Hyphae-specific genes HGC1, ALS3, HWP1, and ECE1 and relevant signaling pathways in Candida albicans

Ctr9 promotes virulence of Candida albicans by regulating methionine metabolism

Candida albicans, a part of normal flora, is an opportunistic fungal pathogen and causes severe health issues in immunocompromised patients. Its pathogenicity is intricately linked to the transcriptional regulation of its metabolic pathways. Paf1 complex (Paf1C) is a crucial transcriptional regulator that is highly conserved in eukaryotes. The objective of this study was to explore the role of Paf1C in the metabolic pathways and how it influences the pathogenicity of C. albicans. Paf1C knockout mutant strains of C. albicans (ctr9Δ/Δ, leo1Δ/Δ, and cdc73Δ/Δ) were generated using the CRISPR-Cas9 system. To investigate the effect of Paf1C on pathogenicity, macrophage interaction assays and mouse survival tests were conducted. The growth patterns of the Paf1C knockout mutants were analyzed through spotting assays and growth curve measurements. Transcriptome analysis was conducted under yeast conditions (30°C without serum) and hyphal conditions (37°C with 10% FBS), to further elucidate the role of Paf1C in the pathogenicity of C. albicans. CTR9 deletion resulted in the attenuation of C. albicans virulence, in macrophage and mouse models. Furthermore, we confirmed that the reduced virulence of the ctr9Δ/Δ mutant can be attributed to a decrease in C. albicans cell abundance. Moreover, transcriptome analysis revealed that metabolic processes required for cell proliferation are impaired in ctr9Δ/Δ mutant. Notably, CTR9 deletion led to the downregulation of methionine biosynthetic genes and the cAMP-PKA signaling pathway-related hypha essential genes, which are pivotal for virulence. Our results suggest that Ctr9-regulated methionine metabolism is a crucial factor for determining C. albicans pathogenicity.

Antifungal properties of abnormal cannabinoid derivatives: Disruption of biofilm formation and gene expression in Candida species

Abnormal cannabinoids (including comp 3) are a class of synthetic lipid compounds with non-psychoactive properties and regioisomer configurations, but distinct from traditional cannabinoids since they do not interact with the established CB1 and CB2 receptors. Previous research showed the cardioprotective and anti-inflammatory potentials of comp 3 and more recently its antimicrobial effect on methicillin-resistant Staphylococcus aureus (MRSA). Given the escalating challenges posed by Candida infections and the rise of antifungal drug resistance, the exploration of novel therapeutic avenues is crucial. This study aimed to assess the anti-Candida properties of newly synthesized AbnCBD derivatives. AbnCBD derivatives were synthesized by acid catalysis-induced coupling and further derivatized. We evaluated the potential of the AbnCBD derivatives to inhibit the growth stages of various Candida species. By in vitro colorimetric assays and in vivo mice experiments, we have shown that AbnCBD derivatives induce differential inhibition of Candida growth. The AbnCBD derivatives, especially comp 3, comp 10, and comp 9 significantly reduced the growth of C. albicans, including FLC-resistant strains, and of C. tropicalis and C. parapsilosis but not of C auris compared to their controls (FLC and 0.5 % DMSO). Comp 3 also disrupted C. albicans biofilm formation and eradicated mature biofilms. Notably, other derivatives of AbnCBD disrupted the biofilm formation and maturation of C. albicans but did not affect yeast growth. In a murine model of VVC, comp 3 demonstrated significant fungal clearance and reduced C. albicans burden compared to vehicle and FLC controls. These findings highlight the potential of AbnCBDs as promising antifungal agents against Candida infections.

Heterologous expression of the insect SVWC peptide WHIS1 inhibits Candida albicans invasion into A549 and HeLa epithelial cells

Candida albicans (C. albicans), a microbe commonly isolated from Candida vaginitis patients with vaginal tract infections, transforms from yeast to hyphae and produces many toxins, adhesins, and invasins, as well as C. albicans biofilms resistant to antifungal antibiotic treatment. Effective agents against this pathogen are urgently needed. Antimicrobial peptides (AMPs) have been used to cure inflammation and infectious diseases. In this study, we isolated whole housefly larvae insect SVWC peptide 1 (WHIS1), a novel insect single von Willebrand factor C-domain protein (SVWC) peptide from whole housefly larvae. The expression pattern of WHIS1 showed a response to the stimulation of C. albicans. In contrast to other SVWC members, which function as antiviral peptides, interferon (IFN) analogs or pathogen recognition receptors (PRRs), which are the prokaryotically expressed MdWHIS1 protein, inhibit the growth of C. albicans. Eukaryotic heterologous expression of WHIS1 inhibited C. albicans invasion into A549 and HeLa cells. The heterologous expression of WHIS1 clearly inhibited hyphal formation both extracellularly and intracellularly. Furthermore, the mechanism of WHIS1 has demonstrated that it downregulates all key hyphal formation factors (ALS1, ALS3, ALS5, ECE1, HWP1, HGC1, EFG1, and ZAP1) both extracellularly and intracellularly. These data showed that heterologously expressed WHIS1 inhibits C. albicans invasion into epithelial cells by affecting hyphal formation and adhesion factor-related gene expression. These findings provide new potential drug candidates for treating C. albicans infection.

Progress of Antimicrobial Mechanisms of Stilbenoids

Antimicrobial drugs have made outstanding contributions to the treatment of pathogenic infections. However, the emergence of drug resistance continues to be a major threat to human health in recent years, and therefore, the search for novel antimicrobial drugs is particularly urgent. With a deeper understanding of microbial habits and drug resistance mechanisms, various creative strategies for the development of novel antibiotics have been proposed. Stilbenoids, characterized by a C6-C2-C6 carbon skeleton, have recently been widely recognized for their flexible antimicrobial roles. Here, we comprehensively summarize the mode of action of stilbenoids from the viewpoint of their direct antimicrobial properties, antibiofilm and antivirulence activities and their role in reversing drug resistance. This review will provide an important reference for the future development and research into the mechanisms of stilbenoids as antimicrobial agents.

Discovery of Antifungal Norsesquiterpenoids from a Soil-Derived Streptomyces microflavus: Targeting Biofilm Formation and Synergistic Combination with Amphotericin B against Yeast-like Fungi

Thirty-five norsesquiterpenoids were isolated from the fermentation broth of Streptomyces microflavus from the forest soil of Ailaoshan in China. The structures of new compounds (1-5, 10-26) were elucidated by comprehensive spectroscopic analysis including data from experimental and calculated ECD spectra, as well as Mosher's reagent derivatives method. Norsesquiterpenoids showed different levels of antifungal activity with MIC80 values ranging from 25 to 200 μg/mL against Candida albicans, Candida parapsilosis, and Cryptococcus neoformans. The combining isolated norsesquiterpenoids with amphotericin B resulted in a synergistic interaction against test yeast-like fungi with a fractional inhibitory concentration index < 0.5. Compound 33 significantly inhibited biofilm formation and destroyed the preformed biofilm of fungi. Moreover, 33 downregulated the expression of adhesion-related genes HWP1, ALS1, ALS3, ECE1, EAP1, and BCR1 to inhibit the adhesion of C. albicans. Findings from the current study highlight the potential usage of norsesquiterpenoids from soil-derived Streptomyces for antifungal leads discovery.

