Candida albicans drug resistance another way to cope with stress

Computer-made peptide RQ18 acts as a dual antifungal and antibiofilm peptide though membrane-associated mechanisms of action

The spread of fungi resistant to conventional drugs has become a threatening problem. In this context, antimicrobial peptides (AMPs) have been considered as one of the main alternatives for controlling fungal infections. Here, we report the antifungal and antibiofilm activity and some clues about peptide RQ18's mechanism of action against Candida and Cryptococcus. This peptide inhibited yeast growth from 2.5 μM and killed all Candida tropicalis cells within 2 h incubation. Moreover, it showed a synergistic effect with antifungal agent the amphotericin b. RQ18 reduced biofilm formation and promoted C. tropicalis mature biofilms eradication. RQ18's mechanism of action involves fungal cell membrane damage, which was confirmed by the results of RQ18 in the presence of free ergosterol in the medium and fluorescence microscopy by Sytox green. No toxic effects were observed in murine macrophage cell lines and Galleria mellonella larvae, suggesting fungal target selectivity. Therefore, peptide RQ18 represents a promising strategy as a dual antifungal and antibiofilm agent that contributes to infection control without damaging mammalian cells.

The anti-staphylococcal fusidic acid as an efflux pump inhibitor combined with fluconazole against vaginal candidiasis in mouse model

BACKGROUND

Candida albicans is the most common fungus that causes vaginal candidiasis in immunocompetent women and catastrophic infections in immunocompromised patients. The treatment of such infections is hindered due to the increasing emergence of resistance to azoles in C. albicans. New treatment approaches are needed to combat candidiasis especially in the dwindled supply of new effective and safe antifungals. The resistance to azoles is mainly attributed to export of azoles outside the cells by means of the efflux pump that confers cross resistance to all azoles including fluconazole (FLC).

OBJECTIVES

This study aimed to investigate the possible efflux pump inhibiting activity of fusidic acid (FA) in C. albicans resistant isolates and the potential use of Fusidic acid in combination with fluconazole to potentiate the antifungal activity of fluconazole to restore its activity in the resistant C. albicans isolates.

METHODS

The resistance of C. albicans isolates was assessed by determination of minimum inhibitory concentration. The effect of Fusidic acid at sub-inhibitory concentration on efflux activity was assayed by rhodamine 6G efflux assay and intracellular accumulation. Mice model studies were conducted to evaluate the anti-efflux activity of Fusidic acid and its synergistic effects in combination with fluconazole. Impact of Fusidic acid on ergosterol biosynthesis was quantified. The synergy of fluconazole when combined with Fusidic acid was investigated by determination of minimum inhibitory concentration. The cytotoxicity of Fusidic acid was tested against erythrocytes. The effect of Fusidic acid on efflux pumps was tested at the molecular level by real-time PCR and in silico study. In vivo vulvovaginitis mice model was used to confirm the activity of the combination in treating vulvovaginal candidiasis.

RESULTS

Fusidic acid showed efflux inhibiting activity as it increased the accumulation of rhodamine 6G, a substrate for ABC-efflux transporter, and decreased its efflux in C. albicans cells. The antifungal activity of fluconazole was synergized when combined with Fusidic acid. Fusidic acid exerted only minimal cytotoxicity on human erythrocytes indicating its safety. The FA efflux inhibitory activity could be owed to its ability to interfere with efflux protein transporters as revealed by docking studies and downregulation of the efflux-encoding genes of both ABC transporters and MFS superfamily. Moreover, in vivo mice model showed that using fluconazole-fusidic acid combination by vaginal route enhanced fluconazole antifungal activity as shown by lowered fungal burden and a negligible histopathological change in vaginal tissue.

CONCLUSION

The current findings highlight FA's potential as a potential adjuvant to FLC in the treatment of vulvovaginal candidiasis.

Antifungal Constituents of Piper crocatum and Their Activities as Ergosterol Biosynthesis Inhibitors Discovered via In Silico Study Using ADMET and Drug-Likeness Analysis

Along with the increasing resistance of Candida spp. to some antibiotics, it is necessary to find new antifungal drugs, one of which is from the medicinal plant Red Betel (Piper crocatum). The purpose of this research is to isolate antifungal constituents from P. crocatum and evaluate their activities as ergosterol biosynthesis inhibitors via an in silico study of ADMET and drug-likeness analysis. Two new active compounds 1 and 2 and a known compound 3 were isolated, and their structures were determined using spectroscopic methods, while their bioactivities were evaluated via in vitro and in silico studies, respectively. Antifungal compound 3 was the most active compared to 1 and 2 with zone inhibition values of 14.5, 11.9, and 13.0 mm, respectively, at a concentration of 10% w/v, together with MIC/MFC at 0.31/1.2% w/v. Further in silico study demonstrated that compound 3 had a stronger ΔG than the positive control and compounds 1 and 2 with -11.14, -12.78, -12.00, and -6.89 Kcal/mol against ERG1, ERG2, ERG11, and ERG24, respectively, and also that 3 had the best Ki with 6.8 × 10-3, 4 × 10-4, 1.6 × 10-3, and 8.88 μM. On the other hand, an ADMET analysis of 1-3 met five parameters, while 1 had one violation of Ro5. Based on the research data, the promising antifungal constituents of P. crocatum allow P. crocatum to be proposed as a new antifungal candidate to treat and cure infections due to C. albicans.

In Vitro Antifungal Activity of Three Synthetic Peptides against Candida auris and Other Candida Species of Medical Importance

Candidiasis is an opportunistic infection affecting immunosuppressed and hospitalized patients, with mortality rates approaching 40% in Colombia. The growing pharmacological resistance of Candida species and the emergence of multidrug-resistant Candida auris are major public health problems. Therefore, different antimicrobial peptides (AMPs) are being investigated as therapeutic alternatives to control candidiasis effectively and safely. This work aimed to evaluate the in vitro antifungal activity of three synthetic AMPs, PNR20, PNR20-1, and 35409, against ATCC reference strains of Candida albicans, Candida glabrata, Candida parapsilosis, Candida krusei, and Candida tropicalis, and clinical isolates of C. auris. Antifungal susceptibility testing, determined by broth microdilution, showed that the AMPs have antifungal activity against planktonic cells of all Candida species evaluated. In C. auris and C. albicans, the peptides had an effect on biofilm formation and cell viability, as determined by the XTT assay and flow cytometry, respectively. Also, morphological alterations in the membrane and at the intracellular level of these species were induced by the peptides, as observed by transmission electron microscopy. In vitro, the AMPs had no cytotoxicity against L929 murine fibroblasts. Our results showed that the evaluated AMPs are potential therapeutic alternatives against the most important Candida species in Colombia and the world.

