Candidalysin is a fungal peptide toxin critical for mucosal infection

Candidalysin biology and activation of host cells

Candida albicans is an opportunistic fungal pathogen that can cause life-threatening systemic infections and distressing mucosal infections. A major breakthrough in understanding C. albicans pathogenicity was the discovery of candidalysin, the first cytolytic peptide toxin identified in a human pathogenic fungus. Secreted by C. albicans hyphae and encoded by the ECE1 gene, this 31-amino acid peptide integrates into and permeabilizes host cell membranes, causing damage across diverse cell types. Beyond its cytolytic activity, candidalysin can trigger potent innate immune responses in epithelial cells, macrophages, and neutrophils. Additionally, candidalysin plays a key role in nutrient acquisition during infection. This review explores the biology of candidalysin, its role in host cell activation, and extends the discussion to non-candidalysin Ece1p peptides, shedding light on their emerging significance.

Deletion of RAP1 affects iron homeostasis, azole resistance, and virulence in Candida albicans

Rap1 is a DNA-binding protein conserved from yeast to mammals for its role in telomeric maintenance. Here, to explore additional functions of Candida albicans Rap1, we performed RNA sequencing analysis. Experimental validations further showed that Rap1 plays a role in iron regulation, especially under low-iron conditions. Moreover, Rap1 was involved in iron acquisition and modulation of iron-related genes. Rap1 was found to be associated with fluconazole resistance in a low-iron condition. Finally, we demonstrated that the deletion of RAP1 leads to reduced C. albicans virulence in a mouse model of infection. Together, this study reveals new functions of C. albicans Rap1, particularly in iron homeostasis, azole resistance, and virulence.

IMPORTANCE

Candida albicans is an important pathogenic fungus that can cause superficial to life-threatening infections. Iron is essential for almost all organisms, yet it is highly restricted within the human host to defend against pathogens. To grow and survive in the iron-limited host environment, C. albicans has evolved multiple iron acquisition mechanisms. Understanding the regulation of iron homeostasis is, therefore, critical for elucidating C. albicans pathogenesis and virulence. This study explores the novel functions of C. albicans Rap1, with a focus on its contribution to iron acquisition and utilization. Our findings further highlight how iron availability impacts antifungal resistance and virulence through Rap1, providing insight into the complex iron regulatory machinery of C. albicans.

Candidalysin induces Tim-3 expression in macrophages to suppress antifungal immunity in oropharyngeal candidiasis

Oropharyngeal candidiasis significantly impacts patients' quality of life. Although the immune mechanisms underlying OPC have been explored, the roles of immune checkpoints and macrophages in this context remain unclear. We employed single-cell techniques to analyze changes in the oral immune microenvironment and explored the role of Tim-3 in OPC. Our single-cell analysis identified distinct macrophage subpopulations in OPC tissue, each exhibiting heterogeneous antifungal immune responses. Further investigation revealed that candidalysin induces Tim-3, which primarily reduces the proportion of macrophage subpopulations 1 and 2 in OPCs. Additionally, it suppresses the inflammatory response during infection. Experimental research showed that Tim-3 inhibited the P65 inflammatory signaling pathway in macrophages, thereby reducing the secretion of inflammatory cytokines such as l1b, Il6, Tnf, Il23, and chemokines including Ccl2, Cxcl1, Cxcl2, Cxcl3, and Cxcl5. Additionally, Tim-3 promoted macrophage apoptosis, potentially contributing to the decreased proportion of macrophages. We also found that Tim-3 suppressed the phagocytic and killing functions of macrophages against C.albicans. Notably, our research revealed that Tim-3's ligand, Galectin-9, also exhibits functional similarities to Tim-3. Specifically, the Galectin-9 gene, Lgals9, is also induced by candidalysin. This study identifies candidalysin in inhibiting macrophage responses to C.albicans through the induction of Galectin-9/Tim-3 in oral mucosal immunity, potentially representing a novel mechanism of immune evasion by C.albicans in OPC. Therefore, our research provides a basis for considering this axis as a potential therapeutic target.

Commensalism and pathogenesis of Candida albicans at the mucosal interface

Fungi are important and often underestimated human pathogens. Infections with fungi mostly originate from the environment, from soil or airborne spores. By contrast, Candida albicans, one of the most common and clinically important fungal pathogens, permanently exists in the vast majority of healthy individuals as a member of the human mucosal microbiota. Only under certain circumstances will these commensals cause infections. However, although the pathogenic behaviour and disease manifestation of C. albicans have been at the centre of research for many years, its asymptomatic colonization of mucosal surfaces remains surprisingly understudied. In this Review, we discuss the interplay of the fungus, the host and the microbiome on the dualism of commensal and pathogenic life of C. albicans, and how commensal growth is controlled and permitted. We explore hypotheses that could explain how the mucosal environment shapes C. albicans adaptations to its commensal lifestyle, while still maintaining or even increasing its pathogenic potential.

Transcriptional control of C. albicans white-opaque switching and modulation by environmental cues and strain background

The opportunistic fungal pathogen Candida albicans can undergo cellular transitions in response to environmental cues that impact its lifestyle and its interactions with the human host. This is exemplified by the white-opaque switch, which is a heritable transition between two phenotypic states that is regulated by a highly interconnected network of transcription factors (TFs). To obtain greater understanding of the transcriptional regulation of the switch, we generated a genome-wide, tetracycline-inducible TF library in the WO-1 strain background and identified those TFs whose forced expression induces white cells to switch to the opaque state. This set of opaque-inducing TFs was also evaluated for their ability to induce switching in a second strain background, that of the standard reference strain SC5314, as well as during growth on different laboratory media. These experiments identify 14 TFs that can drive white-to-opaque switching when overexpressed but that do so in a highly strain- and media-specific manner. In particular, changes in pH, amino acids, and zinc concentrations had marked effects on the ability of TFs to drive phenotypic switching. These results provide insights into the complex transcriptional regulation of switching in C. albicans and reveal that an interplay between genetic and environmental factors determines TF function and cell fate.IMPORTANCEThe white-opaque switch in Candida albicans represents a model system for understanding an epigenetic switch in a eukaryotic pathogen. Here, we generated an inducible library of the set of transcription factors (TFs) present in C. albicans and identify 14 TFs that can drive the white-to-opaque transition when ectopically expressed. We demonstrate that several of these TFs induce the switch in a highly strain- and media-specific manner. This highlights that both strain background and changes in experimental conditions (including different water sources) can profoundly impact the phenotypic consequences of TF overexpression. Moreover, the inducible TF library provides an invaluable tool for the further analysis of TF function in this important human pathogen.

Nanoparticle-based antifungal therapies innovations mechanisms and future prospects

Fungal infections present an increasing global health challenge, with a substantial annual mortality rate of 1.6 million deaths each year in certain situations. The emergence of antifungal resistance has further complicated treatment strategies, underscoring the urgent need for novel therapeutic approaches. This review explores recent advances in nanoparticle-based therapies targeting fungal infections, emphasizing their unique potential to enhance drug solubility, bioavailability, and targeted delivery. Nanoparticles offer the ability to penetrate biological barriers, improve drug stability, and act as direct antifungal agents by disrupting fungal cell walls and generating reactive oxygen species. Despite their promising applications, challenges such as potential toxicity, scalability of production, and the need for controlled drug release remain. Future research should focus on optimizing nanoparticle properties, evaluating long-term safety profiles, developing environmentally sustainable synthesis methods, and exploring synergistic approaches with existing antifungal drugs. Nanotechnology offers a transformative opportunity in the management of fungal diseases, paving the way for more effective and targeted treatments.

Hyphal penetration is the major pathway of translocation of Candida albicans across the blood-cerebrospinal fluid barrier

BACKGROUND

Despite the availability of potent antifungal compounds, invasive fungal disease poses significant morbidity and mortality in immunocompromised patients. Candida albicans is one of the leading pathogens in this setting, and may affect the central nervous system (CNS), which is an extremely severe form of the infection. As the exact pathogenesis of Candida CNS infection is not clear, we investigated the mechanisms and effects of C. albicans transmigration into the CNS, which will be helpful for diagnosis, prevention and treatment.

METHODS

We used a human in vitro model of the Blood-Cerebrospinal Fluid Barrier (BCSFB), and we investigated the mechanisms of Candida albicans translocation into the CNS. Translocation was evaluated using immunofluorescence analysis focusing on tight and adherens junctions and the actin cytoskeleton. Barrier integrity was monitored via measurement of transepithelial resistance and the paracellular permeability of dextran. LIVE/DEAD assays were applied for viability controls and a cytometric bead array was performed to detect cytokine secretion of plexus epithelial cells.

