Candida albicans: A Model Organism for Studying Fungal Pathogens

Amides Derived from Vanillic Acid: Coupling Reactions, Antimicrobial Evaluation, and Molecular Docking

A series of amides derived from vanillic acid were obtained by coupling reactions using PyBOP ((Benzotriazol-1-yloxy)tripyrrolidinophosphonium hexafluorophosphate) and DCC (Dicyclohexylcarbodiimide) coupling reagents. These were submitted to biological evaluation for species of Candida, Staphylococcus, and Pseudomonas. The microdilution method in broth was used for the antimicrobial testing to determine the Minimum Inhibitory Concentration (MIC) and to verify the likely mechanism of action for antifungal activity. The ten amides were obtained with yields ranging from 28.81 to 86.44%, and three compounds were novel. In the antibacterial evaluation, the amides (in their greatest concentrations) were bioactive against Staphylococcus aureus strain ATCC 25925. Meanwhile, all of the tested amides presented antifungal activity against at least one strain. The amide with best antifungal profile was compound 7, which featured an MIC of 0.46 μmol/mL, and a mechanism of action involving the plasma membrane and fungal cell wall. The presence of a methyl group in the para position of the aromatic ring is suggested which enhances the activity of the compound against fungi. Docking studies of the ten compounds using the protein 14α-demethylase as a biological target were also performed. The biological results presented good correlation with molecular docking studies demonstrating that a possible site of antifungal action for bioactive amides is the enzyme 14α-demethylase.

Overproduction of Phospholipids by the Kennedy Pathway Leads to Hypervirulence in Candida albicans

Candida albicans is an opportunistic human fungal pathogen that causes life-threatening systemic infections, as well as oral mucosal infections. Phospholipids are crucial for pathogenesis in C. albicans, as disruption of phosphatidylserine (PS) and phosphatidylethanolamine (PE) biosynthesis within the cytidine diphosphate diacylglycerol (CDP-DAG) pathway causes avirulence in a mouse model of systemic infection. The synthesis of PE by this pathway plays a crucial role in virulence, but it was unknown if downstream conversion of PE to phosphatidylcholine (PC) is required for pathogenicity. Therefore, the enzymes responsible for methylating PE to PC, Pem1 and Pem2, were disrupted. The resulting pem1Δ/Δ pem2Δ/Δ mutant was not less virulent in mice, but rather hypervirulent. Since the pem1Δ/Δ pem2Δ/Δ mutant accumulated PE, this led to the hypothesis that increased PE synthesis increases virulence. To test this, the alternative Kennedy pathway for PE/PC synthesis was exploited. This pathway makes PE and PC from exogenous ethanolamine and choline, respectively, using three enzymatic steps. In contrast to Saccharomyces cerevisiae, C. albicans was found to use one enzyme, Ept1, for the final enzymatic step (ethanolamine/cholinephosphotransferase) that generates both PE and PC. EPT1 was overexpressed, which resulted in increases in both PE and PC synthesis. Moreover, the EPT1 overexpression strain is hypervirulent in mice and causes them to succumb to system infection more rapidly than wild-type. In contrast, disruption of EPT1 causes loss of PE and PC synthesis by the Kennedy pathway, and decreased kidney fungal burden during the mouse systemic infection model, indicating a mild loss of virulence. In addition, the ept1Δ/Δ mutant exhibits decreased cytotoxicity against oral epithelial cells in vitro, whereas the EPT1 overexpression strain exhibits increased cytotoxicity. Taken altogether, our data indicate that mutations that result in increased PE synthesis cause greater virulence and mutations that decrease PE synthesis attenuate virulence.

Phenotypic and genotypic variations in Candida albicans isolates from Romanian patients

Background: During the last two decades a major increase in the proportion of severe fungal infections has been noted due to the excessive use of broad-spectrum antibiotics, catheters, and a growing number of immunocompromised patients.

Objectives: This is the first investigation providing complete data regarding the phenotypic and genotypic profiles of Candida albicans (C. albicans) isolates in Romanian patients.

Methods: We investigated 301 isolates in terms of genotype determination (G), resistogram (R), phospholipase activity (Pl), haemolysis (Hl), proteinase activity (Pt), and biofilm formation (BF).

Results: The analyzed isolates of C. albicans showed low values for Pt (61.73%), Hl (95.49%), and BF (60.71%), and did not present any Pl activity (92.23%). More than half of the investigated samples were genotype A with 450 bp (52.92%) and the majority (86.19%) were resistant to sodium selenite (A), boric acid (B), sodium periodate (D) and silver nitrate (E), but sensitive to cetrimide (-). One-way ANOVA analysis revealed significant effects of the infection site on biofilm formation (p = 0.0137) and no significant correlation was found between the genotype (A, B, C) and the infection site (p =0.449).

Conclusions: Based on the obtained results it can be concluded that C. albicans isolates in Romanian patients exhibit different genotypic and phenotypic patterns, and no significant correlations between genotype and infection site could be observed.

