Role of pH in the pathogenesis of dermatophytoses

Host-Pathogen Interaction and Resistance Mechanisms in Dermatophytes

Dermatophytes are widely distributed in the environment, with an estimated prevalence of 20–25% of the the global population yearly. These fungi are keratinophilic and keratinolytic and cause the infection of keratin-rich structures such as skin, hair, and nails. The pattern of this infectious disease covers a wide spectrum from exposed individuals without symptoms to those with acutely inflammatory or non-inflammatory, chronic to invasive, and even life-threatening symptoms. This review summarizes current information on the pathogenicity, virulence factors, and drug resistance mechanisms associated with dermatophytes. A greater number of virulence factors of these fungi are important for the occurrence of infection and the changes that occur, including those regarding adhesins, the sulfite efflux pump, and proteolytic enzymes. Other virulence factors include mechanisms of evading the host defense, while the development of resistance to antifungal drugs is increasing, resulting in treatment failure. The investigation of host-pathogen interactions is essential for developing a more complete understanding of the mechanisms underlying dermatophyte pathogenesis and host response to inform the use of diagnostics methods and antifungal therapeutics to minimize the high fungal burden caused by dermatophytes and to control the spread of resistance.

The StuA Transcription Factor and Alternative Splicing Mechanisms Drive the Levels of MAPK Hog1 Transcripts in the Dermatophyte Trichophyton rubrum

Trichophyton rubrum is a human fungal pathogen that causes dermatophytosis, an infection that affects keratinized tissues. Integrated molecular signals coordinate mechanisms that control pathogenicity. Transcriptional regulation is a core regulation of relevant fungal processes. Previous RNA sequencing data revealed that the absence of the transcription factor StuA resulted in the differential expression of the MAPK-related high glycerol osmolarity gene (hog1) in T. rubrum. Here we validated the role of StuA in regulating the transcript levels of hog1. We showed through RT-qPCR that transcriptional regulation controls hog1 levels in response to glucose, keratin, and co-culture with human keratinocytes. In addition, we also detected hog1 pre-mRNA transcripts that underwent alternative splicing, presenting intron retention in a StuA-dependent mechanism. Our findings suggest that StuA and alternative splicing simultaneously, but not dependently, coordinate hog1 transcript levels in T. rubrum. As a means of preventing and treating dermatophytosis, our results contribute to the search for new potential drug therapies based on the molecular aspects of signaling pathways in T. rubrum.

Molecular Signaling and Metabolic Responses during the Interaction between Human Keratinocytes (HaCaT) and the Dermatophyte Trichophyton rubrum

Trichophyton rubrum is the leading causative agent of dermatophytosis worldwide. Keratinocytes are the first line of defense that drives an immune response against fungal invasion. Host-specific pattern recognition receptors (PRRs) recognize pathogen-associated molecular patterns (PAMPs) to trigger immunological pathways. Fungal cell wall components are the primary sources of fungal PAMPs, and some pathogens increase cell wall rearrangement to evade the immune system. Glycolysis and enhanced lactate levels are critical for improving host immune responses to fungal infections. Using reverse transcription-quantitative polymerase chain reaction (RT-qPCR), we evaluated the transcriptional responses of human genes involved in fungal recognition and glycolytic metabolism and fungal cell-wall-related genes in a co-culture model of human keratinocytes with T. rubrum. We observed the upregulation of several Toll-like receptors (TLRs), NOD-like receptors (NLRs), and glycolytic genes. Complementarily, we measured intra- and extracellular glucose levels and the increase in lactate production in the co-culture supernatant. We noted a distinct transcriptional regulation pattern of fungal cell-wall-related genes from fungal growth on keratin as the primary carbon source compared to co-culture with human keratinocytes. Our results showed new insights into the transcriptional adaptation of keratinocytes, particularly in regulating genes involved in sensing and metabolic processes, during the interaction with T. rubrum.

