The development of fluconazole resistance in Candida albicans – an example of microevolution of a fungal pathogen

Tackling multi-drug resistant fungi by efflux pump inhibitors

The emergence of multidrug-resistant fungi is of grave concern, and its infections are responsible for significant deaths among immunocompromised patients. The treatment of fungal infections primarily relies on a clinical class of antibiotics, including azoles, polyenes, echinocandins, polyketides, and a nucleotide analogue. However, the incidence of fungal infections is increasing as the treatment for human and plant fungal infections overlaps with antifungal drugs. The need for new antifungal agents acting on different targets than known targets is undeniable. Also, the pace at which loss of fungal susceptibility to antibiotics cannot be undermined. There are several modes by which fungi can develop resistance to antibiotics, including reduced drug uptake, drug target alteration, and a reduction in the cellular concentration of the drug due to active extrusions and biofilm formation. The efflux pump's overexpression in the fungi primarily reduced the antibiotic's concentration to a sub-lethal concentration, thus responsible for developing resistant fungus strains. Several strategies are used to check antibiotic resistance in multi-drug resistant fungi, including synthesizing antibiotic analogs and giving antibiotics in combination therapies. Among them, the efflux pump protein inhibitors are considered potential adjuvants to antibiotics and can block the efflux of antibiotics by inhibiting efflux pump protein transporters. Moreover, it can sensitize the antifungal drugs to multi-drug resistant fungi with overexpressed efflux pump proteins. This review discusses the natural lead molecules, repurposable drugs, and formulation strategies to overcome the efflux pump activity in the fungi.

The TAC1 Gene in Candida albicans: Structure, Function, and Role in Azole Resistance: A Mini-Review

Candidiasis is a common fungal infection caused by Candida species, with Candida albicans being the most prevalent. Resistance to azole drugs, commonly used to treat Candida infections, poses a significant challenge. Transcriptional activator candidate 1 (TAC1) gene has emerged as a key player in regulating drug resistance in C. albicans. This review explores the structure and function of the TAC1 gene and its role in azole resistance. This gene encodes a transcription factor that controls the expression of genes involved in drug resistance, such as efflux pump genes (CDR1, CDR2, and MDR1) and ERG11. Mutations in TAC1 can increase these genes' expression and confer resistance to azoles. Various TAC1 gene mutations, mostly gain-of-function mutations, have been identified, which upregulate CDR1 and CDR2 expression, resulting in azole resistance. Understanding the mechanisms of azole resistance mediated by the TAC1 gene is crucial for the strategies in the effective antifungal development pipeline.

Two different types of tandem sequences mediate the overexpression of TinCYP51B in azole-resistant Trichophyton indotineae

Trichophyton indotineae is an emerging dermatophyte that causes severe tinea corporis and tinea cruris. Numerous cases of terbinafine- and azole-recalcitrant T. indotineae-related dermatophytosis have been observed in India over the past decade, and cases are now being recorded worldwide. Whole genome sequencing of three azole-resistant strains revealed a variable number of repeats of a 2,404 base pair (bp) sequence encoding TinCYP51B in tandem specifically at the CYP51B locus position. However, many other resistant strains (itraconazole MIC ≥0.25 µg/mL; voriconazole MIC ≥0.25 µg/mL) did not contain such duplications. Whole-genome sequencing of three of these strains revealed a variable number of 7,374 bp tandem repeat blocks harboring TinCYP51B. Consequently, two types of T. indotineae azole-resistant strains were found to host TinCYP51B in tandem sequences (type I with 2,404 bp TinCYP51B blocks and type II with 7,374 bp TinCYP51B blocks). Using the CRISPR/Cas9 genome-editing tool, the copy number of TinCYP51B within the genome of types I and II strains was brought back to a single copy. The azole susceptibility of these modified strains was similar to that of strains without TinCYP51B duplication, showing that azole resistance in T. indotineae strains is mediated by one of two types of TinCYP51B amplification. Type II strains were prevalent among 32 resistant strains analyzed using a rapid and reliable PCR test.

Benzamidine Conjugation Converts Expelled Potential Active Agents into Antifungals against Drug-Resistant Fungi

Fungal infections present a growing global public health concern, necessitating the development of novel antifungal drugs. However, many potential antifungals, particularly the expelled potential active agents (EPAAs), are often underestimated owing to their limitations in cellular entry or expulsion by efflux pumps. Herein, we identified 68 EPAAs out of 2322 candidates with activity against a Candida albicans efflux pump-deficient strain and no inhibitory activity against the wild-type strain. Using a novel conjugation strategy involving benzamidine (BM) as a mitochondrion-targeting warhead, we successfully converted EPAAs into potent antifungals against various urgent-threat azole-resistantCandida strains. Among the obtained EPAA-BM conjugates, IS-2-BM (11) exhibited excellent antifungal activities and induced negligible drug resistance. Furthermore, IS-2-BM prevented biofilm formation, eradicated mature biofilms, and exhibited excellent therapeutic effects in a murine model of systemic candidiasis. These findings provide a promising strategy for increasing the possibilities of discovering more antifungals.

Detrimental consequences of tebuconazole on redox homeostasis and fatty acid profile of honeybee brain

Excessive use of azole fungicides in agriculture poses a potential threat to honeybees and other pollinator insects; however, the detailed effects of these molecules remain largely unclear. Hence, in the present study it was aimed to investigate the acute sublethal effects of tebuconazole on the redox homeostasis and fatty acid composition in the brain of honeybees. Our findings demonstrate that tebuconazole decreased total antioxidant capacity, the ratio of reduced to oxidized glutathione and disturbed the function of key antioxidant defense enzymes along with the induction of lipid peroxidation indicated by increased malondialdehyde levels, while it also altered the fatty acid profile of the brain. The present study highlights the negative impact of tebuconazole on honeybees and contributes to the understanding of potential consequences related to azole exposure on pollinator insects' health, such as the occurrence of colony collapse disorder.

Assessing the In Vitro Potential of Glatiramer Acetate (Copaxone®) as a Chemotherapeutic Candidate for the Treatment of Cryptococcus neoformans Infection

Cryptococcosis is a systemic mycosis affecting immunosuppressed individuals, caused by various Cryptococcus species. The current treatment utilizes a combination of antifungal drugs, but issues such as nephrotoxicity, restricted or limited availability in certain countries, and resistance limit their effectiveness. Repurposing approved drugs presents a viable strategy for developing new antifungal options. This study investigates the potential of glatiramer acetate (Copaxone®) as a chemotherapy candidate for Cryptococcus neoformans infection. Various techniques are employed to evaluate the effects of glatiramer acetate on the fungus, including microdilution, XTT analysis, electron and light microscopy, and physicochemical measurements. The results demonstrate that glatiramer acetate exhibits antifungal properties, with an IC50 of 0.470 mg/mL and a minimum inhibitory concentration (MIC) of 2.5 mg/mL. Furthermore, it promotes enhanced cell aggregation, facilitates biofilm formation, and increases the secretion of fungal polysaccharides. These findings indicate that glatiramer acetate not only shows an antifungal effect but also modulates the key virulence factor-the polysaccharide capsule. In summary, repurposing glatiramer acetate as a potential chemotherapy option offers new prospects for combating C. neoformans infection. It addresses the limitations associated with current antifungal therapies by providing an alternative treatment approach.

