Clinical factors associated with systemic sporotrichosis in Brazil.

BACKGROUND: Systemic sporotrichosis occurs when organs, other than subcutaneous tissues and lymph nodes, are infected. Interestingly, systemic sporotrichosis in apparently immunocompetent individuals is increasing in Brazil, but data on clinical manifestations and risk factors are scarce. Most of the existing data on such condition relate to people living with HIV. We aimed to study the risk factors associated with systemic sporotrichosis among HIV-negative and HIV-positive patients. METHODS: We performed a retrospective cross-sectional study with 80 patients from Brazil, diagnosed between 2014 and 2021. The association between disease classification, clinical presentation and risk factors were analysed by logistic regression. RESULTS: Of the 80 patients, 29 (36.3%) presented with systemic sporotrichosis. All HIV-positive patients developed the systemic form, with increased mortality (p = .002). Alcohol ingestion (p = .009) and diabetes (p = .010) were associated with systemic disease. Alcohol ingestion seemed to favour pulmonary infection (p = .013) and, diabetes favoured osteoarticular (p = .009) and ocular involvement (p = .033). The occurrence of fever (p = .001) and weight loss (p = .006) were significantly associated with systemic sporotrichosis, while meningeal involvement (p = .001) increased mortality risk. Nine (11.3%) patients died from sporotrichosis. The presence of fungal structures in the mycological examination of the patients' lesions were associated with the systemic form (p = .017) and death (p = .002). CONCLUSION: Our study points to the factors that drive systemic sporotrichosis other than HIV, such as alcohol ingestion and diabetes. Considering the high number of patients presenting severe sporotrichosis, the recognising these factors may contribute to timely diagnosis and proper treatment.

COVID-19 and candiduria: an investigation of the risk factors and immunological aspects.

Secondary fungal infections are frequently observed in COVID-19 patients. However, the occurrence of candiduria in these patients and its risk factors are underexplored. We evaluated the risk factors of candiduria in COVID-19 patients, including inflammatory mediators that could be used as prognostic markers. Clinical information, laboratory test results, and outcomes were collected from severely ill COVID-19 patients with and without candiduria. Candida species identification, antifungal susceptibility, and plasma inflammatory mediators' measurements were performed. Regression logistic and Cox regression model were used to evaluate the risk factors. A higher risk of longer hospitalization and mortality were observed in patients with candiduria compared to those with COVID-19 only. Candiduria was caused by Candida albicans, C. glabrata, and C. tropicalis. Isolates with intermediate susceptibility to voriconazole and resistant to caspofungin were identified. Classic factors such as the use of corticosteroids and antibacterials, the worsening of renal function, and hematological parameters (hemoglobin and platelets) were found to predispose to candiduria. The mediators IL-1ß, IL-1ra, IL-2, CXCL-8, IL-17, IFN-γ, basic FGF, and MIP-1ß were significantly increased in patients with COVID-19 and candiduria. Furthermore, IFN-γ, IL-1ra, and CXCL-8 were associated with the occurrence of candiduria in COVID-19 patients, whereas basic FGF, IL-1ß, and CXCL-8 were associated with the risk of death in these patients. Classical and immunological factors were associated with worse prognosis among patients with COVID-19 and candiduria. Some mediators, especially CXCL-8, can be a reliable biomarker of fungal coinfection and may guide the diagnostic and the treatment of these patients.

The Dynamics of Cryptococcus neoformans Cell and Transcriptional Remodeling during Infection.

The phenotypic plasticity of Cryptococcus neoformans is widely studied and demonstrated in vitro, but its influence on pathogenicity remains unclear. In this study, we investigated the dynamics of cryptococcal cell and transcriptional remodeling during pulmonary infection in a murine model. We showed that in Cryptococcus neoformans, cell size reduction (cell body ≤ 3 µm) is important for initial adaptation during infection. This change was associated with reproductive fitness and tissue invasion. Subsequently, the fungus develops mechanisms aimed at resistance to the host's immune response, which is determinant for virulence. We investigated the transcriptional changes involved in this cellular remodeling and found an upregulation of transcripts related to ribosome biogenesis at the beginning (6 h) of infection and a later (10 days) upregulation of transcripts involved in the inositol pathway, energy production, and the proteasome. Consistent with a role for the proteasome, we found that its inhibition delayed cell remodeling during infection with the H99 strain. Altogether, these results further our understanding of the infection biology of C. neoformans and provide perspectives to support therapeutic and diagnostic targets for cryptococcosis.