A High-Throughput Candida albicans Two-Hybrid System

Candida albicans is a human fungal pathogen that does not follow the universal codon usage, as it translates the CUG codon into serine rather than leucine. This makes it difficult to study protein-protein interactions using the standard yeast two-hybrid (Y2H) system in the model organism Saccharomyces cerevisiae Due to the lack of adapted tools, only a small number of protein-protein interactions (PPIs) have been detected or studied using C. albicans-optimized tools despite the importance of PPIs to understand cell biology. However, with the sequencing of the whole genome of C. albicans, the availability of an ORFeome collection containing 5,099 open reading frames (ORFs) in Gateway-adapted donor vectors, and the creation of a Gateway-compatible C. albicans-specific two-hybrid (C2H) system, it became possible to study protein-protein interactions on a larger scale using C. albicans itself as the model organism. Erroneous translations are hereby eliminated compared to using the S. cerevisiae Y2H system. Here, we describe the technical adaptations and the first application of the C2H system for a high-throughput screen, thus making it possible to screen thousands of PPIs at once in C. albicans itself. This first, small-scale high-throughput screen, using Pho85 as a bait protein against 1,646 random prey proteins, yielded one interacting partner (Pcl5). The interaction found with the high-throughput setup was further confirmed with a low-throughput C2H experiment and with a coimmunoprecipitation (co-IP) experiment.IMPORTANCECandida albicans is a major fungal pathogen, and due to the rise of fungal infections and emerging resistance to the limited antifungals available, it is important to develop novel and more specific antifungals. Protein-protein interactions (PPIs) can be applied as very specific drug targets. However, because of the aberrant codon usage of C. albicans, the traditional yeast two-hybrid system in Saccharomyces cerevisiae is difficult to use, and only a limited number of PPIs have been described in C. albicans To overcome this, a C. albicans two-hybrid (C2H) system was developed in 2010. The current work describes, for the first time, the application of the C2H system in a high-throughput setup. We hereby show the usefulness of the C2H system to investigate and detect PPIs in C. albicans, making it possible to further elucidate protein networks in C. albicans, which has the potential to lead to the development of novel antifungals which specifically disrupt PPIs important for virulence.

Relative Abundances of Candida albicans and Candida glabrata in In Vitro Coculture Biofilms Impact Biofilm Structure and Formation

Candida is a member of the normal human microbiota and often resides on mucosal surfaces such as the oral cavity or the gastrointestinal tract. In addition to their commensality, Candida species can opportunistically become pathogenic if the host microbiota is disrupted or if the host immune system becomes compromised. An important factor for Candida pathogenesis is its ability to form biofilm communities. The two most medically important species-Candida albicans and Candida glabrata-are often coisolated from infection sites, suggesting the importance of Candida coculture biofilms. In this work, we report that biofilm formation of the coculture population depends on the relative ratio of starting cell concentrations of C. albicans and C. glabrata When using a starting ratio of C. albicans to C. glabrata of 1:3, ∼6.5- and ∼2.5-fold increases in biofilm biomass were observed relative to those of a C. albicans monoculture and a C. albicans/C. glabrata ratio of 1:1, respectively. Confocal microscopy analysis revealed the heterogeneity and complex structures composed of long C. albicans hyphae and C. glabrata cell clusters in the coculture biofilms, and reverse transcription-quantitative PCR (qRT-PCR) studies showed increases in the relative expression of the HWP1 and ALS3 adhesion genes in the C. albicans/C. glabrata 1:3 biofilm compared to that in the C. albicans monoculture biofilm. Additionally, only the 1:3 C. albicans/C. glabrata biofilm demonstrated an increased resistance to the antifungal drug caspofungin. Overall, the results suggest that interspecific interactions between these two fungal pathogens increase biofilm formation and virulence-related gene expression in a coculture composition-dependent manner.IMPORTANCECandida albicans and Candida glabrata are often coisolated during infection, and the occurrence of coisolation increases with increasing inflammation, suggesting possible synergistic interactions between the two Candida species in pathogenesis. During the course of an infection, the prevalence of each Candida species may change over time due to differences in metabolism and in the resistance of each species to antifungal therapies. Therefore, it is necessary to understand the dynamics between C. albicans and C. glabrata in coculture to develop better therapeutic strategies against Candida infections. Existing in vitro work has focused on understanding how an equal-part culture of C. albicans and C. glabrata impacts biofilm formation and pathogenesis. What is not understood, and what is investigated in this work, is how the composition of Candida species in coculture impacts overall biofilm formation, virulence gene expression, and the therapeutic treatment of biofilms.