OMICS and Other Advanced Technologies in Mycological Applications

Fungi play many roles in different ecosystems. The precise identification of fungi is important in different aspects. Historically, they were identified based on morphological characteristics, but technological advancements such as polymerase chain reaction (PCR) and DNA sequencing now enable more accurate identification and taxonomy, and higher-level classifications. However, some species, referred to as "dark taxa", lack distinct physical features that makes their identification challenging. High-throughput sequencing and metagenomics of environmental samples provide a solution to identifying new lineages of fungi. This paper discusses different approaches to taxonomy, including PCR amplification and sequencing of rDNA, multi-loci phylogenetic analyses, and the importance of various omics (large-scale molecular) techniques for understanding fungal applications. The use of proteomics, transcriptomics, metatranscriptomics, metabolomics, and interactomics provides a comprehensive understanding of fungi. These advanced technologies are critical for expanding the knowledge of the Kingdom of Fungi, including its impact on food safety and security, edible mushrooms foodomics, fungal secondary metabolites, mycotoxin-producing fungi, and biomedical and therapeutic applications, including antifungal drugs and drug resistance, and fungal omics data for novel drug development. The paper also highlights the importance of exploring fungi from extreme environments and understudied areas to identify novel lineages in the fungal dark taxa.

Phytochemical profiling of Piper crocatum and its antifungal mechanism action as Lanosterol 14 alpha demethylase CYP51 inhibitor: a review

Mycoses or fungal infections are general health problem that often occurs in healthy and immunocompromised people in the community. The development of resistant strains in Fungi and the incidence of azole antibiotic resistance in the Asia Pacific which reached 83% become a critical problem nowadays. To control fungal infections, substances and extracts isolated from natural resources, especially in the form of plants as the main sources of drug molecules today, are needed. Especially from Piperaceae, which have long been used in India, China, and Korea to treat human ailments in traditional medicine. The purpose of this review is to describe the antifungal mechanism action from Piper crocatum and its phytochemical profiling against lanosterol 14a demethylase CYP51. The methods used to search databases from Google Scholar to find the appropriate databases using Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) Flow Diagram as a clinical information retrieval method. From 1.150.000 results searched by database, there is 73 final results article to review. The review shows that P. crocatum contains flavonoids, tannins, terpenes, saponins, polyphenols, eugenol, alkaloids, quinones, chavibetol acetate, glycosides, triterpenoids or steroids, hydroxychavikol, phenolics, glucosides, isoprenoids, and non-protein amino acids. Its antifungal mechanisms in fungal cells occur due to ergosterol especially lanosterol 14a demethylase (CYP51) inhibition, which is one of the main target sites for antifungal activity because it functions to maintain the integrity and function of cell membranes in Candida. P. crocatum has an antifungal activity through its phytochemical profiling against fungal by inhibiting the lanosterol 14a demethylase, make damaging cell membranes, fungal growth inhibition, and fungal cell lysis.

Facile Synthesis of Magnetic Nigella Sativa Seeds: Advances on Nano-Formulation Approaches for Delivering Antioxidants and Their Antifungal Activity against Candida albicans

This article reports on incorporating magnetic nanoparticles into natural carbon frameworks derived from Nigella Sativa seeds and their synthesis via co-precipitation reactions for application in biomedicine. The magnetic Nigella Sativa Seeds (Magnetic NSS), a metal oxide-based bio-nanomaterial, has shown excellent water diaper presence due to the presence of a wide range of oxygenous hydroxyl and carboxyl groups. The physicochemical properties of the composites were characterized extensively using Fourier transform infrared spectroscopy (FTIR), powder-X-ray diffraction (XRD), scanning electron microscopy (SEM), elemental analysis, transmission electron microscopy (TEM), and vibrating-sample magnetometer. Furthermore, synthesized magnetic NSS showed antioxidant and antifungal activity. The antifungal susceptibility was further tested against Candida albicans with a MIC value of 3.125 µg/mL. Analysis of antioxidant defense enzymes was determined quantitatively; the results suggested that antioxidant enzyme activity increase with increased magnetic NSS concentration. Furthermore, biofilm inhibition assay from scanning electron microscopy results revealed that magnetic NSS at the concentration of 3.5 μg/mL has anti-biofilm properties and can disrupt membrane integrity.

Phytochemical profiling of Piper crocatum and its antifungal mechanism action as Lanosterol 14 alpha demethylase CYP51 inhibitor: a review

Mycoses or fungal infections are a general health problem that often occurs in healthy and immunocompromised people in the community. The development of resistant strains in Fungi and the incidence of azole antibiotic resistance in the Asia Pacific which reached 83% become a critical problem nowadays. To control fungal infections, substances and extracts isolated from natural resources, especially in the form of plants as the main sources of drug molecules today, are needed. Especially from Piperaceae, which have long been used in India, China, and Korea to treat human ailments in traditional medicine. The purpose of this review is to describe the antifungal mechanism action from Piper crocatum and its phytochemical profiling against lanosterol 14a demethylase CYP51. The methods used to search databases from Google Scholar to find the appropriate databases using Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) Flow Diagram as a clinical information retrieval method. From 1.150.000 results searched by database, there is 73 final results article to review. The review shows that P. crocatum contains flavonoids, tannins, terpenes, saponins, polyphenols, eugenol, alkaloids, quinones, chavibetol acetate, glycosides, triterpenoids or steroids, hydroxychavikol, phenolics, glucosides, isoprenoids, and non-protein amino acids. Its antifungal mechanisms in fungal cells occur due to ergosterol, especially lanosterol 14a demethylase (CYP51) inhibition, which is one of the main target sites for antifungal activity because it functions to maintain the integrity and function of cell membranes in Candida. P. crocatum has an antifungal activity through its phytochemical profiling against fungal by inhibiting the lanosterol 14a demethylase, make damaging cell membranes, fungal growth inhibition, and fungal cell lysis.

Phytochemical profiling of Piper crocatum and its antifungal activity as Lanosterol 14 alpha demethylase CYP51 inhibitor: a review

Mycoses or fungal infections are a general health problem that often occurs in healthy and immunocompromised people in the community. The development of resistant strains in Fungi and the incidence of azole antibiotic resistance in the Asia Pacific which reached 83% become a critical problem nowadays. To control fungal infections, substances and extracts isolated from natural resources, especially in the form of plants as the main sources of drug molecules today, are needed. Especially from Piperaceae, which have long been used in India, China, and Korea to treat human ailments in traditional medicine. The purpose of this review was to describe antifungal activity from Piper crocatum and its phytochemical profiling against lanosterol 14 alpha demethylase CYP51. The methods used search databases from Google Scholar to find the appropriate databases using Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) flow diagram as a clinical information retrieval method. From 1,150,000 results search by database, there were 73 selected articles to review. The review shows that P. crocatum contains flavonoids, tannins, terpenes, saponins, polyphenols, eugenol, alkaloids, quinones, chavibetol acetate, glycosides, triterpenoids or steroids, hydroxychavikol, phenolics, glucosides, isoprenoids, and non-protein amino acids. Its antifungal mechanisms in fungal cells occur due to ergosterol especially lanosterol 14 alpha demethylase CYP51 inhibition as a result of 5,6 desaturase (ERG3) downregulation. P. crocatum has an antifungal activity by its phytochemical profiling that act against fungi by inhibiting the fungal cytochrome P 450 pathway, make damaging cell membranes, fungal growth inhibition, morphological changes, and fungal cell lysis.

