Role of Bcr1-activated genes Hwp1 and Hyr1 in Candida albicans oral mucosal biofilms and neutrophil evasion

Molecular Determinants Involved in Candida albicans Biofilm Formation and Regulation

Candida albicans is known for its pathogenicity, although it lives within the human body as a commensal member. The commensal nature of C. albicans is well controlled and regulated by the host's immune system as they live in the harmonized microenvironment. However, the development of certain unusual microhabitat conditions (change in pH, co-inhabiting microorganisms' population ratio, debilitated host-immune system) pokes this commensal fungus to transform into a pathogen in such a way that it starts to propagate very rapidly and tries to breach the epithelial barrier to enter the host's systemic circulations. In addition, Candida is infamous as a major nosocomial (hospital-acquired infection) agent because it enters the human body through venous catheters or medical prostheses. The hysterical mode of C. albicans growth builds its microcolony or biofilm, which is pathogenic for the host. Biofilms propose additional resistance mechanisms from host immunity or extracellular chemicals to aid their survival. Differential gene expressions and regulations within the biofilms cause altered morphology and metabolism. The genes associated with adhesiveness, hyphal/pseudo-hyphal growth, persister cell transformation, and biofilm formation by C. albicans are controlled by myriads of cell-signaling regulators. These genes' transcription is controlled by different molecular determinants like transcription factors and regulators. Therefore, this review has focused discussion on host-immune-sensing molecular determinants of Candida during biofilm formation, regulatory descriptors (secondary messengers, regulatory RNAs, transcription factors) of Candida involved in biofilm formation that could enable small-molecule drug discovery against these molecular determinants, and lead to disrupt the well-structured Candida biofilms effectively.

Antifungal and antibiofilm effects of probiotic Lactobacillus salivarius, zinc nanoparticles, and zinc nanocomposites against Candida albicans from Nile tilapia (Oreochromis niloticus), water and humans

Introduction

Candida albicans (C. albicans) can form biofilms; a critical virulence factor that provides effective protection from commercial antifungals and contributes to public health issues. The development of new antifungal therapies, particularly those targeting biofilms, is imperative. Thus, this study was conducted to investigate the antifungal and antibiofilm effects of Lactobacillus salivarius (L. salivarius), zinc nanoparticles (ZnNPs) and nanocomposites (ZnNCs) on C. albicans isolates from Nile tilapia, fish wash water and human fish sellers in Sharkia Governorate, Egypt.

Methods

A cross-sectional study collected 300 samples from tilapia, fish wash water, and fish sellers (100 each). Probiotic L. salivarius was immobilized with ZnNPs to synthesize ZnNCs. The study assessed the antifungal and antibiofilm activities of ZnNPs, L. salivarius, and ZnNCs compared to amphotericin (AMB).

Results

Candida spp. were detected in 38 samples, which included C. albicans (42.1%), C. glabrata (26.3%), C. krusei (21.1%), and C. parapsilosis (10.5%). A total of 62.5% of the isolates were resistant to at least one antifungal agent, with the highest resistance to nystatin (62.5%). However, 75% of the isolates were highly susceptible to AMB. All C. albicans isolates exhibited biofilm-forming capabilities, with 4 (25%) isolates showing strong biofilm formation. At least one virulence-associated gene (RAS1, HWP1, ALS3, or SAP4) was identified among the C. albicans isolates. Probiotics L. salivarius, ZnNPs, and ZnNCs displayed antibiofilm and antifungal effects against C. albicans, with ZnNCs showing significantly higher inhibitory activity. ZnNCs, with a minimum inhibitory concentration (MIC) of 10 µg/mL, completely reduced C. albicans biofilm gene expression. Additionally, scanning electron microscopy images of C. albicans biofilms treated with ZnNCs revealed asymmetric, wrinkled surfaces, cell deformations, and reduced cell numbers.

Conclusion

This study identified virulent, resistant C. albicans isolates with strong biofilm-forming abilities in tilapia, water, and humans, that pose significant risks to public health and food safety.

Biofilm-associated metabolism via ERG251 in Candida albicans

Biofilm formation by the fungal pathogen Candida albicans is the basis for its ability to infect medical devices. The metabolic gene ERG251 has been identified as a target of biofilm transcriptional regulator Efg1, and here we report that ERG251 is required for biofilm formation but not conventional free-living planktonic growth. An erg251Δ/Δ mutation impairs biofilm formation in vitro and in an in vivo catheter infection model. In both in vitro and in vivo biofilm contexts, cell number is reduced and hyphal length is limited. To determine whether the mutant defect is in growth or some other aspect of biofilm development, we examined planktonic cell features in a biofilm-like environment, which was approximated with sealed unshaken cultures. Under those conditions, the erg251Δ/Δ mutation causes defects in growth and hyphal extension. Overexpression in the erg251Δ/Δ mutant of the paralog ERG25, which is normally expressed more weakly than ERG251, partially improves biofilm formation and biofilm hyphal content, as well as growth and hyphal extension in a biofilm-like environment. GC-MS analysis shows that the erg251Δ/Δ mutation causes a defect in ergosterol accumulation when cells are cultivated under biofilm-like conditions, but not under conventional planktonic conditions. Overexpression of ERG25 in the erg251Δ/Δ mutant causes some increase in ergosterol levels. Finally, the hypersensitivity of efg1Δ/Δ mutants to the ergosterol inhibitor fluconazole is reversed by ERG251 overexpression, arguing that reduced ERG251 expression contributes to this efg1Δ/Δ phenotype. Our results indicate that ERG251 is required for biofilm formation because its high expression levels are necessary for ergosterol synthesis in a biofilm-like environment.

Powder diet exacerbates oropharyngeal candidiasis in a mouse model

This study reports on the influence of a powder diet in a mouse model of oropharyngeal candidiasis (OPC), a significant health concern caused primarily by Candida albicans. Despite identical nutritional composition, we found that a powdered diet significantly increased Candida burdens and oral lesions, and aggravated weight loss compared to a standard pelleted diet. High fungal burdens and severe oral lesions were accomplished within 48 hours after infection with only one dose of cortisone. Moreover, mice on a powder diet recovered a week after infection. Using a powder diet, we thus modified the cortisone OPC murine model in a way that simplifies the infection process, enhances reproducibility, and facilitates studies investigating both pathogenesis and recovery processes. Our findings also underscore the pivotal role of the physical form of the diet in the progression and severity of oral Candida infection in this model. Future research should investigate this relationship further to broaden our understanding of the underlying mechanisms, potentially leading to novel prevention strategies and improved disease management.IMPORTANCEOropharyngeal candidiasis (OPC) is a multifactorial disease and a significant health concern. We found that the physical form of the diet plays a critical role in the severity and progression of OPC. We developed a modified cortisone OPC murine model that facilitates studies investigating pathogenesis and recovery processes.

Quinalizarin as a potential antifungal drug for the treatment of Candida albicans fungal infection in cancer patients

This study aims to analyze the antifungal properties of quinalizarin, a plant-derived compound with proven anticancer effects. Quinalizarin exhibited antifungal activity against opportunistic pathogenic Candida species and Geotrichum capitatum. The treatment with this anthraquinone reduced hyphal growth, inhibited biofilm formation, and damaged mature Candida albicans biofilms. Real-time RT-PCR revealed that quinalizarin downregulated the expression of hyphae-related and biofilm-specific genes. The flow cytometry method used in the study showed that both apoptosis and necrosis were the physiological mechanisms of quinalizarin-induced C. albicans cell death, depending on the dose of the antifungal agent. A further study revealed an increase in the levels of intracellular reactive oxygen species and alterations in mitochondrial membrane potential after treatment with quinalizarin. Finally, quinalizarin was found to have low toxicity in a hemolytic test using human erythrocytes. In conclusion, we have identified quinalizarin as a potential antifungal compound.IMPORTANCEThis article is a study to determine the antifungal activity of quinalizarin (1,2,5,8-tetrahydroxyanthraquinone). Quinalizarin has potential antitumor properties and is effective in different types of tumor cells. The aim of the present study was to prove that quinalizarin can be used simultaneously in the treatment of cancer and in the treatment of intercurrent fungal infections. Quinalizarin was identified as a novel antifungal compound with low toxicity. These results may contribute to the development of a new drug with dual activity in the treatment of cancer-associated candidiasis.

Unveiling the hidden players: exploring the role of gut mycobiome in cancer development and treatment dynamics

The role of gut fungal species in tumor-related processes remains largely unexplored, with most studies still focusing on fungal infections. This review examines the accumulating evidence suggesting the involvement of commensal and pathogenic fungi in cancer biological process, including oncogenesis, progression, and treatment response. Mechanisms explored include fungal influence on host immunity, secretion of bioactive toxins/metabolites, interaction with bacterial commensals, and migration to other tissues in certain types of cancers. Attempts to utilize fungal molecular signatures for cancer diagnosis and fungal-derived products for treatment are discussed. A few studies highlight fungi's impact on the responsiveness and sensitivity to chemotherapy, radiotherapy, immunotherapy, and fecal microbiota transplant. Given the limited understanding and techniques in fungal research, the studies on gut fungi are still facing great challenges, despite having great potentials.