Exposure to itraconazole influences the susceptibility to antifungals, physiology, and virulence of Trichophyton interdigitale.

Dermatophytosis is the most common human skin infection worldwide caused by dermatophytes, such as Trichophyton interdigitale and Trichophyton rubrum. Itraconazole (ITZ) is one of the main antifungals used to treat these infections. However, especially for onychomycosis, the treatment requires long-term regimens, increasing the possibility of drug resistance. We evaluated the effects of ITZ in the physiology, virulence, and interaction of T. interdigitale with phagocytes and mice cutaneous infection. In a screening test, fungal growth in the presence of ITZ led to the spontaneous selection of less susceptible T. interdigitale and T. rubrum strains. Interestingly, this phenotype was permanent for some T. interdigitale strains. Then, we studied three T. interdigitale strains: one susceptible and two ITZ-adapted. The ITZ-adapted strains were also less susceptible to the cell wall and membrane stressors, suggesting a multidrug resistance (MDR) phenotype associated with the increased ERG11 and MDR3 expression. These strains also presented substantial alterations in ergosterol content, lipid peroxidation, biofilm, and extracellular matrix production. During interaction with macrophages, ITZ-adapted strains were less engulfed but increased the intracellular oxidative and nitrosative bursts. In addition, ITZ-adapted strains presented a reduced ability to grow in a murine model of dermatophytosis, although causing the same tissue damage as the parental strain. In conclusion, the T. interdigitale ITZ adaptation increases tolerance to antifungals and alters the interaction with macrophages and a mammalian host. We hypothesized that successive exposure to ITZ may influence the emergence of adapted strains and lead to the recalcitrance of dermatophytosis.

The impact of COVID-19 on antimicrobial prescription and drug resistance in fungi and bacteria.

Secondary infections are one of the complications in COVID-19 patients. We aimed to analyze the antimicrobial prescriptions and their influence on drug resistance in fungi and bacteria isolated from severely ill COVID-19 patients. Seventy-nine severely ill COVID-19 hospitalized patients with secondary bacterial or fungal infections were included. We analyzed the prescribed antimicrobial regimen for these patients and the resistance profiles of bacterial and fungal isolates. In addition, the association between drug resistance and patients' outcome was analyzed using correlation tests. The most prescribed antibacterial were ceftriaxone (90.7% of patients), vancomycin (86.0%), polymyxin B (74.4%), azithromycin (69.8%), and meropenem (67.4%). Micafungin and fluconazole were used by 22.2 and 11.1% of patients, respectively. Multidrug-resistant (MDR) infections were a common complication in severely ill COVID-19 patients in our cohort since resistant bacteria strains were isolated from 76.7% of the patients. Oxacillin resistance was observed in most Gram-positive bacteria, whereas carbapenem and cephalosporin resistance was detected in most Gram-negative strains. Azole resistance was identified among C. glabrata and C. tropicalis isolates. Patients who used more antimicrobials stayed hospitalized longer than the others. The patient's age and the number of antibacterial agents used were associated with the resistance phenotype. The susceptibility profile of isolates obtained from severely ill COVID-19 patients highlighted the importance of taking microbial resistance into account when managing these patients. The continuous surveillance of resistant/MDR infection and the rational use of antimicrobials are of utmost importance, especially for long-term hospitalized patients with COVID-19.

The bZIP Ap1 transcription factor is a negative regulator of virulence attributes of the anthropophilic dermatophyte Trichophyton rubrum.

Trichophyton rubrum is a fungus that causes chronic skin and nail infections in healthy individuals and immunocompromised patients. During infection, T. rubrum invades host cutaneous tissues by adapting to the acidic pH and the innate immune response of the host. Several genes are upregulated during the growth of T. rubrum in substrates found in human tissue, including the ap1 gene, which codes for the transcription factor Ap1. Here, we generated a null mutant strain by deleting the T. rubrum ap1 gene and performed a functional analysis of this gene. Our results showed that the Δap1mutant increased its growth in nail fragments and co-cultures with keratinocytes compared to the wild type. Furthermore, the mutant displayed hyperpigmentation, thickening of the conidia cell wall, increased conidia susceptibility to calcofluor-white compared to the wild type, and loss of control of the keratinolytic activity. Although the ap1 gene was upregulated during exposure to the antifungal drugs amphotericin B, nystatin, and terbinafine, its deletion did not alter the fungal susceptibility to these drugs, revealing the role of the ap1 gene in the physiological response to the stress caused by these drugs, but not in their resistance. Moreover, ap1 was also involved in the oxidative stress response caused by menadione, but not paraquat or hydrogen peroxide. These findings indicate that the ap1 gene plays a role in the negative control of virulence-related attributes and may contribute to the chronicity of nail infection caused by T. rubrum.