Development of a Topical Amphotericin B and Bursera graveolens Essential Oil-Loaded Gel for the Treatment of Dermal Candidiasis

The higher molecular weight and low solubility of amphotericin B (AmB) hinders its topical administration. The aim of this study was to incorporate Bursera graveolens essential oil into an AmB topical gel (AmB + BGEO gel) in order to promote the diffusion of the drug through the skin in the treatment of cutaneous candidiasis. AmB + BGEO gel formulation was determined using a factorial experiment. Physical and chemical parameters, stability, in vitro release profile and ex vivo permeation in human skin were evaluated. In vitro antimicrobial activity was studied using strains of C. albicans, C. glabrata and C. parapsilosis. The tolerability was evaluated using in vitro and in vivo models. AmB + BGEO gel presented appropriate characteristics for topical administration, including pH of 5.85, pseudoplastic behavior, optimal extensibility, as well as high stability and acceptable tolerability. In vitro release studies showed that the formulation releases the drug following a Boltzmann sigmoidal model. Finally, AmB + BGEO gel exhibited higher amount of drug retained inside the skin and lower Minimum Inhibitory Concentration than a formulation sans essential oil. Therefore, these results suggest that the incorporation of B. graveolens essential oil in the formulation could be used as strategy to promote a local effect in the treatment of cutaneous candidiasis.

The SAGA and NuA4 component Tra1 regulates Candida albicans drug resistance and pathogenesis

Candida albicans is the most common cause of death from fungal infections. The emergence of resistant strains reducing the efficacy of first-line therapy with echinocandins, such as caspofungin calls for the identification of alternative therapeutic strategies. Tra1 is an essential component of the SAGA and NuA4 transcriptional co-activator complexes. As a PIKK family member, Tra1 is characterized by a C-terminal phosphoinositide 3-kinase domain. In Saccharomyces cerevisiae, the assembly and function of SAGA and NuA4 are compromised by a Tra1 variant (Tra1Q3) with three arginine residues in the putative ATP-binding cleft changed to glutamine. Whole transcriptome analysis of the S. cerevisiae tra1Q3 strain highlights Tra1's role in global transcription, stress response, and cell wall integrity. As a result, tra1Q3 increases susceptibility to multiple stressors, including caspofungin. Moreover, the same tra1Q3 allele in the pathogenic yeast C. albicans causes similar phenotypes, suggesting that Tra1 broadly mediates the antifungal response across yeast species. Transcriptional profiling in C. albicans identified 68 genes that were differentially expressed when the tra1Q3 strain was treated with caspofungin, as compared to gene expression changes induced by either tra1Q3 or caspofungin alone. Included in this set were genes involved in cell wall maintenance, adhesion, and filamentous growth. Indeed, the tra1Q3 allele reduces filamentation and other pathogenesis traits in C. albicans. Thus, Tra1 emerges as a promising therapeutic target for fungal infections.

Citral derivative activates cell cycle arrest and apoptosis signaling pathways in Candida albicans by generating oxidative stress

For combating life-threatening infections caused by Candida albicans there is an urgent requirement of new antifungal agents with a targeted activity and low host cytotoxicity. Manipulating the mechanistic basis of cell death decision in yeast may provide an alternative approach for future antifungal therapeutics. Herein, the effect of an active citral derivative (Cd1) over the physiology of cell death in C. albicans was assessed. The viability of C. albicans SC5314 cells was determined by broth microdilution assay. The crucial morphological changes and apoptotic markers in Cd1-exposed yeast cells were analyzed. Subsequently the results confirmed that Cd1 arrested growth and caused death in yeast cells. Furthermore, this molecule inhibited antioxidant enzymes that resulted in production of reactive oxygen species. DNA fragmentation and condensation, phosphatidylserine exposure at the outer leaflet of cell membrane, mitochondrial disintegration as well as accumulation of cells at G2/M phase of the cell cycle were recorded. Altogether, this derivative induced apoptotic-type cell death in C. albicans SC5314.

Calcium-calcineurin signaling pathway in Candida albicans: A potential drug target

Increased morbidity and mortality of candidiasis are a notable threat to the immunocompromised patients. At present, the types of drugs available to treat C. albicans infection are relatively limited. Moreover, the emergence of antifungal drug resistance of C. albicans makes the treatment of C. albicans infection more difficult. The calcium-calcineurin signaling pathway plays a crucial role in the survival and pathogenicity of C. albicans and may act as a potential target against C. albicans. In this review, we summarized functions of the calcium-calcineurin signaling pathway in several biological processes, compared the differences of this signaling pathway between C. albicans and humans, and described anti-C. albicans activity of inhibitors of this signaling pathway. We believe that targeting the calcium-calcineurin signaling pathway is a promising strategy to cope with C. albicans infection.

Multidrug Resistance in Mammals and Fungi-From MDR to PDR: A Rocky Road from Atomic Structures to Transport Mechanisms

Multidrug resistance (MDR) can be a serious complication for the treatment of cancer as well as for microbial and parasitic infections. Dysregulated overexpression of several members of the ATP-binding cassette transporter families have been intimately linked to MDR phenomena. Three paradigm ABC transporter members, ABCB1 (P-gp), ABCC1 (MRP1) and ABCG2 (BCRP) appear to act as brothers in arms in promoting or causing MDR in a variety of therapeutic cancer settings. However, their molecular mechanisms of action, the basis for their broad and overlapping substrate selectivity, remains ill-posed. The rapidly increasing numbers of high-resolution atomic structures from X-ray crystallography or cryo-EM of mammalian ABC multidrug transporters initiated a new era towards a better understanding of structure-function relationships, and for the dynamics and mechanisms driving their transport cycles. In addition, the atomic structures offered new evolutionary perspectives in cases where transport systems have been structurally conserved from bacteria to humans, including the pleiotropic drug resistance (PDR) family in fungal pathogens for which high resolution structures are as yet unavailable. In this review, we will focus the discussion on comparative mechanisms of mammalian ABCG and fungal PDR transporters, owing to their close evolutionary relationships. In fact, the atomic structures of ABCG2 offer excellent models for a better understanding of fungal PDR transporters. Based on comparative structural models of ABCG transporters and fungal PDRs, we propose closely related or even conserved catalytic cycles, thus offering new therapeutic perspectives for preventing MDR in infectious disease settings.

Azole resistance mechanisms in pathogenic M. furfur

Malassezia are emerging fungal pathogens causing opportunistic skin and severe systemic infection. Nosocomial outbreaks are associated with azole resistance and understanding of the underlying mechanisms are limited to knowledge from other fungal species. Herein, we identified distinct antifungal susceptibility patterns in 26 Malassezia furfur isolates derived from healthy and diseased individuals. A Y67F CYP51 mutation was identified in five isolates of M. furfur However, this mutation alone was insufficient to induce reduce azole susceptibility in the wild type strain. RNA-seq and differential gene analysis of healthy and disease derived strains exposed to clotrimazole in vitro identified several key metabolic pathways and transporter proteins which are involved in reduce azole susceptibility. The pleiotropic drug transporter PDR10 was the single most highly upregulated transporter gene in multiple strains of M. furfur after azole treatment and increased expression of PDR10 is associated with reduced azole susceptibility in some systemic disease isolates of M. furfur Deletion of PDR10 in a pathogenic M. furfur strain with reduced susceptibility reduced MIC values to the level of that in susceptible isolates. The current dearth of antifungal technologies, globally emerging multi-azole resistance, and broad agriculture and consumer care use of azoles means improved understanding of the mechanisms underlying intrinsic and acquired azole resistance in Malassezia is crucial for development of antibiotic stewardship and antifungal treatment strategies.