Inhibiting pathogenicity of vaginal Candida albicans by lactic acid bacteria and MS analysis of their extracellular compounds

Maintaining healthy vaginal microflora post-puberty is critical. In this study we explore the potential of vaginal lactic acid bacteria (LAB) and their extracellular metabolites against the pathogenicity of Candida albicans. The probiotic culture free supernatant (PCFS) from Lactobacillus crispatus, L. gasseri, and L. vaginalis exhibit an inhibitory effect on budding, hyphae, and biofilm formation of C. albicans. LGPCFS manifested the best potential among the LAB PCFS, inhibiting budding for 24 h and restricting hyphae formation post-stimulation. LGPCFS also pre-eminently inhibited biofilm formation. Furthermore, L. gasseri itself grew under RPMI 1640 stimulation suppressing the biofilm formation of C. albicans. The PCFS from the LAB downregulated the hyphal genes of C. albicans, inhibiting the yeast transformation to fungi. Hyphal cell wall proteins HWP1, ALS3, ECE1, and HYR1 and transcription factors BCR1 and CPH1 were downregulated by the metabolites from LAB. Finally, the extracellular metabolome of the LAB was studied by LC-MS/MS analysis. L.gasseri produced the highest antifungal compounds and antibiotics, supporting its best activity against C. albicans. Vaginal LAB and their extracellular metabolites perpetuate C. albicans at an avirulent state. The metabolites produced by these LAB in vitro have been identified, and can be further exploited as a preventive measure against vaginal candidiasis.

Reappraisal of intra-abdominal candidiasis: insights from peritoneal fluid analysis

BACKGROUND

The understanding of high mortality associated with intra-abdominal candidiasis (IAC) remains limited. While Candida is considered a harmless colonizer in the digestive tract, its role as a true pathogen in IAC is still debated. Evidence regarding Candida virulence in the human peritoneal fluid are lacking. We hypothesized that during IAC, Candida albicans develops virulence factors to survive to new environmental conditions. The objective of this observational exploratory monocentric study is to investigate the influence of peritoneal fluid (PF) on the expression of C. albicans virulence using a multimodal approach.

MATERIALS AND METHODS

A standardized inoculum of a C. albicans (3.106 UFC/mL) reference strain (SC5314) was introduced in vitro into various PF samples obtained from critically ill patients with intra-abdominal infection. Ascitic fluids (AFs) and Sabouraud medium (SBD) were used as control groups. Optical microscopy and conventional culture techniques were employed to assess the morphological changes and growth of C. albicans. Reverse transcriptase qPCR was utilized to quantify the expression levels of five virulence genes. The metabolic production of C. albicans was measured using the calScreener™ technology.

RESULTS

A total of 26 PF samples from patients with secondary peritonitis were included in the study. Critically ill patients were mostly male (73%) with a median age of 58 years admitted for urgent surgery (78%). Peritonitis was mostly hospital-acquired (81%), including 13 post-operative peritonitis (50%). The infected PF samples predominantly exhibited polymicrobial composition. The findings revealed substantial variability in C. albicans growth and morphological changes in the PF compared to ascitic fluid. Virulence gene expression and metabolic production were dependent on the specific PF sample and the presence of bacterial coinfection.

CONCLUSIONS

This study provides evidence of C. albicans virulence expression in the peritoneal fluid. The observed variability in virulence expression suggests that it is influenced by the composition of PF and the presence of bacterial coinfection. These findings contribute to a better understanding of the complex dynamics of intra-abdominal candidiasis and advocate for personalized approach for IAC patients. Trial registration https://clinicaltrials.gov/ (NCT05264571; February 22, 2022).

Characterization of an allosteric inhibitor of fungal-specific C-24 sterol methyltransferase to treat Candida albicans infections

Filamentation is an important virulence factor of the pathogenic fungus Candida albicans. The abolition of Candida albicans hyphal formation by disrupting sterol synthesis is an important concept for the development of antifungal drugs with high safety. Here, we conduct a high-throughput screen using a C. albicans strain expressing green fluorescent protein-labeled Dpp3 to identify anti-hypha agents by interfering with ergosterol synthesis. The antipyrine derivative H55 is characterized to have minimal cytotoxicity and potent inhibition of C. albicans hyphal formation in multiple cultural conditions. H55 monotherapy exhibits therapeutic efficacy in mouse models of azole-resistant candidiasis. H55 treatment increases the accumulation of zymosterol, the substrate of C-24 sterol methyltransferase (Erg6). The results of enzyme assays, photoaffinity labeling, molecular simulation, mutagenesis, and cellular thermal shift assays support H55 as an allosteric inhibitor of Erg6. Collectively, H55, an inhibitor of the fungal-specific enzyme Erg6, holds potential to treat C. albicans infections.

Secretions from Serratia marcescens Inhibit the Growth and Biofilm Formation of Candida spp. and Cryptococcus neoformans

Candida spp. and Cryptococcus are conditional pathogenic fungi that commonly infect immunocompromised patients. Over the past few decades, the increase in antifungal resistance has prompted the development of new antifungal agents. In this study, we explored the potential antifungal effects of secretions from Serratia marcescens on Candida spp. and Cryptococcus neoformans. We confirmed that the supernatant of S. marcescens inhibited fungal growth, suppressed hyphal and biofilm formation, and downregulated the expression of hyphae-specific genes and virulence-related genes in Candida spp. and C. neoformans. Furthermore, the S. marcescens supernatant retained biological stability after heat, pH, and protease K treatment. The chemical profile of the S. marcescens supernatant was characterized by ultra-high-performance liquid chromatography-linear ion trap/orbitrap high resolution mass spectrometry analysis and a total of 61 compounds with an mzCloud best match of greater than 70 were identified. In vivo, treatment with the S. marcescens supernatant reduced the mortality of fungi-infected Galleria mellonella. Taken together, our results revealed that the stable antifungal substances in the supernatant of S. marcescens have promising potential applications in the development of new antifungal agents.

Anti-Candida Potential of Sclareol in Inhibiting Growth, Biofilm Formation, and Yeast-Hyphal Transition

Even though Candida albicans commonly colonizes on most mucosal surfaces including the vaginal and gastrointestinal tract, it can cause candidiasis as an opportunistic infectious fungus. The emergence of resistant Candida strains and the toxicity of anti-fungal agents have encouraged the development of new classes of potential anti-fungal agents. Sclareol, a labdane-type diterpene, showed anti-Candida activity with a minimum inhibitory concentration of 50 μg/mL in 24 h based on a microdilution anti-fungal susceptibility test. Cell membrane permeability with propidium iodide staining and mitochondrial membrane potential with JC-1 staining were increased in C. albicans by treatment of sclareol. Sclareol also suppressed the hyphal formation of C. albicans in both liquid and solid media, and reduced biofilm formation. Taken together, sclareol induces an apoptosis-like cell death against Candida spp. and suppressed biofilm and hyphal formation in C. albicans. Sclareol is of high interest as a novel anti-fungal agent and anti-virulence factor.