Anticandidal activity of nanocomposite based on nanochitosan, nanostarch and mycosynthesized copper oxide nanoparticles against multidrug-resistant Candida

Recently, antimicrobial resistance has increased globally particularly Candida infections. Most of antifungal drugs used for treating candidiasis became resistant to most of Candida species. In the current study, a nanocomposite based on mycosynthesized copper oxide nanoparticles (CuONPs), nanostarch, nanochitosan was prepared. Results illustrated that twenty-four Candida isolates were isolated from clinical samples. Furthermore, three Candida strains were selected as the most resistant among others toward commercial antifungal drugs; these selected strains were identified genetically as C. glabrata MTMA 19, C. glabrata MTMA 21 and C. tropicalis MTMA 24. Characterization of the prepared nanocomposite was carried out using physiochemical analysis included Ultraviolet-visible spectroscopy (Uv-Vis), Fourier-Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), Energy-Dispersive X-ray spectroscopy (EDX) and Transmission Electron Microscopy (TEM). Moreover, the nanocomposite exhibited promising anticandidal activity against C. glabrata MTMA 19, C. glabrata MTMA 21 and C. tropicalis MTMA 24, where the inhibition zones were 15.3, 27 and 28 mm, respectively. Ultrastructure changes observed in nanocomposite-treated C. tropicalis demonstrated disruption of the cell wall which led to cell death. In conclusion, our results confirmed that the novel biosynthesized nanocomposite based on mycosynthesized CuONPs, nanostarch and nanochitosan is a promising anticandidal agent to fight multidrug-resistant Candida.

Azobenzene derivatives with activity against drug-resistant Candida albicans and Candida auris

Increasing resistance against antimycotic drugs challenges anti-infective therapies today and contributes to the mortality of infections by drug-resistant Candida species and strains. Therefore, novel antifungal agents are needed. A promising approach in developing new drugs is using naturally occurring molecules as lead structures. In this work, 4,4'-dihydroxyazobenzene, a compound structurally related to antifungal stilbene derivatives and present in Agaricus xanthodermus (yellow stainer), served as a starting point for the synthesis of five azobenzene derivatives. These compounds prevented the growth of both fluconazole-susceptible and fluconazole-resistant Candida albicans and Candida auris strains. Further in vivo studies are required to confirm the potential therapeutic value of these compounds.

Metabolite profiling, antifungal, biofilm formation prevention and disruption of mature biofilm activities of Erythrina senegalensis stem bark extract against Candida albicans and Candida glabrata

The antifungal activity of the 70% ethanol stem bark extract of Erythrina senegalensis (ESB) against different strains and drug resistant clinical isolates of Candida albicans and Candida glabrata were evaluated in the study. The effect of ESB on biofilms as well as its activity in combination with fluconazole, nystatin or caspofungin against the Candida strains were also evaluated. We then evaluated the antifungal activity of a microemulsion formulation of ESB against planktonic and biofilms of the Candida species. UPLC-QTOF-MS2 analysis was then undertaken to identify the phytoconstituents of the extract and UPLC fingerprints developed for the routine authentication as part of quality control measures. ESB exerted strong antifungal activities against C. albicans ATCC 10231 and SC5314 strains, and C. glabrata ATCC 2001 strain with minimum inhibitory concentration (MIC) values from 3.91 to 31.25 μg/mL and minimum fungicidal concentrations (MFCs) that ranged from 62.5 to 250 μg/mL. It also exhibited potent antifungal activities (MIC = 4-64 μg/mL) against a collection of C. albicans and C. glabrata clinical isolates that were resistant to either nystatin or azole antifungals. The formulated ESB demonstrated higher antifungal potency against the C. albicans and C. glabrata strains with MIC values of 3.91-31.25 μg/mL which was the same as the MFC values. The extract and its microemulsion formulation were active against biofilms of the strains of the Candida species inhibiting their biofilm formations (SMIC50 = 16-64 μg/mL) and their preformed biofilms (SMIC50 = 128 ->512 μg/mL). ESB also exhibited synergistic antifungal action with fluconazole and nystatin against C. albicans ATCC 10231 and C. glabrata ATCC 2001 strains in the checkerboard assay. Chemical characterization of the extract revealed the presence of phenolic compounds such as flavonoids and their prenylated derivatives, anthracene glycosides and alkaloids. UPLC Fingerprints of the extract was also developed and validated for routine identification and authentication of the stem bark of E. senegalensis. The study findings have demonstrated that the stem bark of E. senegalensis is as a potential source of bioactive compounds that could be developed as novel antifungal agents.

Synergistic Effect of the Combination of Deferoxamine and Fluconazole In Vitro and In Vivo against Fluconazole-Resistant Candida Spp

The opportunistic fungal infections are an increasing threat to humans due to the increasing number of patients with immunodeficiency, in which the most popular fungal pathogen is Candida albicans . Fluconazole (FLC) is the common drug for treating C. albicans infections, but increasing drug resistance has limited its clinical use.

The Risk Factors and Mechanisms of Azole Resistance of Candida tropicalis Blood Isolates in Thailand: A Retrospective Cohort Study

In recent decades, an epidemiological shift has been observed from Candida infections to non-albicans species and resistance to azoles. We investigated the associated factors and molecular mechanisms of azole-resistant blood isolates of C. tropicalis. Full-length sequencing of the ERG11 gene and quantitative real-time RT-PCR for the ERG11, MDR1, and CDR1 genes were performed. Male sex (odds ratio, 0.38), leukemia (odds ratio 3.15), and recent administration of azole (odds ratio 10.56) were associated with isolates resistant to azole. ERG11 mutations were found in 83% of resistant isolates, with A395T as the most common mutation (53%). There were no statistically significant differences in the expression of the ERG11, MDR1, and CDR1 genes between the groups resistant and susceptible to azole. The prevalence of azole-resistant isolates was higher than the usage of antifungal drugs, suggesting the possibility of environmental transmission in the healthcare setting. The unknown mechanism of the other 17% of the resistant isolates remains to be further investigated.

A New Variant of Mutational and Polymorphic Signatures in the ERG11 Gene of Fluconazole-Resistant Candida albicans

Background

Resistance to antifungal drugs for treating Candida infections remains a major concern globally despite the range of medications available. Most of these drugs target key proteins essential to the life cycle of the organism. An enzyme essential for fungal cell membrane integrity, lanosterol 14–α demethylase (CYP51), is encoded by the ERG11 gene in Candida species. This enzyme is the target of azole–based drugs. The organism has, however, devised molecular adaptations to evade the activity of these drugs.

Materials and Methods

Classical methods were employed to characterize clinical isolates sampled from women and dogs of reproductive age. For fluconazole efficacy studies, CLSI guidelines on drug susceptibility testing were used. To understand the susceptibility pattern, various molecular and structural analytic approaches, including sequencing, in silico site-directed mutagenesis, and protein-ligand profiling, were applied to the ERG11 gene and CYP51 protein sequences. Several platforms, comprising Clustal Omega, Pymol plugin manager, Pymol molecular visualizer, Chimera–curated Dynameomics rotamer library, protein–ligand interaction profiler, Charmm36 force field, GROMACS, Geneious, and Mega7, were employed for this analysis.

Results

The following Candida species distribution was obtained: 37.84% C. albicans, 8.12% C. glabrata, 10.81% C. krusei, 5.41% C. tropicalis, and 37.84% of other unidentified Candida species. Two codons in the nucleotide sequence of the wild-type (CTC and CCA) coding for LEU–370 and PRO–375, respectively, were mutated to L370S and P375H in the resistant strain. The mutation stabilized the protein at the expense of the heme moiety. We found that the susceptible isolate from dogs (Can–iso–029/dog) is closely related to the most resistant isolate from humans.

Conclusion

Taken together, our results showed new mutations in the heme-binding pocket of caCYP51 that explain the resistance to fluconazole exhibited by the Candida isolates. So far, the L370S and P375H resistance-linked mutations have not been previously reported.

Genomic Variation-Mediating Fluconazole Resistance in Yeast

Fungal infections pose a serious and growing threat to public health. These infections can be treated with antifungal drugs by killing hazardous fungi in the body. However, the resistance can develop over time when fungi are exposed to antifungal drugs by generating genomic variations, including mutation, aneuploidy, and loss of heterozygosity. The variations could reduce the binding affinity of a drug to its target or block the pathway through which drugs exert their activity. Here, we review genomic variation-mediating fluconazole resistance in the yeast Candida, with the hope of highlighting the functional consequences of genomic variations for the antifungal resistance.