Pleiotropic functions of SscA on the asexual spore of the human pathogenic fungus Aspergillus fumigatus

Asexual spores, called conidia, are key reproductive fungal particles that enable survival in harsh environmental conditions or host systems. The conidia can infect humans, animals, and plants to cause various fungal diseases. Transcription factors, including VosA, WetA, and SscA, have key roles in conidia formation and long-term survival in Aspergillus nidulans. Herein, we report the pleiotropic functions of SscA in the conidia of the human pathogen A. fumigatus. The deletion of sscA increased conidia formation despite decreased fungal growth. Absence of sscA impaired long-term survival and reduced spore resistance to various stresses, including heat, UV, and oxidation. Transcriptomic analyses showed that SscA involved the mRNA expression of cell wall organisation-related genes. Importantly, the sscA deletion mutant conidia contained an increased amount of β-glucan and chitin compared to wild type conidia. In addition, conidial gliotoxin production was decreased in the sscA deletion strain. Overall, SscA has pleiotropic roles in conidia formation, maturation and dormancy and mycotoxin production in A. fumigatus.

Decoding the host-pathogen interspecies molecular crosstalk during oral candidiasis in humans: an in silico analysis

Introduction: The objective of this study is to investigate the interaction between Candida albicans and human proteins during oral candidiasis, with the aim of identifying pathways through which the pathogen subverts host cells. Methods: A comprehensive list of interactions between human proteins and C. albicans was obtained from the Human Protein Interaction Database using specific screening criteria. Then, the genes that exhibit differential expression during oral candidiasis in C. albicans were mapped with the list of human-Candida interactions to identify the corresponding host proteins. The identified host proteins were further compared with proteins specific to the tongue, resulting in a final list of 99 host proteins implicated in oral candidiasis. The interactions between host proteins and C. albicans proteins were analyzed using the STRING database, enabling the construction of protein-protein interaction networks. Similarly, the gene regulatory network of Candida proteins was reconstructed using data from the PathoYeastract and STRING databases. Core module proteins within the targeted host protein-protein interaction network were identified using ModuLand, a Cytoscape plugin. The expression levels of the core module proteins under diseased conditions were assessed using data from the GSE169278 dataset. To gain insights into the functional characteristics of both host and pathogen proteins, ontology analysis was conducted using Enrichr and YeastEnrichr, respectively. Result: The analysis revealed that three Candida proteins, HHT21, CYP5, and KAR2, interact with three core host proteins, namely, ING4 (in the DNMT1 module), SGTA, and TOR1A. These interactions potentially impair the immediate immune response of the host against the pathogen. Additionally, differential expression analysis of fungal proteins and their transcription factors in Candida-infected oral cell lines indicated that Rob1p, Tye7p, and Ume6p could be considered candidate transcription factors involved in instigating the pathogenesis of oral candidiasis during host infection. Conclusion: Our study provides a molecular map of the host-pathogen interaction during oral candidiasis, along with potential targets for designing regimens to overcome oral candidiasis, particularly in immunocompromised individuals.

Biofilm Formation in Medically Important Candida Species

Worldwide, the number of infections caused by biofilm-forming fungal pathogens is very high. In human medicine, there is an increasing proportion of immunocompromised patients with prolonged hospitalization, and patients with long-term inserted drains, cannulas, catheters, tubes, or other artificial devices, that exhibit a predisposition for colonization by biofilm-forming yeasts. A high percentage of mortality is due to candidemia caused by medically important Candida species. Species of major clinical significance include C. albicans, C. glabrata, C. tropicalis, C. parapsilosis, C. krusei, and C. auris. The association of these pathogenic species in the biofilm structure is a serious therapeutic problem. Candida cells growing in the form of a biofilm are able to resist persistent therapy thanks to a combination of their protective mechanisms and their ability to disseminate to other parts of the body, thus representing a threat from the perspective of a permanent source of infection. The elucidation of the key mechanisms of biofilm formation is essential to progress in the understanding and treatment of invasive Candida infections.

A prebiotic diet modulates the oral microbiome composition and results in the attenuation of oropharyngeal candidiasis in mice

Oral bacteria can influence the ability of Candida albicans to cause oropharyngeal candidiasis (OPC). We recently reported that a Lactobacillus johnsonii-enriched oral microbiota reduced C. albicans virulence in an immunosuppressed OPC mouse model. As a follow-up, in this work, we aimed to enrich the resident oral Lactobacillus communities with a prebiotic diet to further assess their effect on the severity of OPC. We tested the effect of a prebiotic xylo-oligosaccharides (XOS)-enriched diet in the oral global bacterial composition and severity of OPC. We assessed changes in the oral microbiome composition via 16S-rRNA gene high-throughput sequencing, validated by qPCR. The impact of the prebiotic diet on Candida infection was assessed by quantifying changes in oral fungal and bacterial biomass and scoring tongue lesions. Contrary to expectations, oral Lactobacillus communities were not enriched by the XOS-supplemented diet. Yet, XOS modulated the oral microbiome composition, increasing Bifidobacterium abundance and reducing enterococci and staphylococci. In the OPC model, the XOS diet attenuated Candida virulence and bacterial dysbiosis, increasing lactobacilli and reducing enterococci on the oral mucosa. We conclude that XOS attenuates Candida virulence by promoting a bacterial microbiome structure more resilient to Candida infection. IMPORTANCE This is the first study on the effects of a prebiotic diet on the oral mucosal bacterial microbiome and an oropharyngeal candidiasis (OPC) mouse model. We found that xylo-oligosaccharides change the oral bacterial community composition and attenuate OPC. Our results contribute to the understanding of the impact of the oral bacterial communities on Candida virulence.

Candida albicans stimulates formation of a multi-receptor complex that mediates epithelial cell invasion during oropharyngeal infection

Fungal invasion of the oral epithelium is central to the pathogenesis of oropharyngeal candidiasis (OPC). Candida albicans invades the oral epithelium by receptor-induced endocytosis but this process is incompletely understood. We found that C. albicans infection of oral epithelial cells induces c-Met to form a multi-protein complex with E-cadherin and the epidermal growth factor receptor (EGFR). E-cadherin is necessary for C. albicans to activate both c-Met and EGFR and to induce the endocytosis of C. albicans. Proteomics analysis revealed that c-Met interacts with C. albicans Hyr1, Als3 and Ssa1. Both Hyr1 and Als3 are required for C. albicans to stimulate c-Met and EGFR in oral epithelial cells in vitro and for full virulence during OPC in mice. Treating mice with small molecule inhibitors of c-Met and EGFR ameliorates OPC, demonstrating the potential therapeutic efficacy of blocking these host receptors for C. albicans.

QCR7 affects the virulence of Candida albicans and the uptake of multiple carbon sources present in different host niches

Background

Candida albicans is a commensal yeast that may cause life-threatening infections. Studies have shown that the cytochrome b-c1 complex subunit 7 gene (QCR7) of C. albicans encodes a protein that forms a component of the mitochondrial electron transport chain complex III, making it an important target for studying the virulence of this yeast. However, to the best of our knowledge, the functions of QCR7 have not yet been characterized.

Methods

A QCR7 knockout strain was constructed using SN152, and BALb/c mice were used as model animals to determine the role of QCR7 in the virulence of C. albicans. Subsequently, the effects of QCR7 on mitochondrial functions and use of carbon sources were investigated. Next, its mutant biofilm formation and hyphal growth maintenance were compared with those of the wild type. Furthermore, the transcriptome of the qcr7Δ/Δ mutant was compared with that of the WT strain to explore pathogenic mechanisms.

Results

Defective QCR7 reduced recruitment of inflammatory cells and attenuated the virulence of C. albicans infection in vivo. Furthermore, the mutant influenced the use of multiple alternative carbon sources that exist in several host niches (GlcNAc, lactic acid, and amino acid, etc.). Moreover, it led to mitochondrial dysfunction. Furthermore, the QCR7 knockout strain showed defects in biofilm formation or the maintenance of filamentous growth. The overexpression of cell-surface-associated genes (HWP1, YWP1, XOG1, and SAP6) can restore defective virulence phenotypes and the carbon-source utilization of qcr7Δ/Δ.

Conclusion

This study provides new insights into the mitochondria-based metabolism of C. albicans, accounting for its virulence and the use of variable carbon sources that promote C. albicans to colonize host niches.

Candida albicans stimulates the formation of a multi-receptor complex that mediates epithelial cell invasion during oropharyngeal infection

Fungal invasion of the oral epithelium is central to the pathogenesis of oropharyngeal candidiasis (OPC). Candida albicans invades the oral epithelium by receptor-induced endocytosis but this process is incompletely understood. We found that C. albicans infection of oral epithelial cells induces c-Met to form a multi-protein complex with E-cadherin and the epidermal growth factor receptor (EGFR). E-cadherin is necessary for C. albicans to activate both c-Met and EGFR and to induce the endocytosis of C. albicans . Proteomics analysis revealed that c-Met interacts with C. albicans Hyr1, Als3 and Ssa1. Both Hyr1 and Als3 were required for C. albicans stimulation of c-Met and EGFR in oral epithelial cells in vitro and for full virulence during OPC in mice. Treating mice with small molecule inhibitors of c-Met and EGFR ameliorated OPC, demonstrating the potential therapeutic efficacy of blocking these host receptors for C. albicans .