Predictive Virtual Infection Modeling of Fungal Immune Evasion in Human Whole Blood

Bloodstream infections by the human-pathogenic fungi Candida albicans and Candida glabrata increasingly occur in hospitalized patients and are associated with high mortality rates. The early immune response against these fungi in human blood comprises a concerted action of humoral and cellular components of the innate immune system. Upon entering the blood, the majority of fungal cells will be eliminated by innate immune cells, i.e., neutrophils and monocytes. However, recent studies identified a population of fungal cells that can evade the immune response and thereby may disseminate and cause organ dissemination, which is frequently observed during candidemia. In this study, we investigate the so far unresolved mechanism of fungal immune evasion in human whole blood by testing hypotheses with the help of mathematical modeling. We use a previously established state-based virtual infection model for whole-blood infection with C. albicans to quantify the immune response and identified the fungal immune-evasion mechanism. While this process was assumed to be spontaneous in the previous model, we now hypothesize that the immune-evasion process is mediated by host factors and incorporate such a mechanism in the model. In particular, we propose, based on previous studies that the fungal immune-evasion mechanism could possibly arise through modification of the fungal surface by as of yet unknown proteins that are assumed to be secreted by activated neutrophils. To validate or reject any of the immune-evasion mechanisms, we compared the simulation of both immune-evasion models for different infection scenarios, i.e., infection of whole blood with either C. albicans or C. glabrata under non-neutropenic and neutropenic conditions. We found that under non-neutropenic conditions, both immune-evasion models fit the experimental data from whole-blood infection with C. albicans and C. glabrata. However, differences between the immune-evasion models could be observed for the infection outcome under neutropenic conditions with respect to the distribution of fungal cells across the immune cells. Based on these predictions, we suggested specific experimental studies that might allow for the validation or rejection of the proposed immune-evasion mechanism.

Molecular modeling of inhibitors against fructose bisphosphate aldolase from Candida albicans

Candida albicans is an opportunistic pathogen that causes from vulvovaginal and oropharyngeal candidiasis to systemic infections. The enzyme 1,6-fructose bisphosphate aldolase class II (FBA II), is a macromolecule existing only in lower organisms, being essential for the survival of the pathogen due to its function of maintaining the glycolysis process. The aim of this paper was to evaluate the inhibitors of FBA II regarding their physicochemical, pharmacokinetic and toxicological properties and apply concepts of rational drug development to propose new compounds for the treatment of fungal infections of C. albicans. Physicochemical (HyperChem software and the webserver cactus) and ADME/Tox (PreADMET webserver) properties were calculated to four inhibitors described in the literature and three analogues. None of the compounds presented in this study violated RO5, however all inhibitors demonstrated low or moderate human intestinal absorption (HIA), as well as low or moderate permeability in Caco-2 and MDCK, poor plasma proteins binding (PPB) and low permeability of the blood-brain barrier (BBB); however, Compound 4 is the exception for BBB permeability, being also the only non-mutagenic compound, and therefore, used as a lead compound. Analogues B and C presented high HIA, weak PPB and low BBB permeability, as well as a positive prediction for carcinogenicity in rats and mouse and non-mutagenicity in the Ames test. Through the evaluations carried out, it was concluded that the analogues B and C have proved to be promising candidates for oral administration drugs in the treatment of fungal infections of the genus Candida.

A representative of arylcyanomethylenequinone oximes effectively inhibits growth and formation of hyphae in Candida albicans and influences the activity of protein kinases in vitro

In this study, we applied various assays to reveal new activities of phenylcyanomethylenequinone oxime-4-(hydroxyimino) cyclohexa-2,5-dien-1-ylidene](phenyl)ethanenitrile (4-AN) for potential anti-microbial applications. These assays demonstrated (a) the antimicrobial effect on bacterial and fungal cultures, (b) the effect on the in vitro activity of the kinase CK2, (c) toxicity towards human erythrocytes, the Caco-2 cancer cell line, and embryonic development of Zebrafish. We demonstrated the activity of 4-AN against selected bacteria and Candida spp. The MIC ranging from 4 µg/ml to 125 µg/ml proved effective in inhibition of formation of hyphae and cell aggregation in Candida, which was demonstrated at the cytological level. Noteworthy, 4-AN was found to inhibit the CK2 kinase with moderate potency. Moreover, at low concentrations, it did not exert any evident toxic effects on human erythrocytes, Caco-2 cells, or Zebrafish embryos. 4-AN can be a potential candidate as a novel drug against Candida infections.

Induction of Severe Chronic Hyperplastic Candidiasis in Rat by Opportunistic Infection of C. albicans through Combination of Diabetes and Intermittent Prednisolone Administration

Chronic hyperplastic candidiasis progresses from squamous cell hyperplasia to squamous cell carcinoma (SCC); however, the oncogenic mechanism remains unclear. In the present study, we attempted to induce opportunistic Candida albicans infection and establish chronic hyperplastic candidiasis in rats by combining diabetic condition and prednisolone administration, followed by analysis of the inflammatory cells involved in the disease progression. Female Wistar Bunn/Kobori (WBN/Kob) rats were divided into 3 groups: alloxan-induced diabetic rats (A group) along with diabetic (AP group) and nondiabetic (P group) rats intermittently treated with prednisolone. Animals were euthanized at 42 weeks of age. Squamous cell hyperplasia following C. albicans infection in the forestomach was observed in almost all AP and A group rats. The lesions in the AP group were significantly more severe than those in the A group. In addition, SCC was detected in 1 AP group animal. Cluster of differentiation (CD)4-positive T cell and CD68-positive macrophage infiltration in the AP group was significantly stronger than that in the A group. These findings suggest that the combination of diabetes and intermittent prednisolone administration could induce chronic hyperplastic candidiasis without direct C. albicans inoculation and that CD4-positive T cells and CD68-positive macrophages may be highly involved in the pathogenesis of these hyperplastic lesions.