Antifungal Exposure and Resistance Development: Defining Minimal Selective Antifungal Concentrations and Testing Methodologies

This scoping review aims to summarise the current understanding of selection for antifungal resistance (AFR) and to compare and contrast this with selection for antibacterial resistance, which has received more research attention. AFR is an emerging global threat to human health, associated with high mortality rates, absence of effective surveillance systems and with few alternative treatment options available. Clinical AFR is well documented, with additional settings increasingly being recognised to play a role in the evolution and spread of AFR. The environment, for example, harbours diverse fungal communities that are regularly exposed to antifungal micropollutants, potentially increasing AFR selection risk. The direct application of effect concentrations of azole fungicides to agricultural crops and the incomplete removal of pharmaceutical antifungals in wastewater treatment systems are of particular concern. Currently, environmental risk assessment (ERA) guidelines do not require assessment of antifungal agents in terms of their ability to drive AFR development, and there are no established experimental tools to determine antifungal selective concentrations. Without data to interpret the selective risk of antifungals, our ability to effectively inform safe environmental thresholds is severely limited. In this review, potential methods to generate antifungal selective concentration data are proposed, informed by approaches used to determine antibacterial minimal selective concentrations. Such data can be considered in the development of regulatory guidelines that aim to reduce selection for AFR.

Genome plasticity in Candida albicans: A cutting-edge strategy for evolution, adaptation, and survival

Candida albicans is the most implicated fungal species that grows as a commensal or opportunistic pathogen in the human host. It is associated with many life-threatening infections, especially in immunocompromised persons. The genome of Candida albicans is very flexible and can withstand a wide assortment of variations in a continuously changing environment. Thus, genome plasticity is central to its adaptation and has long been of considerable interest. C. albicans has a diploid heterozygous genome that is highly dynamic and can display variation from small to large scale chromosomal rearrangement and aneuploidy, which have implications in drug resistance, virulence, and pathogenicity. This review presents an up-to-date overview of recent genomic studies involving C. albicans. It discusses the accumulating evidence that shows how mitotic recombination events, ploidy dynamics, aneuploidy, and loss of heterozygosity (LOH) influence evolution, adaptation, and survival in C. albicans. Understanding the factors that affect the genome is crucial for a proper understanding of species and rapid development and adjustment of therapeutic strategies to mitigate their spread.

Activity of poly(methacrylic acid)-silver nanoparticles (PMAA-AgNPs) on fluconazole resistant Candida albicans strains: synergistic and cytotoxic effects

AIMS

To synthesize and evaluate the antifungal activity of poly(methacrylic acid)-silver nanoparticles (PMAA-AgNPs) against nine Candida albicans isolated from clinical specimens.

METHODS AND RESULTS

The effects of PMAA-AgNPs-fluconazole combination was analyzed by checkerboard methodology. The synergistic potential of PMAA-AgNPs-fluconazole was determined by the fractional inhibitory concentration index (FICI). The inhibition of germ tube formation and the determination of PMAA-AgNPs cytotoxicity were also performed. All C. albicans strains were susceptible to PMAA-AgNPs and resistant to fluconazole. PMAA-AgNPs at sub-inhibitory concentrations restored the susceptibility of resistant C. albicans to fluconazole, whose FICI ranged from 0.3 to 0.5. The synergistic interaction of the combination was observed in eight of nine strains. The PMAA-AgNPs-fluconazole combination was also able to inhibit the germ tube formation. PMAA-AgNPs showed a dose-dependent decrease on viability for cells tested, with 50% cytotoxic concentration (CC₅₀ ) values of 6.5, 4.9 and 6.8 μg ml^-1 for macrophages, fibroblasts and Vero cells, respectively.

CONCLUSIONS

This study demonstrated that in general, PMAA-AgNPs acts synergistically in combination with fluconazole, inhibiting fluconazole-resistant C. albicans strains. PMAA-AgNPs-fluconazole combination was also able to inhibit germ tube formation, an important virulence factor. Inhibitory effect of PMAA-AgNPs alone or in combination was higher in C. albicans than in mammalian cells.

SIGNIFICANCE AND IMPACT OF STUDY

This study shows the potential of poly(methacrylic acid)-silver nanoparticles combined with fluconazole to inhibit fluconazole-resistant Candida albicans strains.

The population genetics of adaptation through copy‐number variation in a fungal plant pathogen

Microbial pathogens can adapt rapidly to changing environments such as the application of pesticides or host resistance. Copy number variations (CNVs) are a major source of adaptive genetic variation for recent adaptation. Here, we analyse how a major fungal pathogen of barley, Rhynchosporium commune, has adapted to the host environment and fungicide applications. We screen the genomes of 125 isolates sampled across a worldwide set of populations and identify a total of 7,879 gene duplications and 116 gene deletions. Most gene duplications result from segmental chromosomal duplications. Although CNVs are generally under negative selection, we find that genes affected by CNVs are enriched in functions related to host exploitation (i.e., effectors and cell-wall-degrading enzymes). We perform genome-wide association studies (GWAS) and identify a large segmental duplication of CYP51A that has contributed to the emergence of azole resistance and a duplication encompassing an effector gene affecting virulence. We show that the adaptive CNVs were probably created by recently active transposable element families. Moreover, we find that specific transposable element families are important drivers of recent gene CNV. Finally, we use a genome-wide single nucleotide polymorphism data set to replicate the GWAS and contrast it with the CNV-focused analysis. Together, our findings show how extensive segmental duplications create the raw material for recent adaptation in global populations of a fungal pathogen.

Structure-Guided Discovery of the Novel Covalent Allosteric Site and Covalent Inhibitors of Fructose-1,6-Bisphosphate Aldolase to Overcome the Azole Resistance of Candidiasis

Fructose-1,6-bisphosphate aldolase (FBA) represents an attractive new antifungal target. Here, we employed a structure-based optimization strategy to discover a novel covalent binding site (C292 site) and the first-in-class covalent allosteric inhibitors of FBA from Candida albicans (CaFBA). Site-directed mutagenesis, liquid chromatography-mass spectrometry, and the crystallographic structures of APO-CaFBA, CaFBA-G3P, and C157S-2a4 revealed that S268 is an essential pharmacophore for the catalytic activity of CaFBA, and L288 is an allosteric regulation switch for CaFBA. Furthermore, most of the CaFBA covalent inhibitors exhibited good inhibitory activity against azole-resistant C. albicans, and compound 2a11 can inhibit the growth of azole-resistant strains 103 with the MIC₈₀ of 1 μg/mL. Collectively, this work identifies a new covalent allosteric site of CaFBA and discovers the first generation of covalent inhibitors for fungal FBA with potent inhibitory activity against resistant fungi, establishing a structural foundation and providing a promising strategy for the design of potent antifungal drugs.

Hinokitiol chelates intracellular iron to retard fungal growth by disturbing mitochondrial respiration

Introduction

The increasing morbidity of fungal infections and the prevalence of drug resistance highlighted the discovery of novel antifungal agents and investigation of their modes of action. Iron chelators have been used to treat superficial fungal infections or potentiate the efficacy of certain antifungal drugs. Hinokitiol exhibits potent antifungal activity and iron-chelating ability. However, their relationships have not been established.

Objectives

This study aims to explore the selectivity of hinokitiol against fungal cells and mammalian cells and determine the role of iron-chelating for the antifungal activity of hinokitiol.

Methods

Iron probe FeRhonox-1 was used to determine intracellular Fe²⁺ content. 5-Cyano-2,3-ditolyl tetrazolium chloride probe and Cell Counting Kit-8 were used to detect the mitochondrial respiratory activities. Quantitative real-time PCR and rescue experiments were performed to determine the effect of iron on the antifungal activity of hinokitiol. The effects of hinokitiol on fungal mitochondria were further evaluated using reactive oxygen species probes and several commercial Assay Kits. The ability of hinokitiol to induce resistance in Candida species was carried out using a serial passage method. The in vivo therapeutic effect of hinokitiol was evaluated using Galleria mellonella as an infectious model.