Graphical abstract

Highlights

c-Met is an oral epithelial cell receptor for Candida albicans C. albicans infection causes c-Met and the epidermal growth factor receptor (EGFR) to form a complex with E-cadherin, which is required for c-Met and EGFR function C. albicans Hyr1 and Als3 interact with c-Met and EGFR, inducing oral epithelial cell endocytosis and virulence during oropharyngeal candidiasis Dual blockade of c-Met and EGFR ameliorates oropharyngeal candidiasis.

Molecular Mapping of Antifungal Mechanisms Accessing Biomaterials and New Agents to Target Oral Candidiasis

Oral candidiasis has a high rate of development, especially in immunocompromised patients. Immunosuppressive and cytotoxic therapies in hospitalized HIV and cancer patients are known to induce the poor management of adverse reactions, where local and systemic candidiasis become highly resistant to conventional antifungal therapy. The development of oral candidiasis is triggered by several mechanisms that determine oral epithelium imbalances, resulting in poor local defense and a delayed immune system response. As a result, pathogenic fungi colonies disseminate and form resistant biofilms, promoting serious challenges in initiating a proper therapeutic protocol. Hence, this study of the literature aimed to discuss possibilities and new trends through antifungal therapy for buccal drug administration. A large number of studies explored the antifungal activity of new agents or synergic components that may enhance the effect of classic drugs. It was of significant interest to find connections between smart biomaterials and their activity, to find molecular responses and mechanisms that can conquer the multidrug resistance of fungi strains, and to transpose them into a molecular map. Overall, attention is focused on the nanocolloids domain, nanoparticles, nanocomposite synthesis, and the design of polymeric platforms to satisfy sustained antifungal activity and high biocompatibility with the oral mucosa.

Proteomic profile of Candida albicans biofilm

Candida albicans biofilms are characterized by structural and cellular heterogeneity that confers antifungal resistance and immune evasion. Despite this, biofilm formation remains poorly understood. In this study, we used proteomic analysis to understand biofilm formation in C. albicans related to morphophysiological and architectural features. LC-MS/MS analysis revealed that 64 proteins were significantly modulated, of which 31 were upregulated and 33 were downregulated. The results indicate that metabolism (25 proteins), gene expression (13 proteins), stress response (7 proteins), and cell wall (5 proteins) composition are modulated. The rate of oxidative phosphorylation (OxPhos) and biosynthesis of UDP-N-acetylglucosamine, vitamin B6, and thiamine increased, while the rate of methionine biosynthesis decreased. There was a significant modification of the cell wall architecture due to higher levels of Sun41, Pir1 and Csh1 and increased glycosylation of proteins. It was observed that C. albicans induces hyphal growth by upregulating the expression of genes involved in cAMP-PKA and MAPK pathways. This study is significant in that it suggests an increase in OxPhos and alteration of cell wall architecture that could be contributing to the recalcitrance of C. albicans cells growing in biofilms. Nevertheless, a deeper investigation is needed to explore it further. SIGNIFICANCE: Candida sps is included in the list of pathogens with potential drug resistance threat due to the increased frequency especially colonization of medical devices, and tissues among the patients, in recent years. Significance of our study is that we are reporting traits like modulation in cell wall composition, amino acid and vitamin biosynthesis and importantly energy generation (OxPhos) etc. These traits could be conferring antifungal resistance, host immune evasion etc. and thus survival, in addition to facilitating biofilm formation. These findings are expected to prime the further studies on devising potent strategy against biofilm growth among the patients.

Influence of Propolis Extract (Caffeic Acid Phenethyl Ester) Addition on the Candida albicans Adhesion and Surface Properties of Autopolymerized Acrylic Resin

Background. Denture stomatitis has been linked to the adhesion and proliferation of Candida albicans (C. albicans) on denture bases, which is a common and recurrent problem in denture wearers. The current study aimed to evaluate the effect of incorporating caffeic acid phenethyl ester (CAPE) into autopolymerized polymethyl methacrylate (PMMA) acrylic resin on C. albicans adhesion, surface roughness, and hardness as well as the correlation between tested properties. Methods. Autopolymerized acrylic resin discs (N = 100, 50/C. albicans adhesion; 50/C. albicans surface roughness and hardness test) were fabricated in dimensions 15 × 2.5 mm, samples were categorized into 5 groups (n = 10) based on CAPE concentrations; unmodified (control), 2.5, 5, 10 and 15% wt of acrylic powder. Specimens were stored in distilled water for 48 h at 37°C. C. albicans adhesion was evaluated via direct culture method. Profilometer and Vickers hardness tester were used for surface roughness and hardness measurement. Post hoc Tukey’s HSD with ANOVA test was performed to compare the difference of means amongst groups. $P$ values were statistically significant at ≤0.05. Results. The addition of 2.5% of CAPE to PMMA has significantly reduced C. albicans counts in comparison to higher CAPE concentrations ( $p<0.001$ ). As for surface roughness, it was noticed that it increased with increased CAPE concentrations ( $p<0.0001$ ). While surface hardness decreased as CAPE concentrations increased ( $p<0.0001$ ). All tested properties showed a significant difference amongst groups for C. albicans colony count and surface parameters. Conclusion. The addition of 2.5% of CAPE to PMMA acrylic resin significantly decreased C. albicans count compared to higher CAPE concentrations. CAPE can be used as an adjunct in the prevention of DS by incorporating in the PMMA acrylic resin.

Systematic Genetic Interaction Analysis Identifies a Transcription Factor Circuit Required for Oropharyngeal Candidiasis

Oropharyngeal candidiasis (OPC) is a common infection that complicates a wide range of medical conditions and can cause either mild or severe disease depending on the patient. The pathobiology of OPC shares many features with candidal biofilms of abiotic surfaces. The transcriptional regulation of C. albicans biofilm formation on abiotic surfaces has been extensively characterized and involves six key transcription factors (Efg1, Ndt80, Rob1, Bcr1, Brg1, and Tec1). To determine if the in vitro biofilm transcriptional regulatory network also plays a role in OPC, we carried out a systematic genetic interaction analysis in a mouse model of C. albicans OPC. Whereas each of the six transcription factors are required for in vitro biofilm formation, only three homozygous deletion mutants (tec1ΔΔ, bcr1ΔΔ, and rob1ΔΔ) and one heterozygous mutant (tec1Δ/TEC1) have reduced infectivity in the mouse model of OPC. Although single mutants (heterozygous or homozygous) of BRG1 and EFG1 have no effect on fungal burden, double heterozygous and homozygous mutants have dramatically reduced infectivity, indicating a critical genetic interaction between these two transcription factors during OPC. Using epistasis analysis, we have formulated a genetic circuit, [EFG1+BRG1]→TEC1→BCR1, that is required for OPC infectivity and oral epithelial cell endocytosis. Surprisingly, we also found transcription factor mutants with in vitro defects in filamentation, such as efg1ΔΔ, rob1ΔΔ, and brg1ΔΔ filament, during oral infection and that reduced filamentation does not correlate with infectivity. Taken together, these data indicate that key in vitro biofilm transcription factors are involved in OPC but that the network characteristics and functional connections during infection are distinct from those observed in vivo. IMPORTANCE The pathology of oral candidiasis has features of biofilm formation, a well-studied process in vitro. Based on that analogy, we hypothesized that the network of transcription factors that regulates in vitro biofilm formation has similarities and differences during oral infection. To test this, we employed the first systematic genetic interaction analysis of C. albicans in a mouse model of oropharyngeal infection. This revealed that the six regulators involved in in vitro biofilm formation played roles in vivo but that the functional connections between factors were quite distinct. Surprisingly, we also found that while many of the factors are required for filamentation in vitro, none of the transcription factor deletion mutants was deficient for this key virulence trait in vivo. These observations clearly demonstrate that C. albicans regulates key aspects of its biology differently in vitro and in vivo.

A novel class of Candida glabrata cell wall proteins with β-helix fold mediates adhesion in clinical isolates

Candida glabrata is an opportunistic pathogenic yeast frequently causing infections in humans. Though it lacks typical virulence factors such as hyphal development, C. glabrata contains a remarkably large and diverse set of putative wall adhesins that is crucial for its success as pathogen. Here, we present an analysis of putative adhesins from the homology clusters V and VI. First, sequence similarity network analysis revealed relationships between cluster V and VI adhesins and S. cerevisiae haze protective factors (Hpf). Crystal structures of A-regions from cluster VI adhesins Awp1 and Awp3b reveal a parallel right-handed β-helix domain that is linked to a C-terminal β-sandwich. Structure solution of the A-region of Awp3b via single wavelength anomalous diffraction phasing revealed the largest known lanthanide cluster with 21 Gd³⁺ ions. Awp1-A and Awp3b-A show structural similarity to pectate lyases but binding to neither carbohydrates nor Ca²⁺ was observed. Phenotypic analysis of awp1Δ, awp3Δ, and awp1,3Δ double mutants did also not confirm their role as adhesins. In contrast, deletion mutants of the cluster V adhesin Awp2 in the hyperadhesive clinical isolate PEU382 demonstrated its importance for adhesion to polystyrene or glass, biofilm formation, cell aggregation and other cell surface-related phenotypes. Together with cluster III and VII adhesins our study shows that C. glabrata CBS138 can rely on a set of 42 Awp1-related adhesins with β-helix/α-crystallin domain architecture for modifying the surface characteristics of its cell wall.