Hydrothermal assisted biogenic synthesis of silver nanoparticles: A potential study on virulent candida isolates from COVID-19 patients

Till now the exact mechanism and effect of biogenic silver nanoparticles on fungus is an indefinable question. To focus on this issue, the first time we prepared hydrothermal assisted thyme coated silver nanoparticles (T/AgNPs) and their toxic effect on Candida isolates were determined. The role of thyme (Thymus Vulgaris) in the reduction of silver ions and stabilization of T/AgNPs was estimated by Fourier transforms infrared spectroscopy, structure and size of present silver nanoparticles were detected via atomic force microscopy as well as high-resolution transmission electron microscopy. The biological activity of T/AgNPs was observed against Candida isolates from COVID-19 Patients. Testing of virulence of Candida species using Multiplex PCR. T/AgNPs proved highly effective against Candida albicans, Candida kruzei, Candida glabrata and MIC values ranging from 156.25 to 1,250 μg/mL and MFC values ranging from 312.5 to 5,000 μg/mL. The structural and morphological modifications due to T/AgNPs on Candida albicans were detected by TEM. It was highly observed that when Candida albicans cells were subjected to 50 and 100 μg/mL T/AgNPs, a remarkable change in the cell wall and cell membrane was observed.

Antifungal activity of dexamethasone against fluconazole-resistant Candida albicans and its activity against biofilms

Objective: The present study investigated the antifungal action of dexamethasone disodium phosphate (Dex). Methodology: Susceptibility testing was performed using the Clinical & Laboratory Standards Institute protocol; M27-A3, checkerboard test and biofilm were evaluated with two isolates of Candida albicans, hyphal production test, molecular docking analysis and flow cytometry analysis. Result: Dex and fluconazole (FLC) together had a synergistic effect. Mature biofilm was reduced when treated with Dex alone or in combination. Dex and FLC promoted a decrease in the production of hyphae and changes in the level of mitochondrial depolarization, increased generation of reactive oxygen species, loss of membrane integrity, increased phosphatidylserine externalization and molecular docking; there was interaction with ALS3 and SAP5 targets. Conclusion: Dex showed antifungal activity against FLC-resistant C. albicans strains.

Caspofungin resistance in Candida albicans: genetic factors and synergistic compounds for combination therapies

Caspofungin and other echinocandins have been used for the treatment of human infections by the opportunistic yeast pathogen, Candida albicans. There has been an increase in infections by non-albicans Candida species such as Candida glabrata, Candida parapsilosis, Candida tropicalis, Candida krusei, and Candida auris in clinical or hospital settings. This is problematic to public health due to the increasing prevalence of echinocandin resistant species/strains. This review will present a summary on various studies that investigated the inhibitory action of caspofungin on 1,3-β-D-glucan synthesis, on cell wall structure, and biofilm formation of C. albicans. It will highlight some of the issues linked to caspofungin resistance or reduced caspofungin sensitivity in various Candida species and the potential benefits of antimicrobial peptides and other compounds in synergy with caspofungin.

Streptococcus mutans and Candida albicans Biofilm Inhibitors Produced by Lactiplantibacillus plantarum CCFM8724

Lactiplantibacillus plantarum CCFM8724 inhibits the growth of Streptococcus mutans and Candida albicans in mixed-species biofilm formation. In this study, bioactive compound including cyclo (leu-pro), cyclo (phe-pro), and some organic acids, such as 3-phenyllactic acid, hydrocinnamic acid, and palmitic acid, were identified through GC-MS analysis. At 50 μg·mL^-1, cyclo (leu-pro) reduced biofilm mass (OD₆₀₀) from 3.00 to 2.00, and hydrocinnamic acid at 25 μg·mL^-1 reduced biofilm mass (OD₆₀₀) from 3.00 to 1.00. The expression of ALS3 and HWP1 was downregulated by cyclo (leu-pro). Furthermore, a mixture of cyclo (leu-pro), cyclo (phe-pro), 3-phenyllactic acid, hydrocinnamic acid, and palmitic acid, had anti-biofilm activity. Overall, the results provide promising baseline information for the potential use of this probiotic and its components in preventing biofilm formation.

COVID-19-Associated Candidiasis: Possible Patho-Mechanism, Predisposing Factors, and Prevention Strategies

The coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), is threatening public health. A large number of affected people need to be hospitalized. Immunocompromised patients and ICU-admitted patients are predisposed to further bacterial and fungal infections, making patient outcomes more critical. Among them, COVID-19-associated candidiasis is becoming more widely recognized as a part of severe COVID-19 sequelae. While the molecular pathophysiology is not fully understood, some factors, including a compromised immune system, iron and zinc deficiencies, and nosocomial and iatrogenic transmissions, predispose COVID-19 patients to candidiasis. In this review, we discuss the existing knowledge of the virulence characteristics of Candida spp. and summarize the key concepts in the possible molecular pathogenesis. We analyze the predisposing factors that make COVID-19 patients more susceptible to candidiasis and the preventive measures which will provide valuable insights to guide the effective prevention of candidiasis in COVID-19 patients.

Lactobacilli as Anti-biofilm Strategy in Oral Infectious Diseases: A Mini-Review

The spread of biofilm-related diseases in developed countries has led to increased mortality rates and high health care costs. A biofilm is a community of microorganisms that is irreversibly attached to a surface, behaving very differently from planktonic cells and providing resistance to antimicrobials and immune response. Oral diseases are an excellent example of infection associated with the formation of highly pathogenic biofilms. It is generally accepted that, when the oral homeostasis is broken, the overgrowth of pathogens is facilitated. Among them, Porphyromonas gingivalis and Aggregatibacter actinomycetemcomitans are the main etiological agents of periodontitis, while Streptococcus mutans is strongly associated with the onset of dental caries. Other microorganisms, such as the fungus Candida albicans, may also be present and contribute to the severity of infections. Since the common antibiotic therapies usually fail to completely eradicate biofilm-related oral diseases, alternative approaches are highly required. In this regard, the topical administration of probiotics has recently gained interest in treating oral diseases. Thus, the present mini-review focuses on the possibility of using Lactobacillus spp. as probiotics to counteract biofilm-mediated oral infections. Many evidence highlight that Lactobacillus living cells can impede the biofilm formation and eradicate mature biofilms of different oral pathogens, by acting through different mechanisms. Even more interestingly, lactobacilli derivatives, namely postbiotics (soluble secreted products) and paraprobiotics (cell structural components) are able to trigger anti-biofilm effects too, suggesting that they can represent a novel and safer alternative to the use of viable cells in the management of biofilm-related oral diseases.

MOLECULAR DETECTION OF THE TWO VIRULENCE GENES HWP1 AND ALS1 IN CANDIDA SPECIES ISOLATED FROM ONYCHOMYCOSIS

OBJECTIVE

The aim: This article was aimed to assess the prevalence of Candida species causing nail infections and to investigate the most important virulence genes that cause adhesion.

PATIENTS AND METHODS

Materials and methods: Samples were collected from General Hospital and the outpatient's clinics in Thi-Qar Province, southern Iraq, during the period from January 2021 to May 2021. Samples were inoculated on Sabouraud Dextrose Agar plates containing 0.5 mg chloramphenicol, then Petri dishes were incubated at 30°C under aerobic conditions and observed for Candida species growth for 24-72 hrs. All isolates were identified by morphologic and chromatic properties on CHROMagar and by Api Candida.

RESULTS

Results: Twenty five isolates were obtained from hundred samples, which belong to five species of the genus Candida, distributed in percentage 9(36%), 4(16%), 4(16%), 4(16%) and 3(12%) of C. glabrata, C. krusei, C. albicans, C. famata and C. tropicalis consecutively and one isolate was not identified. Monoplex PCR technique was used to detect virulence genes (hwp1 and als1) of Candida species. Four Candida albicans isolates (16%) were carried of both hwp1 and als1 genes.