A pre-therapeutic coating for medical devices that prevents the attachment of Candida albicans

BACKGROUND

Hospital acquired fungal infections are defined as "never events"-medical errors that should never have happened. Systemic Candida albicans infections results in 30-50% mortality rates. Typically, adhesion to abiotic medical devices and implants initiates such infections. Efficient adhesion initiates formation of aggressive biofilms that are difficult to treat. Therefore, inhibitors of adhesion are important for drug development and likely to have a broad spectrum efficacy against many fungal pathogens. In this study we further the development of a small molecule, Filastatin, capable of preventing C. albicans adhesion. We explored the potential of Filastatin as a pre-therapeutic coating of a diverse range of biomaterials.

METHODS

Filastatin was applied on various biomaterials, specifically bioactive glass (cochlear implants, subcutaneous drug delivery devices and prosthetics); silicone (catheters and other implanted devices) and dental resin (dentures and dental implants). Adhesion to biomaterials was evaluated by direct visualization of wild type C. albicans or a non-adherent mutant edt1 -/- that were stained or fluorescently tagged. Strains grown overnight at 30 °C were harvested, allowed to attach to surfaces for 4 h and washed prior to visualization. The adhesion force of C. albicans cells attached to surfaces treated with Filastatin was measured using Atomic Force Microscopy. Effectiveness of Filastatin was also demonstrated under dynamic conditions using a flow cell bioreactor. The effect of Filastatin under microfluidic flow conditions was quantified using electrochemical impedance spectroscopy. Experiments were typically performed in triplicate.

RESULTS

Treatment with Filastatin significantly inhibited the ability of C. albicans to adhere to bioactive glass (by 99.06%), silicone (by 77.27%), and dental resin (by 60.43%). Atomic force microcopy indicated that treatment with Filastatin decreased the adhesion force of C. albicans from 0.23 to 0.017 nN. Electrochemical Impedance Spectroscopy in a microfluidic device that mimic physiological flow conditions in vivo showed lower impedance for C. albicans when treated with Filastatin as compared to untreated control cells, suggesting decreased attachment. The anti-adhesive properties were maintained when Filastatin was included in the preparation of silicone materials.

CONCLUSION

We demonstrate that Filastatin treated medical devices prevented adhesion of Candida, thereby reducing nosocomial infections.

Early Adhesion of Candida albicans onto Dental Acrylic Surfaces

Denture-associated stomatitis is a common candidal infection that may give rise to painful oral symptoms, as well as be a reservoir for infection at other sites of the body. As poly (methyl methacrylate) (PMMA) remains the main material employed in the fabrication of dentures, the aim of this research was to evaluate the adhesion of Candida albicans cells onto PMMA surfaces by employing an atomic force microscopy (AFM) single-cell force spectroscopy (SCFS) technique. For experiments, tipless AFM cantilevers were functionalized with PMMA microspheres and probed against C. albicans cells immobilized onto biopolymer-coated substrates. Both a laboratory strain and a clinical isolate of C. albicans were used for SCFS experiments. Scanning electron microscopy (SEM) and AFM imaging of C. albicans confirmed the polymorphic behavior of both strains, which was dependent on growth culture conditions. AFM force-spectroscopy results showed that the adhesion of C. albicans to PMMA is morphology dependent, as hyphal tubes had increased adhesion compared with yeast cells ( P < 0.05). C. albicans budding mother cells were found to be nonadherent, which contrasts with the increased adhesion observed in the tube region. Comparison between strains demonstrated increased adhesion forces for a clinical isolate compared with the lab strain. The clinical isolate also had increased survival in blood and reduced sensitivity to complement opsonization, providing additional evidence of strain-dependent differences in Candida-host interactions that may affect virulence. In conclusion, PMMA-modified AFM probes have shown to be a reliable technique to characterize the adhesion of C. albicans to acrylic surfaces.