Reactive oxygen and nitrogen species are crucial for the antifungal activity of amorolfine and ciclopirox olamine against the dermatophyte Trichophyton interdigitale.

Onychomycosis is a nail infection caused by Trichophyton interdigitale and other fungi, which can be treated with topical amorolfine (AMR) and ciclopirox olamine (CPX). Although these drugs are widely used, little is known about the role of reactive oxygen (ROS) and nitrogen (RNS) in their mechanism of action. To better understand the effects of AMR and CPX in dermatophytes, we evaluated whether they act through the production of ROS and peroxynitrite (PRN). We tested a set of strains, all susceptible to AMR and CPX, and these antifungals significantly reduced T. interdigitale viability within 24 h. This effect occurred concomitantly with reduced ergosterol, increased production of ROS and PRN, and consequently increased lipid peroxidation. Together, these mechanisms lead to cell damage and fungal death. These fungicidal effects were abolished when PRN and superoxide scavengers were used in the assays, demonstrating the role of these species in the mechanism of action. We also studied the antioxidant system when T. interdigitale was exposed to AMR and CPX. Interestingly, superoxide dismutase and catalase inhibition lead to altered ROS and PRN production, lipid peroxidation, and ergosterol levels. In fact, the combination of AMR or CPX with a superoxide dismutase inhibitor was antagonistic. Together, these data demonstrate the importance of ROS and PRN in the antifungal action of AMR and CPX against the evaluated T. interdigitale strains. LAY SUMMARY: Onychomycosis is a nail infection, which can be treated with amorolfine and ciclopirox olamine. Here we demonstrate that these drugs exhibit antifungal activity also through the production of oxidative and nitrosative radicals.

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.

Reassessing the Use of Undecanoic Acid as a Therapeutic Strategy for Treating Fungal Infections.

Treating fungal infections is challenging and frequently requires long-term courses of antifungal drugs. Considering the limited number of existing antifungal drugs, it is crucial to evaluate the possibility of repositioning drugs with antifungal properties and to revisit older antifungals for applications in combined therapy, which could widen the range of therapeutic possibilities. Undecanoic acid is a saturated medium-chain fatty acid with known antifungal effects; however, its antifungal properties have not been extensively explored. Recent advances indicate that the toxic effect of undecanoic acid involves modulation of fungal metabolism through its effects on the expression of fungal genes that are critical for virulence. Additionally, undecanoic acid is suitable for chemical modification and might be useful in synergic therapies. This review highlights the use of undecanoic acid in antifungal treatments, reinforcing its known activity against dermatophytes. Specifically, in Trichophyton rubrum, against which the activity of undecanoic acid has been most widely studied, undecanoic acid elicits profound effects on pivotal processes in the cell wall, membrane assembly, lipid metabolism, pathogenesis, and even mRNA processing. Considering the known antifungal activities and associated mechanisms of undecanoic acid, its potential use in combination therapy, and the ability to modify the parent compound structure, undecanoic acid shows promise as a novel therapeutic against fungal infections.

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.

Acanthamoeba castellanii as an alternative interaction model for the dermatophyte Trichophyton rubrum.

BACKGROUND: Trichophyton rubrum (Tr) is the main aetiological agent of human dermatophytosis, being isolated from the environment and keratinised tissues. In the environment, Tr can interact with other organisms, such as free-living amoebas (FLA), which can act as an alternative host system to study the interaction between microbes and phagocytic cells. OBJECTIVES: To characterise the Acanthamoeba castellanii (ALX)-Tr interaction. METHODS: Interaction was characterised in three conditions: trophozoites (PYG), late (PYG/NES) and early (NES) encystation stimulus, evaluating encystation kinetics, phagocytosis, exocytosis and fungicidal activity dynamics. RESULTS: Tr was able to induce ALX encystation and be internalised by ALX. The number of internalised conidia was high at 1 hour, and ALX presented fungicidal activity with increased intracellular ROS production and exocytosis. In PYG/NES, phagocytosis and ROS production were reduced, with decreased ALX's fungicidal activity. However, in NES there was an increased fungal engulfment, and a reduced ROS production and higher fungal burden. Furthermore, exogenous mannose decreased phagocytosis of Tr conidia, and divalent cations induced ROS production and increased ALX's fungicidal activity. Interestingly, phagocytosis was reduced in the presence of cytoskeleton inhibitor, but exocytosis was increased, suggesting that Tr conidia may have alternative pathways to escape ALX's cells. CONCLUSION: A castellanii is a proper model for studying Tr-FLA interaction, since ALX can engulf, produce ROS and kill Tr, and all these parameters are influenced by an encystation stimulus and divalent cations. Moreover, this interaction is likely to occur in the environment implicating in the adaptation to environmental stressful conditions in both organisms.