Results

Hinokitiol was effective against a panel of Candida strains with multiple azole-resistant mechanisms and persistently inhibited Candida albicans growth. Mechanism investigations revealed that hinokitiol chelated fungal intracellular iron and inhibited the respiration of fungal cells but had minor effects on mammalian cells. Hinokitiol further inhibited the activities of mitochondrial respiratory chain complexes I and II and reduced mitochondrial membrane potential, thereby decreasing intracellular ATP synthesis and increasing detrimental intracellular reductive stress. Moreover, hinokitiol exhibited low potential for inducing resistance in several Candida species and greatly improved the survival of Candida-infected Galleria mellonella.

Conclusions

These findings suggested the potential application of hinokitiol as an iron chelator to treat fungal infections.

Lysinibacillus Isolate MK212927: A Natural Producer of Allylamine Antifungal ‘Terbinafine’

Resistance to antifungal agents represents a major clinical challenge, leading to high morbidity and mortality rates, especially in immunocompromised patients. In this study, we screened soil bacterial isolates for the capability of producing metabolites with antifungal activities via the cross-streak and agar cup-plate methods. One isolate, coded S6, showed observable antifungal activity against Candida (C.) albicans ATCC 10231 and Aspergillus (A.) niger clinical isolate. This strain was identified using a combined approach of phenotypic and molecular techniques as Lysinibacillus sp. MK212927. The purified metabolite displayed fungicidal activity, reserved its activity in a relatively wide range of temperatures (up to 60 °C) and pH values (6–7.8) and was stable in the presence of various enzymes and detergents. As compared to fluconazole, miconazole and Lamisil, the minimum inhibitory concentration of the metabolite that showed 90% inhibition of the growth (MIC₉₀) was equivalent to that of Lamisil, half of miconazole and one fourth of fluconazole. Using different spectroscopic techniques such as FTIR, UV spectroscopy, 1D NMR and 2D NMR techniques, the purified metabolite was identified as terbinafine, an allylamine antifungal agent. It is deemed necessary to note that this is the first report of terbinafine production by Lysinibacillus sp. MK212927, a fast-growing microbial source, with relatively high yield and that is subject to potential optimization for industrial production capabilities.

Antimicrobial Photodynamic Therapy: Latest Developments with a Focus on Combinatory Strategies

Antimicrobial photodynamic therapy (aPDT) has become a fundamental tool in modern therapeutics, notably due to the expanding versatility of photosensitizers (PSs) and the numerous possibilities to combine aPDT with other antimicrobial treatments to combat localized infections. After revisiting the basic principles of aPDT, this review first highlights the current state of the art of curative or preventive aPDT applications with relevant clinical trials. In addition, the most recent developments in photochemistry and photophysics as well as advanced carrier systems in the context of aPDT are provided, with a focus on the latest generations of efficient and versatile PSs and the progress towards hybrid-multicomponent systems. In particular, deeper insight into combinatory aPDT approaches is afforded, involving non-radiative or other light-based modalities. Selected aPDT perspectives are outlined, pointing out new strategies to target and treat microorganisms. Finally, the review works out the evolution of the conceptually simple PDT methodology towards a much more sophisticated, integrated, and innovative technology as an important element of potent antimicrobial strategies.

Activity of Compound Agrimony Enteritis Capsules against invasive candidiasis: Exploring the differences between traditional Chinese medicine prescriptions and its main components in the treatment of diseases

ETHNOPHARMACOLOGICAL RELEVANCE

Compound Agrimony Enteritis Capsules (FFXHC) is an ethnomedicine derived from Yi Nationality Herbal Medicine for the treatment of enteritis. We found that compared to berberine hydrochloride (BBR), a component of this medicine, FFXHC was more efficacious in the mouse model of IC mice in significantly alleviating lung and intestinal lesions. " Our study provides a novel perspective into the pharmacological mechanism of action of the ethnic compound FFXHC.

AIM OF THE STUDY

To determine the underlying mechanism of the superiority of FFXHC over BBR in IC.

MATERIALS AND METHODS

The susceptibility of Candida albicans to FFXHC was evaluated in vitro. The mouse model of IC was established and the survival rate, weight change, the number of organ colonies, and immune organ coefficient of the mice were determined, the effect of FFXHC on the immune function of mice, including changes in the number of immune cells, levels of the related inflammatory cytokines (INF-γ, TNF-α, MCP-1, IL-6, and IL-17A), and the antimicrobial peptide, LL-37 (CRAMP in mice), were determined. Mice feces were collected and changes in the intestinal microecology were studied.

RESULTS

Our findings indicated that FFXHC was not active against Candida albicans and did not restore the sensitivity of the resistant strain in vitro; however, it had a therapeutic effect that improve survival rate on mice with IC. The number of lymphocytes and neutrophils of mice with IC treated with FFXHC increased significantly. The intestinal microecology of mice was restored and the abundance of the probiotic Bacteroides was increased, which further stimulated the production of the antimicrobial peptide, LL-37, which is required for acquired immunity. Furthermore, the levels of Th cell-related cytokines, including INF-γ, TNF-α, and IL-17A were significantly increased, whereas those of the proinflammatory cytokines, IL-6 and MCP-1, decreased. With the activation of acquired immunity, the immune function of mice was restored, the body weight and survival rate of mice improved considerably, the coefficients of the thymus and spleen increased, and the number of fungal colonies in the lung and kidney decreased.

CONCLUSIONS

FFXHC could eliminate fungi by increasing the relative abundance of probiotics in Bacteroides and the number of neutrophils, thereby promoting the production of CRAMP and resulting in a fungicidal effect, leading to acquired immunity. Although BBR has an antifungal effect, we found that it was not as effective as FFXHC.

8-hydroxyquinoline-5-(N-4-chlorophenyl) sulfonamide and fluconazole combination as a preventive strategy for Candida biofilm in haemodialysis devices

Introduction. The presence of Candida biofilms in medical devices is a concerning and important clinical issue for haemodialysis patients who require constant use of prosthetic fistulae and catheters.Hypothesis/Gap Statement. This prolonged use increases the risk of candidaemia due to biofilm formation. PH151 and clioquinol are 8-hydroxyquinoline derivatives that have been studied by our group and showed interesting anti-Candida activity.Aim. This study evaluated the biofilm formation capacity of Candida species on polytetrafluoroethylene (PTFE) and polyurethane (PUR) and investigated the synergistic effects between the compounds PH151 and clioquinol and fluconazole, amphotericin B and caspofungin against biofilm cells removed from those materials. Further, the synergistic combination was evaluated in terms of preventing biofilm formation on PTFE and PUR discs.Methodology. Susceptibility testing was performed for planktonic and biofilm cells using the broth microdilution method. The checkerboard method and the time-kill assay were used to evaluate the interactions between antifungal agents. Antibiofilm activity on PTFE and PUR materials was assessed to quantify the prevention of biofilm formation.Results. Candida albicans, Candida glabrata and Candida tropicalis showed ability to form biofilms on both materials. By contrast, Candida parapsilosis did not demonstrate this ability. Synergistic interaction was observed when PH151 was combined with fluconazole in 77.8 % of isolates and this treatment was shown to be concentration- and time-dependent. On the other hand, indifferent interactions were predominantly observed with the other combinations. A reduction in biofilm formation on PUR material of more than 50 % was observed when using PH151 combined with fluconazole.Conclusion. PH151 demonstrated potential as a local treatment for use in a combination therapy approach against Candida biofilm formation on haemodialysis devices.