pH-Responsive swimming behavior of light-powered rod-shaped micromotors

Micromotors have emerged as promising devices for a wide range of applications e.g., microfluidics, lab-on-a-chip devices, active matter, environmental monitoring, etc. The control over the activity of micromotors with the ability to exhibit multimode swimming is one of the most desirable features for many of the applications. Here, we demonstrate a rod-shaped light-driven micromotor whose activity and swimming behavior can easily be controlled. The rod-shaped micromotors are fabricated through the dynamic shadowing growth (DSG) technique, where a 2 μm long arm of titanium dioxide (TiO2) is grown over spherical silica (SiO2) particles (1 μm diameter). Under low-intensity UV light exposure, the micromotors exhibit self-propulsion in an aqueous peroxide medium. When activated, the swimming behavior of micromotors greatly depends on the pH of the medium. The swimming direction, i.e., forward or backward movement, as well as swimming modes like translational or rotational motion, can be controlled by changing the pH values. The observed dynamics has been rationalized using a theoretical model incorporating chemical activity, hydrodynamic flow, and the effect of gravity for a rod-shaped active particle near a planar wall. The pH-dependent translational and rotational dynamics of micromotors provide a versatile platform for achieving controlled and responsive behaviors. Continued research and development in this area hold great promise for advancing micromotors and enabling novel applications in microfluidics, micromachining, environmental sciences, and biomedicine.

Graphene Scaffolds: A Striking Approach to Combat Dermatophytosis

Exclusive physicochemical and biological properties of carbon allotrope graphene have attracted the peer attention of researchers for the synthesis and development of newer topical remedies including films, scaffolds, microspheres, and hydrogels. Here, graphene nanoplatelets (GN) were embedded into a different ratio of polymeric ERL100/ERS100 solution and fabricated in the form of a scaffold through the electrospinning process. FTIR spectra displayed characteristic similar peaks present both in GN and GN-loaded scaffold owing to the compatibility of GN and polymeric mixture. XRD curve revealed a distinct GN peak at nearly 26° whereas from DSC/TGA thermal stability was observed between polymers and graphene nanoplatelets. FESEM images showed ultrathin architecture of GN-loaded scaffold in a range of 280 ± 90 nm. The fabricated scaffold exhibited hydrophilicity (contact angle 48.8 ± 2.8°) and desirable swelling index (646% in skin pH media) which were desired criteria for the scaffold for topical application. In vitro, antifungal activity was conducted through the broth microdilution method against different virulent dermatophytes i.e., Microsporum gypseum, M. canis, M. fulvum, and Trychophyton rubrum. For in vivo evaluation, T. rubrum inoculum was applied on the dorsal surface of each group of Swiss albino mice, and the degree and intensity of mycelial growth or erythema on skin surfaces was visually investigated. The study depicted complete signs of cure after 14 days of application of G3-loaded scaffold on the infected dorsal site. Hence graphene-loaded scaffold represented a possible alternative for the treatment of topical fungal infections caused by dermatophytes.

Insights and Perspectives on the Role of Proteostasis and Heat Shock Proteins in Fungal Infections

Fungi are a diverse group of eukaryotic organisms that infect humans, animals, and plants. To successfully colonize their hosts, pathogenic fungi must continuously adapt to the host's unique environment, e.g., changes in temperature, pH, and nutrient availability. Appropriate protein folding, assembly, and degradation are essential for maintaining cellular homeostasis and survival under stressful conditions. Therefore, the regulation of proteostasis is crucial for fungal pathogenesis. The heat shock response (HSR) is one of the most important cellular mechanisms for maintaining proteostasis. It is activated by various stresses and regulates the activity of heat shock proteins (HSPs). As molecular chaperones, HSPs participate in the proteostatic network to control cellular protein levels by affecting their conformation, location, and degradation. In recent years, a growing body of evidence has highlighted the crucial yet understudied role of stress response circuits in fungal infections. This review explores the role of protein homeostasis and HSPs in fungal pathogenicity, including their contributions to virulence and host-pathogen interactions, as well as the concerted effects between HSPs and the main proteostasis circuits in the cell. Furthermore, we discuss perspectives in the field and the potential for targeting the components of these circuits to develop novel antifungal therapies.

Biophysical Characterization of the C-Terminal Tail of T. rubrum PacC Reveals an Inherent Intrinsically Disordered Structure with pH-Induced Structural Plasticity

PacC is a key transcriptional regulator of human pathogenic fungus Trichophyton rubrum with pivotal roles in pH homeostasis and virulence. We report the first biophysical characterization of the C-terminal inhibitory tail of PacC, pertinent to its physiological role in maintaining the inactive state of PacC at acidic pH which undergoes conformational changes for its proteolytic removal and activation, at alkaline pH. To gain insights into the structural features of PacC that enable the required conformational flexibility, we performed gel filtration chromatography, dynamic light scattering, circular dichroism, and 1-anilino-8-naphthalenesulfonate binding and showed that the tail exhibits properties similar to intrinsically disordered proteins, as also predicted by bioinformatics tools. We demonstrate that the C-terminal tail is conformationally flexible and attains a molten globule-like state at extremely acidic pH and undergoes biphasic GdmCl-induced unfolding in a noncooperative manner with an intermediate X state. We hypothesize that the conformational plasticity of the C-terminal tail of PacC may play a significant role in modulating its pH-dependent transcriptional activation.