Exploring Small Heat Shock Proteins (sHSPs) for Targeting Drug Resistance in Candida albicans and other Pathogenic Fungi

Fungal infections have predominantly increased worldwide that leads to morbidity and mortality in severe cases. Invasive candidiasis and other pathogenic fungal infections are a major problem in immunocompromised individuals and post-operative patients. Increasing resistance to existing antifungal drugs calls for the identification of novel antifungal drug targets for chemotherapeutic interventions. This demand for identification and characterization of novel drug targets leads to the development of effective antifungal therapy against drug resistant fungi. Heat shock proteins (HSPs) are important for various biological processes like protein folding, posttranslational modifications, transcription, translation, and protein aggregation. HSPs are involved in maintaining homeostasis of the cell. A subgroup of HSPs is small heat shock proteins (sHSPs), which functions as cellular chaperones. They are having a significant role in the many cellular functions like development, cytoskeletal organization, apoptosis, membrane lipid polymorphism, differentiation, autophagy, in infection recognition and are major players in various stresses like osmotic stress, pH stress, etc. Studies have shown that fungal cells express increased levels of sHSPs upon antifungal drug induced stress responses. Here we review the important role of small heat shock proteins (sHSPs) in fungal diseases and their potential as antifungal targets.

A comparative proteomic analysis of Candida species in response to the oxidizing agent cumene hydroperoxide

Candida genus comprises several species that can be found in the oral cavity and the gastrointestinal and genitourinary tracts of healthy individuals. Under certain conditions, however, they behave as opportunistic pathogens that colonize these tissues, most frequently when the immune system is compromised by a disease or under certain medical treatments. To colonize the human host, these organisms require to express cell wall proteins (CWP) that allowed them to adhere and adapt to the reactive oxygen (ROS) and nitrogen (RNS) species produced in the macrophage during the respiratory burst. The aim of this study was to determine how four Candida species respond to the oxidative stress imposed by cumene hydroperoxide (CHP). To this purpose, C. albicans, C. glabrata, C. krusei and C. parapsilosis were exposed to this oxidant which is known to generate ROS in the membrane phospholipids. Accordingly, both mock and CHP-exposed cells were used to extract and analyze CWP and also to measure catalase activity and the levels of protein carbonylation. Results indicated that all four species express different CWP to neutralize ROS. Most relevant among these proteins were the glycolytic enzymes enolase and glyceraldehyde-3-phosphate dehydrogenase, known as moonlight proteins because in addition to participate in glycolysis they play an important role in the cell response to ROS. In addition, a thiol-specific antioxidant enzyme (Tsa) was also found to counteract ROS.

Identification of Cryptic Binding Sites Using MixMD with Standard and Accelerated Molecular Dynamics

Protein dynamics play an important role in small molecule binding and can pose a significant challenge in the identification of potential binding sites. Cryptic binding sites have been defined as sites which require significant rearrangement of the protein structure to become physically accessible to a ligand. Mixed-solvent MD (MixMD) is a computational protocol which maps the surface of the protein using molecular dynamics (MD) of the unbound protein solvated in a 5% box of probe molecules with explicit water. This method has successfully identified known active and allosteric sites which did not require reorganization. In this study, we apply the MixMD protocol to identify known cryptic sites of 12 proteins characterized by a wide range of conformational changes. Of these 12 proteins, three require reorganization of side chains, five require loop movements, and four require movement of more significant structures such as whole helices. In five cases, we find that standard MixMD simulations are able to map the cryptic binding sites with at least one probe type. In two cases (guanylate kinase and TIE-2), accelerated MD, which increases sampling of torsional angles, was necessary to achieve mapping of portions of the cryptic binding site missed by standard MixMD. For more complex systems where movement of a helix or domain is necessary, MixMD was unable to map the binding site even with accelerated dynamics, possibly due to the limited timescale (100 ns for individual simulations). In general, similar conformational dynamics are observed in water-only simulations and those with probe molecules. This could imply that the probes are not driving opening events but rather take advantage of mapping sites that spontaneously open as part of their inherent conformational behavior. Finally, we show that docking to an ensemble of conformations from the standard MixMD simulations performs better than docking the apo crystal structure in nine cases and even better than half of the bound crystal structures. Poorer performance was seen in docking to ensembles of conformations from the accelerated MixMD simulations.

Phytogenic Fabrication of Ag-Fe Bimetallic Nanoparticles for Cell Cycle Arrest and Apoptosis Signaling Pathways in Candida auris by Generating Oxidative Stress

Novel green synthetic nanomedicines have been recognized as alternative therapies with the potential to be antifungal agents. Apoptosis induction, cell cycle arrest and activation of the antioxidant defense system in fungal cells have also gained attention as emerging drug targets. In this study, a facile and biodegradable synthetic route was developed to prepare Ag-Fe bimetallic nanoparticles using aqueous extract of Beta vulgaris L. Surface plasmon resonance of Beta vulgaris-assisted AgNPs nanoparticles was not observed in the UV-visible region of Ag-Fe bimetallic NPs, which confirms the formation of Ag-Fe nanoparticles. Beta vulgaris-assisted Ag-Fe NPs were characterized by FTIR spectroscopy, scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction and TGA-DTG analysis for their structural and morphological properties. The as-prepared Ag-Fe NPs were well dispersed and spherical with the average particle size of 15 nm. The antifungal activity of these Ag-Fe NPs against clinical isolates of Candida auris was determined by broth microdilution and cell viability assays. For insights into mechanisms, induction of apoptosis and triggering cell cycle arrest were studied following standard protocols. Furthermore, analysis of antioxidant defense enzymes was determined spectrophotometrically. Antifungal susceptibility results revealed high antifungal activity with MIC values ranging from 0.19 to 0.39 µg/mL. Further studies showed that Ag-Fe NPs were able to induce apoptosis, cell cycle arrest in G2/M phase and disturbances in primary and secondary antioxidant enzymes. This study presents the potential of Ag-Fe NPs to inhibit and potentially eradicate C. auris by inducing apoptosis, cell cycle arrest and increased levels of oxidative stress.