Adhesion to host cells and abiotic, often hydrophobic surfaces, e.g. that of medical equipment like catheters, is an indispensable virulence factor for many pathogenic fungi. Among the latter, the yeast Candida glabrata excels by encoding in its genome large sets of surface-exposed cell wall proteins. Here, we show that in the clinical isolate PEU382 of C. glabrata, hyper-adhesiveness to plastics and the tendency to biofilm formation is conferred by a single adhesin, Awp2. An integrative bioinformatic and structural analysis of this and the related Awp1 and Awp3 adhesins unifies four, so far separately assigned Awp clusters—III, V, VI and VII–into one consisting of 42 Awp1-related adhesins. These adhesins commonly present an N-terminal module consisting of a right-handed β-helix and an α-crystallin domain on the yeast surface and use a calcium-independent mode for adhesion. Their sheer number contrasts to the 20 members of the well characterized Epa and 7 members of the Pwp family of surface proteins. Given these findings we suggest that C. glabrata utilizes just two structurally distinct motifs for colonizing different host niches by adhesion: the β-helix/α-crystallin module of Awp1-related adhesins and the C-type lectin PA14-domain for Epa and Pwp proteins.

The Role of B-Cells and Antibodies against Candida Vaccine Antigens in Invasive Candidiasis

Systemic candidiasis is an invasive fungal infection caused by members of the genus Candida. The recent emergence of antifungal drug resistance and increased incidences of infections caused by non-albicans Candida species merit the need for developing immune therapies against Candida infections. Although the role of cellular immune responses in anti-Candida immunity is well established, less is known about the role of humoral immunity against systemic candidiasis. This review summarizes currently available information on humoral immune responses induced by several promising Candida vaccine candidates, which have been identified in the past few decades. The protective antibody and B-cell responses generated by polysaccharide antigens such as mannan, β-glucan, and laminarin, as well as protein antigens like agglutinin-like sequence gene (Als3), secreted aspartyl proteinase (Sap2), heat shock protein (Hsp90), hyphally-regulated protein (Hyr1), hyphal wall protein (Hwp1), enolase (Eno), phospholipase (PLB), pyruvate kinase (Pk), fructose bisphosphate aldolase (Fba1), superoxide dismutase gene (Sod5) and malate dehydrogenase (Mdh1), are outlined. As per studies reviewed, antibodies induced in response to leading Candida vaccine candidates contribute to protection against systemic candidiasis by utilizing a variety of mechanisms such as opsonization, complement fixation, neutralization, biofilm inhibition, direct candidacidal activity, etc. The contributions of B-cells in controlling fungal infections are also discussed. Promising results using anti-Candida monoclonal antibodies for passive antibody therapy reinforces the need for developing antibody-based therapeutics including anti-idiotypic antibodies, single-chain variable fragments, peptide mimotopes, and antibody-derived peptides. Future research involving combinatorial immunotherapies using humanized monoclonal antibodies along with antifungal drugs/cytokines may prove beneficial for treating invasive fungal infections.

Transcription Factors of CAT1, EFG1, and BCR1 Are Effective in Persister Cells of Candida albicans-Associated HIV-Positive and Chemotherapy Patients

Background

Biofilm is an accumulation of cells, which are formed on mucosal surfaces of the host as well as on medical devices. The inherent resistance of Candida strains producing biofilms to antimicrobial agents is an important and key feature for biofilm growth, which can lead to treatment failure. This resistance is due to the regulatory increase of the output pumps, the presence of extracellular matrix, and the existence of persister cells. Persister cells are phenotypic variants that have MICs similar to antibiotic-sensitive populations and are able to tolerate high doses of antibiotics. The current study investigated the possible role of EFG1, BCR1, and CAT1 in the establishment or maintenance of persister cells in Candida albicans strains that produce biofilms.

Methods

After identifying Candida isolates by molecular methods, C. albicans isolates were confirmed by sequencing. Isolation of persister cells and determination of their MIC were performed by microdilution method. Then, RNA extraction and cDNA synthesis were performed from 60 C. albicans isolates under promoting and inducing conditions. Afterward, the mean expression of BCR1, EFG1, and CAT1 genes in both persister and non-persister groups was calculated using real-time qPCR. Phylogeny tree of persister and non-persister group isolates was drawn using ITS fragment.

Results

A total of 77 persister isolates were taken from the oral cavity of HIV patients as well as from patients undergoing chemotherapy. Biofilm intensity in persister isolates separated from HIV-infected patients was different from the non-persister group. The mean fold change of BCR1 (10.73), CAT1 (15.34), and EFG1 (2.41) genes in persister isolates was significantly higher than these genes in isolates without persister.

Conclusion

It can be concluded that the most important factor in the production of persister cells is biofilm binding and production, not biofilm development or mature biofilm production, which was found in the expression of BCR1 gene without change in the expression of EFG1 gene in the persister group. Also, catalase plays an essential role in the production of persister in C. albicans biofilm producers with ROS detoxification.

Metabolic flexibility and extensive adaptability governing multiple drug resistance and enhanced virulence in Candida albicans

Commensal fungus-Candida albicans turn pathogenic during the compromised immunity of the host, causing infections ranging from superficial mucosal to dreadful systemic ones. C. albicans has evolved various adaptive measures which collectively contribute towards its enhanced virulence. Among fitness attributes, metabolic flexibility and vigorous stress response are essential for its pathogenicity and virulence. Metabolic flexibility provides a means for nutrient assimilation and growth in diverse host microenvironments and reduces the vulnerability of the pathogen to various antifungals besides evading host immune response(s). Inside the host micro-environments, C. albicans efficiently utilizes the multiple fermentable and non-fermentable carbon sources to sustain and proliferate in glucose deficit conditions. The utilization of alternative carbon sources further highlights the importance of understanding these pathways as the attractive and potential therapeutic target. A thorough understanding of metabolic flexibility and adaptation to environmental stresses is warranted to decipher in-depth insights into virulence and molecular mechanisms of fungal pathogenicity. In this review, we have attempted to provide a detailed and recent understanding of some key aspects of fungal biology. Particular focus will be placed on processes like nutrient assimilation and utilization, metabolic adaptability, virulence factors, and host immune response in C. albicans leading to its enhanced pathogenicity.

Candida albicans biofilms and polymicrobial interactions

Candida albicans is a common fungus of the human microbiota. While generally a harmless commensal in healthy individuals, several factors can lead to its overgrowth and cause a range of complications within the host, from localized superficial infections to systemic life-threatening disseminated candidiasis. A major virulence factor of C. albicans is its ability to form biofilms, a closely packed community of cells that can grow on both abiotic and biotic substrates, including implanted medical devices and mucosal surfaces. These biofilms are extremely hard to eradicate, are resistant to conventional antifungal treatment and are associated with high morbidity and mortality rates, making biofilm-associated infections a major clinical challenge. Here, we review the current knowledge of the processes involved in C. albicans biofilm formation and development, including the central processes of adhesion, extracellular matrix production and the transcriptional network that regulates biofilm development. We also consider the advantages of the biofilm lifestyle and explore polymicrobial interactions within multispecies biofilms that are formed by C. albicans and selected microbial species.

Virulence Factors in Sporothrix schenckii, One of the Causative Agents of Sporotrichosis

Sporothrix schenckii is one of the etiological agents of sporotrichosis, a fungal infection distributed worldwide. Both, the causative organism and the disease have currently received limited attention by the medical mycology community, most likely because of the low mortality rates associated with it. Nonetheless, morbidity is high in endemic regions and the versatility of S. schenckii to cause zoonosis and sapronosis has attracted attention. Thus far, virulence factors associated with this organism are poorly described. Here, comparing the S. schenckii genome sequence with other medically relevant fungi, genes involved in morphological change, cell wall synthesis, immune evasion, thermotolerance, adhesion, biofilm formation, melanin production, nutrient uptake, response to stress, extracellular vesicle formation, and toxin production are predicted and discussed as putative virulence factors in S. schenckii.

Microbial interactions and immunity response in oral Candida species

Oral candidiasis are among the most common noncommunicable diseases, related with serious local and systemic illnesses. Although these infections can occur in all kinds of patients, they are more recurrent in immunosuppressed ones such as patients with HIV, hepatitis, cancer or under long antimicrobial treatments. Candida albicans continues to be the most frequently identified Candida spp. in these disorders, but other non-C. albicans Candida are rising. Understanding the immune responses involved in oral Candida spp. infections is a key feature to a successful treatment and to the design of novel therapies. In this review, we performed a literature search in PubMed and WoS, in order to examine and analyze common oral Candida spp.-bacteria/Candida-Candida interactions and the host immunity response in oral candidiasis.