Relevance of Nutrient-Sensing in the Pathogenesis of Trichophyton rubrum and Trichophyton interdigitale

The growth and development of organisms depend on nutrient availability. Dermatophytes must sense nutrient levels and adapt to the host environment to colonize human and animal keratinized tissues. Owing to the clinical importance of the Trichophyton genus, this study compared the expression profile of genes involved in metabolism, cell cycle control, and proteases in two Trichophyton species, Trichophyton rubrum, and Trichophyton interdigitale, in response to nutrients and environmental pH. In addition, we evaluated the activity of enzymes in the tricarboxylic acid, glyoxylate, and methylcitrate cycles. Moreover, the effects of interruption of the transcription factor pacC on T. interdigitale in the same conditions as for the wild-type strain were determined. Our analyses revealed specific responses in each species to the nutritional and pH variation. An improved adaptation of T. interdigitale to keratin was observed, compared with that of T. rubrum. T. rubrum growth in buffered keratin media indicated pH 8.0 as an optimal pH condition for metabolic activity, which differed from that for T. interdigitale. Tricarboxylic acid components in T. rubrum showed increased enzymatic activity and transcript accumulation. In T. interdigitale, a higher activity of enzymes in glyoxylate and methylcitrate cycles was observed, with no direct correlation to the transcriptional profile. T. interdigitale fungal metabolism suggests the requirement of anaplerotic pathways in the late cultivation period. The identified differences between T. rubrum and T. interdigitale may represent determinants for adaptation to the host and the incidence of infection with each species.

State-of-the-Art Dermatophyte Infections: Epidemiology Aspects, Pathophysiology, and Resistance Mechanisms

The burden of fungal infections is not widely appreciated. Although these infections are responsible for over one million deaths annually, it is estimated that one billion people are affected by severe fungal diseases. Mycoses of nails and skin, primarily caused by fungi known as dermatophytes, are the most common fungal infections. Trichophyton rubrum appears to be the most common causative agent of dermatophytosis, followed by Trichophyton interdigitale. An estimated 25% of the world’s population suffers from dermatomycosis. Although these infections are not lethal, they compromise the quality of life of infected patients. The outcome of antidermatophytic treatments is impaired by various conditions, such as resistance and tolerance of certain dermatophyte strains. The adage “know your enemy” must be the focus of fungal research. There is an urgent need to increase awareness about the significance of these infections with precise epidemiological data and to improve knowledge regarding fungal biology and pathogenesis, with an emphasis on adaptive mechanisms to tackle adverse conditions from host counteractions. This review outlines the current knowledge about dermatophyte infections, with a focus on signaling pathways required for fungal infection establishment and a broad perspective on cellular and molecular factors involved in antifungal resistance and tolerance.

Comprehensive genome and transcriptome analysis of the dermatophyte Trichophyton schoenleinii reveals the candidate pathogenic genes

BACKGROUND

Trichophyton schoenleinii is an anthropophilic dermatophyte that causes tinea favosa. Nowadays, it remains an important pathogen in some regions of the world, mainly epidemic in Africa and West Asia. Despite the medical importance of T. schoenleinii infections, a high-quality reference genome for T. schoenleinii is still unavailable, neither its transcriptomic profile.

OBJECTIVES

The aim of the current study was to improve understanding of the underlying pathogenic mechanism of T. schoenleinii, and to define the candidate pathogenic genes of T. schoenleinii.

METHODS

Comprehensive genomic analysis of T. schoenleinii was carried out by Illumina and PacBio sequencing platforms. Transcriptome profiles of T. schoenleinii cultured in vitro in two media containing either keratin or soy protein were determined using RNA sequencing (RNA-seq) technology.

RESULTS

Here, we present the first draft genome sequence of T. schoenleinii strain T2s, which consists of 11 scaffolds containing 7474 predicted genes. Transcriptome analysis showed that genes involved in keratin hydrolysis have higher expression in T. schoenleinii grown in keratin medium, including genes encoding proteases, cysteine dioxygenase and acetamidase. Other genes with higher expression include genes encoding the components of the pH-responsive signal transduction pathways and transcription factors, many of which may play a role in pathogenicity.