RESULTS

Translocation at low doses occurs transcellularly in the absence of cytotoxicity or secretion of proinflammatory cytokines. This is accomplished by the formation of a tunnel-like structure exploiting the actin cytoskeleton. With higher infection doses of Candida albicans, a reduction in barrier integrity due to disruption of tight and adherens junctions was observed and cytotoxicity also increased.

CONCLUSION

Our findings reveal that Candida albicans can use transcellular translocation to invade into the CNS and is able to circumvent major host immune response, which may impact on diagnostic and preventive strategies.

Forward genetic screen in zebrafish identifies new fungal regulators that limit host-protective Candida-innate immune interaction

Candida is one of the most frequent causes of bloodstream infections, and our first line of defense against these invasive infections is the innate immune system. The early immune response is critical in controlling Candida albicans infection, but C. albicans has several strategies to evade host immune attack. Phagocytosis of C. albicans blocks hyphal growth, limiting host damage and virulence, but how C. albicans limits early recruitment and phagocytosis in vertebrate infection is poorly understood. To study innate immune evasion by intravital imaging, we utilized the transparent larval zebrafish infection model to screen 131 C. albicans mutants for altered virulence and phagocyte response. Infections with each of the seven hypovirulent mutants led to altered phagocyte recruitment and/or phagocytosis, falling into four categories. Of particular interest among these is NMD5, a predicted β-importin and newly identified virulence factor. The nmd5∆/∆ mutant fails to limit phagocytosis, and its virulence defects are eliminated when phagocyte activity is compromised, suggesting that its role in virulence is limited to immune evasion. These quantitative intravital imaging experiments are the first to document altered Candida-phagocyte interactions for several additional mutants and clearly distinguish recruitment from phagocytic uptake, suggesting that Candida modulates both events. This initial large-scale screen of individual C. albicans mutants in a vertebrate, coupled with high-resolution imaging of Candida-phagocyte interactions, provides a more nuanced view of how diverse mutations can lead to more effective phagocytosis, a key immune process that blocks germination and drives anti-fungal immunity.

IMPORTANCE

Candida albicans is part of the human microbial community and is a dangerous opportunistic pathogen, able to prevent its elimination by the host immune system. Although Candida avoids immune attack through several strategies, we still understand little about how it regulates when immune phagocytes get recruited to the infection site and when they engulf fungal cells. We tested over 130 selected Candida mutants for their ability to cause lethal infection and found several hypovirulent mutants, which provoked altered innate immune responses, resulting in lower overall inflammation and greater host survival. Of particular interest is NMD5, which acts to limit fungal phagocytosis and is predicted to regulate the activity of stress-associated transcription factors. Our high-content screening was enabled by modeling Candida infection in transparent vertebrate zebrafish larva. Our findings help us understand how Candida survives immune attack during commensal and pathogenic growth, and may eventually inform new strategies for controlling disease.

Leveraging Organ-on-Chip Models to Investigate Host-Microbiota Dynamics and Targeted Therapies for Inflammatory Bowel Disease

Inflammatory bowel disease (IBD) is an idiopathic gastrointestinal disease with drastically increasing incidence rates. Due to its multifactorial etiology, a precise investigation of the pathogenesis is extremely difficult. Although reductionist cell culture models and more complex disease models in animals have clarified the understanding of individual disease mechanisms and contributing factors of IBD in the past, it remains challenging to bridge research and clinical practice. Conventional 2D cell culture models cannot replicate complex host-microbiota interactions and stable long-term microbial culture. Further, extrapolating data from animal models to patients remains challenging due to genetic and environmental diversity leading to differences in immune responses. Human intestine organ-on-chip (OoC) models have emerged as an alternative in vitro model approach to investigate IBD. OoC models not only recapitulate the human intestinal microenvironment more accurately than 2D cultures yet may also be advantageous for the identification of important disease-driving factors and pharmacological interventions targets due to the possibility of emulating different complexities. The predispositions and biological hallmarks of IBD focusing on host-microbiota interactions at the intestinal mucosal barrier are elucidated here. Additionally, the potential of OoCs to explore microbiota-related therapies and personalized medicine for IBD treatment is discussed.

Candida Infections: The Role of Saliva in Oral Health-A Narrative Review

Candida species, particularly Candida albicans, are causative agents of oral infections to which immunocompromised patients are especially susceptible. Reduced saliva flow (xerostomia) can lead to Candida overgrowth, as saliva contains antibacterial components such as histatins and β-defensins that inhibit fungal growth and adhesion to the oral mucosa. Candida adheres to host tissues, forms biofilms, and secretes enzymes required for tissue invasion and immune evasion. Secretory asparaginyl proteinases (Saps) and candidalysin, a cytolytic peptide toxin, are vital to Candida virulence, and agglutinin-like sequence (Als) proteins are crucial for adhesion, invasion, and biofilm formation. C. albicans is a risk factor for dental caries and may increase periodontal disease virulence when it coexists with Porphyromonas gingivalis. Candida infections have been suggested to heighten the risk of oral cancer based on a relationship between Candida species and oral squamous cell carcinoma (OSCC) or oral potentially malignant disorder (OPMD). Meanwhile, β-glucan in the Candida cell wall has antitumor effects. In addition, Candida biofilms protect viruses such as herpesviruses and coxsackieviruses. Understanding the intricate interactions between Candida species, host immune responses, and coexisting microbial communities is essential for developing preventive and therapeutic strategies against oral Candida infections, particularly in immunocompromised individuals.

Exploring the female genital tract mycobiome in young South African women using metaproteomics

BACKGROUND

Female genital tract (FGT) diseases such as bacterial vaginosis (BV) and sexually transmitted infections are prevalent in South Africa, with young women being at an increased risk. Since imbalances in the FGT microbiome are associated with FGT diseases, it is vital to investigate the factors that influence FGT health. The mycobiome plays an important role in regulating mucosal health, especially when the bacterial component is disturbed. However, we have a limited understanding of the FGT mycobiome since many studies have focused on bacterial communities and have neglected low-abundance taxonomic groups, such as fungi. To reduce this knowledge deficit, we present the first large-scale metaproteomic study to define the taxonomic composition and potential functional processes of the FGT mycobiome in South African reproductive-age women.

RESULTS

We examined FGT fungal communities present in 123 women by collecting lateral vaginal wall swabs for liquid chromatography-tandem mass spectrometry. From this, 39 different fungal genera were identified, with Candida dominating the mycobiome (53.2% relative abundance). We observed changes in relative abundance at the protein, genus, and functional (gene ontology biological processes) level between BV states. In women with BV, Malassezia and Conidiobolus proteins were more abundant, while Candida proteins were less abundant compared to BV-negative women. Correspondingly, Nugent scores were negatively associated with total fungal protein abundance. The clinical variables, Nugent score, pro-inflammatory cytokines, chemokines, vaginal pH, Chlamydia trachomatis, and the presence of clue cells were associated with fungal community composition.

CONCLUSIONS

The results of this study revealed the diversity of FGT fungal communities, setting the groundwork for understanding the FGT mycobiome. Video Abstract.

A Novel Benzopyrone Derivative from Streptomyces chrestomyceticus ADP4 Inhibits Growth and Virulence Factors of Candida albicans

Antimicrobial resistance (AMR) poses a serious threat to human health globally. Expeditious discovery and development of new drugs has become indispensable for addressing this challenge. In this context, a novel benzopyrone derivative, designated as 82B1, has been isolated from S. chrestomyceticus strain ADP4. This compound exhibited significant inhibitory activity against different Candida species including C. albicans, C. tropicalis, C. krusei, C. parapsilosis and C. auris with minimum inhibitory concentration (MIC90) values in the concentration range of 25-125 µg/mL. The structure of 82B1 was elucidated through analyses of the spectral data obtained using liquid chromatography-tandem mass spectrometry (LCMS/MS), Nuclear Magnetic Resonance (NMR), Fourier Transform Infrared Spectroscopy (FTIR) and Ultraviolet (UV) spectroscopy, that led to its identity as 7, 13, 14-trihydroxy-6H-benzo-[c]-chromen-6-one8-[1'β-carboxycyclopentanyl]-2'β-[8'β-ethylcyclopentane]. It significantly inhibited the major virulence factors of C. albicans such as yeast to hyphae transition, biofilm formation, and secretion of hydrolytic enzymes at its subinhibitory concentrations. It did not display cytotoxicity on human hepatoblastoma cell line (HepG2 cells), signifying its potential as a candidate for anti-Candida drug development.

