, and elastin induced the expression of similar protease genes, and the expression patterns and dynamics of these protease genes in media containing human skin sections were different from those in media containing individual protein substrates. According to the expression dynamics of these protease genes, we conclude that Sub3, Sub4, and Mep4 may be the dominant proteases secreted by T. rubrum during host infection, and that these proteases could be good targets for new antifungal chemotherapy and molecular diagnostic markers. This work presents useful molecular details to further our understanding of the pathogenesis of dermatophytosis.

CD4+ and CD8+ T cells mediated direct cytotoxic effect against Trichophyton rubrum and Trichophyton mentagrophytes

BACKGROUND

The cellular immune system is the most dominant factor in curing acute dermatophytosis. However, the exact immune mechanisms involved in generating this defense are complex and still obscure. The aim of this study was to investigate the fungicidal mechanism of T cells in the normal population versus patients with chronic fungal infections.

METHODS

Thirty patients were included in the study: 15 patients with chronic dermatophytosis and 15 normal healthy patients with a history of acute dermatophytosis. The procedures were performed as follows. 1) Proliferation and cytotoxic activity of lymphocytes cultured with various dermatophytes homogenate such as, Trichophyton rubrum, Trichophyton mentagrophytes and Microsporum gypseum. 2) CD4(+) and CD8(+) T cells were separated by magnetic beads before culture with fresh spores of either T. mentagrophytes or T. rubrum. 3) Routine histology and ultrastructural study were performed to illustrate the mode of activity of the T cells against the dermatophytes.

RESULTS

The study showed that both CD4 and CD8 possess cytotoxic activity against dermatophytes. However, the results demonstrated a suppression of lymphocyte proliferation response and a significant lower cytotoxic effect in chronic patients. Ultra structure and histological evaluation of the culture of hyphae with CD4(+) or CD8(+) T cells showed more prominently destructive effects in the culture of cells that had been obtained from normal population than those of patients with long-lasting fungal infections.

CONCLUSION

The study suggests a selective impairment of lymphocyte function against dermatophytes, in patients with chronic dermatophytoses.

Preclinical studies with 5,10,15-Tris(4-methylpyridinium)-20-phenyl-[21H,23H]-porphine trichloride for the photodynamic treatment of superficial mycoses caused by Trichophyton rubrum

Dermatophytes are fungi that cause infections of keratinized tissues. We have recently demonstrated the susceptibility of the dermatophyte Trichophyton rubrum to photodynamic treatment (PDT) with 5,10,15-Tris(4-methylpyridinium)-20-phenyl-[21H,23H]-porphine trichloride (Sylsens B) in 5 mm citric acid/sodium citrate buffer (pH 5.2, formulation I). In this work, we examined the penetration of Sylsens B in healthy and with T. rubrum infected skin and we investigated the susceptibility of T. rubrum to PDT using formulation I and UVA-1 radiation (340-550 nm). Skin penetration studies were performed with formulations I and II (Sylsens B in PBS, pH 7.4) applied on dermatomed skin, human stratum corneum (SC), disrupted SC by T. rubrum growth and SC pretreated with a detergent. No penetration was observed in healthy skin. Disruption of SC by preceding fungal growth caused Sylsens B penetration at pH 7.4, but not at pH 5.2. However, chemically damaged SC allowed Sylsens B to penetrate also at pH 5.2. UVA-1 PDT was applied ex vivo during two fungal growth stages of two T. rubrum strains (CBS 304.60 and a clinical isolate). Both strains could be killed by UVA-1 alone (40 J/cm(2)). Combined with formulation I (1 and 10 microm Sylsens B for, respectively, CBS 304.60 and the clinical isolate), only 18 J/cm(2) UVA-1 was required for fungal kill. Therefore, PDT with 10 microm Sylsens B (formulation I) and 18 J/cm(2) UVA-1 could be considered as effective and safe. This offers the possibility to perform clinical studies in future.

Secreted subtilisins of Microsporum canis are involved in adherence of arthroconidia to feline corneocytes

Microsporum canis is a pathogenic fungus that causes a superficial cutaneous infection called dermatophytosis, mainly in cats and humans. The mechanisms involved in adherence of M. canis to epidermis have never been investigated. Here, a model was developed to study the adherence of M. canis to feline corneocytes through the use of a reconstructed interfollicular feline epidermis (RFE). In this model, adherence of arthroconidia to RFE was found to be time-dependent, starting at 2 h post-inoculation and still increasing at 6 h. Chymostatin, a serine protease inhibitor, inhibited M. canis adherence to RFE by 53%. Moreover, two mAbs against the keratinolytic protease subtilisin 3 (Sub3) inhibited M. canis adherence to RFE by 23%, suggesting that subtilisins, and Sub3 in particular, are involved in the adherence process.

Preliminary study of activity of the thioredoxin inhibitor pleurotin against Trichophyton mentagrophytes: a novel anti-dermatophyte possibility

Dermatophyte infections, while not life-threatening, are very common, and there is great interest in developing new antifungal agents. Transcriptional profiling of Trichophyton on keratin has identified some antioxidant genes as induced on this host substrate, including a thioredoxin gene TmTRX1. If thioredoxin is a virulence factor, or necessary for the growth on keratin, thioredoxin inhibitors should act as antifungals. As a first evaluation of this hypothesis, we have tested the activity of a thioredoxin-inhibitory natural product, pleurotin, against a clinical isolate of each of two fungal pathogens: the dermatophyte T. mentagrophytes and Candida albicans. Pleurotin inhibited the growth of the dermatophyte in vitro and in an ex vivo skin model, but had no effect on Candida. It may be possible to develop and optimise thioredoxin inhibitors, some of which are already under study in cancer chemotherapy, as antifungals.