CONCLUSION

In summary, this study provides new insights into the pathogenic mechanism of T. schoenleinii and highlights candidate genes for further development of novel targets in disease diagnosis and treatment of tinea favosa.

Comprehensive analysis of the dermatophyte Trichophyton rubrum transcriptional profile reveals dynamic metabolic modulation

The environmental challenges imposed onto fungal pathogens require a dynamic metabolic modulation, which relies on activation or repression of critical factors and is essential for the establishment and perpetuation of host infection. Wherefore, to overcome the different host microenvironments, pathogens not only depend on virulence factors but also on metabolic flexibility, which ensures their dynamic response to stress conditions in the host. Here, we evaluate Trichophyton rubrum interaction with keratin from a metabolic perspective. We present information about gene modulation of the dermatophyte during early infection stage after shifting from glucose- to keratin-containing culture media, in relation to its use of glucose as the carbon source. Analyzing T. rubrum transcriptome using high-throughput RNA-sequencing technology, we identified the modulation of essential genes related to nitrogen, fatty acid, ergosterol, and carbohydrate metabolisms, among a myriad of other genes necessary for the growth of T. rubrum in keratinized tissues. Our results provide reliable and critical strategies for adaptation to keratin and confirm that the urea-degrading activity associated with the reduction in disulfide bonds and proteolytic activity facilitated keratin degradation. The global modulation orchestrates the responses that support virulence and the proper adaptation to keratin compared with glucose as the carbon source. The gene expression profiling of the host-pathogen interaction highlights candidate genes involved in fungal adaptation and survival and elucidates the machinery required for the establishment of the initial stages of infection.

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.

In vitro and ex vivo biofilms of dermatophytes: a new panorama for the study of antifungal drugs

This study describes an ex vivo model that creates an environment for dermatophyte biofilm growth, with features that resemble those of in vivo conditions, designing a new panorama for the study of antifungal susceptibility. Regarding planktonic susceptibility, MIC ranges were 0.125-1 µg ml^-1 for griseofulvin and 0.000097-0.25 µg ml^-1 for itraconazole and terbinafine. sMIC50 ranges were 2->512 µg ml^-1 for griseofulvin and 0.25->64 µg ml^-1 for itraconazole and terbinafine. CLSM images demonstrated a reduction in the amount of cells within the biofilm, but hyphae and conidia were still observed and biofilm biomass was maintained. SEM analysis demonstrated a retraction in the biofilm matrix, but fungal structures and water channels were preserved. These results show that ex vivo biofilms are more tolerant to antifungal drugs than in vitro biofilms, suggesting that environmental and nutritional conditions created by this ex vivo model favor biofilm growth and robustness, and hence drug tolerance.

Saline stress affects the pH-dependent regulation of the transcription factor PacC in the dermatophyte Trichophyton interdigitale

Fungal growth and development depend on adaptation to the particular pH of their environment. Ambient pH sensing implies the activation of the pacC signaling pathway, which then acts as a critical regulator for different physiological conditions. The PacC transcription factor may also be associated with the control of salt stress tolerance. In a pH-dependent manner, salinity stress is surpassed by changes in gene expression and coordinated activation of other signaling pathways, thus permitting survival in the challenging environment. In this study, we assessed the regulatory role of Trichophyton interdigitale PacC in response to pH variation and salinity stress. By employing gene expression analysis, we evaluated the influence of PacC in the modulation of salt stress-related genes, including the transcription factors crz1, egr2, and the MAP kinase hog1 in the dermatophyte T. interdigitale. In our analysis, we also included the evaluation of a potassium/sodium efflux P-type ATPase aiming to identify the role of PacC on its ion pumping activity. Here we demonstrated that salinity stress and buffered pH conditions might affect the pacC gene modulation in the dermatophyte T. interdigitale.