Mycobiome: an underexplored kingdom in cancer

SUMMARYThe human microbiome, including bacteria, fungi, archaea, and viruses, is intimately linked to both health and disease. The relationship between bacteria and disease has received much attention and intensive investigation, while that of the fungal microbiome, also known as mycobiome, has lagged far behind bacteria. There is growing evidence showing mycobiome dysbiosis in cancer patients, and certain cancer-specific fungi may contribute to cancer progression by interacting with both host and bacteria. It was also demonstrated that the role of fungi-derived products in cancer should also not be underestimated. Therefore, investigating how fungal pathogenesis contributes to the onset and spread of cancer would yield crucial information for cancer diagnosis, prevention, and anti-cancer therapy.

Would global warming bring an increase of invertebrate-associated cutaneous invasive fungal infections?

Invasive mold-associated cutaneous disease is a rare but potentially catastrophic consequence of trauma. However, invertebrate bites are not well recognized as a mechanism for the inoculation of fungi into subcutaneous tissue that can also result in severe infections. Invertebrates often carry fungi with human pathogenic potential as part of their microbiome, and bites break the skin, providing a conduit for them to penetrate subcutaneous tissues where the establishment of infection can produce serious skin and soft tissue fungal diseases. In this essay, we review the existing data for invertebrate bite-associated cutaneous invasive fungal infections (IBA-cIFIs) and consider the potential consequences of global warming on their epidemiology. Climate changes will be associated with changes in the range of invertebrates and adaptation of their associated microbes to warmer temperatures. Fungal adaptation to higher temperatures can defeat the mammalian protective barrier and be associated with both more and different IBA-cIFIs.

Microbiota in inflammatory bowel disease: mechanisms of disease and therapeutic opportunities

Perturbations in the intestinal microbiome are strongly linked to the pathogenesis of inflammatory bowel disease (IBD). Bacteria, fungi and viruses all make up part of a complex multi-kingdom community colonizing the gastrointestinal tract, often referred to as the gut microbiome. They can exert various effects on the host that can contribute to an inflammatory state. Advances in screening, multiomics and experimental approaches have revealed insights into host-microbiota interactions in IBD and have identified numerous mechanisms through which the microbiota and its metabolites can exert a major influence on the gastrointestinal tract. Looking into the future, the microbiome and microbiota-associated processes will be likely to provide unparalleled opportunities for novel diagnostic, therapeutic and diet-inspired solutions for the management of IBD through harnessing rationally designed microbial communities, powerful bacterial and fungal metabolites, individually or in combination, to foster intestinal health. In this Review, we examine the current understanding of the cross-kingdom gut microbiome in IBD, focusing on bacterial and fungal components and metabolites. We examine therapeutic and diagnostic opportunities, the microbial metabolism, immunity, neuroimmunology and microbiome-inspired interventions to link mechanisms of disease and identify novel research and therapeutic opportunities for IBD.

Roles of P-body factors in Candida albicans filamentation and stress response

Hyphal growth is strongly associated with virulence in the human fungal pathogen Candida albicans. While hyphal transcriptional networks have been the subject of intense study, relatively little is known about post-transcriptional regulation. Previous work reported that P-Body (PB) factors Dhh1 and Edc3 were required for C. albicans virulence and filamentation, suggesting an essential role for post-transcriptional regulation of these processes. However, the molecular roles of these factors have not been determined. To further study the function of PB factors in filamentation, we generated homozygous deletions of DHH1 and EDC3 in diverse prototrophic clinical strains using transient CRISPR-Cas9. Homozygous DHH1 deletion strongly impaired growth, altered filamentation, and exhibited unusual colony morphology in response to heat stress in five strain backgrounds. Using RNA-seq, we found DHH1 deletion disrupts the regulation of thousands of genes under both yeast and hyphal growth conditions in SC5314 and P57055. This included upregulation of many stress response genes in the absence of external stress, similar to deletion of the S. cerevisiae DHH1 homolog. In contrast, we found EDC3 was not required for heat tolerance or filamentation in diverse strains. These results support a model in which DHH1, but not EDC3, represses hyphal stress response transcripts in yeast and remodels the transcriptome during filamentation. Our work supports distinct requirements for specific mRNA decay factors, bolstering evidence for post-transcriptional regulation of filamentation in C. albicans.

Synergistic effects of Candida albicans and Porphyromonas gingivalis biofilms on epithelial barrier function in a 3D aspiration pneumonia model

Introduction

Polymicrobial infections involving Candida albicans and Porphyromonas gingivalis represent a significant challenge in maintaining epithelial barrier integrity. This study explores their synergistic effects on epithelial cells using an air-liquid interface (ALI) model.

Methods

Mixed-species biofilms were developed and analyzed for their impact on epithelial permeability and tight junction proteins. The effects of biofilm supernatants on IL-8 secretion and oxidative stress markers were also evaluated. The role of P. gingivalis proteases was assessed using a gingipain-null mutant (ΔKΔRAB) compared to the wild-type strain (W83). Survival experiments were conducted using Galleria mellonella larvae to examine the pathogenicity of dual-species biofilms.

Results

Mixed-species biofilms significantly increased epithelial permeability and disrupted tight junction proteins, as evidenced by reduced levels of ZO-1 and E-cadherin. These changes were accompanied by oxidative stress, characterized by decreased HO-1 expression and enhanced Bax/Bcl-xL ratios, indicating increased pro-apoptotic activity. Supernatants from dual-species biofilms demonstrated a pronounced effect on epithelial cells, modulating IL-8 secretion and exacerbating oxidative damage. C. albicans was identified as the dominant driver of pro-inflammatory responses, while P. gingivalis contributed through immune modulation and enzymatic activity, primarily via gingipains. The ΔKΔRAB mutant biofilms caused less epithelial disruption and oxidative stress compared to the wild-type, highlighting the critical role of gingipains in pathogenesis.

Discussion

Survival experiments using Galleria mellonella larvae supported these findings, highlighting the reduced survival associated with dual-species biofilms and the potential for high-dose antimicrobial therapies to mitigate this effect. These results emphasize the cooperative mechanisms of C. albicans and P. gingivalis in compromising epithelial barriers and underline the importance of combination therapies targeting both fungal and bacterial components in polymicrobial infections.

Blocking the shikimate pathway amplifies the impact of carvacrol on biofilm formation in Candida albicans

Candida albicans typically thrives in a commensal relationship with humans but is also an opportunistic fungal pathogen. As an opportunistic pathogen, C. albicans relies heavily on its ability to assimilate nutrients, for which it must compete with the host and other microorganisms. Amino acid biosynthesis, sensing, and uptake play pivotal roles in C. albicans growth and pathogenicity. C. albicans biosynthesizes aromatic amino acids and co-enzyme Q de novo through the shikimate pathway, including the Aro1, Aro2, and Aro7 enzymes, but also has amino acid transporters for uptake from the environment. Thus, antifungal approaches targeting aromatic amino acid biosynthesis must simultaneously inhibit amino acid biosynthesis and uptake. Herein, we investigate the plant-based antifungal, carvacrol, in conjunction with aromatic amino acid biosynthetic mutants, as a potential anti-candidal strategy. Growth of the WT, ARO2, and ARO7 strains were inhibited by 150 µg/mL carvacrol, whereas the ARO1 mutant was slightly more sensitive (with MIC 125 µg/mL). All repressed mutants exposed to carvacrol are partially rescued in the presence of para-aminobenzoic acid (PABA) (CoQ precursor), indicating that blocking the shikimate pathway impacts both aromatic amino acid and CoQ biosynthesis. Moreover, carvacrol at sublethal concentrations significantly inhibits ARO1 adhesion and hyphal formation, along with pre-attached and pre-formed hyphae, ultimately impacting biofilm metabolic activity and biomass accumulation and significantly reducing biofilm growth. In summary, carvacrol increases the sensitivity of C. albicans to ARO1 repression, with attenuated adhesion, hyphal formation, mycelial growth and biofilm formation, likely by blocking aromatic amino acid uptake.IMPORTANCEThe opportunistic pathogen Candida albicans remains the leading cause of candidemia and invasive candidiasis (IC), causing significant morbidity and mortality in immunocompromised patients. Our current arsenal of effective antifungal drugs is limited in number, mechanistic diversity, and efficacy, are cytotoxic and associated with antifungal resistance, necessitating the development of novel antifungals and combination therapies. Here, we show how simultaneously blocking the shikimate pathway, through ARO1 repression, and disrupting aromatic amino acid uptake by carvacrol prevent C. albicans biofilm formation. Thus, inhibitors of the Aro1 enzyme in combination with carvacrol are expected to shut down C. albicans biofilm formation and virulence.