Verapamil inhibits efflux pumps in Candida albicans, exhibits synergism with fluconazole, and increases survival of Galleria mellonella

The emergence of resistance requires alternative methods to treat Candida albicans infections. We evaluated efficacy of the efflux pump inhibitor (EPI) verapamil (VER) with fluconazole (FLC) against FLC-resistant (CaR) and -susceptible C. albicans (CaS). The susceptibility of both strains to VER and FLC was determined, as well as the synergism of VER with FLC. Experiments were performed in vitro for planktonic cultures and biofilms and in vivo using Galleria mellonella. Larval survival and fungal recovery were evaluated after treatment with VER and FLC. Data were analyzed by analysis of variance and Kaplan-Meier tests. The combination of VER with FLC at sub-lethal concentrations reduced fungal growth. VER inhibited the efflux of rhodamine 123 and showed synergism with FLC against CaR. For biofilms, FLC and VER alone reduced fungal viability. The combination of VER with FLC at sub-lethal concentrations also reduced biofilm viability. In the in vivo assays, VER and FLC used alone or in combination increased the survival of larvae infected with CaR. Reduction of fungal recovery was observed only for larvae infected with CaR and treated with VER with FLC. VER reverted the FLC-resistance of C. albicans. Based on the results obtained, VER reverted the FLC-resistance of C. albicans and showed synergism with FLC against CaR. VER also increased the survival of G. mellonella infected with CaR and reduced the fungal recovery.

Candida Pathogenicity and Interplay with the Immune System

Candida species are opportunistic fungal pathogens that are part of the normal skin and mucosal microflora. Overgrowth of Candida can cause infections such as thrush or life-threatening invasive candidiasis in immunocompromised patients. Though Candida albicans is highly prevalent, several non-albicans species are also isolated from nosocomial infections. Candida sp. are over presented in the gut of people with Crohn's disease and certain types of neurological disorders, with hyphal form and biofilms being the most virulent states. In addition, Candida uses several secreted and cell surface molecules such as pH related antigen 1, High affinity glucose transporter, Phosphoglycerate mutase 1 and lipases to establish pathogenicity. A strong innate immune response is elicited against Candida via dendritic cells, neutrophils and macrophages. All three complement pathways are also activated. Production of proinflammatory cytokines IL-10 and IL-12 signal differentiation of CD4⁺ cells into Th1 and Th2 cells, whereas IL-6, IL-17 and IL-23 induce Th17 cells. Importance of T-lymphocytes is reflected in depleted T-cell count patients being more prone to Candidiasis. Anti- Candida antibodies also play a role against candidiasis using various mechanisms such as targeting virulent enzymes and exhibiting direct candidacidal activity. However, the significance of antibody response during infection remains controversial. Furthermore, some of the Candida strains have evolved molecular strategies to evade the sophisticated host attack by proteolysis of components of immune system and interfering with immune signalling pathways. Emergence of several non-albicans species that are resistant to current antifungal agents makes treatment more difficult. Therefore, deeper insight into interactions between Candida and the host immune system is required for discovery of novel therapeutic options.

Polarization-sensitive stimulated Raman scattering imaging resolves amphotericin B orientation in Candida membrane

Ergosterol-targeting amphotericin B (AmB) is the first line of defense for life-threatening fungal infections. Two models have been proposed to illustrate AmB assembly in the cell membrane; one is the classical ion channel model in which AmB vertically forms transmembrane tunnel and the other is a recently proposed sterol sponge model where AmB is laterally adsorbed onto the membrane surface. To address this controversy, we use polarization-sensitive stimulated Raman scattering from fingerprint C═C stretching vibration to visualize AmB, ergosterol, and lipid in single fungal cells. Intracellular lipid droplet accumulation in response to AmB treatment is found. AmB is located in membrane and intracellular droplets. In the 16 strains studied, AmB residing inside cell membrane was highly ordered, and its orientation is primarily parallel to phospholipid acyl chains, supporting the ion channel model. Label-free imaging of AmB and chemical contents offers an analytical platform for developing low-toxicity, resistance-refractory antifungal agents.

The first intracellular loop is essential for the catalytic cycle of the human ABCG2 multidrug resistance transporter

The human multidrug transporter ABCG2 is required for physiological detoxification and mediates anticancer drug resistance. Here, we identify pivotal residues in the first intracellular loop (ICL1), constituting an intrinsic part of the transmission interface. The architecture includes a triple helical bundle formed by the hot spot helix of the nucleotide‐binding domain, the elbow helix, and ICL1. We show here that the highly conserved ICL1 residues G462, Y463, and Y464 are essential for the proper cross talk of the closed nucleotide‐binding domain dimer with the transmembrane domains. Hence, ICL1 acts as a molecular spring, triggering the conformational switch of ABCG2 before substrate extrusion. These data suggest that the ABCG2 transmission interface may offer therapeutic options for the treatment of drug‐resistant malignancies.

Attenuated apoptotic BAX expression as a xenobiotic reporter in Saccharomyces cerevisiae

Fungal infections are a major challenge to medicine and agriculture. Repeated and prophylactic use of antifungals can lead to pathogen cross-resistance to different classes of drugs. The early development of multidrug resistance in pathogenic fungi includes drug tolerance mediated by drug-dependent activation of drug efflux. In Saccharomyces cerevisiae and the fungal pathogen Candida glabrata, xenobiotic sensing motifs in transcription factors upregulate expression of several ATP-binding cassette (ABC) drug efflux pumps. We have therefore considered how drug candidates that trigger or prevent drug resistance could be identified and evaluated during drug discovery. We report a robust and sensitive, S. cerevisiae-based xenobiotic sensing system using the Pdr1 protein as a sensor and an attenuated version of the apoptotic murine BCL2-associated X (BAX) gene as a reporter. A molecular mechanism of attenuation that involves frameshift reversal may be associated with translation coupling and requires further investigation.

Amphotericin B from antifungal to antiviral therapy: promising modern therapeutic branch

Introduction: Amphotericin B (AmB) which belongs to the polyene group has a wide spectrum in vitro and in vivo antimicrobial activity against fungi and parasites, but resistance to AmB is rare despite extensive use.

Material and methods: Atotal of 2530 articles were investigated in PubMed (n = 1525), Medline (n = 705), and Google Scholar (n = 300). From 2530 articles, only 61 studies were included in this review. All the short and full articles were searched that were scheduled to be published until April 2020.

Results: After its discovery, AmB has been one of the most common first-line choices in treating systemic fungal infection for over seven decades from its discovery. Recently, some studies have focused on the potential antimicrobial action of AmB against some enveloped and non-enveloped viruses, such as human immunodeficiency virus, Japanese encephalitis virus, herpes simplex virus, and Rubella virus.

Discussion: Among the invading pathogens, viruses constitute the most common ones,Due to the continuous spreading of viral infections with the rise in death numbers, new therapeutics development is urgent, as in general, some lethal viruses have no specific antiviral drugs or vaccines. So, this review may serve as an impetus for researchers working in the field of medical microbiology, vaccination, and antiviral drug design by discussing the most recent information about the antiviral action of AmB, as well as trying to provide a deeper understanding of major properties, mechanisms of action, immune system responses, and antimicrobial efficiency of AmB.

Conclusion: Since AmB is expected to alter the structure of the viral envelope, membrane integrity of cells, and internal cellular organelles, besides its other unique properties, such as host immunomodulatory effects, this review suggested that AmB as an effective anti-fungi drug may hold the promise of formulating a novel therapeutic option to treat many dangerous viruses, including those for treating which there are no active drugs or vaccines.