Evaluation of the proximate composition, antioxidant potential, and antimicrobial activity of mango seed kernel extracts

After pulp extraction in fruit processing industry, a significant quantity of mango seed kernels are discarded as solid wastes. These seed kernels can be ideal raw materials for obtaining extracts rich in bioactive compounds with good antioxidant properties. The conversion of these wastes into utilizable food ingredients would help in reducing environmental problems associated with processing waste disposal. In order to determine their potential use, this study evaluated some of the biochemical characteristics and antimicrobial potential of mango seed kernel extracts on medically important human bacterial and fungal pathogens. Four mango varieties (Apple, Ngowe, Kent and Sabine) from Makueni and Embu counties in Kenya were used for this study. The analyzed mango seed kernel powders were found to contain on average, 6.74-9.20% protein content. Apple and Ngowe mango seed kernels had significantly higher fat content of 13.04 and 13.08, respectively, while Sabine from Makueni had the least fat content of 9.84%. The ash, fiber, and carbohydrate contents ranged from 1.78 to 2.87%, 2.64 to 3.71% and 72.86 to 75.92%, respectively. The mean percentage scavenging ability of mango kernel extracts at the concentration of 20 mg/mL was 92.22%. Apple and Sabine mango kernel extracts had significantly high inhibition zones of 1.93 and 1.73 compared to Kent and Ngowe with 1.13 and 1.10, respectively, against E. coli. For C. albicans, the inhibition of Kent mango kernel extract, 1.63, was significantly lower than that of Ngowe, Apple, and Sabine with 2.23, 2.13, and 1.83, respectively. This study demonstrates that mango seed powder is an abundant and cost-effective potential natural antibiotic and antifungal that can be utilized in addressing the challenge of food poisoning and infections caused by pathogenic microorganisms in the food industry.

Characterization of the Candida albicans Amino Acid Permease Family: Gap2 Is the Only General Amino Acid Permease and Gap4 Is an S-Adenosylmethionine (SAM) Transporter Required for SAM-Induced Morphogenesis

Candida albicans is a commensal organism that can thrive in many niches in its human host. The environmental conditions at these different niches differ quite a bit, and this fungus must be able to sense these changes and adapt its metabolism to them. Apart from glucose and other sugars, the uptake of amino acids is very important. This is underscored by the fact that the C. albicans genome encodes 6 orthologues of the Saccharomyces. cerevisiae general amino acid permease Gap1 and many other amino acid transporters. In this work, we characterize these six permeases and we show that C. albicans Gap2 is the functional orthologue of ScGap1 and that C. albicans Gap4 is an orthologue of ScSam3, an S-adenosylmethionine (SAM) transporter. Furthermore, we show that Gap4 is required for SAM-induced morphogenesis, an important virulence factor of C. albicans.

Amino acids are key sources of nitrogen for growth of Candida albicans. In order to detect and take up these amino acids from a broad range of different and changing nitrogen sources inside the host, this fungus must be able to adapt via its expression of genes for amino acid uptake and further metabolism. We analyzed six C. albicans putative general amino acid permeases based on their homology to the Saccharomyces cerevisiae Gap1 general amino acid permease. We generated single- and multiple-deletion strains and found that, based on growth assays and transcriptional or posttranscriptional regulation, Gap2 is the functional orthologue to ScGap1, with broad substrate specificity. Expression analysis showed that expression of all GAP genes is under control of the Csy1 amino acid sensor, which is different from the situation in S. cerevisiae, where the expression of ScGAP1 is not regulated by Ssy1. We show that Gap4 is the functional orthologue of ScSam3, the only S-adenosylmethionine (SAM) transporter in S. cerevisiae, and we report that Gap4 is required for SAM-induced morphogenesis.

IMPORTANCECandida albicans is a commensal organism that can thrive in many niches in its human host. The environmental conditions at these different niches differ quite a bit, and this fungus must be able to sense these changes and adapt its metabolism to them. Apart from glucose and other sugars, the uptake of amino acids is very important. This is underscored by the fact that the C. albicans genome encodes 6 orthologues of the Saccharomyces. cerevisiae general amino acid permease Gap1 and many other amino acid transporters. In this work, we characterize these six permeases and we show that C. albicans Gap2 is the functional orthologue of ScGap1 and that C. albicans Gap4 is an orthologue of ScSam3, an S-adenosylmethionine (SAM) transporter. Furthermore, we show that Gap4 is required for SAM-induced morphogenesis, an important virulence factor of C. albicans.

Blad-Containing Oligomer Fungicidal Activity on Human Pathogenic Yeasts. From the Outside to the Inside of the Target Cell

Blad polypeptide comprises residues 109-281 of Lupinus albus β-conglutin precursor. It occurs naturally as a major subunit of an edible, 210 kDa oligomer which accumulates to high levels, exclusively in the cotyledons of Lupinus seedlings between the 4th and 14th day after the onset of germination. Blad-containing oligomer (BCO) exhibits a potent and broad spectrum fungicide activity toward plant pathogens and is now on sale in the US under the tradename FractureTM. In this work we demonstrate its antifungal activity toward human pathogens and provide some insights on its mode of action. BCO bioactivity was evaluated in eight yeast species and compared to that of amphotericin B (AMB). BCO behaved similarly to AMB in what concerns both cellular inhibition and cellular death. As a lectin, BCO binds strongly to chitin. In addition, BCO is known to possess 'exochitinase' and 'endochitosanase' activities. However, no clear disruption was visualized at the cell wall after exposure to a lethal BCO concentration, except in cell buds. Immunofluorescent and immunogold labeling clearly indicate that BCO enters the cell, and membrane destabilization was also demonstrated. The absence of haemolytic activity, its biological origin, and its extraordinary antifungal activity are the major outcomes of this work, and provide a solid background for a future application as a new antifungal therapeutic drug. Furthermore, its predictable multisite mode of action suggests a low risk of inducing resistance mechanisms, which are now a major problem with other currently available antifungal drugs.