CONCLUSION

Conclusions: The virulence gene (hwp1) can be relied upon in molecular detection as a special diagnostic tool of Candida albicans species except other types causing Candidal onychomycosis.

Faecalibacterium prausnitzii Attenuates DSS-Induced Colitis by Inhibiting the Colonization and Pathogenicity of Candida albicans

SCOPE

Intestinal commensal microbiota interactions play critical roles in the inflammatory bowel disease (IBD) development. Candida albicans (CA) can aggravate intestinal inflammation; however, whether Faecalibacterium prausnitzii (FP) can antagonize CA is unknown.

METHODS AND RESULTS

CA are co-cultured with bacteria (FP and Escherichia coli (EC)), bacterial supernatant, and bacterial medium, respectively. Then, the CA hyphae-specific genes' expression and CA cells' morphology are investigated. The Nod-like receptor pyrin-containing protein 6 (NLRP6) inflammasome, inflammatory cytokines, and antimicrobial peptides (AMPs) production are evaluated in intestinal epithelial cells pre-treated with bacteria, bacterial med, and bacterial supernatant and exposed without or with CA. Both bacteria significantly prohibit CA numbers, while only FP and FP supernatant prohibit the transformation and virulence factors (extracellular phospholipase, secreted aspartyl proteinase, and hemolysin) secretion of CA in a co-culture system compared with media controls. Further, FP and FP supernatant promote the production of the NLRP6 inflammasome, interleukin (IL)-1β, IL-18, and antibacterial peptides (β-defensin (BD)-2 and BD-3) and inhibit in vitro and in vivo CA growth and pathogenicity, and alleviate DSS-colitis in mice, while EC do not show the similar effect.

CONCLUSION

FP improve intestinal inflammation by inhibiting CA reproduction, colonization, and pathogenicity and inducing AMP secretion in the gut. This study uncovers new relationships between intestinal microbes and fungi in IBD patients.

The Discrepancy between Clove and Non-Clove Cigarette Smoke-Promoted Candida albicans Biofilm Formation with Precoating RNA-aptamer

This study explores the influence of precoating aptamer (Ca-apt1) on C. albicans viability while the fungus was growing in the presence of exposing condensed cigarette smoke (CSC), prepared from clove (CCSC) and non-clove (NCSC) cigarettes, for 48 h. Using qPCR, we found that mRNA expression of adhesion-associated genes ( ALS3 and HWP1) was impaired by precoating C. albicans yeast cells with the aptamer. Conversely, the gene transcription was upregulated when aptamer-uncoated yeast was pre-treated with either CSC. In addition, by analysing the result of MTT ([3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide] assay, we found that the presence of added CCSC or NCSC in growth medium for 48 h was significantly enhanced C. albicans biofilm development. However, the presence of precoated aptamer was significantly impaired biofilm development accelerated by the NCSC. The inhibitory effect of the Ca-apt1 was not dependent on the precoated aptamer (1ng/μL and 10 ng/μL). Interestingly, we noted that the enhancer effect of treated CCSC was no longer effective when the yeast had been precoated with 10 ng/μL aptamer tested. Additionally, light microscopy analysis revealed that precoating aptamer alleviates morphological changes of C. albicans (from yeast to hypha formation) that are enhanced by adding CCSC or NCSC in the growth medium.

In conclusion, these results suggest that administration on Ca-ap1 exhibits a significant protective effect on CSC-induced biofilm formation by C. albicans.

Mathematical modeling of the Candida albicans yeast to hyphal transition reveals novel control strategies

Candida albicans, an opportunistic fungal pathogen, is a significant cause of human infections, particularly in immunocompromised individuals. Phenotypic plasticity between two morphological phenotypes, yeast and hyphae, is a key mechanism by which C. albicans can thrive in many microenvironments and cause disease in the host. Understanding the decision points and key driver genes controlling this important transition and how these genes respond to different environmental signals is critical to understanding how C. albicans causes infections in the host. Here we build and analyze a Boolean dynamical model of the C. albicans yeast to hyphal transition, integrating multiple environmental factors and regulatory mechanisms. We validate the model by a systematic comparison to prior experiments, which led to agreement in 17 out of 22 cases. The discrepancies motivate alternative hypotheses that are testable by follow-up experiments. Analysis of this model revealed two time-constrained windows of opportunity that must be met for the complete transition from the yeast to hyphal phenotype, as well as control strategies that can robustly prevent this transition. We experimentally validate two of these control predictions in C. albicans strains lacking the transcription factor UME6 and the histone deacetylase HDA1, respectively. This model will serve as a strong base from which to develop a systems biology understanding of C. albicans morphogenesis.

Diazepam's antifungal activity in fluconazole-resistant Candida spp. and biofilm inhibition in C. albicans: evaluation of the relationship with the proteins ALS3 and SAP5

The genus Candida spp. has been highlighted as one of the main etiological agents causing fungal infections, with Candida albicans being the most prominent, responsible for most cases of candidemia. Due to its capacity for invasion and tissue adhesion, it is associated with the formation of biofilms, mainly in the environment and hospital devices, decreasing the effectiveness of available treatments. The repositioning of drugs, which is characterized by the use of drugs already on the market for other purposes, together with molecular-docking methods can be used aiming at the faster development of new antifungals to combat micro-organisms. This study aimed to evaluate the antifungal effect of diazepam on mature C. albicans biofilms in vitro and its action on biofilm in formation, as well as its mechanism of action and interaction with structures related to the adhesion of C. albicans, ALS3 and SAP5. To determine the MIC, the broth microdilution test was used according to protocol M27-A3 (CLSI, 2008). In vitro biofilm formation tests were performed using 96-well plates, followed by molecular-docking protocols to analyse the binding agent interaction with ALS3 and SAP5 targets. The results indicate that diazepam has antimicrobial activity against planktonic cells of Candida spp. and C. albicans biofilms, interacting with important virulence factors related to biofilm formation (ALS3 and SAP5). In addition, treatment with diazepam triggered a series of events in C. albicans cells, such as loss of membrane integrity, mitochondrial depolarization and increased production of EROs, causing DNA damage and consequent cell apoptosis.

The regulation of hyphae growth in Candida albicans

In the last decades, Candida albicans has served as the leading causal agent of life-threatening invasive infections with mortality rates approaching 40% despite treatment. Candida albicans (C. albicans) exists in three biological phases: yeast, pseudohyphae, and hyphae. Hyphae, which represent an important phase in the disease process, can cause tissue damage by invading mucosal epithelial cells then leading to blood infection. In this review, we summarized recent results from different fields of fungal cell biology that are instrumental in understanding hyphal growth. This includes research on the differences among C. albicans phases; the regulatory mechanism of hyphal growth, extension, and maintaining cutting-edge polarity; cross regulations of hyphal development and the virulence factors that cause serious infection. With a better understanding of the mechanism on mycelium formation, this review provides a theoretical basis for the identification of targets in candidiasis treatment. It also gives some reference to the study of antifungal drugs.