Antifungal Activity of ZnO Nanoparticles and Nystatin and Downregulation of SAP1-3 Genes Expression in Fluconazole-Resistant Candida albicans Isolates from Vulvovaginal Candidiasis

Purpose

Antifungal resistance and virulence properties of Candida albicans (C. albicans) are growing health problems worldwide. The present study aims to investigate the effect of Zinc Oxide (ZnO) nanoparticles and Nystatin on SAP1-3 genes expression in C. albicans isolates of females with Vulvovaginal Candidiasis (VVC) isolated from Sayad Shirazi Obstetrics and Gynecology Hospital in Northeastern Iran during 2017–2018.

Patients and Methods

In this descriptive-analytic study, vaginal samples were collected from 280 VVC women. 196 (70%) of C. albicans isolates were identified by phenotypic and ITS genotypic methods. Susceptibility to Fluconazole C. albicans isolates was determined by the disk diffusion method. Detection of ERG11 gene was done by RT-PCR technique.

Results

It was revealed that PCR amplified the ERG11 gene in all of the Fluconazole-resistant isolates. Real-time PCR was used to survey the effects of 3±1.7µg/mL concentrations of ZnO nanoparticles and Nystatin on expression of SAP1-3 genes before and after treatment. 186 (95%) susceptible C. albicans and 10 (5%) Fluconazole-resistant C. albicans isolates from VVC were exposed to sub-minimum inhibitory concentrations (Sub-MIC) of ZnO-np (range=0.02–12 μg/mL). Sub-MIC concentration was used for each strain, which reduced the expression of SAP1-3 genes to 1.8 MIC in the vaginal swabs. The observed reduction in gene expression was significant for both ZnO nanoparticles and Nystatin (P=0.01 and P=0.07, respectively).

Conclusion

ZnO as antifungal agent can well reduce the growth and gene expression of SAP1-3 in the pathogenesis of VVC.

Candida albicans Antifungal Resistance and Tolerance in Bloodstream Infections: The Triad Yeast-Host-Antifungal

Candida albicans represents the most frequent isolated yeast from bloodstream infections. Despite the remarkable progress in diagnostic and therapeutic approaches, these infections continue to be a critical challenge in intensive care units worldwide. The economic cost of bloodstream fungal infections and its associated mortality, especially in debilitated patients, remains unacceptably high. Candida albicans is a highly adaptable microorganism, being able to develop resistance following prolonged exposure to antifungals. Formation of biofilms, which diminish the accessibility of the antifungal, selection of spontaneous mutations that increase expression or decreased susceptibility of the target, altered chromosome abnormalities, overexpression of multidrug efflux pumps and the ability to escape host immune defenses are some of the factors that can contribute to antifungal tolerance and resistance. The knowledge of the antifungal resistance mechanisms can allow the design of alternative therapeutically options in order to modulate or revert the resistance. We have focused this review on the main factors that are involved in antifungal resistance and tolerance in patients with C. albicans bloodstream infections.

Anticandidal agent for multiple targets: the next paradigm in the discovery of proficient therapeutics/overcoming drug resistance

Candida albicans is a prominent human fungal pathogen. Current treatments are suffering a massive gap due to emerging resistance against available antifungals. Therefore, there is an ardent need for novel antifungal candidates that essentially have more than one target, as most antifungal repertoires are single-target drugs. Exploration of multiple-drug targeting in antifungal therapeutics is still pending. An extensive literature survey was performed to categorize and comprehend relevant studies and the current therapeutic scenario that led researchers to preferentially consider multitarget drug-based Candida infection therapy. With this article, we identified and compiled a few potent antifungal compounds that are directed toward multiple virulent targets in C. albicans. Such compound(s) provide an optimistic platform of multiple targeting and could leave a substantial impact on the development of effective antifungals.

Synergistic anticandidal activity of etomidate and azoles against clinical fluconazole-resistant Candida isolates

Aim: The purpose of this study was to evaluate the effect of etomidate alone and in combination with azoles on resistant strains of Candida spp. in both planktonic cells and biofilms. Materials & methods: The antifungal activity of etomidate was assessed by the broth microdilution test; flow cytometric procedures to measure fungal viability, mitochondrial transmembrane potential, free radical generation and cell death; as well detection of DNA damage using the comet assay. The interaction between etomidate and antifungal drugs (itraconazole and fluconazole) was evaluated by the checkerboard assay. Results: Etomidate showed antifungal activity against resistant strains of Candida spp. in planktonic cells and biofilms. Etomidate also presented synergism with fluconazole and itraconazole in planktonic cells and biofilms. Conclusion: Etomidate showed antifungal activity against Candida spp., indicating that it is a possible therapeutic alternative.

A Novel Antifungal System With Potential for Prolonged Delivery of Histatin 5 to Limit Growth of Candida albicans

Currently 75-88% of fungal infections are caused by Candida species, and Candida albicans is the main microorganism that causes these infections, especially oral candidiasis. An option for treatment involves the use of the antifungal peptide Histatin 5 (Hst 5), which is naturally found in human saliva but undergoes rapid degradation when present in the oral cavity, its site of action. For this reason, it is important to develop a way of applying this peptide to the oral lesions, which promotes the gradual release of the peptide. In the present study, we have evaluated the development of liposomes of different lipid compositions, loaded with the peptide as a way to promote its release slowly and gradually, preserving its antifungal potential. For this, the peptide 0WHistatin 5, an analog of the peptide Hst 5, was synthesized, which contains the amino acid tryptophan in its sequence. The solid phase synthesis method was used, followed by cleavage and purification. The liposomes were produced by thin film hydration technique in three different lipid compositions, F1, F2, and F3 and were submitted to an extrusion and sonication process to standardize the size and study the best technique for their production. The liposomes were characterized by dynamic light scattering, and tests were performed to determine the encapsulation efficiency, release kinetics, stability, and evaluation of antifungal activity. The extruded liposomes presented average size in the range of 100 nm, while sonicated liposomes presented a smaller size in the range of 80 nm. The encapsulation efficiency was higher for the sonicated liposomes, being 34.5% for F1. The sonicated F3 presented better stability when stored for 60 days at 4°C. The liposomes showed the ability to release the peptide for the total time of 96 h, with the first peak after 5 h, and a further increase of the released after 30 h. Time-kill assay showed that the liposomes were able to control yeast growth for 72 h. The data suggest that the liposomes loaded with 0WHistatin 5 maintained the action of the peptide and were able to limit the growth of C. albicans, being a suitable system for use in the treatment of oral candidiasis.