The Candida Genome Database (CGD): incorporation of Assembly 22, systematic identifiers and visualization of high throughput sequencing data

The Candida Genome Database (CGD, http://www.candidagenome.org/) is a freely available online resource that provides gene, protein and sequence information for multiple Candida species, along with web-based tools for accessing, analyzing and exploring these data. The mission of CGD is to facilitate and accelerate research into Candida pathogenesis and biology, by curating the scientific literature in real time, and connecting literature-derived annotations to the latest version of the genomic sequence and its annotations. Here, we report the incorporation into CGD of Assembly 22, the first chromosome-level, phased diploid assembly of the C. albicans genome, coupled with improvements that we have made to the assembly using additional available sequence data. We also report the creation of systematic identifiers for C. albicans genes and sequence features using a system similar to that adopted by the yeast community over two decades ago. Finally, we describe the incorporation of JBrowse into CGD, which allows online browsing of mapped high throughput sequencing data, and its implementation for several RNA-Seq data sets, as well as the whole genome sequencing data that was used in the construction of Assembly 22.

Determination of Biofilm Initiation on Virus-infected Cells by Bacteria and Fungi

The study of polymicrobial interactions across the taxonomic kingdoms that include fungi, bacteria and virus have not been previously examined with respect to how viral members of the microbiome affect subsequent microbe interactions with these virus-infected host cells. The co-habitation of virus with bacteria and fungi is principally present on the mucosal surfaces of the oral cavity and genital tract. Mucosal cells, particularly those with persistent chronic or persistent latent viral infections, could have a significant impact on members of the microbiome through virus alteration in number and type of receptors expressed. Modification in host cell membrane architecture would result in altered ability of subsequent members of the normal flora and opportunistic pathogens to initiate the first step in biofilm formation, i.e., adherence. This study describes a method for quantitation and visual examination of HSV's effect on the initiation of biofilm formation (adherence) of S. aureus and C. albicans.

Candida albicans PROTEIN PROFILE CHANGES IN RESPONSE TO THE BUTANOLIC EXTRACT OF Sapindus saponariaL

Candida albicans is an opportunistic human pathogen that is capable of causing superficial and systemic infections in immunocompromised patients. Extracts of Sapindus saponaria have been used as antimicrobial agents against various organisms. In the present study, we used a combination of two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) and matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) to identify the changes in protein abundance of C. albicans after exposure to the minimal inhibitory concentration (MIC) and sub-minimal inhibitory concentration (sub-MIC) of the butanolic extract (BUTE) of S. saponaria and also to fluconazole. A total of six different proteins with greater than 1.5 fold induction or repression relative to the untreated control cells were identified among the three treatments. In general, proteins/enzymes involved with the glycolysis (GPM1, ENO1, FBA1), amino acid metabolism (ILV5, PDC11) and protein synthesis (ASC1) pathways were detected. In conclusion, our findings reveal antifungal-induced changes in protein abundance of C. albicans. By using the previously identified components of the BUTE of S. saponaria(e.g., saponins and sesquiterpene oligoglycosides), it will be possible to compare the behavior of compounds with unknown mechanisms of action, and this knowledge will help to focus the subsequent biochemical work aimed at defining the effects of these compounds.

Impaired ergosterol biosynthesis mediated fungicidal activity of Co(II) complex with ligand derived from cinnamaldehyde

In this study, we have used aldehyde function of cinnamaldehyde to synthesize N, N'-Bis (cinnamaldehyde) ethylenediimine [C20H20N2] and Co(II) complex of the type [Co(C40H40N4)Cl2]. The structures of the synthesized compounds were determined on the basis of physiochemical analysis and spectroscopic data ((1)H NMR, FTIR, UV-visible and mass spectra) along with molar conductivity measurements. Anticandidal activity of cinnamaldehyde its ligand [L] and Co(II) complex was investigated by determining MIC80, time-kill kinetics, disc diffusion assay and ergosterol extraction and estimation assay. Ligand [L] and Co(II) complex are found to be 4.55 and 21.0 folds more efficient than cinnamaldehyde in a liquid medium. MIC80 of Co(II) complex correlated well with ergosterol inhibition suggesting ergosterol biosynthesis to be the primary site of action. In comparison to fluconazole, the test compounds showed limited toxicity against H9c2 rat cardiac myoblasts. In confocal microscopy propidium iodide (PI) penetrates the yeast cells when treated with MIC of metal complex, indicating a disruption of cell membrane that results in imbibition of dye. TEM analysis of metal complex treated cells exhibited notable alterations or damage to the cell membrane and the cell wall. The structural disorganization within the cell cytoplasm was noted. It was concluded that fungicidal activity of Co(II) complex originated from loss of membrane integrity and a decrease in ergosterol content is only one consequence of this.