Vacuole and Mitochondria Patch (vCLAMP) Protein Vam6 Is Involved in Maintenance of Mitochondrial and Vacuolar Functions under Oxidative Stress in Candida albicans

Candida albicans is one of the most common opportunistic fungal pathogens in human beings. When infecting host cells, C. albicans is often exposed to oxidative stress from the host immune defense system. Maintenance of mitochondrial and vacuolar functions is crucial for its resistance to oxidative stress. However, the role of vacuole and mitochondria patchs (vCLAMPs) in cellular oxidative stress resistance and in the maintenance of organelle functions remains to be elucidated. Herein, the function of the vCLAMP protein Vam6 in response to oxidative stress was explored. The results showed that the vam6∆/∆ mutant exhibited obvious mitochondrial swelling, mtDNA damage, reduced activity of antioxidant enzymes, and abnormal vacuolar morphology under H₂O₂ treatment, indicating its important role in maintaining the structures and functions of both mitochondria and vacuoles under oxidative stress. Further studies showed that deletion of VAM6 attenuated hyphal development under oxidative stress. Moreover, loss of Vam6 obviously affected host tissue invasion and virulence of C. albicans. Taken together, this paper reveals the critical role of vCLAMPs in response to oxidative stress in C. albicans.

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.

Pathogenesis and Clinical Relevance of Candida Biofilms in Vulvovaginal Candidiasis

The ability of Candida spp. to form biofilms is crucial for its pathogenicity, and thus, it should be considered an important virulence factor in vulvovaginal candidiasis (VVC) and recurrent VVC (RVVC). Its ability to generate biofilms is multifactorial and is generally believed to depend on the site of infection, species and strain involved, and the microenvironment in which the infection develops. Therefore, both cell surface proteins, such as Hwp1, Als1, and Als2, and the cell wall-related protein, Sun41, play a critical role in the adhesion and virulence of the biofilm. Immunological and pharmacological approaches have identified the NLRP3 inflammasome as a crucial molecular factor contributing to host immunopathology. In this context, we have earlier shown that Candida albicans associated with hyphae-secreted aspartyl proteinases (specifically SAP4-6) contribute to the immunopathology of the disease. Transcriptome profiling has revealed that non-coding transcripts regulate protein synthesis post-transcriptionally, which is important for the growth of Candida spp. Other studies have employed RNA sequencing to identify differences in the 1,245 Candida genes involved in surface and invasive cellular metabolism regulation. In vitro systems allow the simultaneous processing of a large number of samples, making them an ideal screening technique for estimating various physicochemical parameters, testing the activity of antimicrobial agents, and analyzing genes involved in biofilm formation and regulation (in situ) in specific strains. Murine VVC models are used to study C. albicans infection, especially in trials of novel treatments and to understand the cause(s) for resistance to conventional therapeutics. This review on the clinical relevance of Candida biofilms in VVC focuses on important advances in its genomics, transcriptomics, and proteomics. Moreover, recent experiments on the influence of biofilm formation on VVC or RVVC pathogenesis in laboratory animals have been discussed. A clear elucidation of one of the pathogenesis mechanisms employed by Candida biofilms in vulvovaginal candidiasis and its applications in clinical practice represents the most significant contribution of this manuscript.

Role of arthroconidia in biofilm formation by Trichosporon asahii

BACKGROUND

Trichosporon asahii is the major causative agent of disseminated and deep-seated trichosporonosis. It is capable of forming biofilms on surfaces, leading to medical device-related infection.Trichosporon asahii may be present as yeast form, hyphae and/or arthroconidia; however, the relationship between its biofilm-forming ability and its morphological transition is unclear.

OBJECTIVES

We investigated whether the T. asahii morphological transition contributes to its biofilm formation. We also determined the conditions required to induce each of the morphologies.

METHODS

Three high- and three low-biofilm-producing strains (HBS and LBS, respectively) were selected using a biofilm formation assay, and the cell surface hydrophobicity of these six strains was measured. For each strain, the morphology was observed and the number of each morphological form (yeast form, hypha and arthroconidium) was counted to calculate the ratio. Finally, the ability of cells each morphological type to adhere to the polystyrene substrate was evaluated.

RESULTS

The HBS exhibited abundant arthroconidia and hyphae; in contrast, the LBS produced mainly hyphae with few or no arthroconidia. The production of hyphae was increased by nitrogen-containing medium, and the production of arthroconidia was increased by nitrogen-deficient medium. Cells incubated under nitrogen-deficient conditions showed higher adherence to a polystyrene surface than those incubated in the presence of nitrogen.

CONCLUSION

Arthroconidia of T. asahii play a key role in biofilm formation by promoting cellular adhesion.

Perillaldehyde: A promising antifungal agent to treat oropharyngeal candidiasis

Perillaldehyde (PAE), a natural monoterpenoid agent extracted from Perilla frutescence, PAE has been reported to present various physiological capabilities, such as anti-inflammation, anti-oxidative and anti-fungal. In this study, we show that PAE exhibits strong antifungal activity against Candida albicans (C. albicans). C. albicans, a fungal pathogen with high incidence of antifungal resistance in clinical settings, is the major cause of oropharyngeal candidiasis (OPC). OPC is characterized by inflammatory immunological responses to fungal infections. Our in vitro results show PAE inhibited several virulence attributes of C. albicans including biofilm formation, yeast-to-hyphal transition and secreted aspartic proteinases (SAPs) gene expression. Using an experimental murine model of OPC, we found that PAE inhibited NLRP3 inflammasome assembly, reduced the excessive accumulation of ROS and prevented the p65 transfer in nuclear; processes all leading to reduced inflammation burden in the host. Together, this supports use PAE as a promising new agent to improve OPC.

Anandamide prevents the adhesion of filamentous Candida albicans to cervical epithelial cells

Candidiasis is a fungal infection caused by Candida species that have formed a biofilm on epithelial linings of the body. The most frequently affected areas include the vagina, oral cavity and the intestine. In severe cases, the fungi penetrate the epithelium and cause systemic infections. One approach to combat candidiasis is to prevent the adhesion of the fungal hyphae to the epithelium. Here we demonstrate that the endocannabinoid anandamide (AEA) and the endocannabinoid-like N-arachidonoyl serine (AraS) strongly prevent the adherence of C. albicans hyphae to cervical epithelial cells, while the endocannabinoid 2-arachidonoylglycerol (2-AG) has only a minor inhibitory effect. In addition, we observed that both AEA and AraS prevent the yeast-hypha transition and perturb hyphal growth. Real-time PCR analysis showed that AEA represses the expression of the HWP1 and ALS3 adhesins involved in Candida adhesion to epithelial cells and the HGC1, RAS1, EFG1 and ZAP1 regulators of hyphal morphogenesis and cell adherence. On the other hand, AEA increased the expression of NRG1, a transcriptional repressor of filamentous growth. Altogether, our data show that AEA and AraS have potential anti-fungal activities by inhibiting hyphal growth and preventing hyphal adherence to epithelial cells.

Investigating the expression of ALS2 and ALS9 genes along with allele frequency of ALS9 in patients with vulvovaginal candidiasis

BACKGROUND

Vulvovaginal candidiasis (VVC) is a vaginal mucosal infection that usually infects women in their reproductive age. When the signs of VVC persist on a daily basis or last for a long time and repeat at least three times per year, the disease is considered chronic and recurrent.

OBJECTIVES

The purpose of this study was to determine the expression rate of 2 genes responsible for adhesion and virulence of candida in RVVC patients using Real-time PCR, and comparing them together and assess the presence or absence of ALS9-2 allele in these patients.

PATIENTS/METHODS

The vaginal discharge was collected from 120 women aged (22-55) attending lolagar hospital which were all diagnosed with RVVC and 120 age-matched healthy controls. The expression rate of ALS2 and ALS 9 genes was quantified using real-time PCR. PCR method was used for Identification of ALS9 gene alleles.