HacA Governs Virulence Traits and Adaptive Stress Responses in Trichophyton rubrum.

The ability of fungi to sense environmental stressors and appropriately respond is linked to secretory system functions. The dermatophyte infection process depends on an orchestrated signaling regulation that triggers the transcription of genes responsible for adherence and penetration of the pathogen into host-tissue. A high secretion system is activated to support the host-pathogen interaction and assures maintenance of the dermatophyte infection. The gateway of secretion machinery is the endoplasmic reticulum (ER), which is the primary site for protein folding and transport. Current studies have shown that ER stress that affects adaptive responses is primarily regulated by UPR and supports fungal pathogenicity; this has been assessed for yeasts and Aspergillus fumigatus, in regard to how these fungi cope with host environmental stressors. Fungal UPR consists of a transmembrane kinase sensor (Ire1/IreA) and a downstream target Hac1/HacA. The active form of Hac is achieved via non-spliceosomal intron removal promoted by endonuclease activity of Ire1/IreA. Here, we assessed features of HacA and its involvement in virulence and susceptibility in Trichophyton rubrum. Our results showed that exposure to antifungals and ER-stressing agents initiated the activation of HacA from T. rubrum. Interestingly, the activation occurs when a 20 nt fragment is removed from part of the exon-2 and part of intron-2, which in turn promotes the arisen of the DNA binding site motif and a dimer interface domain. Further, we found changes in the cell wall and cellular membrane composition in the ΔhacA mutant as well as an increase in susceptibility toward azole and cell wall disturbing agents. Moreover, the ΔhacA mutant presented significant defects in important virulence traits like thermotolerance and growth on keratin substrates. For instance, the development of the ΔhacA mutant was impaired in co-culture with keratinocytes or human nail fragments. Changes in the pro-inflammatory cytokine release were verified for the ΔhacA mutant during the co-culture assay, which might be related to differences in pathogen-associated molecular patterns (PAMPs) in the cell wall. Together, these results suggested that HacA is an integral part of T. rubrum physiology and virulence, implying that it is an important molecular target for antidermatophytic therapy.

Genes coding for LysM domains in the dermatophyte Trichophyton rubrum: A transcription analysis.

The filamentous fungus Trichophyton rubrum is a pathogen that causes superficial mycoses in humans, predominantly in keratinized tissues. The occurrence of dermatophytoses has increased in the last decades, mainly in immunocompromised patients, warranting research on the mechanisms involved in dermatophyte virulence. The genomes of dermatophytes are known to be enriched in genes coding for proteins containing the LysM domain, a carbohydrate-binding module, indicating the possible involvement of these genes in virulence. Although the LysM domains have already been described in other fungi, their biological functions in dermatophytes are unknown. Here we assessed the transcription of genes encoding proteins containing the LysM domains in T. rubrum grown on different substrates using quantitative real-time polymerase chain reaction. Some of these genes showed changes in transcription levels when T. rubrum was grown on keratin. In silico analyses suggest that some of these proteins share features, namely, they are anchored in the plasma membrane and contain the catalytic domain chitinase II and signal peptide domains. Here we show a detailed study of genes encoding the proteins with LysM-containing domains in T. rubrum, aiming to contribute to the understanding of their functions in dermatophytes.

Macrophages From Subjects With Isolated GH/IGF-I Deficiency Due to a GHRH Receptor Gene Mutation Are Less Prone to Infection by Leishmania amazonensis.