Composition, Influencing Factors, and Effects on Host Nutrient Metabolism of Fungi in Gastrointestinal Tract of Monogastric Animals

Intestinal fungi, collectively referred to as mycobiota, constitute a small (0.01-2%) but crucial component of the overall intestinal microbiota. While fungi are far less abundant than bacteria in the gut, the volume of an average fungal cell is roughly 100-fold greater than that of an average bacterial cell. They play a vital role in nutrient metabolism and maintaining intestinal health. The composition and spatial organization of mycobiota vary across different animal species and are influenced by a multitude of factors, including age, diet, and the host's physiological state. At present, quantitative research on the composition of mycobiota in monogastric animals remains scarce, and investigations into the mechanisms underlying their metabolic functions are also relatively restricted. This review delves into the distribution characteristics of mycobiota, including Candida albicans, Saccharomyces cerevisiae, Kazachstania slooffiae, in monogastric animals, the factors influencing their composition, and the consequent impacts on host metabolism and health. The objective is to offer insights for a deeper understanding of the nutritional significance of intestinal fungi in monogastric animals and to explore the mechanisms by which they affect host health in relation to inflammatory bowel disease (IBD), diarrhea, and obesity. Through a systematic evaluation of their functional contributions, this review shifts our perception of intestinal fungi from overlooked commensals to key components in gut ecosystem dynamics, emphasizing their potential in personalized metabolic control regulation and the enhancement of disease prevention and treatment strategies.

Roles of P-body factors in Candida albicans filamentation and stress response

Hyphal growth is strongly associated with virulence in the human fungal pathogen Candida albicans. While hyphal transcriptional networks have been the subject of intense study, relatively little is known about post-transcriptional regulation. Previous work reported that P-Body (PB) factors Dhh1 and Edc3 were required for C. albicans virulence and filamentation, suggesting an essential role for post-transcriptional regulation of these processes. However, the molecular roles of these factors have not been determined. To further study the function of PB factors in filamentation, we generated homozygous deletions of DHH1 and EDC3 in diverse prototrophic clinical strains using transient CRISPR-Cas9. Homozygous DHH1 deletion strongly impaired growth, altered filamentation, and exhibited unusual colony morphology in response to heat stress in five strain backgrounds. Using RNA-seq, we found DHH1 deletion disrupts the regulation of thousands of genes under both yeast and hyphal growth conditions in SC5314 and P57055. This included upregulation of many stress response genes in the absence of external stress, similar to deletion of the S. cerevisiae DHH1 homolog. In contrast, we found EDC3 was not required for heat tolerance or filamentation in diverse strains. These results support a model in which DHH1, but not EDC3, represses hyphal stress response transcripts in yeast and remodels the transcriptome during filamentation. Our work supports distinct requirements for specific mRNA decay factors, bolstering evidence for post-transcriptional regulation of filamentation in C. albicans.

A screen to identify antifungal antagonists reveals a variety of pharmacotherapies induce echinocandin tolerance in Candida albicans

Through screening a comprehensive collection of drugs approved for human use, we identified over 20 that oppose the antifungal activity of the echinocandins upon the infectious yeast, Candida albicans . More detailed evaluation of five such drugs, including the atypical antipsychotic aripiprazole and the tyrosine kinase inhibitor ponatinib, indicated they promote C. albicans survival following exposure to the echinocandin antifungals. The activity of the five selected antagonists was dependent upon the Mkc1p MAPK pathway, however, ponatinib was paradoxically shown to suppress phosphorylation and therefore activation of Mkc1p itself. Components of several other signaling pathways are also required, including those of calcineurin and casein kinase-2, suggesting the observed antagonism required much of the cell wall stress responses previously described for C. albicans . Transcriptome analysis revealed that the antagonists stimulated the expression of genes involved in xenobiotic and antifungal resistance, and suppressed the expression of genes associated with hyphal growth. Thus, the echinocandin antagonistic drugs modulate C. albicans physiology in ways that could impact its pathogenicity and/or response to therapeutic intervention. Finally, a mutant lacking the Efg1p transcription factor, which has a central role in the activation of C. albicans hyphal growth was found to have intrinsically high levels of echinocandin tolerance, suggesting a link between modulation of morphogenesis related signaling and echinocandin tolerance.

Importance

We report a substantial number of previously unknown drug interactions that modulate the echinocandin sensitivity of one of the most prevalent human fungal pathogens, Candida albicans . The echinocandins are the first line therapy for treating disseminated and often lethal Candida infections, that account for >75% of invasive fungal infections in the U.S.. For largely unknown reasons, a substantial number of patients with invasive candidiasis fail to respond to treatment with these drugs. The finding of this study suggest that co-administered medications have the potential to influence the therapeutic outcomes of invasive fungal infections through modulating antifungal drug tolerance and/or fungal pathogenicity. The potential for echinocandin antagonistic medications to influence therapeutic outcomes is discussed.

Forward genetic screen in zebrafish identifies new fungal regulators that limit host-protective Candida-innate immune interaction

Candida is one of the most frequent causes of bloodstream infections, and our first line of defense against these invasive infections is the innate immune system. The early immune response is critical in controlling C. albicans infection, but C. albicans has several strategies to evade host immune attack. Phagocytosis of C. albicans blocks hyphal growth, limiting host damage and virulence, but how C. albicans limits early recruitment and phagocytosis in vertebrate infection is poorly understood. To study innate immune evasion by intravital imaging, we utilized the transparent larval zebrafish infection model to screen 131 C. albicans mutants for altered virulence and phagocyte response. Infections with each of seven hypovirulent mutants led to altered phagocyte recruitment and/or phagocytosis, falling into four categories. Of particular interest among these is NMD5, a predicted β-importin and newly-identified virulence factor. The nmd5∆/∆ mutant fails to limit phagocytosis and its virulence defects are eliminated when phagocyte activity is compromised, suggesting that its role in virulence is limited to immune evasion. These quantitative intravital imaging experiments are the first to document altered Candida-phagocyte interactions for several additional mutants, and clearly distinguish recruitment from phagocytic uptake, suggesting that Candida modulates both events. This initial large-scale screen of individual C. albicans mutants in a vertebrate, coupled with high-resolution imaging of Candida-phagocyte interactions, provides a more nuanced view of how diverse mutations can lead to more effective phagocytosis, a key immune process which blocks germination and drives anti-fungal immunity.

Breaking Barriers: Candidalysin Disrupts Epithelial Integrity and Induces Inflammation in a Gut-on-Chip Model

Candida albicans is an opportunistic pathogenic yeast commonly found in the gastrointestinal tract of healthy humans. Under certain conditions, it can become invasive and cause life-threatening systemic infections. One mechanism used by C.albicans to breach the epithelial barrier is the secretion of candidalysin, a cytolytic peptide toxin. Candidalysin damages epithelial membranes and activates the innate immune response, making it key to C.albicans' pathogenicity and a promising therapeutic target. Although candidalysin mediates C. albicans translocation through intestinal layers, its impact on epithelial responses is not fully understood. This study aims to characterize this response and develop scalable, quantitative methodologies to assess candidalysin's toxicological effects using gut-on-chip models. We used the OrganoPlate® platform to expose Caco-2 tubules to candidalysin and evaluated their response with trans-epithelial electrical resistance (TEER), protein detection, and immunostaining. We then validated our findings in a proof-of-concept experiment using human intestinal organoid tubules. Candidalysin impaired barrier integrity, induced actin remodeling, and increased cell permeability. It also induced the release of LDH, cytokines, and the antimicrobial peptide LL37, suggesting cellular damage, inflammation, and antimicrobial activity. This study strengthens our understanding of candidalysin's role in C. albicans pathogenesis and suggests new therapeutic strategies targeting this toxin. Moreover, patient-derived organoids show promise for capturing patient heterogeneity and developing personalized treatments.