Alternative Splicing in Heat Shock Protein Transcripts as a Mechanism of Cell Adaptation in Trichophyton rubrum

Heat shock proteins (HSPs) are involved in critical processes like host tissue invasion, resistance, and pathogenicity in dermatophytes. RNA-Seq analysis of Trichophyton rubrum exposed to undecanoic acid (UDA) revealed intron retention events in HSP transcripts. Because HSPs are modulated in response to various stimuli and as alternative splicing (AS) can result in a broad diversity in the proteome of eukaryotic cells, our objective was to confirm the aforementioned retention events, investigating their consequences and extent. Furthermore, we aimed to determine: (1) the expression profile of HSP genes in an infection-like scenario and (2) the importance of Hsp90 for the keratinolytic potential of T. rubrum. RT and qPCR analyses comparing the exposure to UDA and terbinafine (TRB) confirmed the presence of two mRNA isoforms of the hsp7-like gene, with distinct expression patterns in response to UDA and TRB. The HSP expression profile revealed two upregulated, three downregulated, and four unmodulated transcripts; Hsp90 inhibition by 17-AAG resulted in a significant decrease in keratinolytic potential at 37 °C. Altogether, these results broaden the current knowledge on the importance of HSP-mediated pathways for cell adaptation and other aspects of dermatophyte biology, indicating that HSP network proteins can be potential targets for antifungal therapy.

A microtiter plate-based quantitative method to monitor the growth rate of dermatophytes and test antifungal activity

Dermatophytosis is one of the most common superficial fungal infections, which is mainly caused by filamentous fungi such as Trichophyton species. A challenging aspect in dermatophyte research is the lack of a straightforward method to measure the rate of growth, in particular when growing dermatophytes in small volumes such as in microtitre plates. However, one characteristic of dermatophytes is their ability to produce compounds such as ammonia that make the growth medium more alkaline. The objective of this study was to test whether the change in pH in a liquid medium, colourimetrically established using the indicator phenol red, was linearly and directly proportional to the growth rate for Trichophyton rubrum and Trichophyton interdigitale. The changes in the colour determined by the phenol-red based assay showed a good correlation with the amount of fungal biomass over an incubation period of 24-120 h. The functionality of the phenol red assay was also validated in experiments on the growth of T. rubrum in the presence of antifungals. The changes in colour showed a clear dose-response relationship compounds and enabled determination of the minimum inhibitory concentration. The phenol red assay is thus a simple and straightforward assay to monitor the rate of growth of Trichophyton spp. and test antifungal activity.

Influence of the cultivation medium and pH on the pigmentation of Trichophyton rubrum

Trichophyton rubrum is a human pathogenic fungus. As a dermatophyte it causes athlete's foot, fungal infection of nails, jock itch and ringworm. The pigmentation of T. rubrum is variable and can range from white or yellow to wine-red. We demonstrate that the pigmentation is strongly influenced by pH. Under alkaline conditions, T. rubrum has a red pigmentation, whereas at acid conditions, T. rubrum has a yellow pigmentation. Moreover, the color change immediately from yellow to red by adding NaOH and reverse immediately from red to yellow by adding HCl. We suggest that the chemical compound Xanthomegnin is responsible for red as well for yellow pigmentation in T. rubrum. To figure out, why T. rubrum has red pigmentation on Trichophyton medium, adjust to alkaline, but not on Synthetic-Complete medium, also adjusted to alkaline, we measure the pH of liquid media, adjusted to pH 3.5, 6 and 8, over a period of four weeks. The pH of both cultivation media changes significantly, with a maximum of five pH levels. Whereas the Trichophyton medium, initially adjusted to pH 8, stays alkaline, the pH of the Synthetic-Complete medium drops to acid conditions. The acidification of the SC medium and the alkalization of the Trichophyton medium explains the different pigment color of the T. rubrum colonies.

Understanding the regulation of extracellular protease gene expression in fungi: a key step towards their biotechnological applications

The secretion of proteases by certain species of yeast and filamentous fungi is of importance not only for their biological function and survival, but also for their biotechnological application to various processes in the food, beverage, and bioprocessing industries. A key step towards understanding the role that these organisms play in their environment, and how their protease-secreting ability may be optimally utilised through industrial applications, involves an evaluation of those factors which influence protease production. The objective of this review is to provide an overview of the findings from investigations directed at elucidating the regulatory mechanisms underlying extracellular protease secretion in yeast and filamentous fungi, and the environmental stimuli that elicit these responses. The influence of nitrogen-, carbon-, and sulphur-containing compounds, as well as proteins, temperature, and pH, on extracellular protease regulation, which is frequently exerted at the transcriptional level, is discussed in particular depth. Protease-secreting organisms of biotechnological interest are also presented in this context, in an effort to explore the areas of industrial significance that could possibly benefit from such knowledge. In this way, the establishment of a platform of existing knowledge regarding fungal protease regulation is attempted, with the particular goal of aiding in the practical application of these organisms to processes that require secretion of this enzyme.