Integrative Model of Oxidative Stress Adaptation in the Fungal Pathogen Candida albicans

The major fungal pathogen of humans, Candida albicans, mounts robust responses to oxidative stress that are critical for its virulence. These responses counteract the reactive oxygen species (ROS) that are generated by host immune cells in an attempt to kill the invading fungus. Knowledge of the dynamical processes that instigate C. albicans oxidative stress responses is required for a proper understanding of fungus-host interactions. Therefore, we have adopted an interdisciplinary approach to explore the dynamical responses of C. albicans to hydrogen peroxide (H₂O₂). Our deterministic mathematical model integrates two major oxidative stress signalling pathways (Cap1 and Hog1 pathways) with the three major antioxidant systems (catalase, glutathione and thioredoxin systems) and the pentose phosphate pathway, which provides reducing equivalents required for oxidative stress adaptation. The model encapsulates existing knowledge of these systems with new genomic, proteomic, transcriptomic, molecular and cellular datasets. Our integrative approach predicts the existence of alternative states for the key regulators Cap1 and Hog1, thereby suggesting novel regulatory behaviours during oxidative stress. The model reproduces both existing and new experimental observations under a variety of scenarios. Time- and dose-dependent predictions of the oxidative stress responses for both wild type and mutant cells have highlighted the different temporal contributions of the various antioxidant systems during oxidative stress adaptation, indicating that catalase plays a critical role immediately following stress imposition. This is the first model to encapsulate the dynamics of the transcriptional response alongside the redox kinetics of the major antioxidant systems during H₂O₂ stress in C. albicans.

Chlorhexidine markedly potentiates the oxidants scavenging abilities of Candida albicans

The oxidant scavenging ability (OSA) of catalase-rich Candida albicans is markedly enhanced by chlorhexidine digluconate (CHX), polymyxin B, the bile salt ursodeoxycholate and by lysophosphatidylcholine, which all act as detergents facilitating the penetration of oxidants and their intracellular decomposition. Quantifications of the OSA of Candida albicans were measured by a highly sensitive luminol-dependent chemiluminescence assay and by the Thurman's assay, to quantify hydrogen peroxide (H2O2). The OSA enhancing activity by CHX depends to some extent on the media on which candida grew. The OSA of candida treated by CHX was modulated by whole human saliva, red blood cells, lysozyme, cationic peptides and by polyphenols. Concentrations of CHX, which killed over 95 % of Candida albicans cells, did not affect the cells' abilities to scavenge reactive oxygen species (ROS). The OSA of Candida cells treated by CHX is highly refractory to H2O2 (50 mM) but is strongly inhibited by hypochlorous acid, lecithin, trypan blue and by heparin. We speculate that similarly to catalase-rich red blood cells, Candida albicans and additional catalase-rich microbiota may also have the ability to scavenge oxidants and thus can protect catalase-negative anaerobes and facultative anaerobes cariogenic streptococci against peroxide and thus secure their survival in the oral cavity.

The Candida albicans Exocyst Subunit Sec6 Contributes to Cell Wall Integrity and Is a Determinant of Hyphal Branching

The yeast exocyst is a multiprotein complex comprised of eight subunits (Sec3, Sec5, Sec6, Sec8, Sec10, Sec15, Exo70, and Exo84) which orchestrates trafficking of exocytic vesicles to specific docking sites on the plasma membrane during polarized secretion. To study SEC6 function in Candida albicans, we generated a conditional mutant strain in which SEC6 was placed under the control of a tetracycline-regulated promoter. In the repressed state, the tetR-SEC6 mutant strain (denoted tSEC6) was viable for up to 27 h; thus, all phenotypic analyses were performed at 24 h or earlier. Strain tSEC6 under repressing conditions had readily apparent defects in cytokinesis and endocytosis and accumulated both post-Golgi apparatus secretory vesicles and structures suggestive of late endosomes. Strain tSEC6 was markedly defective in secretion of aspartyl proteases and lipases as well as filamentation under repressing conditions. Lack of SEC6 expression resulted in markedly reduced lateral hyphal branching, which requires the establishment of a new axis of polarized secretion. Aberrant localization of chitin at the septum and increased resistance to zymolyase activity were observed, suggesting that C. albicans Sec6 plays an important role in mediating trafficking and delivery of cell wall components. The tSEC6 mutant was also markedly defective in macrophage killing, indicating a role of SEC6 in C. albicans virulence. Taken together, these studies indicate that the late secretory protein Sec6 is required for polarized secretion, hyphal morphogenesis, and the pathogenesis of C. albicans.