Fungal Als proteins hijack host death effector domains to promote inflammasome signaling

High-damaging Candida albicans strains tend to form hyphae and exacerbate intestinal inflammation in ulcerative colitis patients through IL-1β-dependent mechanisms. Fungal agglutinin-like sequence (Als) proteins worsen DSS-induced colitis in mouse models. FADD and caspase-8 are important regulators of gut homeostasis and inflammation. However, whether they link directly to fungal proteins is not fully understood. Here, we report that Als proteins induce IL-1β release in immune cells. We show that hyphal Als3 is internalized in macrophages and interacts with caspase-8 and the inflammasome adaptor apoptosis-associated speck-like protein containing a CARD (ASC). Caspase-8 is essential for Als3-mediated ASC oligomerization and IL-1β processing. In non-immune cells, Als3 is associated with cell death core components FADD and caspase-8. N-terminal Als3 (N-Als3) expressed in Jurkat cells partially inhibits apoptosis. Mechanistically, N-Als3 promotes oligomerization of FADD and caspase-8 through their death effector domains (DEDs). N-Als3 variants with a mutation in the peptide-binding cavity or amyloid-forming region are impaired in DED oligomerization. Together, these results demonstrate that DEDs are intracellular sensors of Als3. This study identifies additional potential targets to control hypha-induced inflammation.

Identification of Candida albicans Antigens Recognized by Murine Intestinal IgAs by a Gel-Independent Immunoproteomic Approach

As part of the intestinal microbiota, Candida albicans can elicit a humoral response in the gastrointestinal tract (GIT) that is mainly directed toward hyphal antigens. This response has been implicated in controlling the invasive form of the fungus and maintaining the yeast as an innocuous commensal. However, the specific targets of this response are still unknown. Here, we used a gel-free immunoproteomic methodology to identify C. albicans gut immunogens. For this goal, we previously obtained specific secreted IgA from mice colonized with C. albicans. Then, secretome and surfome from C. albicans wild-type filaments were obtained and incubated with magnetic beads linked to antimouse IgA antibodies. sIgA targets were immunoprecipitated and analyzed by mass spectrometry. A third sample bearing the C. albicans antigen-sIgA complex was also examined. Those identified proteins that exhibited a higher percentile of relative abundance were considered for further analysis. From those, 35 proteins coincided among the three samples. Remarkably, about 40% of the identified proteins appeared in the databases as uncharacterized. The results were then validated by immunofluorescence assays overexpressing some of the genes identified in a yeast-lock C. albicans mutant. Adhesins such as Als3, Als1, and Hwp1 were corroborated to be IgA targets, as well as the chaperone Ssa2. Therefore, this gel-free immunoproteomic approach has been useful to identify new C. albicans antigens that generate a specific humoral response in the murine gut.

Fungi, immunosenescence and cancer

Fungal microbes are a small but immunoreactive component of the human microbiome, which may influence cancer development, progression and therapeutic response. Immunosenescence is a process of immune dysfunction that occurs with aging, including lymphoid organ remodeling, contributing to alterations in the immune system in the elderly, which plays a critical role in many aspects of cancer. There is evidence for the interactions between fungi and immunosenescence in potentially regulating cancer progression and remodeling the tumor microenvironment (TME). In this review, we summarize potential roles of commensal and pathogenic fungi in modulating cancer-associated processes and provide more-detailed discussions on the mechanisms of which fungi affect tumor biology, including local and distant regulation of the TME, modulating antitumor immune responses and interactions with neighboring bacterial commensals. We also delineate the features of immunosenescence and its influence on cancer development and treatment, and highlight the interactions between fungi and immunosenescence in cancer. We discuss the prospects and challenges for harnessing fungi and immunosenescence in cancer diagnosis and/or treatment. Considering the limited understanding and techniques in conducting such research, we also provide our view on how to overcome challenges faced by the exploration of fungi, immunosenescence and their interactions on tumor biology.

Fungal Influences on Cancer Initiation, Progression, and Response to Treatment

Fungal dysbiosis is increasingly recognized as a key factor in cancer, influencing tumor initiation, progression, and treatment outcomes. This review explores the role of fungi in carcinogenesis, with a focus on mechanisms such as immunomodulation, inflammation induction, tumor microenvironment remodeling, and interkingdom interactions. Fungal metabolites are involved in oncogenesis, and antifungals can interact with anticancer drugs, including eliciting potential adverse effects and influencing immune responses. Furthermore, mycobiota profiles have potential as diagnostic and prognostic biomarkers, emphasizing their clinical relevance. The interplay between fungi and cancer therapies can affect drug resistance, therapeutic efficacy, and risk of invasive fungal infections associated with targeted therapies. Finally, emerging strategies for modulating mycobiota in cancer care are promising approaches to improve patient outcomes.

n-butanol extract of Pulsatilla decoction alleviates vulvovaginal candidiasis via the regulation of mitochondria-associated Type I interferon signaling pathways

ETHNOPHARMACOLOGICAL RELEVANCE

Vulvovaginal candidiasis (VVC) is a relatively common fungal infectious disease in the female reproductive tract. The pathogenesis of VVC not only involves Candida albicans (C. albicans) infection, but also the improper immune response of the vaginal mucosal immune system to the fungus. As a classical formula, Pulsatilla decoction has been proven to exert protective effect in both clinical and experimental research in VVC. However, the specific mechanism of Pulsatilla decoction in VVC remains elusive. This study investigated the mechanism of n-butanol extract of Pulsatilla decoction (BEPD) in treating VVC from the perspective of type I interferon signaling and related mitochondrial function.

MATERIALS AND METHODS

A VVC-rat model was developed using an estrogen-based method to evaluate the effectiveness of BEPD in treating VVC, and the therapeutic efficacy of BEPD against VVC was comprehensively evaluated by fungal morphology and burden, neutrophil numbers, histopathology, pro-inflammatory and anti-inflammatory cytokines production, and LDH level. Immunohistochemistry (IHC), immune fluorescence (IF), Western Blot (WB) and RT-qPCR assays were conducted to assess type I interferon signaling and mitochondria functions. Candidalysin-induced vaginal epithelial inflammation in vitro, as cellular models, was employed to detect the changes in type I interferon signaling and mitochondria function before and after BEPD-containing serum intervention.

RESULTS

BEPD could significantly improve the inflammation, reduce fungal loads and inhibit fungal growth, balance pro-inflammatory and anti-inflammatory cytokine levels in VVC model rats. The findings from IHC, IF, WB and RT-qPCR revealed that BEPD could promote type I interferon signaling and alleviate mitochondrial functional damage in VVC model rats, and BEPD-containing serum could play the same role in vitro.

CONCLUSION

The study findings generally demonstrated that BEPD could improve the inflammation and correct the immune imbalance in VVC through regulation of type I interferon signaling and mitochondrial function.

Image-based quantification of Candida albicans filamentation and hyphal length using the open-source visual programming language JIPipe

The formation of hyphae is one of the most crucial virulence traits the human pathogenic fungus Candida albicans possesses. The assessment of hyphal length in response to various stimuli, such as exposure to human serum, provides valuable insights into the adaptation strategies of C. albicans to the host environment. Despite the increasing high-throughput capacity live-cell imaging and data generation, the accurate analysis of hyphal growth has remained a laborious, error-prone, and subjective manual process. We developed an analysis pipeline utilizing the open-source visual programming language Java Image Processing Pipeline (JIPipe) to overcome the limitations associated with manual analysis of hyphal growth. By comparing our automated approach with manual analysis, we refined the strategies to achieve accurate differentiation between yeast cells and hyphae. The automated method enables length measurements of individual hyphae, facilitating a time-efficient, high-throughput, and user-friendly analysis. By utilizing this JIPipe analysis approach, we obtained insights into the filamentation behavior of two C. albicans strains when exposed to human serum albumin (HSA), the most abundant protein in human serum. Our findings indicate that despite the known role of HSA in stimulating fungal growth, it reduces filamentous growth. The implementation of our automated JIPipe analysis approach for hyphal growth represents a long-awaited and time-efficient solution to meet the demand of high-throughput data generation. This tool can benefit different research areas investigating the virulence aspects of C. albicans.

When HSFs bring the heat-mapping the transcriptional circuitries of HSF-type regulators in Candida albicans

Heat shock factor (HSF)-type regulators are stress-responsive transcription factors widely distributed among eukaryotes, including fungi. They carry a four-stranded winged helix-turn-helix DNA-binding domain considered as the signature domain for HSFs. The genome of the opportunistic yeast Candida albicans encodes four HSF members, namely, Sfl1, Sfl2, Skn7, and the essential regulator, Hsf1. C. albicans HSFs do not only respond to heat shock and/or temperature variation but also to CO2 levels, oxidative stress, and quorum sensing, acting this way as central decision makers. In this minireview, I follow on the heels of my mSphere of Influence commentary (2020) to provide an overview of the repertoire of HSF regulators in Saccharomyces cerevisiae and C. albicans and describe how their genetic perturbation in C. albicans, coupled with genome-wide expression and location analyses, allow to map their transcriptional circuitry. I highlight how they can regulate, in common, a crucial developmental program: filamentous growth.