Systematic truncations of chromosome 4 and their responses to antifungals in Candida albicans

BACKGROUND

Candida albicans is an opportunistic human fungal pathogen responsible for superficial and systemic life-threatening infections. Treating these infections is challenging as many clinical isolates show increased drug resistance to antifungals. Chromosome (Chr) 4 monosomy was implicated in a fluconazole-resistant mutant. However, exposure to fluconazole adversely affects Candida cells and can generate numerous mutations. Hence, the present study aimed to truncate Chr4 and challenge the generated Candida strains to antifungals and evaluate their role in drug response.

RESULTS

Herein, Chr4 was truncated in C. albicans using the telomere-mediated chromosomal truncation method. The resulting eight Candida strains carrying one truncated homolog of Chr4 were tested for response to multiple antifungals. The minimal inhibitory concentration (MIC) for these strains was determined against three classes of antifungals. The MIC values against fluconazole, amphotericin B, and caspofungin were closer to that of the wild type strain. Microdilution assay against fluconazole showed that the mutants and wild type strains had similar sensitivity to fluconazole. The disc diffusion assay against five azoles and two polyenes revealed that the zones of inhibition for all the eight strains were similar to those of the wild type. Thus, none of the generated strains showed any significant resistance to the tested antifungals. However, spot assay exhibited a reasonably high tolerance of a few generated strains with increasing concentrations of fluconazole.

CONCLUSION

This analysis suggested that Chr4 aneuploidy might not underlie drug resistance but rather drug tolerance in Candida albicans.

Chronic recurrent vulvovaginitis is not only due to Candida

BACKGROUND

Recurrent vulvovaginitis is a growing problem that affects millions of women worldwide. In many cases it is treated as vulvovaginal candidiasis, but there is not always microbiological confirmation.

AIMS

To determine the etiology of vulvovaginitis in a group of patients.

METHODS

This is a cross-sectional study in which the data from the medical records of 316 adult patients who consulted for vulvovaginitis were analyzed. Eighty nine percent of the cases had already suffered previous episodes.

RESULTS

The median age was 34 (265 patients were between 16 and 45 years old). Yeasts were isolated in culture from 211 (66.8%) patients, although pseudo-hyphae and yeasts were observed in only 166 samples (52.5%) in the direct microscopic examination. Multiple predisposing factors were found, among which the use of contraceptives or previous antibiotics stand out. Most of the patients (almost 90%) had been treated with antifungals, with or without microbiological confirmation. Candida albicans was isolated in 187 (88.6%) patients, followed by Candida glabrata in 6 (2.8%) patients. Association with bacterial vaginosis was found in 35.1% and with intermediate bacterial microbiota in 33.2% of the cases. A remarkably high proportion of C. albicans isolates resistant to fluconazole (80.1%) and itraconazole (58.8%) was found.

CONCLUSIONS

A microbiological analysis is essential to confirm the diagnosis of vulvovaginal candidiasis, whether simple, complicated, or recurrent. Identifying the isolated yeast species and determining its susceptibility to antifungal agents are particularly important.

Etoposide and Camptothecin Reduce Growth, Viability, the Generation of Petite Mutants, and Recognize the Active Site of DNA Topoisomerase I and II Enzymes in Candida glabrata

Candidemia, one of the most common invasive fungal infections in hospitalized patients, can lead to death and huge financial losses. Candida albicans is the main causative agent of this disorder and Candida glabrata occupies the second or third place, for which new therapeutic alternatives must be found. The objective of the present study was to evaluate the inhibitory effect of etoposide and camptothecin (inhibitors of deoxyribonucleic acid (DNA) topoisomerase) on the C. glabrata CBS138 strain. Etoposide and camptothecin showed better or similar MIC (minimum inhibitory concentration) (5 and 2.5 μg/mL, respectively), with respect to fluconazole (8 μg/mL) and itraconazole (4 μg/mL). They also suppressed colony formation during the 12-h test. On the other hand, petite colonies were less formed by exposing C. glabrata to etoposide or camptothecin (indicating low toxicity), with respect fluconazole and itraconazole. Such colonies are phenotypically observed as limited growth in medium containing a non-fermentable carbon source, and are genotypically characterized by a partial or total loss of mitochondrial DNA (mtDNA) fragments. Using PCR techniques and cell staining with 4',6-diamidino-2-phenylindole (DAPI), loss of mtDNA was detected only in yeast cells treated with fluconazole. Additionally, molecular docking studies with etoposide and camptothecin showed recognition in the active site of the Topo I and II enzymes from C. glabrata. Since etoposide and camptothecin showed good inhibitory activity and low toxicity on C. glabrata; they should certainly be of interest for the treatment of C. glabrata infections and the design and development of new antifungal compounds derived from these drugs.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12088-021-00942-6.

Genetic diversity and molecular epidemiology of Candida albicans from vulvovaginal candidiasis patients

Candida albicans (C. albicans) is a common cause of vulvovaginal candidiasis (VVC). In this paper, the genetic diversity and molecular epidemiology of 173C. albicans strains were investigated by multilocus sequence typing (MLST). A total of 52 diploid sequence types (DSTs) were recognized, and 27 (51.9%) of which have not been reported in the MLST database. Genotyping was performed on the multiple isolates collected from patients with recurrent VVC (RVVC, referring to VVC which attacks more than 4 times in one year) in different acute infectious phases. The results showed that 59.1% (26/44) of the patients suffered a relapse, with DST 79 (65.4%) as the dominant genotype. The etiology of the remaining 40.9% (18/44) of patients was reinfection, and the main genotypes included DST 79 (33.3%), DST 124 (8.6%) and DST 1895 (8.6%). DST 79 (45%) and DST 1395 (7.5%) were the main isolates of VVC patients, while DST 79 (24.1%), DST 727 (6.9%), DST 732 (6.9%) and DST 1867 (6.9%) were the main types of healthy volunteers. The results of the genotypes between RVVC patients and other groups were statistically different. Furthermore, cluster analysis was carried out on 1468 isolates, among which 1337 were downloaded from the MLST database, 130 were divided into 8 Clades in the present study and the remaining one was taken as a singleton. 92.3% isolates from relapse patients, 58.3% isolates from re-infected patients, 77.5% isolates from VVC patients and 51.7% isolates from volunteers were distributed in Clade 1. The analysis of the genotypes of multiple isolates from RVVC patients further demonstrated that point mutation and loss of heterozygosity contributed to the microevolution of C. albicans.

New Approach to Antifungal Activity of Fluconazole Incorporated into the Porous 6-Anhydro-α-l-Galacto-β-d-Galactan Structures Modified with Nanohydroxyapatite for Chronic-Wound Treatments-In Vitro Evaluation

New fluconazole-loaded, 6-Anhydro-α-l-Galacto-β-d-Galactan hydrogels incorporated with nanohydroxyapatite were prepared and their physicochemical features (XRD, X-ray Diffraction; SEM-EDS, Scanning Electron Microscopy-Energy Dispersive X-ray Spectroscopy; ATR-FTIR, Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy), fluconazole release profiles and enzymatic degradation were determined. Antifungal activity of pure fluconazole was tested using Candida species (C. albicans, C. tropicalis, C. glabarata), Cryptococcus species (C. neoformans, C. gatti) and Rhodotorula species (R. mucilaginosa, R. rubra) reference strains and clinical isolates. Standard microdilution method was applied, and fluconazole concentrations of 2-250 µg/mL were tested. Moreover, biofilm production ability of tested isolates was tested on the polystyrene surface at 28 and 37 ± 0.5 °C and measured after crystal violet staining. Strains with the highest biofilm production ability were chosen for further analysis. Confocal microscopy photographs were taken after live/dead staining of fungal suspensions incubated with tested hydrogels (with and without fluconazole). Performed analyses confirmed that polymeric hydrogels are excellent drug carriers and, when fluconazole-loaded, they may be applied as the prevention of chronic wounds fungal infection.