RESULTS

Results showed an increase in ALS2 gene expression and a decrease in ALS9 gene expression, comparing to basic level and standard sample. 42.5% (51 of total 120 samples) contained the small allele.

CONCLUSIONS

The significant difference in expression rates of ALS2 and ALS9 genes indicates their different roles in making morphogenesis changes during the virulence of Candida albicans. Emergence of heterogeneous form and detection of ALS's short allele in invasive form of fungi proves the significant pathogenic role of this allele, specially when attached to mucosal tissue. Invasive and recurrent form of the disease can be accompanied by genetic-morphologic changes in fungi. Considering the form of this disease and the reduction in ALS9 gene expression, it can be concluded that this gene plays a significant role in attachment and initiation of the pathogenic phase.

Inhibition of adhesion-specific genes by Solidago virgaurea extract causes loss of Candida albicans biofilm integrity

AIMS

Candida albicans biofilms are commonly associated with severe oral infections. We previously discovered that a crude extract from the Solidago virgaurea plant (SV extract) was a potent inhibitor of C. albicans biofilm formation. Here, we further investigate the mechanisms underlying C. albicans biofilm inhibition by the SV extract.

METHODS AND RESULTS

The SV extract was shown to inhibit laboratory and clinical C. albicans isolates adherence and hyphal transition on inert support and epithelial human cells, without affecting viability and growth of planktonic yeasts. Interestingly, RT-PCR-based experiments demonstrated that some key genes involved in adhesion and hyphal morphological switch (e.g. Hwp1p, Ece1p, Als3p) were strongly down-regulated by the SV extract. Moreover, antimicrobial synergy testing (checkerboard assay) demonstrated that antifungal effects of miconazole, nystatin or a common antiseptic mouthwash were synergistically improved when used in combination with the SV extract.

CONCLUSIONS

The SV extract prevents C. albicans biofilm formation through direct inhibition of key adherence and hyphae-associated genes.

SIGNIFICANCE AND IMPACT OF THE STUDY

Biofilm is considered as a key virulence factor of C. albicans infection. Our discovery of an inhibitor specifically acting on genes involved in biofilm formation paves the way for the future development of a new class of antifungal product.

Targeting the fungal cell wall: current therapies and implications for development of alternative antifungal agents

Fungal infections are a worldwide problem associated with high morbidity and mortality. There are relatively few antifungal agents, and resistance has emerged within these pathogens for the newest antifungal drugs. As the fungal cell wall is critical for growth and development, it is one of the most important targets for drug development. In this review, the currently available cell wall inhibitors and suitable drug candidates for the treatment of fungal infections are explored. Future studies of the fungal cell wall and compounds that have detrimental effects on this important outer structural layer could aid in antifungal drug discovery and lead to the development of alternative cell wall inhibitors to fill gaps in clinical therapies for difficult-to-treat fungal infections.

Zinc Oxide Nanoparticles Inhibition of Initial Adhesion and ALS1 and ALS3 Gene Expression in Candida albicans Strains from Urinary Tract Infections

OBJECTIVE

The aim of this study was to evaluate effects of zinc oxide nanoparticles (ZnO-np) on initiation adhesion and agglutinin-like sequence (ALS) 1 and ALS3 gene expression, which is the first cell surface protein known to be, required for biofilm formation in 125 Candida albicans (C. albicans) from urinary tract infections (UTIs).

METHODS

In this descriptive-analytic study, Candida UTIs was cultured from 280 women admitted in hospital Sayad Shirazi, in Northeastern Iran in the 2018 year. 125 (44.62%) of C. albicans strains were identified by phenotypic and genotypic methods. Susceptibility testing C. albicans strains were determined by the disk diffusion method. ZnO-np with 20-40 nm diameters were prepared, there were confirmed by the X-ray diffraction and scanning electron microscope methods.

RESULTS

115 susceptible C. albicans and 10 fluconazole-resistant C. albicans strain from UTIs were exposed to sub-minimum inhibitory concentration (Sub-MIC) of ZnO-np (range 0.02-18.1 μg/ml). Expression of the ALS1 and ALS3 genes which are affected by adhesion was evaluated by real-time PCR. One-way ANOVA test statistical analysis was performed with SPSS 16.0. The MIC range of ZnO-np was 0.05-296 µg/ml. Sub-MIC concentration ZnO-np initial adhesion inhibition, and significantly reduced ALS1 and ALS3 gene expression was observed in all strains (P < 0.05). The finding indicated that ZnO-np is effective in reduction of ALS1 and ALS3 expression in fluconazole-resistant strains.

CONCLUSIONS

Therefore, ZnO-np could be a candidate in the elimination of biofilm C. albicans strains from UTIs in medicine, particularly in medical instruments.

Physical Interaction of Sodium Houttuyfonate With β-1,3-Glucan Evokes Candida albicans Cell Wall Remodeling

Candida albicans is a commonly isolated opportunistic yeast and can endanger immune-compromised human health. As increasingly isolated strains present resistance to currently used antifungals, it is necessary to develop novel antimycotics. In a previous study, sodium houttuyfonate (SH) alone or in combination with fluconazole revealed relatively strong antifungal potential against C. albicans, and the underlying mechanism might be likely to be associated with β-glucan synthesis and transportation (Shao et al., 2017). In the present experiment, we used a standard C. albicans isolate and a phr1 mutant (phr1−/−) to investigate the interaction of SH with β-glucan, one of the critical components in cell wall and biofilm matrix. We showed that lyticase was the most effective enzyme that could significantly increase the antifungal inhibition of SH at 64 μg/mL in C. albicans SC5314 but became futile in phr1−/−. Although the minimum inhibitory concentrations (MICs) of SH were comparable in the two Candida strains used, phr1−/− appeared to be more susceptible to SH compared with C. albicans SC5314 in biofilms (64 versus 512 μg/mL). The peak areas of SH decreased markedly by 71.6, 38.2, and 62.6% in C. albicans SC5314 and by 70% and 53.2% in phr1−/− by ultra-performance liquid chromatography (UPLC) analysis after co-incubation of SH with laminarin, extracellular matrix (EM) and cell wall. The chitin appeared to not interact with SH. We further demonstrated that sub-MIC SH (8 μg/mL) was able to induce cell wall remodeling by unmasking β-1,3-glucan and chitin in both C. albicans SC5314 and phr1−/−. Based on these findings, we propose that β-1,3-glucan can block the entrance of SH through non-specific absorption, and then the fungus senses the interaction of SH with β-1,3-glucan and exposes more β-1,3-glucan that contributes to SH blocking in turn.

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.