Mechanism of Candida pathogenesis: revisiting the vital drivers

Candida is the most implicated fungal pathogen in the clinical setting. Several factors play important roles in the pathogenesis of Candida spp. Multiple transcriptional circuits, morphological and phenotypic switching, biofilm formation, tissue damaging extracellular hydrolytic enzymes, metabolic flexibility, genome plasticity, adaptation to environmental pH fluctuation, robust nutrient acquisition system, adherence and invasions (mediated by adhesins and invasins), heat shock proteins (HSPs), cytolytic proteins, escape from phagocytosis, evasion from host immune system, synergistic coaggregation with resident microbiota, resistance to antifungal agents, and the ability to efficiently respond to multiple stresses are some of the major pathogenic determinants of Candida species. The existence of multiple connections, in addition to the interactions and associations among all of these factors, are distinctive features that play important roles in the establishment of Candida infections. This review describes all the underlying factors and mechanisms involved in Candida pathogenesis by evaluating pathogenic determinants of Candida species. It reinforces the already available pool of data on the pathogenesis of Candida species by providing a clear and simplified understanding of the most important factors implicated in the pathogenesis of Candida species. The Candida pathogenesis network, an illustration linking all the major determinants of Candida pathogenesis, is also presented. Taken together, they will further improve our current understanding of how these factors modulate virulence and consequent infection(s). Development of new antifungal drugs and better therapeutic approaches to candidiasis can be achieved in the near future with continuing progress in the understanding of the mechanisms of Candida pathogenesis.

Clade II Candida auris possess genomic structural variations related to an ancestral strain

Candida auris is an invasive and multidrug-resistant ascomycetous yeast that is under global surveillance. All clinical cases of C. auris infection diagnosed from 1997 to 2019 in Japan were non-invasive and sporadic otitis media cases. In the present study, we performed whole-genome sequencing of seven C. auris strains isolated from patients with otitis media in Japan, all of which belonged to clade II. Comparative genome analysis using the high-quality draft genome sequences JCM 15448T revealed that single nucleotide variations (SNVs), clade-specific accessory genes, and copy number variations (CNVs) were identified in each C. auris clade. A total of 61 genes involved in cell wall and stress response-related functions was absent in clade II, and the pattern of conserved CNVs in each clade was more stable in clade II than in other clades. Our data suggest that the genomic structural diversity is stable in C. auris isolated from each biogeographic location, and Japanese strains isolated from patients with otitis media might belong to an ancestral type of C. auris. One Japanese strain, TWCC 58362, with reduced susceptibility to fluconazole, exhibited no mutation in ergosterol biosynthesis-related genes (ERG). However, TWCC 58362-specific variations, including SNVs, indels, and CNVs were detected, suggesting that gene duplication events in C. auris might contribute to antifungal drug resistance. Taken together, we demonstrated that genomic structural variations in C. auris could correlate to geographical dissemination, epidemiology, lesions in the host, and antifungal resistance.

The Effectiveness of Nigella Sativa Alcoholic Extract on the Inhibition of Candida Albicans Colonization and Formation of Plaque on Acrylic Denture Plates: an In Vitro Study

STATEMENT OF THE PROBLEM

Due to growing concerns on complications of chemical drugs, the use of herbal extracts has been considered as denture cleaning solutions.

PURPOSE

The aim of this study was to evaluate the in-vitro effects of Nigella sativa on the cleansing of the formation of Candida albicans plaque on the acrylic resin pieces.

MATERIALS AND METHOD

In this experimental study, 30 pieces of acrylic resin were contaminated by Candida albicans suspension. Then, the acrylic pieces were randomly divided into six groups and treated with 0.2, 0.4, 20, and 200 mg/ml of Nigella sativa, 100,000 units of nystatin (positive control), and distilled water (negative control) for 8 hours. At the end of the exposure period of the drugs, the rinse solution from acrylic pieces was cultured in Sabouraud Dextrose Agar and the average of the colonies from each group was compared.

RESULTS

The average number of colonies obtained at concentrations of 0.2, 0.4, 20, and 200 mg/ml of Nigella sativa were 122.6, 117.8, 73.4, and 14.4 colonies, respectively, as compared to distilled water (141.6) and nystatin (0) that had a significant difference (p< 0.001).

CONCLUSION

Nigella sativa extract at definite concentration is capable of clearing dental prosthesis, but compared to nystatin, it is weaker. However, due to the indirect immune-regulatory effects of Nigella sativa, it is suggested that other studies be conducted to investigate the therapeutic properties of Nigella sativa from the aspects of antimicrobial, anti-inflammatory, and oral ulcer healing in candida oral lesions.

The Fungal Histone Acetyl Transferase Gcn5 Controls Virulence of the Human Pathogen Candida albicans through Multiple Pathways

Fungal virulence is regulated by a tight interplay of transcriptional control and chromatin remodelling. Despite compelling evidence that lysine acetylation modulates virulence of pathogenic fungi such as Candida albicans, the underlying mechanisms have remained largely unexplored. We report here that Gcn5, a paradigm lysyl-acetyl transferase (KAT) modifying both histone and non-histone targets, controls fungal morphogenesis - a key virulence factor of C. albicans. Our data show that genetic removal of GCN5 abrogates fungal virulence in mice, suggesting strongly diminished fungal fitness in vivo. This may at least in part arise from increased susceptibility to killing by macrophages, as well as by other phagocytes such as neutrophils or monocytes. Loss of GCN5 also causes hypersensitivity to the fungicidal drug caspofungin. Caspofungin hypersusceptibility requires the master regulator Efg1, working in concert with Gcn5. Moreover, Gcn5 regulates multiple independent pathways, including adhesion, cell wall-mediated MAP kinase signaling, hypersensitivity to host-derived oxidative stress, and regulation of the Fks1 glucan synthase, all of which play critical roles in virulence and antifungal susceptibility. Hence, Gcn5 regulates fungal virulence through multiple mechanisms, suggesting that specific inhibition of Gcn5 could offer new therapeutic strategies to combat invasive fungal infections.

Contributions of Candida albicans Dimorphism, Adhesive Interactions, and Extracellular Matrix to the Formation of Dual-Species Biofilms with Streptococcus gordonii

Microbial communities have a great impact in health and disease. C. albicans interacts with multiple microorganisms in the oral cavity, frequently forming polymicrobial biofilms. We report on the synergistic interactions between C. albicans and the Gram-positive bacterium S. gordonii, for which we have examined the different contributions of adhesive interactions, filamentation, and the extracellular matrix to the formation of dual-species biofilms. Our results demonstrate that growth in the presence of the bacterium can restore the biofilm-forming ability of different C. albicans mutant strains with defects in adhesion and filamentation. The mixed-species biofilms also show high levels of resistance to antibacterial and antifungal antibiotics, and our results indicate that the fungal biofilm matrix protects bacterial cells within these mixed-species biofilms. Our observations add to a growing body of evidence indicating a high level of complexity in the reciprocal interactions and consortial behavior of fungal/bacterial biofilms.

Fungal and bacterial populations coexist in the oral cavity, frequently forming mixed-species biofilms that complicate treatment against polymicrobial infections. However, despite relevance to oral health, the bidirectional interactions between these microbial populations are poorly understood. In this study, we aimed to elucidate the mechanisms underlying the interactions between the fungal species Candida albicans and the bacterial species Streptococcus gordonii as they coexist in mixed-species biofilms. Specifically, the interactions of different C. albicans mutant strains deficient in filamentation (efg1Δ/Δ and brg1Δ/Δ), adhesive interactions (als3Δ/Δ and bcr1Δ/Δ), and production of matrix exopolymeric substances (EPS) (kre5Δ/Δ, mnn9Δ/Δ, rlm1Δ/Δ, and zap1Δ/Δ) were evaluated with S. gordonii under different conditions mimicking the environment in the oral cavity. Interestingly, our results revealed that growth of the biofilm-deficient C. albicansals3Δ/Δ and bcr1Δ/Δ mutant strains in synthetic saliva or with S. gordonii restored their biofilm-forming ability. Moreover, challenging previous observations indicating an important role of morphogenetic conversions in the interactions between these two species, our results indicated a highly synergistic interaction between S. gordonii and the C. albicans filamentation-deficient efg1Δ/Δ and brg1Δ/Δ deletion mutants, which was particularly noticeable when the mixed biofilms were grown in synthetic saliva. Importantly, dual-species biofilms were found to exhibit increase in antimicrobial resistance, indicating that components of the fungal exopolymeric material confer protection to streptococcal cells against antibacterial treatment. Collectively, these findings unravel a high degree of complexity in the interactions between C. albicans and S. gordonii in mixed-species biofilms, which may impact homeostasis in the oral cavity.

Candida glabrata Has No Enhancing Role in the Pathogenesis of Candida-Associated Denture Stomatitis in a Rat Model

Many denture wearers suffer from Candida-associated denture stomatitis (DS), a fungal infection of the hard palate in contact with dentures. Biofilm formation by Candida albicans on denture/palate surfaces is considered a central process in the infection onset. Although Candida glabrata is frequently coisolated with C. albicans, its role in DS pathogenesis is unknown. We show here, using a contemporary rat model that employed a patented intraoral denture system, that C. glabrata established stable colonization on the denture/palate. However, in contrast to C. albicans inoculated rats, rats inoculated with C. glabrata exhibited minimal changes in weight gain or palatal tissue damage. Likewise, coinoculation with the two Candida species resulted in no exacerbation of C. albicans-induced DS pathology. Together, our findings indicate that C. glabrata has no inducing/enhancing role in DS pathogenesis.