Isolated growth hormone (GH) deficiency (IGHD) affects approximately 1 in 4,000 to 1 in 10,000 individuals worldwide. We have previously described a large cohort of subjects with IGHD due to a homozygous mutation in the GH releasing hormone (GHRH) receptor gene. These subjects exhibit throughout the life very low levels of GH and its principal mediator, the Insulin Growth Factor-I (IGF-I). The facilitating role of IGF-I in the infection of mouse macrophages by different Leishmania strains is well-known. Nevertheless, the role of IGF-I in Leishmania infection of human macrophages has not been studied. This study aimed to evaluate the behavior of Leishmania infection in vitro in macrophages from untreated IGHD subjects. To this end, blood samples were collected from 14 IGHD individuals and 14 age and sex-matched healthy controls. Monocytes were isolated and derived into macrophages and infected with a strain of Leishmania amazonensis. In addition, IGF-I was added to culture medium to evaluate its effect on the infection. Cytokines were measured in the culture supernatants. We found that macrophages from IGHD subjects were less prone to Leishmania infection compared to GH sufficient controls. Both inflammatory and anti-inflammatory cytokines increase only in the supernatants of the control macrophages. Addition of IGF-I to the culture medium increased infection rates. In conclusion, we demonstrated that IGF-I is crucial for Leishmania infection of human macrophages.

Dermatophyte Resistance to Antifungal Drugs: Mechanisms and Prospectus.

Dermatophytes comprise pathogenic fungi that have a high affinity for the keratinized structures present in nails, skin, and hair, causing superficial infections known as dermatophytosis. A reasonable number of antifungal drugs currently exist on the pharmaceutical market to control mycoses; however, their cellular targets are restricted, and fungi may exhibit tolerance or resistance to these agents. For example, the stress caused by antifungal and cytotoxic drugs in sub-inhibitory concentrations promotes compensatory stress responses, with the over-expression of genes involved in cellular detoxification, drug efflux, and signaling pathways being among the various mechanisms that may contribute to drug tolerance. In addition, the ATP-binding cassette transporters in dermatophytes that are responsible for cellular efflux can act synergistically, allowing one to compensate for the absence of the other, revealing the complexity of drug tolerance phenomena. Moreover, mutations in genes coding for target enzymes could lead to substitutions in amino acids involved in the binding of antifungal agents, hindering their performance and leading to treatment failure. The relevance of each one of these mechanisms of resistance to fungal survival is hard to define, mainly because they can act simultaneously in the cell. However, an understanding of the molecular mechanisms involved in the resistance/tolerance processes, the identification of new antifungal targets, as well as the prospective of new antifungal compounds among natural or synthetic products, are expected to bring advances and new insights that facilitate the improvement or development of novel strategies for antifungal therapy.

Leishmania infantum Induces the Release of sTREM-1 in Visceral Leishmaniasis.

Visceral leishmaniasis (VL) is a systemic transmissible disease that remains to be a major global health problem. The inflammatory response during VL is characterized by the release of several cytokines and other pro-inflammatory mediators. Triggering Receptor Expressed on Myeloid Cells (TREM) are a group of evolutionarily conserved membrane-bound surface receptors expressed on neutrophils and monocytes. Engagement of TREM-1 directs intracellular signaling events that drive cytokine production, degranulation, and phagocytosis. In certain inflammatory-associated diseases, TREM-1 can also be found as a soluble form (sTREM-1), which can negatively regulate TREM-1 receptor signaling. In these studies, we now find that high levels of circulating sTREM-1 correlate directly with VL disease severity. In particular, high levels of sTREM-1 were observed in non-survivor VL patients. Furthermore, these levels of sTREM-1 positively correlated with liver size and negatively correlated with leukocyte counts and hemoglobin concentration. Moreover, we found that neutrophils exposure in vitro to Leishmania infantum modulates TREM-1, DAP12, and IL-8 gene expression, while also increasing release of sTREM-1. Finally, results revealed that higher sTREM-1 levels are associated with increasing parasite ratio. Taken together, these studies suggest that L. infantum may modulate TREM-1 in neutrophils and high levels of this molecule is associated with severe VL.

Pathogenesis of Dermatophytosis: Sensing the Host Tissue.

The genera Trichophyton, Microsporum, and Epidermophyton include filamentous fungi that cause dermatophytosis, a superficial infection of the skin, stratum corneum, nail beds, and hair follicles. The ability of dermatophytes to adhere to these substrates and adapt to the host environment is essential for the establishment of infection. Several fungal enzymes and proteins participate in this adaptive response to the environment and to keratin degradation. Transcription factors such as PacC and Hfs1, as well as heat shock proteins, are involved in sensing and adapting to the acidic pH of the skin in the early stages of fungal-host interaction. During dermatophyte growth, with keratin as the sole carbon source, the extracellular pH shifts from acidic to alkaline. This creates an environment in which most of the known keratinolytic proteases exhibit optimal activity. These events culminate in the establishment and maintenance of the infection, which can be chronic or acute depending on the dermatophyte species. This review focuses on these and other molecular aspects of the dermatophyte-host interaction.

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.

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.