Aloin remodels the cell wall of Candida albicans to reduce its hyphal virulence against oral candidiasis

Aloe vera (L.) Burm.f. is a traditional Chinese medicine known for treating various ailments, including fungal infections. Aloin is one of the major components from A. vera, but its antifungal mechanism and therapeutic potential against oral candidiasis are not clear. This study aimed to examine the mechanism of aloin against Candida albicans and its inhibitory activity against oral candidiasis. In this study, we for the first time found that aloin could induce the formation of abnormal hyphae with smaller hyphal diameters and fewer branching points in C. albicans including 11 clinical isolates without growth inhibition. The transcriptome and further cell wall contents analysis indicated that aloin remodeled the cell wall to increase the contents of β-1,3-glucan and furtherly showed an antagonistic effect with micafungin. Aloin also significantly inhibited the cell damage of oral epithelial cells and oral candidiasis in mice infected by C. albicans due to its inhibitory actions on the hyphal development and expressions of virulence factors, including candidalysin (coded by ECE1). Our results suggest that aloin is a promising antifungal agent for controlling candidiasis and targeting hyphal development and pathogenesis represents a practical strategy for developing new antifungal drugs. KEY POINTS: • Aloin remodels the C. albicans cell wall to form avirulent hyphae. • Aloin inhibits C. albicans infections in oral epithelial cells and mouse mucosa without toxicity. • Aloin is a promising antifungal agent with therapeutic potential against C. albicans infections.

Retinoids as Alternative Antifungal Agents Against Candida albicans: In Vitro and In Silico Evidence

Candida albicans (C. albicans) is the most common pathogen responsible for a wide spectrum of human infections ranging from superficial mucocutaneous mycoses to systemic life-threatening diseases. Its main virulence factors are the morphological transition between yeast and hyphal forms and the ability to produce biofilm. Novel antifungal strategies are required given the severity of systemic candidiasis, especially in immunocompromised patients, and the lack of effective anti-biofilm treatments. We previously demonstrated that all-trans retinoic acid (ATRA), an active metabolite of vitamin A, exerted an inhibitory effect on Candida growth, yeast-hyphal transition and biofilm formation. Here, we further investigated the possible anti-Candida potential of trifarotene and tazarotene, which are the other two molecules belonging to the retinoid family, compared to ATRA. The results indicate that both drugs were able to suppress Candida growth, germination and biofilm production, although trifarotene was proven to be more effective than tazarotene, showing effectiveness comparable to ATRA. In silico studies suggest that all three retinoids may exert antifungal activity through their molecular interactions with the heat shock protein (Hsp) 90 and 14α-demethylase of C. albicans. Moreover, interactions between retinoids and ergosterol have been observed, suggesting that those compounds have great potential against C. albicans infections.

A mouse model of immunosuppression facilitates oral Candida albicans biofilms, bacterial dysbiosis and dissemination of infection

Opportunistic pathogens are a major threat to people, especially those with impaired immune systems. Two of the most important microbes in this category are the fungus Candida albicans and Gram-positive bacteria of the genus Enterococcus, which share overlapping niches in the oral cavity, gastrointestinal and urogenital tracts. The clinical importance of oral C. albicans biofilm and its interaction with the host under immunosuppressive conditions remains largely understudied. Here, we used a mouse model of oropharyngeal candidiasis (OPC) with cortisone acetate injection on alternate days and a continuous supply of C. albicans in drinking water for three days, resulting in immunosuppression. Results showed abundant growth of resident oral bacteria and a strong C. albicans biofilm on the tongue consisting of hyphae which damaged papillae, the epidermal layer, and invaded tongue tissue with the accumulation of inflammatory cells as demonstrated by Grocott's methenamine silver and hematoxylin and eosin staining, respectively. The dispersed microbes from the oral biofilm colonized the gastrointestinal (GI) tract and damaged its integrity, disseminating microbes to other organs. Although no visible damage was observed in the kidney and liver, except increased lipid vacuoles in the liver cells, C. albicans was found in the liver homogenate. Intriguingly, we found co-occurrence of Enterococcus faecalis in the tongue, liver, and stool of immunosuppressed control and C. albicans infected organs. Targeted 16S rRNA and ITS2 amplicon sequencing of microbes from the fecal samples of mice confirmed the above results in the stool samples and revealed an inverse correlation of beneficial microbes in the dysbiosis condition. Our study shows that mucosal-oral infection of C. albicans under immunosuppressed conditions causes tissue damage and invasion in local and distant organs; the invasion may be aided by the overgrowth of the resident endogenous Enterobacteriaceae and other members, including the opportunistic pathogen Enterococcus faecalis.

The mycobiome in human cancer: analytical challenges, molecular mechanisms, and therapeutic implications

The polymorphic microbiome is considered a new hallmark of cancer. Advances in High-Throughput Sequencing have fostered rapid developments in microbiome research. The interaction between cancer cells, immune cells, and microbiota is defined as the immuno-oncology microbiome (IOM) axis. Fungal microbes (the mycobiome), although representing only ∼ 0.1-1% of the microbiome, are a critical immunologically active component of the tumor microbiome. Accumulating evidence suggests a possible involvement of commensal and pathogenic fungi in cancer initiation, progression, and treatment responsiveness. The tumor-associated mycobiome mainly consists of the gut mycobiome, the oral mycobiome, and the intratumoral mycobiome. However, the role of fungi in cancer remains poorly understood, and the diversity and complexity of analytical methods make it challenging to access this field. This review aims to elucidate the causal and complicit roles of mycobiome in cancer development and progression while highlighting the issues that need to be addressed in executing such research. We systematically summarize the advantages and limitations of current fungal detection and analysis methods. We enumerate and integrate these recent findings into our current understanding of the tumor mycobiome, accompanied by the prospect of novel and exhilarating clinical implications.

Host cell responses to Candida albicans biofilm-derived extracellular vesicles

Candida albicans is a prevalent fungal pathogen responsible for infections in humans. As described recently, nanometer-sized extracellular vesicles (EVs) produced by C. albicans play a crucial role in the pathogenesis of infection by facilitating host inflammatory responses and intercellular communication. This study investigates the functional properties of EVs released by biofilms formed by two C. albicans strains-3147 (ATCC 10231) and SC5314-in eliciting host responses. We demonstrate the capability of C. albicans EVs to trigger reactions in human epithelial and immune cells. The involvement of EVs in pathogenesis was evidenced from the initial stages of infection, specifically in adherence to epithelial cells. We further established the capacity of these EVs to induce cytokine production in the epithelial A549 cell line, THP-1 macrophage-like cells, and blood-derived monocytes differentiated into macrophages. Internalization of EVs by THP-1 macrophage-like cells was confirmed, identifying macropinocytosis and phagocytosis as the most probable mechanisms, as demonstrated using various inhibitors that target potential vesicle uptake pathways in human cells. Additionally, C. albicans EVs and their cargo were identified as chemoattractants for blood-derived neutrophils. After verification of the in vivo effect of biofilm-derived EVs on the host, using Galleria mellonella larvae as an alternative model, it was demonstrated that vesicles from C. albicans SC5314 increased mortality in the injected larvae. In conclusion, for both types of EVs a predominantly pro-inflammatory effect on host was observed, highlighting their significant role in the inflammatory response during C. albicans infection.

Microbial adaptive pathogenicity strategies to the host inflammatory environment

Pathogenic microorganisms can infect a variety of niches in the human body. During infection, these microbes can only persist if they adapt adequately to the dynamic host environment and the stresses imposed by the immune system. While viruses entirely rely on host cells to replicate, bacteria and fungi use their pathogenicity mechanisms for the acquisition of essential nutrients that lie under host restriction. An inappropriate deployment of pathogenicity mechanisms will alert host defence mechanisms that aim to eradicate the pathogen. Thus, these adaptations require tight regulation to guarantee nutritional access without eliciting strong immune activation. To work efficiently, the immune system relies on a complex signalling network, involving a myriad of immune mediators, some of which are quite directly associated with imminent danger for the pathogen. To manipulate the host immune system, viruses have evolved cytokine receptors and viral cytokines. However, among bacteria and fungi, selected pathogens have evolved the capacity to use these inflammatory response-specific signals to regulate their pathogenicity. In this review, we explore how bacterial and fungal pathogens can sense the immune system and use adaptive pathogenicity strategies to evade and escape host defence to ensure their persistence in the host.