Dermatomycoses and inflammation: The adaptive balance between growth, damage, and survival

Dermatomycosis is characterized by both superficial and subcutaneous infections of keratinous tissues and mucous membranes caused by a variety of fungal agents, the two most common classes being dermatophytes and yeasts. Overall, the stepwise process of host infection is similar among the main dermatomycotic species; however, the species-specific ability to elicit a host reaction upon infection is distinct. Yeasts such as Candida albicans elicit a relatively low level of host tissue damage and inflammation during pathogenic infection, while dermatophytes may induce a higher level of tissue damage and inflammatory reaction. Both pathogens can, however, manipulate the host's immune response, ensuring survival and prolonging chronic infection. One common element of most dermatomycotic infections is the disease burden caused by inflammation and associated signs and symptoms, such as erythema, burning and pruritus. There is a strong clinical rationale for the addition of a topical corticosteroid agent to an effective antimycotic therapy, especially in patients who present with inflammatory dermatomycoses (e.g., tinea inguinalis). In this review, we aim to compare the pathogenesis of common dermatomycotic species, including Candida yeasts (Candida albicans), dermatophytes (Trichophyton, Epidermophyton or Microsporum species), and other pathogenic yeasts (Malassezia), with a special focus on unique species-specific aspects of the respective infection processes, the interaction between essential aspects of pathogenic infection, the different roles of the host inflammatory response, and the clinical consequences of the infection-related tissue damage and inflammation. We hope that a broader understanding of the various mechanisms of dermatomycoses may contribute to more effective management of affected patients.

Nicotine: Its Stimulating and Inhibitory Effects on Oral Microorganisms

Tobacco users are much more susceptible to dental caries and periodontal diseases than non-tobacco users. Research suggests that this increased susceptibility may be due in part to nicotine, a primary active component of tobacco. Five bacterial species and one yeast species commonly found in the human oral cavity, Lactobacillus casei, Actinomyces viscosus, Actinomyces naeslundii, Rothia dentocariosa, Enterococcus faecalis, and Candida albicans respectively, were utilized to investigate if any correlation existed between exposure to various concentrations of nicotine ranging from 0 to 32 mg/ml and the growth of each microorganism. The minimum inhibitory concentration (MIC), minimum biofilm inhibitory concentration (MBIC), and planktonic growth were measured. The MIC was determined to be 16 mg/ml for all organisms except E. faecalis, which had an MIC of 32 mg/ml. Nicotine had a varying effect on planktonic growth across the different species. A distinct upward trend in biofilm formation was found in A. viscosus, L. casei, E. faecalis, and C. albicans through 8 mg/ml. Nicotine also enhanced R. dentocariosa biofilm formation in all concentrations through 8 mg/ml but was most enhanced at 1 mg/ml. Alternatively, A. naeslundii exhibited a complete downward trend through 32 mg/ml. The MBIC was found to be 16 mg/ml in all organisms studied. These findings further support research suggesting that the increased susceptibility to oral health diseases experienced by tobacco users may be caused in part by an upregulation in biofilm formation of these oral pathogens.

New pharmacological properties of Medicago sativa and Saponaria officinalis saponin-rich fractions addressed to Candida albicans

The antifungal activity of the saponin-rich fractions (SFs) from Medicago sativa (aerial parts and roots) and Saponaria officinalis (used as a well-known source of plant saponins) against Candida albicans reference and clinical strains, their yeast-to-hyphal conversion, adhesion, and biofilm formation was investigated. Direct fungicidal/fungistatic properties of the tested phytochemicals used alone, as well as their synergy with azoles (probably resulting from yeast cell wall instability) were demonstrated. Here, to the best of our knowledge, we report for the first time the ability of saponin-rich extracts of M. sativa and S. officinalis to inhibit C. albicans germ tube formation, limit hyphal growth, reduce yeast adherence and biofilm formation, and eradicate mature (24 h) Candida biofilm. Moreover, M. sativa SFs (mainly obtained from aerial parts), in the range of concentrations which were active modulators of Candida virulence factors, exhibited low cytotoxicity against the mouse fibroblast line L929. These properties seem to be very promising in the context of using plant-derived SFs as potential novel antifungal therapeutics supporting classic drugs or as ingredients of disinfectants.

Candida albicans Niche Specialization: Features That Distinguish Biofilm Cells from Commensal Cells

The fungus Candida albicans is a frequent commensal colonizer of the human gastrointestinal (GI) tract, but is also an opportunistic pathogen. This review explores features that distinguish the colonizing and pathogenic forms of C. albicans. Candida albicans in a biofilm is used as an example of a pathogenic form of the organism, because biofilms are a common feature of device-associated C. albicans infections. Biofilms (complex, sessile communities of cells) have been the subject of several large-scale gene expression studies. Biofilms and commensal C. albicans colonizing the murine GI tract show a variety of differentially expressed genes. Cell surface proteins encoded by these differentially expressed genes are especially attractive as targets for new clinical prevention, diagnosis, or treatment tools that are specific for C. albicans in its pathogenic biofilm state.