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.

Tolnaftate–graphene composite-loaded nanoengineered electrospun scaffolds as efficient therapeutic dressing material for regimen of dermatomycosis

Graphene “The novel carbon nano-trope” tailors auspicious platform for designing antimicrobial regimen by virtue of its conspicuous molecular interaction with the microorganism. In this work, Tolnaftate (Tf), an antifungal drug, was mingled with Graphene nanoplatelets (Gn) to develop composite (Tf–Gn) via the wet chemical route, embedded in a biocompatible polymeric blend of Eudragit RL100/Eudragit RS100 (EuRL100/EuRS100) and subjected to electrospinning to obtain nonwoven nanoengineered scaffolds (nanofibers) for enhanced anti-dermatophytic virtue. Pursuing cluster of optimization experiments, 20% w/v EuRL100/EuRS 100 was found to be adequate for formation of smooth, defect-free, and regular fibers. Field emission electron microscopy (FESEM) acknowledged zestfully fabrication of smooth, shiny, nano-range, and mesh-like architecture, comprising distinct pockets within their structure. Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimeter (DSC) conceded formation of the composite Tf–Gn, its physical compatibility with polymers, and improved thermal behavior. Exceptional swelling capacity, significant hydrophilicity, and immense drug entrapment efficiency were obtained of nanofibers fabricated from 3:1 ratio of EuRL100/EuRS100 polymers blend owing to relatively higher permeability which gratified essential benchmark for fabrication of nanofibrous scaffold to alleviate fungal infections caused by dermatophytes. In vitro drug release interpreted controlled liberation of Tf in dissolution media, following Korsmeyer–Peppas model kinetics, and suggested a diffusion-based mechanism. Microdilution broth method was performed for in vitro antifungal efficacy against extremely devastating dermatophytes, i.e., anthropophilic Trichophyton rubrum and zoophilic Microsporum canis, exhibited preeminent growth inhibition against T.rubrum and scanty for M.canis. Findings revealed the superior antifungal activity of Tf–Gn-loaded nanofibers as compared to Tf-loaded nanofibers and recommended potential dressing materials for an effective regimen of dermatomycosis.

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.

Effect of Culture Supernatant Derived from Trichophyton Rubrum Grown in the Nail Medium on the Innate Immunity-related Molecules of HaCaT

BACKGROUND

Trichophyton rubrum is superficial fungi characteristically confined to dead keratinized tissues. These observations suggest that the soluble components released by the fungus could influence the host immune response in a cell in contact-free manner. Therefore, this research aimed to analyze whether the culture supernatant derived from T. rubrum grown in the nail medium could elicit the immune response of keratinocyte effectively.

METHODS

The culture supernatants of two strains (T1a, T XHB ) were compared for the β-glucan concentrations and their capacity to impact the innate immunity of keratinocytes. The β-glucan concentrations in the supernatants were determined with the fungal G-test kit and protein concentrations with bicinchoninic acid protein quantitative method, then HaCaT was stimulated with different concentrations of culture supernatants by adopting morphological method to select a suitable dosage. Expressions of host defense genes were assessed by quantitative polymerase chain reaction after the HaCaT was stimulated with the culture supernatants. Data were analyzed with one-way analysis of variance, followed by the least significant difference test.

RESULTS

The T. rubrum strains (T1a and T XHB ) released β-glucan of 87.530 ± 37.581 pg/ml and 15.747 ± 6.453 pg/ml, respectively into the media. The messenger RNA (mRNA) expressions of toll-like receptor-2 (TLR2), TLR4, and CARD9 were moderately up-regulated in HaCaT within 6-h applications of both supernatants. HaCaT cells were more responsive to T1a than T XHB . The slight increase of dendritic cells-specific intercellular adhesion molecule 3-grabbing nonintegrin expression was faster and stronger, induced by T1a supernatant than T XHB . The moderate decreases of RNase 7, the slight up-regulations of Dectin-1 and interleukin-8 at the mRNA level were detected only in response to T1a rather than T XHB . After a long-time contact, all the elevated defense genes decreased after 24 h.

CONCLUSION

The culture supernatant of T. rubrum could directly and transiently activate the innate immune response of keratinocytes.