Relationships Between Candida auris and the Rest of the Candida World-Analysis of Dual-Species Biofilms and Infections

In this study, we investigated the interactions between Candida auris and C. albicans, C. tropicalis, C. glabrata, and C. krusei in mixed infections. Initially, these interactions were studied qualitatively and quantitatively in dual-species biofilms formed in vitro. The MTT assays, determination of the total CFU/mL, and SEM analysis showed that C. auris interacted differentially with the other Candida spp. during the dual-species biofilm formation. Depending on the stage of the biofilm development, C. auris was found to be a particularly dominant species during its interaction with the C. krusei biofilms but significantly submissive in the C. auris-C. albicans biofilms. These studies were then extended to in vivo host models of experimental candidiasis. G. mellonella larvae were inoculated with monotypic and heterotypic suspensions of Candida. The survival rates and quantification of fungal cells in the hemolymph showed that the highest mortality was exhibited by larvae in the C. auris-C. albicans co-infection (100% mortality after 36 h). The CFU/mL values of C. auris from the larval hemolymph were lower in the interactive groups compared to the mono-species group. As a newly emerging species, C. auris persists in environments in the presence of other Candida species and is involved in both competitive and noncompetitive interactions with other Candida species during biofilm formation and development of experimental candidiasis.

The Oral Microbiome: A Key Determinant of Oral Health

As the second largest reservoir of human microbes, the oral cavity is colonized by millions of tiny creatures collectively named as oral microbiome. Species detected in human mouth are diverse, including bacteria, fungi, viruses, and protozoa. Active bidirectional interaction exists between the oral microbiome and the host. Stresses from hosts shape the composition, distribution pattern, and the community behaviors of the oral microbiome, while any changes occurring on the oral microbiome may disrupt its symbiosis relationship with the host and ultimately lead to oral and systemic diseases that jeopardize the host's health. In this chapter, the latest understanding about the role of oral microbiome in common oral diseases, including dental caries, periodontal disease, oral candidiasis, and hyposalivation, is discussed.

Role of Candida species in pathogenesis, immune regulation, and prognostic tools for managing ulcerative colitis and Crohn's disease

The gut microbiome plays a key role in the pathogenesis and disease activity of inflammatory bowel disease (IBD). While research has focused on the bacterial microbiome, recent studies have shifted towards host genetics and host-fungal interactions. The mycobiota is a vital component of the gastrointestinal microbial community and plays a significant role in immune regulation. Among fungi, Candida species, particularly Candida albicans (C. albicans), have been extensively studied due to their dual role as gut commensals and invasive pathogens. Recent findings indicate that various strains of C. albicans exhibit considerable differences in virulence factors, impacting IBD's pathophysiology. Intestinal fungal dysbiosis and antifungal mucosal immunity may be associated to IBD, especially Crohn's disease (CD). This article discusses intestinal fungal dysbiosis and antifungal immunity in healthy individuals and CD patients. It discusses factors influencing the mycobiome's role in IBD pathogenesis and highlights significant contributions from the scientific community aimed at enhancing understanding of the mycobiome and encouraging further research and targeted intervention studies on specific fungal populations. Our article also provided insights into a recent study by Wu et al in the World Journal of Gastroenterology regarding the role of the gut microbiota in the pathogenesis of CD.

HDAC1 fine-tunes Th17 polarization in vivo to restrain tissue damage in fungal infections

Histone deacetylases (HDACs) contribute to shaping many aspects of T cell lineage functions in anti-infective surveillance; however, their role in fungus-specific immune responses remains poorly understood. Using a T cell-specific deletion of HDAC1, we uncover its critical role in limiting polarization toward Th17 by restricting expression of the cytokine receptors gp130 and transforming growth factor β receptor 2 (TGF-βRII) in a fungus-specific manner, thus limiting Stat3 and Smad2/3 signaling. Controlled release of interleukin-17A (IL-17A) and granulocyte-macrophage colony-stimulating factor (GM-CSF) is vital to minimize apoptotic processes in renal tubular epithelial cells in vitro and in vivo. Consequently, animals harboring excess Th17-polarized HDCA1-deficient CD4+ T cells develop increased kidney pathology upon invasive Candida albicans infection. Importantly, pharmacological inhibition of class I HDACs similarly increased IL-17A release by both mouse and human CD4+ T cells. Collectively, this work shows that HDAC1 controls T cell polarization, thus playing a critical role in the antifungal immune defense and infection outcomes.

Alpha1-antitrypsin impacts innate host-pathogen interactions with Candida albicans by stimulating fungal filamentation

Our immune system possesses sophisticated mechanisms to cope with invading microorganisms, while pathogens evolve strategies to deal with threats imposed by host immunity. Human plasma protein α1-antitrypsin (AAT) exhibits pleiotropic immune-modulating properties by both preventing immunopathology and improving antimicrobial host defence. Genetic associations suggested a role for AAT in candidemia, the most frequent fungal blood stream infection in intensive care units, yet little is known about how AAT influences interactions between Candida albicans and the immune system. Here, we show that AAT differentially impacts fungal killing by innate phagocytes. We observed that AAT induces fungal transcriptional reprogramming, associated with cell wall remodelling and downregulation of filamentation repressors. At low concentrations, the cell-wall remodelling induced by AAT increased immunogenic β-glucan exposure and consequently improved fungal clearance by monocytes. Contrastingly, higher AAT concentrations led to excessive C. albicans filamentation and thus promoted fungal immune escape from monocytes and macrophages. This underscores that fungal adaptations to the host protein AAT can differentially define the outcome of encounters with innate immune cells, either contributing to improved immune recognition or fungal immune escape.

EGR1 regulates oral epithelial cell responses to Candida albicans via the EGFR- ERK1/2 pathway

Candida albicans is a fungal pathobiont colonizing mucosal surfaces of the human body, including the oral cavity. Under certain predisposing conditions, C. albicans invades mucosal tissues activating EGFR-MAPK signalling pathways in epithelial cells via the action of its peptide toxin candidalysin. However, our knowledge of the epithelial mechanisms involved during C. albicans colonization is rudimentary. Here, we describe the role of the transcription factor early growth response protein 1 (EGR1) in human oral epithelial cells (OECs) in response to C. albicans. EGR1 expression increases in OECs when exposed to C. albicans independently of fungal viability, morphology, or candidalysin release, suggesting EGR1 is involved in the fundamental recognition of C. albicans, rather than in response to invasion or "pathogenesis." Upregulation of EGR1 is mediated by EGFR via Raf1, ERK1/2, and NF-κB signalling but not PI3K/mTOR signalling. Notably, EGR1 mRNA silencing impacts on anti-C. albicans immunity, reducing GM-CSF, IL-1α and IL-1β release, and increasing IL-6 and IL-8 production. These findings identify an important role for EGR1 in priming epithelial cells to respond to subsequent invasive infection by C. albicans and elucidate the regulation circuit of this transcription factor after contact.

Pathophysiological microenvironments in oral candidiasis

Oral candidiasis (OC), a prevalent opportunistic infection of the oral mucosa, presents a considerable health challenge, particularly in individuals with compromised immune responses, advanced age, and local predisposing conditions. A considerable part of the population carries Candida in the oral cavity, but only few develop OC. Therefore, the pathogenesis of OC may depend on factors other than the attributes of the fungus, such as host factors and other predisposing factors. Mucosal trauma and inflammation compromise epithelial integrity, fostering a conducive environment for fungal invasion. Molecular insights into the immunocompromised state reveal dysregulation in innate and adaptive immunity, creating a permissive environment for Candida proliferation. Detailed examination of Candida species (spp.) and their virulence factors uncovers a nuanced understanding beyond traditional C. albicans focus, which embrace diverse Candida spp. and their strategies, influencing adhesion, invasion, immune evasion, and biofilm formation. Understanding the pathophysiological microenvironments in OC is crucial for the development of targeted therapeutic interventions. This review aims to unravel the diverse pathophysiological microenvironments influencing OC development focusing on microbial, host, and predisposing factors, and considers Candida resistance to antifungal therapy. The comprehensive approach offers a refined perspective on OC, seeking briefly to identify potential therapeutic targets for future effective management.