Thermoreversible Gel-Loaded Amphotericin B for the Treatment of Dermal and Vaginal Candidiasis

The present study was designed to develop a thermoreversible gel of Pluronic (P407) loaded amphotericin B (AmB-gel) for the dermal and vaginal treatment of candidiasis. P407 was used as a copolymer to exploit potential advantages related to increasing drug concentration in the tissue layer in order to provide a local effect. Parameters including internal structure, swelling, porosity, and short-term stability were determined. In addition, drug release profile and ex vivo skin and vaginal permeation studies were carried out. Antifungal efficacy was evaluated against strains of Candida spp. and atomic force microscopy (AFM) supported the results. The tolerance of AmB-gel was studied by evaluating biomechanical properties of skin and determining the irritation level in scarified rabbit skin supported by histological analysis. Results confirmed the development of a thermoreversible AmB-gel with high porosity exhibiting Newtonian behavior at 4 °C and pseudoplasticity at 32 °C as well as optimal stability for at least 90 days. The Amb-gel provided a sustained drug release following a Boltzmann sigmoidal model. Non permeation was observed in skin and vaginal mucosa, showing a high retained amount of AmB of 960.0 and 737.3 µg/g/cm², respectively. In vitro antifungal efficacy showed that AmB-gel was more effective than Free-AmB in inhibiting strains of Candida spp. and these results were corroborated by AFM. Finally, tolerance studies showed that its application did not induce skin irritation nor alter its biophysical properties. Together, these results confirmed that AmB-gel could be proposed as a promising candidate for the clinical status in the treatment of skin and vaginal candidiasis.

Calcium signaling pathway is involved in non-CYP51 azole resistance in Aspergillus fumigatus

The opportunistic fungal pathogen Aspergillus fumigatus, which is one of the primary airborne ascomycete pathogens and allergens worldwide, causes invasive fungal infections, which have high morbidity and mortality rates among immunosuppressed patients. The abuse of azole antifungals results in serious drug resistance in clinical therapy. Thus, a thorough understanding of the azole drug resistance mechanism and screening of antifungal agents with a novel mode of action and new drug targets are required to fight against drug resistance. Current studies suggest that there are three major azole resistance mechanisms in fungal pathogens, including changes of the drug target Cyp51, activation of drug efflux pumps and induction of cellular stress responses. Fungi must adapt to a variety of external environmental stressors to survive. These obstacles include stress to the plasma membrane after azole antifungal treatments, high temperature, pH variation, and oxidative stress. As a filamentous fungus, A. fumigatus has evolved numerous signal-transduction systems to sense and respond to azole stresses to survive and proliferate in harsh environmental conditions. Among these signal-transduction systems, the Ca2+ signaling pathway is one of the most important response systems, which has been verified to be involved in stress adaptation. In this review, we have summarized how the components of the calcium-signaling pathway and their interaction network are involved in azole stress response in A. fumigatus.

TLS dependent and independent functions of DNA polymerase eta (Polη/Rad30) from Pathogenic Yeast Candida albicans

Polη, a unique TLS DNA polymerase that promotes efficient bypass of UV-induced CPDs and cisplatin adducts, has not been explored in Candida species yet. Here, we show that CaPolη plays a vital role in protecting Candida albicans genome from diverse array of DNA damaging agents, not limited to UV and cisplatin. Polη deficient strain did not exhibit any hyphal development in the presence of UV and cisplatin while the wild type strain profusely developed DNA damage induced filamentation. The polarized growth induced by HU and MMS was found to be Polη independent. No common regulatory pathway of morphogenesis operates in C. albicans due to genomic stress, rather Polη branches away from RAD53 dependent pathway to be specific to UV/cisplatin. Interestingly, serum that does not inflict any DNA damage also induces hyphal growth in C. albicans, and requires a functionally active Polη. Importantly, deletion of RAD30 sensitized the strain to amphotericin B; but its presence resulted in azole drug tolerance only in DNA damaging conditions. We suggest that the roles of CaPolη in genome stability and genotoxins induced filamentation are due to its TLS activities; whereas its TLS independent functions play a vital role in serum induced morphogenesis and amphotericin B resistance.

Effect of Chloroaluminium phthalocyanine in cationic nanoemulsion on photoinactivation of multispecies biofilm

BACKGROUND

Photosensitizers in nanocarriers have been investigated for antimicrobial Photodynamic Therapy (aPDT). However, most studies are focused against microorganisms in planktonic or monospecies biofilm. Thus, this in vitro study evaluated the effect of aPDT using Chloroaluminium phthalocyanine (ClAlPc) in cationic nanoemulsion (NE) against Candida albicans, Candida glabrata and Streptococcus mutans grown as multispecies biofilm.

METHODS

Standard suspensions of each microorganism were added into wells of a microtiter plate for biofilm growth for 48 h in a candle jar. The biofilms were incubated with ClAlPc in cationic NE at 31.8 μM for 30 min and illuminated with red light fluence of 39.3 J/cm² (P+L+ group). Additional samples were treated only with photosensitizer (P+L-) or red light (P-L+) or neither (P-L-, control group). aPDT efficacy was assessed by colony quantification, biofilm's metabolic activity, total biomass, and confocal microscopy. Data were analyzed by ANOVA/Welch and post-hoc Tukey/Games-Howell tests (α = 0.05).

RESULTS

aPDT (P+L+) reduced the colony count in 1.30 to 2.24 lg₁₀ and the metabolic activity in 53.7% compared with the control group (P-L-). The total biomass showed no statistical difference among the groups. The confocal microscopy analyzes showed uptake of the PS in the biofilm, and dead cells were observed in the biofilm treated with aPDT.

CONCLUSION

aPDT mediated by ClAlPc in cationic NE promoted photoinactivation of the multispecies biofilm, which was confirmed by colony quantification, metabolic activity, and confocal microscopy. However, the total biomass of the biofilm was not affected by the treatment.

Iron Restriction to Clinical Isolates of Candida albicans by the Novel Chelator DIBI Inhibits Growth and Increases Sensitivity to Azoles In Vitro and In Vivo in a Murine Model of Experimental Vaginitis

Candida albicans is an important opportunistic pathogen causing various human infections that are often treated with azole antifungals. The U.S. CDC now regards developing candidal antifungal resistance as a threat, creating a need for new and more effective antifungal treatments. Iron is an essential nutrient for all living cells, and there is growing evidence that interference with iron homeostasis of C. albicans can improve its response to antifungals. This study was aimed at establishing whether withholding iron by currently used medical iron chelators and the novel chelator DIBI could restrict growth and also enhance the activity of azoles against clinical isolates of C. albicans DIBI, but not deferoxamine or deferiprone, inhibited the growth of C. albicans at relatively low concentrations in vitro, and this inhibition was reversed by iron addition. DIBI in combination with various azoles demonstrated stronger growth inhibition than the azoles alone and greatly prolonged the inhibition of cell multiplication. In addition, the administration of DIBI along with fluconazole (FLC) to mice inoculated with an FLC-sensitive isolate in a model of experimental C. albicans vaginitis showed a markedly improved clearance of infection. These results suggest that iron chelation by DIBI has the potential to enhance azole efficacy for the treatment of candidiasis.