Denture stomatitis (DS) is a condition characterized by inflammation of the oral mucosa in direct contact with dentures and affects a significant number of otherwise healthy denture wearers. Candida-associated DS is predominantly caused by Candida albicans, a dimorphic fungus that readily colonizes and forms biofilms on denture materials. Previous studies showed a requirement for Candida biofilm formation on both palate and dentures in infection and identified fungal morphogenic transcription factors, Efg1 and Bcr1, as key players in DS pathogenesis. While both C. albicans and Candida glabrata are frequently coisolated in mucosal candidiasis, a pathogenic role for C. glabrata in DS remains unknown. Using an established rat model of DS, we sought to determine whether C. glabrata alone or coinoculation with C. albicans establishes colonization and causes palatal tissue damage and inflammation. Rats fitted with custom dentures were inoculated with C. albicans and/or C. glabrata and monitored over a 4-week period for fungal burden (denture/palate), changes in body weight, and tissue damage via lactate dehydrogenase (LDH) release as well as palatal staining by hematoxylin and eosin (H&E) and immunohistochemistry for myeloperoxidase (MPO) as measures of inflammation. C. glabrata colonized the denture/palate similarly to C. albicans. In contrast to C. albicans, colonization by C. glabrata resulted in minimal changes in body weight, palatal LDH release, and MPO expression. Coinoculation with both species had no obvious modulation of C. albicans-mediated pathogenic effects. These data suggest that C. glabrata readily establishes colonization on denture and palate but has no apparent role for inducing/enhancing C. albicans pathogenesis in DS.

IMPORTANCE Many denture wearers suffer from Candida-associated denture stomatitis (DS), a fungal infection of the hard palate in contact with dentures. Biofilm formation by Candida albicans on denture/palate surfaces is considered a central process in the infection onset. Although Candida glabrata is frequently coisolated with C. albicans, its role in DS pathogenesis is unknown. We show here, using a contemporary rat model that employed a patented intraoral denture system, that C. glabrata established stable colonization on the denture/palate. However, in contrast to C. albicans inoculated rats, rats inoculated with C. glabrata exhibited minimal changes in weight gain or palatal tissue damage. Likewise, coinoculation with the two Candida species resulted in no exacerbation of C. albicans-induced DS pathology. Together, our findings indicate that C. glabrata has no inducing/enhancing role in DS pathogenesis.

Activity of coumarin against Candida albicans biofilms

OBJECTIVE

The aim of this study was to investigate the antibiofilm activity of coumarin against Candida albicans.

METHODS

The efficacy of coumarin against biofilm formation and the mature biofilm of C. albicans was quantified by crystal violet (CV) staining and the 2,3-bis (2-methoxy-4-nitro-5-sulfophenyl)-5-[(phenylamino)carbonyl]-2H-tetrazolium hydroxide (XTT) reduction assay. The effect of coumarin on C. albicans adhesion was assessed on polystyrene plates and by using the cell surface hydrophobicity (CSH) assay. The morphological transition of C. albicans was conducted in two types of hyphae-inducing media at 37°C. The expression of hypha/biofilm-related genes was evaluated using qRT-PCR analysis. A rescue experiment involving addition of exogenous cyclic adenosine monophosphate (cAMP) was performed to investigate the involvement of cAMP in the yeast-to-hyphae transition. A C. albicans-infected Caenorhabditis elegans model was used to test the anti-virulence efficacy of coumarin.

RESULTS

Treatment with coumarin strongly affected the capacity of C. albicans to form biofilm and significantly impaired the preformed mature biofilm. The addition of coumarin notably inhibited C. albicans adhesion, CSH, and filamentation. The expression of some adhesion- and hypha-related genes, including HWP1, HYR1, ECE1, and ALS3, was remarkably down-regulated upon exposure to coumarin. Supplementation with cAMP partly rescued the coumarin-induced defects in hyphal development. Finally, coumarin prolonged survival in C. albicans-infected nematodes.

CONCLUSION

Coumarin inhibited C. albicans biofilm, which was associated with attenuated adhesion and hyphal growth.

Biofilms and vulvovaginal candidiasis

Candida species, including C. albicans, are part of the mucosal flora of most healthy women, and inhabit the gastrointestinal and genitourinary tracts. Under favourable conditions, they can colonize the vulvovaginal mucosa, giving rise to symptomatic vulvovaginal candidiasis (VVC). The mechanism by which Candida spp. produces inflammation is unknown. Both, the blastoconidia and the pseudohyphae are capable of destroying the vaginal epithelium by direct invasion. Although the symptoms are not always related to the fungal burden, in general, VVC is associated with a greater number of yeasts and pseudohyphae. Some years ago, C. albicans was the species most frequently involved in the different forms of VVC. However, infections by different species have emerged during the last two decades producing an increase in causative species of VVC such as C. glabrata, C. parapsilosis, C. krusei and C. tropicalis. Candida species are pathogenic organisms that have two forms of development: planktonic and biofilm. A biofilm is defined as a community of microorganisms attached to a surface and encompassed by an extracellular matrix. This form of presentation gives microorganisms greater resistance to antifungal agents. This review, about Candia spp. with a special emphasis on Candida albicans discusses specific areas such as biofilm structure and development, cell morphology and biofilm formation, biofilm-associated gene expression, the cell surface and adherence, the extracellular matrix, biofilm metabolism, and biofilm drug resistance in vulvovaginitis biofilms as an important virulence factor in fungi.

Adhesins of Yeasts: Protein Structure and Interactions

The ability of yeast cells to adhere to other cells or substrates is crucial for many yeasts. The budding yeast Saccharomyces cerevisiae can switch from a unicellular lifestyle to a multicellular one. A crucial step in multicellular lifestyle adaptation is self-recognition, self-interaction, and adhesion to abiotic surfaces. Infectious yeast diseases such as candidiasis are initiated by the adhesion of the yeast cells to host cells. Adhesion is accomplished by adhesin proteins that are attached to the cell wall and stick out to interact with other cells or substrates. Protein structures give detailed insights into the molecular mechanism of adhesin-ligand interaction. Currently, only the structures of a very limited number of N-terminal adhesion domains of adhesins have been solved. Therefore, this review focuses on these adhesin protein families. The protein architectures, protein structures, and ligand interactions of the flocculation protein family of S. cerevisiae; the epithelial adhesion family of C. glabrata; and the agglutinin-like sequence protein family of C. albicans are reviewed and discussed.

Influence of Streptococcus mitis and Streptococcus sanguinis on virulence of Candida albicans: in vitro and in vivo studies

The aim was to evaluate in vitro possible interactions, gene expression, and biofilm formation in species of Candida albicans, Streptococcus mitis, and Streptococcus sanguinis and their in vivo pathogenicity. The in vitro analysis evaluated the effects of S. mitis and S. sanguinis on C. albicans's biofilm formation by CFU count, filamentation capacity, and adhesion (ALS1, ALS3, HWP1) and transcriptional regulatory gene (BCR1, CPH1, EFG1) expression. In vivo studies evaluated the pathogenicity of the interaction of the microorganisms on Galleria mellonella, with analyses of the CFU per milliliter count and filamentation. In vitro results indicated that there was an observed decrease in CFU (79.4-71.5%) in multi-species biofilms. The interaction with S. mitis inhibited filamentation, which seems to increase its virulence factor with over-expression of genes ALS1, ALS3, and HWP1 as well the interaction with S. sanguinis as ALS3 and HWP1. S. mitis upregulated BRC1, CPH1, and EFG1. The histological images of in vivo study indicate an increase in the filamentation of C. albicans when in interaction with the other species. It was concluded that S. mitis interaction suggests increased virulence factors of C. albicans, with periods of lower virulence and proto-cooperation in the interaction with S. sanguinis.

Tipping the Balance: C. albicans Adaptation in Polymicrobial Environments

Candida albicans is a pleiomorphic fungus which co-exists with commensal bacteria in mucosal and skin sites of mammalian hosts. It is also a major co-isolated organism from polymicrobial systemic infections, with high potential for morbidity or mortality in immunocompromised patients. Traditionally, resident mucosal bacteria have been thought to antagonize C. albicans in its ability to colonize or cause infection. However, recent investigations have revealed synergistic relationships with certain bacterial species that colonize the same mucosal sites with C. albicans. Such relationships broaden the research landscape in pathogenesis but also contribute to clinical challenges in the prevention or treatment of mucosal candidiasis. This review sheds light on interactions of C. albicans and mucosal bacteria, with special emphasis on the effects of the resident bacterial microbiota on C. albicans physiology as they relate to its adaptation in mucosal sites as a commensal colonizer or as a pathogenic organism.