Azole-triphenylphosphonium conjugates combat antifungal resistance and alleviate the development of drug-resistance

Azole antifungals are commonly used to treat fungal infections but have resulted in the occurrence of drug resistance. Therefore, developing azole derivatives (AZDs) that can both combat established drug-resistant fungal strains and evade drug resistance is of great importance. In this study, we synthesized a series of AZDs with a fluconazole (FLC) skeleton conjugated with a mitochondria-targeting triphenylphosphonium cation (TPP⁺). These AZDs displayed potent activity against both azole-sensitive and azole-resistant Candida strains without eliciting obvious resistance. Moreover, two representative AZDs, 20 and 25, exerted synergistic antifungal activity with Hsp90 inhibitors against C. albicans strains resistant to the combination treatment of FLC and Hsp90 inhibitors. AZD 25, which had minimal cytotoxicity, was effective in preventing C. albicans biofilm formation. Mechanistic investigation revealed that AZD 25 inhibited the biosynthesis of the fungal membrane component ergosterol and interfered with mitochondrial function. Our findings provide an alternative approach to address fungal resistance problems.

Adaptive Laboratory Evolution of Native Torulaspora delbrueckii YCPUC10 With Enhanced Ethanol Resistance and Evaluation in Co-inoculated Fermentation

Torulaspora delbrueckii is a yeast species typically present in the early stages of the fermentation process. T. delbrueckii positively modifies the aromatic properties of wines. However, its contribution to the final quality of the wine is restricted by its low tolerance to ethanol. T. delbrueckii is capable of fermenting and tolerating an ethanol concentration ranging from 7.4% (v/v) to slightly higher than 9% (v/v). For this reason, it cannot complete fermentation, when alcohol reach levels higher than 12% (v/v), limiting their use in the industry. The objective of this work was to obtain new variants of T. delbrueckii with improved resistance to ethanol through adaptive laboratory evolution. Variants capable of tolerating ethanol levels of 11.5% (v/v) were obtained. These presented improved kinetic parameters, and additionally showed an increase in resistance to SO₂ in ethanol compared to the original strain. Co-inoculated fermentations were performed with the original strain (FTd/Sc) and with the evolved strain (FTdF/Sc), in addition to a control fermentation using only Saccharomyces cerevisiae EC1118 (FSc). The results obtained show that FTdF/Sc present higher levels of 2-Ethylhexanol, compared to FTd/Sc and FSc. Furthermore, FTdF/Sc presents higher levels of total alcohols, total aldehydes, total phenolic derivatives, and total sulfur compounds with significant differences with FSc. These results provide a T. delbrueckii YCPUC10-F yeast with higher resistance to ethanol, which can be present throughout the fermentation process and be used in co-inoculated fermentations. This would positively impact the performance of T. delbrueckii by allowing it to be present not only in the early stages of fermentation but to remain until the end of fermentation.

Identification and Characterization of Mediators of Fluconazole Tolerance in Candida albicans

Candida albicans is an important human pathogen and a major concern in intensive care units around the world. C. albicans infections are associated with a high mortality despite the use of antifungal treatments. One of the causes of therapeutic failures is the acquisition of antifungal resistance by mutations in the C. albicans genome. Fluconazole (FLC) is one of the most widely used antifungal and mechanisms of FLC resistance occurring by mutations have been extensively investigated. However, some clinical isolates are known to be able to survive at high FLC concentrations without acquiring resistance mutations, a phenotype known as tolerance. Mechanisms behind FLC tolerance are not well studied, mainly due to the lack of a proper way to identify and quantify tolerance in clinical isolates. We proposed here culture conditions to investigate FLC tolerance as well as an easy and efficient method to identity and quantify tolerance to FLC. The screening of C. albicans strain collections revealed that FLC tolerance is pH- and strain-dependent, suggesting the involvement of multiple mechanisms. Here, we addressed the identification of FLC tolerance mediators in C. albicans by an overexpression strategy focusing on 572 C. albicans genes. This strategy led to the identification of two transcription factors, CRZ1 and GZF3. CRZ1 is a C2H2-type transcription factor that is part of the calcineurin-dependent pathway in C. albicans, while GZF3 is a GATA-type transcription factor of unknown function in C. albicans. Overexpression of each gene resulted in an increase of FLC tolerance, however, only the deletion of CRZ1 in clinical FLC-tolerant strains consistently decreased their FLC tolerance. Transcription profiling of clinical isolates with variable levels of FLC tolerance confirmed a calcineurin-dependent signature in these isolates when exposed to FLC.

Genotype, biofilm formation ability and specific gene transcripts characteristics of endodontic Enterococcus faecalis under glucose deprivation condition

OBJECTIVE

To study the relationship between the specific gene and biofilm formation ability of seven wild type Enterococcus faecalis (E. faecalis) under glucose deprivation conditions.

DESIGN

Wild type E. faecalis (3RC, 5RC, 25RC, 31RC, 33RC, 37RC, 58RC) extracted from the teeth with persistent apical periodontitis were cultured under glucose deprivation conditions and then resequenced. The biofilm formation ability was compared using primary adherence assay, confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM). The transcriptional level of biofilm formation-related genes (ace, gelE, efa, esp and fsrB) were detected.

RESULTS

Genomic resequencing showed that 3RC and 58RC (Class B) were similar, while 5RC, 25RC, 31RC, 33RC and 37RC (Class A) were similar. Based on primary adherence assay, CLSM and SEM results, biofilm formation ability of Class B strains was lower, while Class A strains were higher when compared with control group (0.25 % glucose). Furthermore, compared with control group (0.25 % glucose), the transcriptional levels of ace, efa and fsrB genes were upregulated in all strains; the transcriptional levels of gelE were downregulated in Class B strains, upregulated in Class A strains; the transcriptional levels of esp of Class B strains were downregulated, while upregulated in 25RC, 31RC and 37RC (Class A), and not observed in 5RC and 33RC.

CONCLUSION

The genotypes of wild type E. faecalis of different persistent periapical periodontitis teeth are different. The genotype differences and the transcription levels of related virulence genes (ace, gelE, efa, esp and fsrB) are related to the biological phenotype.

Differentially Regulated Transcription Factors and ABC Transporters in a Mitochondrial Dynamics Mutant Can Alter Azole Susceptibility of Aspergillus fumigatus

Azole resistance of the fungal pathogen Aspergillus fumigatus is an emerging problem. To identify novel mechanisms that could mediate azole resistance in A. fumigatus, we analyzed the transcriptome of a mitochondrial fission/fusion mutant that exhibits increased azole tolerance. Approximately 12% of the annotated genes are differentially regulated in this strain. This comprises upregulation of Cyp51A, the azole target structure, upregulation of ATP-binding cassette (ABC) superfamily and major facilitator superfamily (MFS) transporters and differential regulation of transcription factors. To study their impact on azole tolerance, conditional mutants were constructed of seven ABC transporters and 17 transcription factors. Under repressed conditions, growth rates and azole susceptibility of the mutants were similar to wild type. Under induced conditions, several transcription factor mutants showed growth phenotypes. In addition, four ABC transporter mutants and seven transcription factor mutants exhibited altered azole susceptibility. However, deletion of individual identified ABC transporters and transcription factors did not affect the increased azole tolerance of the fission/fusion mutant. Our results revealed the ability of multiple ABC transporters and transcription factors to modulate the azole susceptibility of A. fumigatus and support a model where mitochondrial dysfunctions trigger a drug resistance network that mediates azole tolerance of this mold.

A Zinc Cluster Transcription Factor Contributes to the Intrinsic Fluconazole Resistance of Candida auris

Candida auris is a recently emerged pathogenic yeast that within a few years after its initial description has spread all over the globe. C. auris is a major concern for human health, because it can cause life-threatening systemic infections, is easily transmissible, and is difficult to eradicate from hospital environments. Furthermore, C. auris is highly drug resistant, especially against the widely used antifungal drug fluconazole. Mutations in the drug target and high activity of efflux pumps are associated with azole resistance, but it is not known how drug resistance genes are regulated in C. auris. We have investigated the potential role of several candidate transcriptional regulators in the intrinsic fluconazole resistance of C. auris and identified a transcription factor that contributes to the high resistance to fluconazole and voriconazole of two C. auris strains from different genetic clades, thereby providing insight into the molecular basis of drug resistance of this medically important yeast.