Heat Shock Proteins in Dermatophytes: Current Advances and Perspectives

Heat shock proteins (HSPs) are proteins whose transcription responds rapidly to temperature shifts. They constitute a family of molecular chaperones, involved in the proper folding and stabilisation of proteins under physiological and adverse conditions. HSPs also assist in the protection and recovery of cells exposed to a variety of stressful conditions, including heat. The role of HSPs extends beyond chaperoning proteins, as they also participate in diverse cellular functions, such as the assembly of macromolecular complexes, protein transport and sorting, dissociation of denatured protein aggregates, cell cycle control, and programmed cell death. They are also important antigens from a variety of pathogens, are able to stimulate innate immune cells, and are implicated in acquired immunity. In fungi, HSPs have been implicated in virulence, dimorphic transition, and drug resistance. Some HSPs are potential targets for therapeutic strategies. In this review, we discuss the current understanding of HSPs in dermatophytes, which are a group of keratinophilic fungi responsible for superficial mycoses in humans and animals. Computational analyses were performed to characterise the group of proteins in these dermatophytes, as well as to assess their conservation and to identify DNA-binding domains (5′-nGAAn-3′) in the promoter regions of the hsp genes. In addition, the quantification of the transcript levels of few genes in a pacC background helped in the development of an extended model for the regulation of the expression of the hsp genes, which supports the participation of the pH-responsive transcriptional regulator PacC in this process.

Amorolfine 5% Nail Lacquer Exhibits Potent Antifungal Activity Compared to Three Acid-Based Devices Indicated for the Treatment of Onychomycosis: An In Vitro Nail Penetration Assay

Introduction

Onychomycosis is the most common infectious disease involving nails. The aim of this study was to evaluate the antifungal activity of amorolfine 5% nail lacquer and three different acid-based medical devices indicated in the treatment of onychomycosis using an in vitro nail penetration assay.

Methods

Four products were tested in vitro: (a) amorolfine 5% nail lacquer; (b) ethyl lactate and acetic acid; (c) citric acid and urea; (d) ethyl lactate, glycerin, lactic acid, and citric acid. Test products were applied to healthy human cadaver nails and allowed to dry. Disks were cut from each piece of nail and placed on seeded agar plates of Trichophyton rubrum. Following incubation at 30 °C, zones of inhibition were measured.

Results

Amorolfine-treated nails exhibited inhibitory activity against T. rubrum with a mean zone of inhibition of 59.2 mm in diameter. In contrast, all three acid-based medical devices and the untreated controls showed no zones of inhibition (mean effective zones of 0 mm).

Conclusion

In this in vitro nail penetration model, head-on, comparative study, we showed that amorolfine 5% nail lacquer possesses potent antifungal activity, whereas no antifungal activity was detected for three commercially available acid-based medical devices under identical assay conditions.

Funding

Galderma.

Electronic supplementary material

The online version of this article (doi:10.1007/s13555-016-0093-x) contains supplementary material, which is available to authorized users.

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 activity of chitooligosaccharides against the dermatophyte Trichophyton rubrum

Antifungal activity against the dermatophytic fungus Trichophyton rubrum by a well-characterized chitooligosaccharides (COS) sample, hydrolyzed using a recombinant chitosanase, was investigated in vitro and in vivo. The minimum inhibitory concentration (MIC) of COS ranged between 0.25 and 0.50%, which was measured using a microdilution method. Analysis of inhibition rates using an agar diffusion method showed that treatment with 0.5% and 1% COS significantly suppressed T. rubrum cell growth (p<0.05 and p<0.01, respectively, in comparison with untreated control). Morphological changes and structural alterations of cells were observed by TEM. In vivo efficacy of COS in treatment of T. rubrum dermatophytosis was evaluated using a guinea pig model. Skin lesion scores revealed a strong, dose-dependent therapeutic effect of COS. The 5% COS group showed a reduction of skin lesions even greater than that of the positive control group treated with 1% fluconazole (FCZ). Histological analysis revealed no inflammation or tissue destruction in the groups treated with 5% COS or 1% FCZ. Hyperkeratosis was also observed, perhaps resulting from a defensive response of the tissue cells to COS. The findings indicate that COS has excellent potential for development of novel antifungal drugs for clinical treatment/remission of dermatophytoses.