Overexpression or Deletion of Ergosterol Biosynthesis Genes Alters Doubling Time, Response to Stress Agents, and Drug Susceptibility in Saccharomyces cerevisiae

Ergosterol (ERG) is a critical sterol in the cell membranes of fungi, and its biosynthesis is tightly regulated by 25 known enzymes along the ERG production pathway. The effects of changes in expression of each ERG biosynthesis enzyme in Saccharomyces cerevisiae were analyzed by the use of gene deletion or plasmid-borne overexpression constructs. The strains overexpressing the ERG pathway genes were examined for changes in doubling time and responses to a variety of stress agents. In addition, ERG gene overexpression strains and ERG gene deletion strains were tested for alterations in antifungal drug susceptibility. The data show that disruptions in ergosterol biosynthesis regulation can affect a diverse set of cellular processes and can cause numerous phenotypic effects. Some of the phenotypes observed include dramatic increases in doubling times, respiratory deficiencies on glycerol media, cell wall insufficiencies on Congo red media, and disrupted ion homeostasis under iron or calcium starvation conditions. Overexpression or deletion of specific enzymes in the ERG pathway causes altered susceptibilities to a variety of classes of antifungal ergosterol inhibitors, including fluconazole, fenpropimorph, lovastatin, nystatin, amphotericin B, and terbinafine. This analysis of the effect of perturbations to the ERG pathway caused by systematic overexpression of each of the ERG pathway genes contributes significantly to the understanding of the ergosterol biosynthetic pathway and its relationship to stress response and basic biological processes. The data indicate that precise regulation of ERG genes is essential for cellular homeostasis and identify several ERG genes that could be exploited in future antifungal development efforts.IMPORTANCE A common target of antifungal drug treatment is the fungal ergosterol biosynthesis pathway. This report helps to identify ergosterol biosynthesis enzymes that have not previously been appreciated as drug targets. The effects of overexpression of each of the 25 ERG genes in S. cerevisiae were analyzed in the presence of six stress agents that target essential cellular processes (cell wall biosynthesis, protein translation, respiration, osmotic/ionic stress, and iron and calcium homeostasis), as well as six antifungal inhibitors that target ergosterol biosynthesis. The importance of identifying cell perturbations caused by gene overexpression or deletion is emphasized by the prevalence of gene expression alterations in many pathogenic and drug-resistant clinical isolates. Genes whose altered expression causes the most extensive phenotypic alterations in the presence of stressors or inhibitors have the potential to be drug targets.

Structure-activity relationship studies of ultra-short peptides with potent activities against fluconazole-resistant Candida albicans

Vulvovaginal candidiasis (VVC) is a genital fungal infection afflicting approximately 75% of women globally and is primarily caused by the yeast Candida albicans. The extensive use of fluconazole, the first-line antifungal drug of choice, has led to the emergence of fluconazole-resistant C. albicans, creating a global clinical concern. This, coupled to the lack of new antifungal drugs entering the market over the past decade, has made it imperative for the introduction of new antifungal drug classes. Peptides with antifungal properties are deemed potential drug candidates due to their rapid membrane-disrupting mechanism of action. By specifically targeting and rapidly disrupting fungal membranes, they reduce the chances of resistance development and treatment duration. In a previous screening campaign involving an antimicrobial peptide library, we identified an octapeptide (IKIKIKIK-NH₂) with potent activity against C. albicans. Herein, we report a structure-activity relationship study on this peptide with the aim of designing a more potent peptide for further development. The lead peptide was then tested against a panel of fluconazole-resistant C. albicans, subjected to a fungicidal/static determination assay, a human dermal fibroblast viability assay and a homozygous profiling assay to gain insights into its mechanism of action and potential for further development as a topical antifungal agent.

Photodynamic antimicrobial chemotherapy (PACT) using toluidine blue inhibits both growth and biofilm formation by Candida krusei

Among non-albicans Candida species, the opportunistic pathogen Candida krusei emerges because of the high mortality related to infections produced by this yeast. The Candida krusei is an opportunistic pathogen presenting an intrinsic resistance to fluconazol. In spite of the reduced number of infections produced by C. krusei, its occurrence is increasing in some groups of patients submitted to the use of fluconazol for prophylaxis. Photodynamic antimicrobial chemotherapy (PACT) is a potential antimicrobial therapy that combines visible light and a nontoxic dye, known as a photosensitizer, producing reactive oxygen species (ROS) that can kill the treated cells. The objective of this study was to investigate the effects of PACT, using toluidine blue, as a photosensitizer on both growth and biofilm formation by Candida krusei. In this work, we studied the effect of the PACT, using TB on both cell growth and biofilm formation by C. krusei. PACT was performed using a light source with output power of 0.068 W and peak wavelength of 630 nm, resulting in a fluence of 20, 30, or 40 J/cm². In addition, ROS production was determined after PACT. The number of samples used in this study varied from 6 to 8. Statistical differences were evaluated by analysis of variance (ANOVA) and post hoc comparison with Tukey-Kramer test. PACT inhibited both growth and biofilm formation by C. krusei. It was also observed that PACT stimulated ROS production. Comparing to cells not irradiated, irradiation was able to increase ROS production in 11.43, 6.27, and 4.37 times, in the presence of TB 0.01, 0.02, and 0.05 mg/mL, respectively. These results suggest that the inhibition observed in the cell growth after PACT could be related to the ROS production, promoting cellular damage. Taken together, these results demonstrated the ability of PACT reducing both cell growth and biofilm formation by C. krusei.

Response of Ustilago maydis against the Stress Caused by Three Polycationic Chitin Derivatives

Chitosan is a stressing molecule that affects the cells walls and plasma membrane of fungi. For chitosan derivatives, the action mode is not clear. In this work, we used the yeast Ustilago maydis to study the effects of these molecules on the plasma membrane, focusing on physiologic and stress responses to chitosan (CH), oligochitosan (OCH), and glycol-chitosan (GCH). Yeasts were cultured with each of these molecules at 1 mg·mL⁻¹ in minimal medium. To compare plasma membrane damage, cells were cultivated in isosmolar medium. Membrane potential (Δψ) as well as oxidative stress were measured. Changes in the total plasma membrane phospholipid and protein profiles were analyzed using standard methods, and fluorescence-stained mitochondria were observed. High osmolarity did not protect against CH inhibition and neither affected membrane potential. The OCH did produce higher oxidative stress. The effects of these molecules were evidenced by modifications in the plasma membrane protein profile. Also, mitochondrial damage was evident for CH and OCH, while GCH resulted in thicker cells with fewer mitochondria and higher glycogen accumulation.

The Candida albicans transcription factor Cas5 couples stress responses, drug resistance and cell cycle regulation

The capacity to coordinate environmental sensing with initiation of cellular responses underpins microbial survival and is crucial for virulence and stress responses in microbial pathogens. Here we define circuitry that enables the fungal pathogen Candida albicans to couple cell cycle dynamics with responses to cell wall stress induced by echinocandins, a front-line class of antifungal drugs. We discover that the C. albicans transcription factor Cas5 is crucial for proper cell cycle dynamics and responses to echinocandins, which inhibit β-1,3-glucan synthesis. Cas5 has distinct transcriptional targets under basal and stress conditions, is activated by the phosphatase Glc7, and can regulate the expression of target genes in concert with the transcriptional regulators Swi4 and Swi6. Thus, we illuminate a mechanism of transcriptional control that couples cell wall integrity with cell cycle regulation, and uncover circuitry governing antifungal drug resistance.Cas5 is a transcriptional regulator of responses to cell wall stress in the fungal pathogen Candida albicans. Here, Xie et al. show that Cas5 also modulates cell cycle dynamics and responses to antifungal drugs.