The recently emerged pathogenic yeast Candida auris is a major concern for human health, because it is easily transmissible, difficult to eradicate from hospitals, and highly drug resistant. Most C. auris isolates are resistant to the widely used antifungal drug fluconazole due to mutations in the target enzyme Erg11 and high activity of efflux pumps, such as Cdr1. In the well-studied, distantly related yeast Candida albicans, overexpression of drug efflux pumps also is a major mechanism of acquired fluconazole resistance and caused by gain-of-function mutations in the zinc cluster transcription factors Mrr1 and Tac1. In this study, we investigated a possible involvement of related transcription factors in efflux pump expression and fluconazole resistance of C. auris. The C. auris genome contains three genes encoding Mrr1 homologs and two genes encoding Tac1 homologs, and we generated deletion mutants lacking these genes in two fluconazole-resistant strains from clade III and clade IV. Deletion of TAC1b decreased the resistance to fluconazole and voriconazole in both strain backgrounds, demonstrating that the encoded transcription factor contributes to azole resistance in C. auris strains from different clades. CDR1 expression was not or only minimally affected in the mutants, indicating that Tac1b can confer increased azole resistance by a CDR1-independent mechanism.

IMPORTANCECandida auris is a recently emerged pathogenic yeast that within a few years after its initial description has spread all over the globe. C. auris is a major concern for human health, because it can cause life-threatening systemic infections, is easily transmissible, and is difficult to eradicate from hospital environments. Furthermore, C. auris is highly drug resistant, especially against the widely used antifungal drug fluconazole. Mutations in the drug target and high activity of efflux pumps are associated with azole resistance, but it is not known how drug resistance genes are regulated in C. auris. We have investigated the potential role of several candidate transcriptional regulators in the intrinsic fluconazole resistance of C. auris and identified a transcription factor that contributes to the high resistance to fluconazole and voriconazole of two C. auris strains from different genetic clades, thereby providing insight into the molecular basis of drug resistance of this medically important yeast.

Dispiropyrrolidine tethered piperidone heterocyclic hybrids with broad-spectrum antifungal activity against Candida albicans and Cryptococcus neoformans

Invasive fungal infections along with rising incidence of resistance to antifungal drugs pose increasing threat to immunocompromised individuals, including cancer patients. In this study, we examined the antifungal activity of dispiropyrrolidine tethered piperidone heterocyclic hybrids. Results indicate that compounds 5a and 6i have demonstrated a potent antifungal effect on multiple fungal strains, including Candida albicans, without exhibiting cytotoxicity to mammalian cells. Furthermore, these two compounds exhibited significant inhibition on Candida albicans hyphae and biofilm development that surpasses the FDA-approved antifungal drug currently used for treatment. Taken together, our results suggest that 5a and 6i are promising candidates for development into new antifungal drugs.

Lipid composition and cell surface hydrophobicity of Candida albicans influence the efficacy of fluconazole-gentamicin treatment

Adherence of the fungus, Candida albicans, to biotic (e.g. human tissues) and abiotic (e.g. catheters) surfaces can lead to emergence of opportunistic infections in humans. The process of adhesion and further biofilm development depends, in part, on cell surface hydrophobicity (CSH). In this study, we compared the resistance of C. albicans strains with different CSH to the most commonly prescribed antifungal drug, fluconazole, and the newly described synergistic combination, fluconazole and gentamicin. The hydrophobic strain was more resistant to fluconazole due to, among others, overexpression of the ERG11 gene encoding the fluconazole target protein (CYP51A1, Erg11p), which leads to overproduction of ergosterol in this strain. Additionally, the hydrophobic strain displayed high efflux activity of the multidrug resistance Cdr1 pump due to high expression of the CDR1 gene. On the other hand, the hydrophobic C. albicans strain was more susceptible to fluconazole-gentamicin combination because of its different effect on lipid content in the two strains. The combination resulted in ergosterol depletion with subsequent Cdr1p mislocalization and loss of activity in the hydrophobic strain. We propose that C. albicans strains with different CSH may possess altered lipid metabolism and consequently may differ in their response to treatment.

The Impact of Gene Dosage and Heterozygosity on The Diploid Pathobiont Candida albicans

Candida albicans is a fungal species that can colonize multiple niches in the human host where it can grow either as a commensal or as an opportunistic pathogen. The genome of C. albicans has long been of considerable interest, given that it is highly plastic and can undergo a wide variety of alterations. These changes play a fundamental role in determining C. albicans traits and have been shown to enable adaptation both to the host and to antifungal drugs. C. albicans isolates contain a heterozygous diploid genome that displays variation from the level of single nucleotides to largescale rearrangements and aneuploidy. The heterozygous nature of the genome is now increasingly recognized as being central to C. albicans biology, as the relative fitness of isolates has been shown to correlate with higher levels of overall heterozygosity. Moreover, loss of heterozygosity (LOH) events can arise frequently, either at single polymorphisms or at a chromosomal level, and both can alter the behavior of C. albicans cells during infection or can modulate drug resistance. In this review, we examine genome plasticity in this pathobiont focusing on how gene dosage variation and loss of heterozygosity events can arise and how these modulate C. albicans behavior.

The Magnitude of Candida albicans Stress-Induced Genome Instability Results from an Interaction Between Ploidy and Antifungal Drugs

Organismal ploidy and environmental stress impact the rates and types of mutational events. The opportunistic fungal pathogen Candida albicans, serves as a clinically relevant model for studying the interaction between eukaryotic ploidy and drug-induced mutagenesis. In this study, we compared the rates and types of genome perturbations in diploid and tetraploid C. albicans following exposure to two different classes of antifungal drugs; azoles and echinocandins. We measured mutations at three different scales: point mutation, loss-of-heterozygosity (LOH), and total DNA content for cells exposed to fluconazole and caspofungin. We found that caspofungin induced higher mutation rates than fluconazole, although this is likely an indirect consequence of stress-associated cell wall perturbations, rather than an inherent genotoxicity. Surprisingly, we found that antifungal drugs disproportionately elevated genome and ploidy instability in tetraploid C. albicans compared to diploids. Taken together, our results suggest that the magnitude of stress-induced mutagenesis results from an interaction between ploidy and antifungal drugs. These findings have both clinical and evolutionary implications for how fungal pathogens generate mutations in response to antifungal drug stress and how these mutations may facilitate the emergence of drug resistance.

Antifungal Activity of a Hydroethanolic Extract From Astronium urundeuva Leaves Against Candida albicans and Candida glabrata

We have previously reported on the activity of different extracts from Astronium sp. against Candida albicans, with the hydroethanolic extract prepared from leaves of A. urundeuva, an arboreal species widely distributed in arid environments of South America and often used in folk medicine, displaying the highest in vitro activity. Here we have further evaluated the antifungal activity of this extract against strains of C. albicans and C. glabrata, the two most common etiological agents of candidiasis. The extract was tested alone and loaded into a nanostructured lipid system (10% oil phase, 10% surfactant and 80% aqueous phase, 0.5% Poloxamer 407^®). In vitro susceptibility assays demonstrated the antifungal activity of the free extract and the microemulsion against both Candida species, with increased activity against C. glabrata, including collection strains and clinical isolates displaying different levels of resistance against the most common clinically used antifungal drugs. Checkerboard results showed synergism when the free extract was combined with amphotericin B against C. albicans. Serial passage experiments confirmed development of resistance to fluconazole but not to the free extract upon prolonged exposure. Although preformed biofilms were intrinsically resistant to treatment with the extract, it was able to inhibit biofilm formation by C. albicans at concentrations comparable to those inhibiting planktonic growth. Cytotoxicity assays in different cell lines as well as an alternative model using Artemia salina L. confirmed a good safety profile of the both free and loaded extracts, and an in vivo assay demonstrated the efficacy of the free and loaded extracts when used topically in a rat model of vaginal candidiasis. Overall, these results reveal the promise of the A. urundeuva leaves extract to be further investigated and developed as an antifungal.