Ambient pH sensing in filamentous fungi: pitfalls in elucidating regulatory hierarchical signaling networks

In this article, the experiments used to construct the ambient pH-signaling network involved in the secretion of enzymes by filamentous fungi have been reviewed, focusing on the phosphate-repressible phosphatases in Aspergillus nidulans. Classic and molecular genetics have been used to demonstrate that proteolysis of the transcription factor PacC at alkaline ambient pH is imperative for its action, implying that the full-length version is not an active molecular form of PacC. It has been hypothesized that the transcriptional regulator PacC may be functional at both acidic and alkaline ambient pH, in either the full-length or the proteolyzed form, if it carries a pal-dependent molecular tag. The products of the pal genes are involved in a metabolic pathway that led to the synthesis of effector molecules that tag the pacC product, perhaps facilitating its proteolysis.

Adaptation to pH and role of PacC in the rice blast fungus Magnaporthe oryzae

Fungi are known to adapt to pH partly via specific activation of the Pal signaling pathway and subsequent gene regulation through the transcription factor PacC. The role of PacC in pathogenic fungi has been explored in few species, and each time its partaking in virulence has been found. We studied the impact of pH and the role of PacC in the biology of the rice pathogen Magnaporthe oryzae. Conidia formation and germination were affected by pH whereas fungal growth and appressorium formation were not. Growth in vitro and in planta was characterized by alkalinization and ammonia accumulation in the surrounding medium. Expression of the MoPACC gene increased when the fungus was placed under alkaline conditions. Except for MoPALF, expression of the MoPAL genes encoding the pH-signaling components was not influenced by pH. Deletion of PACC caused a progressive loss in growth rate from pH 5 to pH 8, a loss in conidia production at pH 8 in vitro, a loss in regulation of the MoPALF gene, a decreased production of secreted lytic enzymes and a partial loss in virulence towards barley and rice. PacC therefore plays a significant role in M. oryzae’s biology, and pH is revealed as one component at work during interaction between the fungus and its host plants.

PacC and pH-dependent transcriptome of the mycotrophic fungus Trichoderma virens

BACKGROUND

In fungi, environmental pH is an important signal for development, and successful host colonization depends on homeostasis. Surprisingly, little is known regarding the role of pH in fungal-fungal interactions. Species of Trichoderma grow as soil saprobes but many are primarily mycotrophic, using other fungi as hosts. Therefore, Trichoderma spp. are studied for their potential in biocontrol of plant diseases. Particularly in alkaline soil, pH is a critical limiting factor for these biofungicides, whose optimal growth pH is 4-6. Gaining an understanding of pH adaptability is an important step in broadening the activity spectrum of these economically important fungi.

RESULTS

We studied the pH-responsive transcription factor PacC by gene knockout and by introduction of a constitutively active allele (pacCc). ΔpacC mutants exhibited reduced growth at alkaline pH, while pacCc strains grew poorly at acidic pH. In plate confrontation assays ΔpacC mutants showed decreased ability to compete with the plant pathogens Rhizoctonia solani and Sclerotium rolfsii. The pacCc strain exhibited an overgrowth of R. solani that was comparable to the wild type, but was unable to overgrow S. rolfsii. To identify genes whose expression is dependent on pH and pacC, we designed oligonucleotide microarrays from the transcript models of the T. virens genome, and compared the transcriptomes of wild type and mutant cultures exposed to high or low pH. Transcript levels from several functional classes were dependent on pacC, on pH, or on both. Furthermore, the expression of a set of pacC-dependent genes was increased in the constitutively-active pacCc strain, and was pH-independent in some, but not all cases.

CONCLUSIONS

PacC is important for biocontrol-related antagonism of other fungi by T. virens. As much as 5% of the transcriptome is pH-dependent, and of these genes, some 25% depend on pacC. Secondary metabolite biosynthesis and ion transport are among the relevant gene classes. We suggest that ΔpacC mutants may have lost their full biocontrol potential due to their inability to adapt to alkaline pH, to perceive ambient pH, or both. The results raise the novel possibility of genetically manipulating Trichoderma in order to improve adaptability and biocontrol at alkaline pH.

Transcription of N- and O-linked mannosyltransferase genes is modulated by the pacC gene in the human dermatophyte Trichophyton rubrum

In fungi, ambient pH sensing involves the activation of the Pal/PacC signalling pathway. In the dermatophyte Trichophyton rubrum, pH-dependent secretion of keratinases, which are major virulence determinants, is affected by disruption of the pacC gene. Here, the transcription profiling of the genes coding for N- and O-linked mannosyltransferases, enzymes involved in protein glycosylation, was evaluated in T. rubrum in response to disruption of the pacC gene and growth in keratin, glucose, and glucose plus glycine. We show that transcription of these mannosyltransferase genes is affected by nutrients at acidic pH and by PacC.