Release of transcriptional repression through the HCR promoter region confers uniform expression of HWP1 on surfaces of Candida albicans germ tubes

The mechanisms that fungi use to co-regulate subsets of genes specifically associated with morphogenic states represent a basic unsolved problem in fungal biology. Candida albicans is an important model of fungal differentiation both for rapid interconversion between yeast and hyphal growth forms and for white/opaque switching mechanisms. The Sundstrom lab is interested in mechanisms regulating hypha-specific expression of adhesin genes that are critical for C. albicans hyphal growth phenotypes and pathogenicity. Early studies on hypha-specific genes such as HWP1 and ALS3 reported 5’ intergenic regions that are larger than those typically found in an average promoter and are associated with hypha-specific expression. In the case of HWP1, activation and repression involves a 368 bp region, denoted the HWP1 control region (HCR), located 1410 bp upstream of its transcription start site. In previous work we showed that HCR confers developmental regulation to a heterologous ENO1 promoter, indicating that HCR by itself contains sufficient information to couple gene expression to morphology. Here we show that the activation and repression mediated by HCR are localized to distinct HCR regions that are targeted by the transcription factors Nrg1p and Efg1p. The finding that Efg1p mediates both repression via HCR under yeast morphological conditions and activation conditions positions Efg1p as playing a central role in coupling HWP1 expression to morphogenesis through the HCR region. These localization studies revealed that the 120 terminal base pairs of HCR confer Efg1p-dependent repressive activity in addition to the Nrg1p repressive activity mediated by DNA upstream of this subregion. The 120 terminal base pair subregion of HCR also contained an initiation site for an HWP1 transcript that is specific to yeast growth conditions (HCR-Y) and may function in the repression of downstream DNA. The detection of an HWP1 mRNA isoform specific to hyphal growth conditions (HWP1-H) showed that morphology-specific mRNA isoforms occur under both yeast and hyphal growth conditions. Similar results were found at the ALS3 locus. Taken together, these results, suggest that the long 5’ intergenic regions upstream of hypha-specific genes function in generating mRNA isoforms that are important for morphology-specific gene expression. Additional complexity in the HWP1 promoter involving HCR-independent activation was discovered by creating a strain lacking HCR that exhibited variable HWP1 expression during hyphal growth conditions. These results show that while HCR is important for ensuring uniform HWP1 expression in cell populations, HCR independent expression also exists. Overall, these results elucidate HCR-dependent mechanisms for coupling HWP1-dependent gene expression to morphology uniformly in cell populations and prompt the hypothesis that mRNA isoforms may play a role in coupling gene expression to morphology in C. albicans.

Candida-Epithelial Interactions

A plethora of intricate and dynamic molecular interactions occur between microbes and the epithelial cells that form the mucosal surfaces of the human body. Fungi, particularly species of Candida, are commensal members of our microbiota, continuously interacting with epithelial cells. Transient and localised perturbations to the mucosal environment can facilitate the overgrowth of fungi, causing infection. This minireview will examine the direct and indirect mechanisms by which Candida species and epithelial cells interact with each other, and explore the factors involved in the central processes of adhesion, invasion, and destruction of host mucosal surfaces.

Pharmacological targeting of ROS reaction network in myeloid leukemia cells monitored by ultra-weak photon emission

Acute myeloid leukemia (AML) is a blood cancer that is caused by a disorder of the process that normally generates neutrophils. Function and dysfunction of neutrophils are key to physiologic defense against pathogens as well as pathologies including autoimmunity and cancer. A major mechanism through which neutrophils contribute to health and disease is oxidative burst, which involves rapid release of reactive oxygen species (ROS) generated by a chemical reaction network catalyzed by enzymes including NADPH oxidase and myeloperoxidase (MPO). Due to the involvement of neutrophil-derived reactive oxygen species in many diseases and importance of NADPH oxidase and MPO-mediated reactions in progression and treatment of myeloid leukemia, monitoring this process and modulating it by pharmacological interventions is of great interest. In this work, we have evaluated the potential of a label-free method using ultra-weak photon emission (UPE) to monitor ROS production in neutrophil-like HL60 myeloid leukemia cells. Suppression of ROS was achieved by several drug candidates that target different parts of the reaction pathway. Our results show that UPE can report on ROS production as well as suppression by pharmacological inhibitors. We find that UPE is primarily generated by MPO catalyzed reaction and thus will be affected when an upstream reaction is pharmacologically modulated.

Noninvasive in vivo optical coherence tomography tracking of chronic otitis media in pediatric subjects after surgical intervention

In an institutional review board-approved study, 25 pediatric subjects diagnosed with chronic or recurrent otitis media were observed over a period of six months with optical coherence tomography (OCT). Subjects were followed throughout their treatment at the initial patient evaluation and preoperative consultation, surgery (intraoperative imaging), and postoperative follow-up, followed by an additional six months of records-based observation. At each time point, the tympanic membrane (at the light reflex region) and directly adjacent middle-ear cavity were observed in vivo with a handheld OCT probe and portable system. Imaging results were compared with clinical outcomes to correlate the clearance of symptoms in relation to changes in the image-based features of infection. OCT images of most all participants showed the presence of additional infection-related biofilm structures during their initial consultation visit and similarly for subjects imaged intraoperatively before myringotomy. Subjects with successful treatment (no recurrence of infectious symptoms) had no additional structures visible in OCT images during the postoperative visit. OCT image findings suggest surgical intervention consisting of myringotomy and tympanostomy tube placement provides a means to clear the middle ear of infection-related components, including middle-ear fluid and biofilms. Furthermore, OCT was demonstrated as a rapid diagnostic tool to prospectively monitor patients in both outpatient and surgical settings.

Yeast casein kinase 2 governs morphology, biofilm formation, cell wall integrity, and host cell damage of Candida albicans

The regulatory networks governing morphogenesis of a pleomorphic fungus, Candida albicans are extremely complex and remain to be completely elucidated. This study investigated the function of C. albicans yeast casein kinase 2 (CaYck2p). The yck2Δ/yck2Δ strain displayed constitutive pseudohyphae in both yeast and hyphal growth conditions, and formed enhanced biofilm under non-biofilm inducing condition. This finding was further supported by gene expression analysis of the yck2Δ/yck2Δ strain which showed significant upregulation of UME6, a key transcriptional regulator of hyphal transition and biofilm formation, and cell wall protein genes ALS3, HWP1, and SUN41, all of which are associated with morphogenesis and biofilm architecture. The yck2Δ/yck2Δ strain was hypersensitive to cell wall damaging agents and had increased compensatory chitin deposition in the cell wall accompanied by an upregulation of the expression of the chitin synthase genes, CHS2, CHS3, and CHS8. Absence of CaYck2p also affected fungal-host interaction; the yck2Δ/yck2Δ strain had significantly reduced ability to damage host cells. However, the yck2Δ/yck2Δ strain had wild-type susceptibility to cyclosporine and FK506, suggesting that CaYck2p functions independently from the Ca+/calcineurin pathway. Thus, in C. albicans, Yck2p is a multifunctional kinase that governs morphogenesis, biofilm formation, cell wall integrity, and host cell interactions.

Immune Recognition of Fungal Polysaccharides

The incidence of fungal infections has dramatically increased in recent years, in large part due to increased use of immunosuppressive medications, as well as aggressive medical and surgical interventions that compromise natural skin and mucosal barriers. There are relatively few currently licensed antifungal drugs, and rising resistance to these agents has led to interest in the development of novel preventative and therapeutic strategies targeting these devastating infections. One approach to combat fungal infections is to augment the host immune response towards these organisms. The polysaccharide-rich cell wall is the initial point of contact between fungi and the host immune system, and therefore, represents an important target for immunotherapeutic approaches. This review highlights the advances made in our understanding of the mechanisms by which the immune system recognizes and interacts with exopolysaccharides produced by four of the most common fungal pathogens: Aspergillus fumigatus, Candida albicans, Cryptococcus neoformans, and Histoplasma capsulatum. Work to date suggests that inner cell wall polysaccharides that play an important structural role are the most conserved across diverse members of the fungal kingdom, and elicit the strongest innate immune responses. The immune system senses these carbohydrates through receptors, such as lectins and complement proteins. In contrast, a greater diversity of polysaccharides is found within the outer cell walls of pathogenic fungi. These glycans play an important role in immune evasion, and can even induce anti-inflammatory host responses. Further study of the complex interactions between the host immune system and the fungal polysaccharides will be necessary to develop more effective therapeutic strategies, as well as to explore the use of immunosuppressive polysaccharides as therapeutic agents to modulate inflammation.

In Vitro Evaluation of the Inhibitory Activity of Thymoquinone in Combatting Candida albicans in Denture Stomatitis Prevention

Candida albicans adhesion and proliferation on denture bases may lead to denture stomatitis, which is a common and recurrent problem in denture wearers. The goal of this study was to assess the inhibitory effect of thymoquinone incorporated in the polymethyl methacrylate denture base material against Candida albicans. Eighty acrylic resin specimens were fabricated and divided into eight groups (n = 10) according to thymoquinone concentrations of 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, and 5% of acrylic powder. Two methods were used to evaluate the effect of thymoquinone on Candida albicans: the slide count and the serial dilution test. A multivariate analysis of variance (MANOVA) and the post-hoc Tukey’s Honestly Significant Difference (HSD) test were performed to compare the difference of means between the observations taken at various intervals with baseline. The p value was statistically significant at ≤0.05. According to the slide count and the serial dilution test, the mean number of adhered Candida albicans in the control group was 5436.9 ± 266 and 4691.4 ± 176.8; however, this number dramatically decreased to 0 ± 0 and 32.4 ± 1.7 in group 8 (concentration 5%). These results suggest that the incorporation of thymoquinone into the acrylic resin denture base material might be effective in preventing Candida albicans adhesion.