Modulation of C. albicans-Induced Immune Response in Vaginal Epithelial Cells by Garcinoic Acid

Vulvovaginal candidiasis (VVC) is a prevalent women's infection characterized by excessive inflammation and damage of the vaginal epithelium that, in its recurrent form (RVVC), causes more than three symptomatic episodes per year, impacting nearly 8% of women globally. Current antifungal treatments alleviate symptoms but often fail to restore the inflammatory homeostasis of mucosal tissue and prevent recurrences. α-Tocopherol (α-TOH) and garcinoic acid (GA), a vitamin E metabolite, with immunomodulatory properties, were investigated for the first time in vaginal epithelial cells exposed to C. albicans infection to assess their effects on inflammatory signaling parameters important to restore cellular homeostasis. For this purpose, the protein kinases MKK3/6, p38 stress kinase (SAPK), and ERK1/2 were studied together with c-Fos transcription factor and IL-6, IL-1α, and IL-1β secretion in A-431 vaginal epithelial cells pre-treated with GA or with α-TOH and then infected with C. albicans. GA, differently from α-TOH, significantly reduced the C. albicans-induced activation of p38-SAPK while increasing pro-survival MAPK ERK1/2 activity. This resulted in a significant reduction in the secretion levels of the inflammatory cytokines IL-6 and IL-1α, as well as IL-1β. Overall, our data indicate that GA holds potential for restoring the immuno-metabolic properties of the vaginal epithelium exposed to C. albicans infection, which may help to treat inflammatory symptoms in VVC/RVVC.

Different fungal signatures in ALD and MAFLD

Objective

This study investigates the differential impact of fecal fungal microbiota on the pathogenesis of alcohol-associated liver disease (ALD) and metabolic-associated fatty liver disease (MAFLD). We aim to delineate distinct microbial patterns across various stages of each disease.

Methods

We conducted fungal internal transcribed spacer 2 (ITS2) sequencing analysis on fecal samples from 48 ALD patients, 55 MAFLD patients, and 64 healthy controls (HCs).

Results

Distinct fungal microbiota profiles were significantly identified between the ALD and MAFLD patients. In the ALD group, genera such as Trichosporon, Davidiella and Asterotremella along with species like Trichosporon unclassified and Davidiella unclassified were elevated compared to those in the MAFLD group. Conversely, Fungi unclassified, Rhizopus, Periconia, and Candida albicans were more prevalent in MAFLD patients. A specific fungal signature comprising Asterotremella_pseudolonga, Malassezia_restricta and Malassezia, was notably effective in differentiating ALD from MAFLD, achieving an area under the curve (AUC) of 0.94. Periconia and Periconia byssoides were more abundant in non-obese MAFLD patients compared to obese MAFLD and HCs. Rhizopus microsporus var. chinensis and var. rhizopodiformis, along with Pleosporales unclassified, were predominantly found in MAFLD patients with moderate to severe hepatic steatosis (HS). The genera Pleosporales_unclassified and the species Candida_albicans were markedly elevated in ALC patients when contrasted with AFL or HCs.

Conclusion

This investigation introduces a novel fungal signature that successfully differentiates between ALD and MAFLD, underscoring Pleosporales unclassified, as biomarkers for disease progression in ALD and MAFLD. The findings also suggest a significant role for Periconia in the progression of non-obese MAFLD.

Shining a light on Candida-induced epithelial damage with a luciferase reporter

Host cell damage is a key parameter for research in infection biology, drug testing, and substance safety screening. In this study, we introduce a luciferase reporter system as a new and reliable assay to measure cell damage and validate it with the pathogenic yeast, Candida albicans, as a test case. We transduced human epithelial cell lines with a lentiviral vector to stably express an optimized luciferase enzyme, Nanoluc. Upon cell damage, the release of cytoplasmic luciferase into the extracellular space can be easily detected by a luminometer. We used the luciferase reporter system to investigate the damage caused by C. albicans to different newly generated epithelial reporter cell lines. We found that fungus-induced cell damage, as determined by established methods, correlated tightly with the release of the luciferase. The new luciferase reporter system is a simple, sensitive, robust, and inexpensive method for measuring host cell damage and has a sensitivity comparable to the standard assay, release of lactate dehydrogenase. It is suitable for high-throughput studies of pathogenesis mechanisms of any microbe, for antimicrobial drug screening, and many other applications.IMPORTANCEWe present a quick, easy, inexpensive, and reliable assay to measure damage to mammalian cells. To this end, we created reporter cell lines which artificially express luciferase, an enzyme that can be easily detected in the supernatant when these cells are damaged. We used infections with the well-investigated fungal pathogen of humans, Candida albicans, as a test case of our system. Using our reporter, we were able to recapitulate the known effects of strain variability, gene deletions, and antifungal treatments on host cell damage. This easily adaptable reporter system can be used to screen for damage in infection models with different microbial species, assay cell-damaging potential of substances, discover new non-toxic antibiotics, and many other damage-based applications.

Moxidectin elevates Candida albicans ergosterol levels to synergize with polyenes against oral candidiasis

Candida albicans, the most common opportunistic pathogenic fungus, is also the main pathogenic organism for oral candidiasis. This condition is particularly prevalent among the elderly, children, and individuals undergoing radiotherapy or suffering from HIV. The lack of new antifungal drugs, and drug resistance coupled with the side effects of current antifungal agents have increased the challenges of clinical antifungal therapies. Polyenes, including amphotericin B and nystatin, are clinical fungicidal drugs, however, their side effects and low solubility have limited their clinical applications. Here, we identified that moxidectin, a novel approved antiparasitic agent, could synergize with both amphotericin B and nystatin to inhibit the growth and biofilm formation of Candida albicans including 60 clinical isolates. The transcriptome and RT-PCR analysis indicated that moxidectin activated the biosynthesis pathway of ergosterol, the direct target of polyenes, further being verified by the loss of the synergistic activities with polyenes against ergosterol pathway mutants, including Δ/Δerg3, Δ/Δerg11 and Δ/Δerg3 Δ/Δerg11. Moxidectin was then confirmed to elevate the ergosterol biosynthesis levels of C. albicans and enhance the binding between cells and polyenes. In a mouse oral candidiasis model, moxidectin combined with low dosages of polyenes to significantly reduce the infection area, colonization of C. albicans and the inflammatory degree of tongue mucosa. Our study originally demonstrated that moxidectin could activate the ergosterol biosynthesis then elevate the ergosterol contents to enhance the antifungal effects of polyenes against C. albicans and its infections. Moxidectin can serve as the candidate potentiator of polyenes for further clinical practice. KEY POINTS: • Moxidectin synergized with polyenes against Candida albicans. • Moxidectin activated the ergosterol biosynthesis of Candida albicans. • Moxidectin combined with polyenes to effectively combat oral candidiasis in mice.

Rapid and accurate identification of yeast subspecies by MALDI-MS combined with a cell membrane disruption reagent

Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) has been widely used for microbial analysis. However, due to the impenetrable shell of fungi the direct identification of fungi remains challenges. Targeting on this problem, the yeast Saccharomyces cerevisiae (S. cerevisiae) was selected as a model fungus, and a new fungal cell membrane disruption reagent C18-G1 was used before MALDI-MS detection. As a result, much more intensive peaks which distributed in wider m/z range of S. cerevisiae have been identified in comparison with the use of traditional fungal pretreatment methods. Furthermore, a differential peak at m/z 4993 between two subspecies of S. cerevisiae has been identified. The corresponding protein with exclusive sequence of the specific peak was obtained based on MS/MS fragments and database searching. In addition, the method was successfully applied for the discrimination of four commercial yeasts.

The pathobiology of human fungal infections

Human fungal infections are a historically neglected area of disease research, yet they cause more than 1.5 million deaths every year. Our understanding of the pathophysiology of these infections has increased considerably over the past decade, through major insights into both the host and pathogen factors that contribute to the phenotype and severity of these diseases. Recent studies are revealing multiple mechanisms by which fungi modify and manipulate the host, escape immune surveillance and generate complex comorbidities. Although the emergence of fungal strains that are less susceptible to antifungal drugs or that rapidly evolve drug resistance is posing new threats, greater understanding of immune mechanisms and host susceptibility factors is beginning to offer novel immunotherapeutic options for the future. In this Review, we provide a broad and comprehensive overview of the pathobiology of human fungal infections, focusing specifically on pathogens that can cause invasive life-threatening infections, highlighting recent discoveries from the pathogen, host and clinical perspectives. We conclude by discussing key future challenges including antifungal drug resistance, the emergence of new pathogens and new developments in modern medicine that are promoting susceptibility to infection.