THR1 mediates GCN4 and CDC4 to link morphogenesis with nutrient sensing and the stress response in Candida albicans

Candida albicans (C. albicans) CDC4 (CaCDC4), encoding the F-box protein for the substrate specificity of the Skp1-cullin-F-box E3 ubiquitin ligase complex, suppresses the yeast-to-filament transition in C. albicans. In our previous study, Thr1 was identified as a CaCdc4-associated protein using affinity purification. THR1 encodes a homoserine kinase, which is involved in the threonine biosynthesis pathway. The present study generated a strain with repressible CaCDC4 expression and continuous THR1 expression. Colony and cell morphology analyses, as well as immunoblotting, revealed that the Thr1 protein was detectable under conditions in which the expression of CaCDC4 was repressed and that the filaments resulting from the repressed expression of CaCDC4 were suppressed by the constitutive expression of THR1 in C. albicans. Additionally, by using the CaSAT1-flipper method, the present study produced null mutants of THR1, GCN4, and CaCDC4. The phenotypic consequences were evaluated by growth curves, spotting assays, microscopic analysis, reverse transcription-polymerase chain reaction and XTT-based biofilm formation ability. The results revealed that fewer cells lacking THR1 entered the stationary phase but had no apparent morphological alteration. It was observed that the expression of THR1 was upregulated concurrently with GCN4 during nutrient depletion and that cells lacking GCN4 rescued the lethality of cells in the absence of THR1 in conditions accumulating homoserine in the threonine biosynthesis pathway. Of note, it was found that cells with either CaCDC4 or THR1 loss were sensitive to oxidative stress and osmotic stress, with those with THR1 loss being more sensitive. In addition, it was observed that cells with loss of either CaCDC4 or THR1 exhibited the ability to increase biofilm formation, with those lacking CaCDC4 exhibiting a greater extent of enhancement. It was concluded that CaCDC4 is important in the coordination of morphogenesis, nutrient sensing, and the stress response through THR1 in C. albicans.

Promising Antifungal Targets Against Candida albicans Based on Ion Homeostasis

In recent decades, invasive fungal infections have been increasing significantly, contributing to high incidences and mortality in immunosuppressed patients. Candida albicans (C. albicans) is the most prevalent opportunistic fungal pathogen in humans that can cause severe and often fatal bloodstream infections. Current antifungal agents have several limitations, including that only a small number of classes of antifungals are available, certain of which have severe toxicity and high cost. Moreover, the emergence of drug resistance is a new limitation to successful patient outcomes. Therefore, the development of antifungals with novel targets is an essential strategy for the efficient management of C. albicans infections. It is widely recognized that ion homeostasis is crucial for all living cells. Many studies have identified that ion-signaling and transduction networks are central to fungal survival by regulating gene expression, morphological transition, host invasion, stress response, and drug resistance. Dysregulation of ion homeostasis rapidly mediates cell death, forming the mechanistic basis of a growing number of compounds that elicit antifungal activity. Most of the potent antifungals have been widely used in the clinic, and certain of them have low toxicity, meaning that they may be expected to be used as antifungal drugs in the future. Hence, we briefly summarize the homeostasis regulation of several important ions, potential antifungal targets based on these ion-signaling networks, and antifungal compounds based on the disruption of ion homeostasis. This summary will help in designing effective drugs and identifying new targets for combating fungal diseases.

Streptococcus agalactiae Inhibits Candida albicans Hyphal Development and Diminishes Host Vaginal Mucosal TH17 Response

Streptococcus agalactiae and Candida albicans often co-colonize the female genital tract, and under certain conditions induce mucosal inflammation. The role of the interaction between the two organisms in candidal vaginitis is not known. In this study, we found that co-infection with S. agalactiae significantly attenuated the hyphal development of C. albicans, and that EFG1-Hwp1 signal pathway of C. albicans was involved in this process. In a mouse model of vulvovaginal candidiasis (VVC), the fungal burden and the levels of pro-inflammatory cytokines, IL-1β, IL-6 and TNF-α showed a increase on co-infection with S. agalactiae, while the level of TH17 T cells and IL-17 in the cervicovaginal lavage fluid were significantly decreased. Our results indicate that S. agalactiae inhibits C. albicans hyphal development by downregulating the expression of EFG1-Hwp1. The interaction between S. agalactiae and C. albicans may attenuate host vaginal mucosal TH17 immunity and contribute to mucosal colonization by C. albicans.

Antifungal activity of clinical Lactobacillus strains against Candida albicans biofilms: identification of potential probiotic candidates to prevent oral candidiasis

This study isolated Lactobacillus strains from caries-free subjects and evaluated the inhibitory effects directly on three strains of C. albicans, two clinical strains and one reference strain. Thirty Lactobacillus strains were isolated and evaluated for antimicrobial activity against in vitro C. albicans biofilms. L. paracasei 28.4, L. rhamnosus 5.2 and L. fermentum 20.4 isolates exhibited the most significant inhibitory activity against C. albicans. Co-incubation between these microorganisms resulted in deterrence of biofilm development and retardation of hyphal formation. The hindrance of biofilm development was characterized by the downregulated expression of C. albicans biofilm-specific genes (ALS3, HWP1, EFG1 and CPH1). L. paracasei 28.4, L. rhamnosus 5.2 and L. fermentum 20.4 demonstrated the ability to exert antifungal activity through the inhibition of C. albicans biofilms.

Modulation of the Fungal-Host Interaction by the Intra-Species Diversity of C. albicans

The incidence of human infections caused by the opportunistic fungal pathogen Candida albicans is on the rise due to increasing numbers of immunosuppressed patients. The importance of the immune system in preventing overgrowth of the colonizing fungus and thereby limiting infection is well recognized and host protective mechanisms widely investigated. Only recently, it was recognized that the natural diversity in the fungal species could also influence the outcome of the interaction between the fungus and the host. C. albicans strain-specific differences are complex and their regulation at the genomic, genetic, and epigenetic level and by environmental factors is only partially understood. In this review, we provide an overview of the natural diversity of C. albicans and discuss how it impacts host-fungal interactions and thereby affects the balance between commensalism versus disease.

From Genes to Networks: The Regulatory Circuitry Controlling Candida albicans Morphogenesis

Candida albicans is a commensal yeast of most healthy individuals, but also one of the most prevalent human fungal pathogens. During adaptation to the mammalian host, C. albicans encounters different niches where it is exposed to several types of stress, including oxidative, nitrosative (e.g., immune system), osmotic (e.g., kidney and oral cavity) stresses and pH variation (e.g., gastrointestinal (GI) tract and vagina). C. albicans has developed the capacity to respond to the environmental changes by modifying its morphology, which comprises the yeast-to-hypha transition, white-opaque switching, and chlamydospore formation. The yeast-to-hypha transition has been very well characterized and was shown to be modulated by several external stimuli that mimic the host environment. For instance, temperature above 37 ℃, serum, alkaline pH, and CO₂ concentration are all reported to enhance filamentation. The transition is characterized by the activation of an intricate regulatory network of signaling pathways, involving many transcription factors. The regulatory pathways that control either the stress response or morphogenesis are required for full virulence and promote survival of C. albicans in the host. Many of these transcriptional circuitries have been characterized, highlighting the complexity and the interconnections between the different pathways. Here, we present the major signaling pathways and the main transcription factors involved in the yeast-to-hypha transition. Furthermore, we describe the role of heat shock transcription factors in the morphogenetic transition, providing an edifying example of the complex cross talk between pathways involved in morphogenesis and stress response.

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.