S. oralis activates the Efg1 filamentation pathway in C. albicans to promote cross-kingdom interactions and mucosal biofilms

Candida albicans and Streptococcus oralis are ubiquitous oral commensal organisms. Under host-permissive conditions these organisms can form hypervirulent mucosal biofilms. C. albicans biofilm formation is controlled by 6 master transcriptional regulators: Bcr1, Brg1, Efg1, Tec1, Ndt80, and Rob1. The objective of this work was to test whether any of these regulators play a role in cross-kingdom interactions between C. albicans and S. oralis in oral mucosal biofilms, and identify downstream target gene(s) that promote these interactions. Organotypic mucosal constructs and a mouse model of oropharyngeal infection were used to analyze mucosal biofilm growth and fungal gene expression. By screening 6 C. albicans transcription regulator reporter strains we discovered that EFG1 was strongly activated by interaction with S. oralis in late biofilm growth stages. EFG1 gene expression was increased in polymicrobial biofilms on abiotic surfaces, mucosal constructs and tongue tissues of mice infected with both organisms. EFG1 was required for robust Candida-streptococcal biofilm growth in organotypic constructs and mouse oral tissues. S. oralis stimulated C. albicans ALS1 gene expression in an EFG1-dependent manner, and Als1 was identified as a downstream effector of the Efg1 pathway which promoted C. albicans-S. oralis coaggregation interactions in mixed biofilms. We conclude that S. oralis induces an increase in EFG1 expression in C. albicans in late biofilm stages. This in turn increases expression of ALS1, which promotes coaggregation interactions and mucosal biofilm growth. Our work provides novel insights on C. albicans genes which play a role in cross-kingdom interactions with S. oralis in mucosal biofilms.

Synthesis, Antifungal Activity, and Biocompatibility of Novel 1,4-Diazabicyclo[2.2.2]Octane (DABCO) Compounds and DABCO-Containing Denture Base Resins

The fungal pathogen Candida albicans causes a variety of oral infections, including denture stomatitis, which is characterized by inflammation of the oral mucosa in direct contact with dentures and affects a significant number of otherwise healthy denture wearers. While antifungal treatment reduces symptoms, infections are often recurrent. One strategy to address this problem is to incorporate compounds with fungicidal activities into denture materials to prevent colonization. Our laboratory synthesized novel derivatives of 1,4-diazabicyclo[2.2.2]octane (DABCO), which is an organic compound typically used as a catalyst in polymerization reactions. DABCO derivatives with different aliphatic chain lengths (DC16, DC16F, DC18, and C6DC16), as well as methacrylate monomers conjugated to DABCO compounds (DC11MAF and C2DC11MAF), were synthesized and tested for antimicrobial activity. All the compounds exhibited fungicidal activity against several Candida species at concentrations ranging between 2 and 4 μg/ml. Moreover, acrylic denture base resins fabricated to contain 1, 2, or 4 wt% DABCO compounds inhibited surface C. albicans biofilm formation, as well as fungal growth, in disc diffusion assays. Remarkably, discs (4 wt%) aged for 2 months also exhibited approximately 100% growth-inhibitory activity. While some DABCO compounds exerted intermediate to high cytotoxicity against mammalian oral cell types, DC11MAF and denture base resin discs containing 2 or 4 wt% C2DC11MAF exhibited relatively low cytotoxicity against periodontal ligament (PDL) cell and gingival fibroblast (GF) lines, as well as primary oral epithelial cells. These studies demonstrate that DABCO derivatives can be incorporated into denture materials and exert fungicidal activity with minimal cytotoxicity to mammalian cells. DC11MAF and C2DC11MAF are considered strong candidates as therapeutic or preventive alternatives against Candida-associated denture stomatitis.

Phenotypic switch: The enigmatic white-gray-opaque transition system of Candida albicans

Candida albicans represents the most common commensal and opportunistic fungal pathogen colonizing humans. As a member of the normal microflora, it is present on the skin and the mucous membranes of the upper respiratory tract, gastrointestinal tract and female genital tracts. It is therefore not transmitted. It lies in wait for a change in some aspect of the host physiology that normally suppress growth and invasiveness through an enigmatic phenomenon called Phenotypic Switch System or White-Opaque Transition. This system involves reversible and heritable switching between alternative cellular phenotypes. White–opaque switching in Candida albicans was first discovered in 1987. This was initially identified in strain WO-1. Switching has been demonstrated to occur at sites of infection and to occur between recurrent episodes of infection in select cases esp. AIDS and diabetes.

Transcription Factors Efg1 and Bcr1 Regulate Biofilm Formation and Virulence during Candida albicans-Associated Denture Stomatitis

Denture stomatitis (DS) is characterized by inflammation of the oral mucosa in direct contact with dentures and affects a significant number of otherwise healthy denture wearers. The disease is caused by Candida albicans, which readily colonizes and form biofilms on denture materials. While evidence for biofilms on abiotic and biotic surfaces initiating Candida infections is accumulating, a role for biofilms in DS remains unclear. Using an established model of DS in immunocompetent animals, the purpose of this study was to determine the role of biofilm formation in mucosal damage during pathogenesis using C. albicans or mutants defective in morphogenesis (efg1^-/-) or biofilm formation (bcr1^-/-). For in vivo analyses, rats fitted with custom dentures, consisting of fixed and removable parts, were inoculated with wild-type C. albicans, mutants or reconstituted strains and monitored weekly for fungal burden (denture and palate), body weight and tissue damage (LDH) for up to 8 weeks. C. albicans wild-type and reconstituted mutants formed biofilms on dentures and palatal tissues under in vitro, ex vivo and in vivo conditions as indicated by microscopy demonstrating robust biofilm architecture and extracellular matrix (ECM). In contrast, both efg1^-/- and bcr1^-/- mutants exhibited poor biofilm growth with little to no ECM. In addition, quantification of fungal burden showed reduced colonization throughout the infection period on dentures and palates of rats inoculated with efg1^-/-, but not bcr1^-/-, compared to controls. Finally, rats inoculated with efg1^-/- and bcr1^-/- mutants had minimal palatal tissue damage/weight loss while those inoculated with wild-type or reconstituted mutants showed evidence of tissue damage and exhibited stunted weight gain. These data suggest that biofilm formation is associated with tissue damage during DS and that Efg1 and Bcr1, both central regulators of virulence in C. albicans, have pivotal roles in pathogenesis of DS.

Candida albicans Biofilms and Human Disease

In humans, microbial cells (including bacteria, archaea, and fungi) greatly outnumber host cells. Candida albicans is the most prevalent fungal species of the human microbiota; this species asymptomatically colonizes many areas of the body, particularly the gastrointestinal and genitourinary tracts of healthy individuals. Alterations in host immunity, stress, resident microbiota, and other factors can lead to C. albicans overgrowth, causing a wide range of infections, from superficial mucosal to hematogenously disseminated candidiasis. To date, most studies of C. albicans have been carried out in suspension cultures; however, the medical impact of C. albicans (like that of many other microorganisms) depends on its ability to thrive as a biofilm, a closely packed community of cells. Biofilms are notorious for forming on implanted medical devices, including catheters, pacemakers, dentures, and prosthetic joints, which provide a surface and sanctuary for biofilm growth. C. albicans biofilms are intrinsically resistant to conventional antifungal therapeutics, the host immune system, and other environmental perturbations, making biofilm-based infections a significant clinical challenge. Here, we review our current knowledge of biofilms formed by C. albicans and closely related fungal species.

The Host's Reply to Candida Biofilm

Candida spp. are among the most common nosocomial fungal pathogens and are notorious for their propensity toward biofilm formation. When growing on a medical device or mucosal surface, these organisms reside as communities embedded in a protective matrix, resisting host defenses. The host responds to Candida biofilm by depositing a variety of proteins that become incorporated into the biofilm matrix. Compared to free-floating Candida, leukocytes are less effective against Candida within a biofilm. This review highlights recent advances describing the host's response to Candida biofilms using ex vivo and in vivo models of mucosal and device-associated biofilm infections.

The role of pattern recognition receptors in the innate recognition of Candida albicans

Candida albicans is both a commensal microorganism in healthy individuals and a major fungal pathogen causing high mortality in immunocompromised patients. Yeast-hypha morphological transition is a well known virulence trait of C. albicans. Host innate immunity to C. albicans critically requires pattern recognition receptors (PRRs). In this review, we summarize the PRRs involved in the recognition of C. albicans in epithelial cells, endothelial cells, and phagocytic cells separately. We figure out the differential recognition of yeasts and hyphae, the findings on PRR-deficient mice, and the discoveries on human PRR-related single nucleotide polymorphisms (SNPs).