Activity of Sanguinarine against Candida albicans Biofilms

Candida albicans biofilms show resistance to many clinical antifungal agents and play a considerable contributing role in the process of C. albicans infections. New antifungal agents against C. albicans biofilms are sorely needed. The aim of this study was to evaluate sanguinarine (SAN) for its activity against Candida albicans biofilms and explore the underlying mechanism. The MIC₅₀ of SAN was 3.2 μg/ml, while ≥0.8 μg/ml of SAN could suppress C. albicans biofilms. Further study revealed that ≥0.8 μg/ml of SAN could decrease cellular surface hydrophobicity (CSH) and inhibited hypha formation. Real-time reverse transcription-PCR (RT-PCR) results indicated that the exposure of C. albicans to SAN suppressed the expression of some adhesion- and hypha-specific/essential genes related to the cyclic AMP (cAMP) pathway, including ALS3, HWP1, ECE1, HGC1, and CYR1 Consistently, the endogenous cAMP level of C. albicans was downregulated after SAN treatment, and the addition of cAMP rescued the SAN-induced filamentation defect. In addition, SAN showed relatively low toxicity to human umbilical vein endothelial cells, the 50% inhibitory concentration (IC₅₀) being 7.8 μg/ml. Collectively, the results show that SAN exhibits strong activity against C. albicans biofilms, and the activity was associated with its inhibitory effect on adhesion and hypha formation due to cAMP pathway suppression.

Antimicrobial Compounds Produced by Vaginal Lactobacillus crispatus Are Able to Strongly Inhibit Candida albicans Growth, Hyphal Formation and Regulate Virulence-related Gene Expressions

The female vaginal environment contains diverse microorganisms, and their interactions play significant roles in health and disease. Lactobacillus species are the predominant vaginal microorganisms in healthy women and relevant as a barrier to defense against pathogens, including Candida albicans. The yeast-to-hyphae transition is believed to be a determinant of C. albicans pathogenesis. In this study, we investigated the effects of vaginal isolates of L. crispatus (seven strains), L. gasseri (six strains), and L. jensenii (five strains) on growth, hyphal formation and virulence-related genes expression of C. albicans ATCC 10231. We found that the L. crispatus showed the most significant antimicrobial activities in microplate-based liquid medium assay (P < 0.05). All seven cell-free supernatants (CFS) from L. crispatus strains reduced the growth of C. albicans by >60%. The effects might be due to their productions of some secretory antimicrobial compounds in addition to H₂O₂ and organic acids. Furthermore, each of the CFS of Lactobacillus strains was found to significantly suppress the yeast-to-hyphae transition of C. albicans under hyphae-inducing conditions (RPMI 1640 medium supplemented with 10% fetal bovine serum). The hyphae inhibition rates of C. albicans treated by CFS from L. crispatus, L. gasseri, and L. jensenii were 88.3 ± 3.02%, 84.9 ± 6.0%, and 81.9 ± 6.2%, respectively. Moreover, the expression of hyphae-specific genes (ALS3, HWP1, ECE1, EAP1, and SAP5) and transcriptional regulatory genes (EFG1, TEC1, and NRG1) were analyzed using quantitative real-time PCR. The results demonstrated that L. crispatus CFS significantly down-regulated the expression of hyphae-specific genes ALS3 (0.140-fold)), HWP1 (0.075-fold), and ECE1 (0.045-fold), while up-regulated the expression of the negative transcriptional regulator gene NRG1 with 1.911-fold. The antimicrobial compounds from L. crispatus B145 against Candida growth were heat stable and protease resistance, but those against hyphal formation were partially sensitive to the same treatments. Our novel findings suggest that L. crispatus, a dominant Lactobacillus species associated with a healthy vagina, could strongly inhibit C. albicans growth and hyphal formation. L. crispatus might repress the expression of hyphae-specific genes (ALS3, HWP1, and ECE1) in a NRG1-dependent manner. Besides, L. crispatus B145 is highly worthwhile for probiotic investigation.

The Hog1 MAP Kinase Promotes the Recovery from Cell Cycle Arrest Induced by Hydrogen Peroxide in Candida albicans

Eukaryotic cell cycle progression in response to environmental conditions is controlled via specific checkpoints. Signal transduction pathways mediated by MAPKs play a crucial role in sensing stress. For example, the canonical MAPKs Mkc1 (of the cell wall integrity pathway), and Hog1 (of the HOG pathway), are activated upon oxidative stress. In this work, we have analyzed the effect of oxidative stress induced by hydrogen peroxide on cell cycle progression in Candida albicans. Hydrogen peroxide was shown to induce a transient arrest at the G1 phase of the cell cycle. Specifically, a G1 arrest was observed, although phosphorylation of Mkc1 and Hog1 MAPKs can take place at all stages of the cell cycle. Interestingly, hog1 (but not mkc1) mutants required a longer time compared to wild type cells to resume growth after hydrogen peroxide challenge. Using GFP-labeled cells and mixed cultures of wild type and hog1 cells we were able to show that hog1 mutants progress faster through the cell cycle under standard growth conditions in the absence of stress (YPD at 37°C). Consequently, hog1 mutants exhibited a smaller cell size. The altered cell cycle progression correlates with altered expression of the G1 cyclins Cln3 and Pcl2 in hog1 cells compared to the wild type strain. In addition, Hgc1 (a hypha-specific G1 cyclin) as well as Cln3 displayed a different kinetics of expression in the presence of hydrogen peroxide in hog1 mutants. Collectively, these results indicate that Hog1 regulates the expression of G1 cyclins not only in response to oxidative stress, but also under standard growth conditions. Hydrogen peroxide treated cells did not show fluctuations in the mRNA levels for SOL1, which are observed in untreated cells during cell cycle progression. In addition, treatment with hydrogen peroxide prevented degradation of Sol1, an effect which was enhanced in hog1 mutants. Therefore, in C. albicans, the MAPK Hog1 mediates cell cycle progression in response to oxidative stress, and further participates in the cell size checkpoint during vegetative growth.

Anti-Immune Strategies of Pathogenic Fungi

Pathogenic fungi have developed many strategies to evade the host immune system. Multiple escape mechanisms appear to function together to inhibit attack by the various stages of both the adaptive and the innate immune response. Thus, after entering the host, such pathogens fight to overcome the immune system to allow their survival, colonization and spread to different sites of infection. Consequently, the establishment of a successful infectious process is closely related to the ability of the pathogen to modulate attack by the immune system. Most strategies employed to subvert or exploit the immune system are shared among different species of fungi. In this review, we summarize the main strategies employed for immune evasion by some of the major pathogenic fungi.

Specificity characterization of the α-mating factor hormone by Kex2 protease

Kex2 is a Ca²⁺-dependent serine protease from S. cerevisiae. Characterization of the substrate specificity of Kex2 is of particular interest because this protease serves as the prototype of a large family of eukaryotic subtilisin-related proprotein-processing proteases that cleave sites consisting of pairs or clusters of basic residues. Our goal was to study the prime region subsite S' of Kex2 because previous studies have only taken into account non-prime sites using AMC substrates but not the specificity of prime sites identified through structural modeling or predicted cleavage sites. Therefore, we used peptides derived from Abz-KR↓EADQ-EDDnp and Abz-YKR↓EADQ-EDDnp based on the pro-α-mating factor sequence. The specificity of Kex2 due to basic residues at P₁' is affected by the type of residue in the P₃ position. Some residues in P₁' with large or bulky side chains yielded poor substrate specificity. The k_cat/K_M values for peptides with P₂' substitutions containing Tyr in P₃ were higher than those obtained for the peptides without Tyr. In fact, P' and P modifications mainly promoted changes in k_cat and K_M, respectively. The pH profile of Kex2 was fit to a double-sigmoidal pH-titration curve. The specificity results suggest that Kex2 might be involved in the processing of the putative cleavage sites in a polypeptide involved in cell elongation, hyphal formation and the processing of a toxin, which result in host cell lysis. In summary, the specificity of Kex2 is dependent on the set of interactions with prime and non-prime subsites, resulting in synergism.