Accelerated evolution at chaperone promoters among Antarctic notothenioid fishes

BACKGROUND

Antarctic fishes of the Notothenioidei suborder constitutively upregulate multiple inducible chaperones, a highly derived adaptation that preserves proteostasis in extreme cold, and represent a system for studying the evolution of gene frontloading. We screened for Hsf1-binding sites, as Hsf1 is a master transcription factor of the heat shock response, and highly-conserved non-coding elements within proximal promoters of chaperone genes across 10 Antarctic notothens, 2 subpolar notothens, and 17 perciform fishes. We employed phylogenetic models of molecular evolution to determine whether (i) changes in motifs associated with Hsf1-binding and/or (ii) relaxed purifying selection or exaptation at ancestral cis-regulatory elements coincided with the evolution of chaperone frontloading in Antarctic notothens.

RESULTS

Antarctic notothens exhibited significantly fewer Hsf1-binding sites per bp at chaperone promoters than subpolar notothens and Serranoidei, the most closely-related suborder to Notothenioidei included in this study. 90% of chaperone promoters exhibited accelerated substitution rates among Antarctic notothens relative to other perciformes. The proportion of bases undergoing accelerated evolution (i) was significantly greater in Antarctic notothens than in subpolar notothens and Perciformes in 70% of chaperone genes and (ii) increased among bases that were more conserved among perciformes. Lastly, we detected evidence of relaxed purifying selection and exaptation acting on ancestrally conserved cis-regulatory elements in the Antarctic notothen lineage and its major branches.

CONCLUSION

A large degree of turnover has occurred in Notothenioidei at chaperone promoter regions that are conserved among perciform fishes following adaptation to the cooling of the Southern Ocean. Additionally, derived reductions in Hsf1-binding site frequency suggest cis-regulatory modifications to the classical heat shock response. Of note, turnover events within chaperone promoters were less frequent in the ancestral node of Antarctic notothens relative to younger Antarctic lineages. This suggests that cis-regulatory divergence at chaperone promoters may be greater between Antarctic notothen lineages than between subpolar and Antarctic clades. These findings demonstrate that strong selective forces have acted upon cis-regulatory elements of chaperone genes among Antarctic notothens.

Two New 1,3,4-Oxadiazoles With Effective Antifungal Activity Against Candida albicans

Candida infections have become a serious public health problem with high mortality rates, especially in immunocompromised patients, since Candida albicans is the major opportunistic pathogen responsible for systemic or invasive candidiasis. Commercially available antifungal agents are restricted and fungal resistance to such drugs has increased; therefore, the development of a more specific antifungal agent is necessary. Using assays for antifungal activity, here we report that two new compounds of 1,3,4-oxadiazoles class (LMM5 and LMM11), which were discovered by in silico methodologies as possible thioredoxin reductase inhibitors, were effective against C. albicans. Both compounds had in vitro antifungal activity with MIC 32 μg/ml. Cytotoxicity in vitro demonstrated that LMM5 and LMM11 were non-toxic in the cell lines evaluated. The kinetic of the time-kill curve suggested a fungistatic profile and showed an inhibitory effect of LMM5 and LMM11 in 12 h that remained for 24 and 36 h, which is better than fluconazole. In the murine systemic candidiasis model by C. albicans, the two compounds significantly reduced the renal and spleen fungal burden. According to the SEM and TEM images, we hypothesize that the mechanism of action of LMM5 and LMM11 is directly related to the inhibition of the enzyme thioredoxin reductase and internally affect the fungal cell. In view of all in vitro and in vivo results, LMM5 and LMM11 are effective therapeutic candidates for the development of new antifungal drugs addressing the treatment of human infections caused by C. albicans.

The small GTPase Rhb1 is involved in the cell response to fluconazole in Candida albicans

Candida albicans is an important fungal pathogen in humans. Rhb1 is a small GTPase of the Ras superfamily and is conserved from yeasts to humans. In C. albicans, Rhb1 regulates the expression of secreted protease 2, low nitrogen-mediated morphogenesis, and biofilm formation. Moreover, our previous studies have indicated that Rhb1 is associated with the target of rapamycin (TOR) signaling pathway. In this study, we further explored the relationship between Rhb1 and drug susceptibility. The RHB1 deletion mutant exhibited reduced fluconazole susceptibility, and this phenotype occurred mainly through the increased gene expression and activity of efflux pumps. In addition, Mrr1 and Tac1 are transcription factors that can activate efflux pump gene expression. However, the RHB1 deletion, RHB1/MRR1 and RHB1/TAC1 double deletion mutants had no significant differences in efflux pump gene expression and fluconazole susceptibility, suggesting that Rhb1-regulated efflux pump genes do not act through Mrr1 and Tac1. We also showed that membrane localization is crucial for Rhb1 activity in response to fluconazole. Finally, Rhb1 was linked not only to the TOR but also to the Mkc1 mitogen-activated protein kinase signaling pathway in response to fluconazole. In sum, this study unveiled a new role of Rhb1 in the regulation of C. albicans drug susceptibility.

Elevation of cell wall chitin via Ca2+ -calcineurin-mediated PKC signaling pathway maintains the viability of Candida albicans in the absence of β-1,6-glucan synthesis

β-1,6-glucan is an important cell wall component of Candida albicans. Deleted mutants of the two β-1,6-glucan synthase genes KRE6 and SKN1 are viable albeit with a range of defects including slow growth. It remains unclear whether β-1,6-glucan synthesis is not required under culture conditions or compensatory mechanisms exist in C. albicans. Here, we report that depleting β-1,6-glucan synthases leads to a significant increase in cell wall chitin levels through the posttranscriptional regulation of the chitin synthase Chs3 which maintains cell viability. And depleting β-1,6-glucan synthases in chs3Δ/Δ cells results in cell death. The elevation of cell wall chitin is mediated by the activation of the PKC signaling pathway and an unknown pathway(s) involving Ca²⁺ -calcineurin. Also, kre6Δ/Δ skn1Δ/Δ cells are not more susceptible to caspofungin, the antifungal drug that inhibits β-1,3-glucan synthases, suggesting that β-1,3-glucan has no role in compensating β-1,6-glucan synthesis. Given the vital importance of elevating chitin synthesis in the absence of β-1,6-glucan synthesis in C. albicans, antifungal drugs targeting β-1,6-glucan and chitin synthesis could be used in combination therapies.

Detection of ERG11 point mutations in Iranian fluconazole-resistant Candida albicans isolates

Background and Purpose

Candidiasis is referred to a group of superficial and deep-tissue fungal infections often caused by Candida albicans. The superficial infections affect the oral, oropharynx, esophagus, and vaginal mucosa. The treatment of choice for these infections is the use of azoles, such as fluconazole. However, the increased use of these antifungal agents has led to the emergence of azole-resistant isolates of C. albicans. Different mechanisms have been suggested for the development of drug resistance, such as mutations in the encoding gene ERG11. Mutations in ERG11 result in changes in the ERG11p spatial construction and reduce the affinity between the protein and azole. This study aimed to determine the susceptibility profile of C. albicans clinical isolates to fluconazole using microdilution method. The present research was also targeted toward the detection of mutations that might be related to fluconazole resistance by the amplification and sequencing of ERG11 gene.

Materials and Methods

This study was conducted on a total of 216 clinical isolates obtained from Mashhad, Isfahan, and Tehran cities in Iran, during 2016-2018. The clinical isolates were identified using molecular techniques. Furthermore, minimum inhibitory concentration (MICs) was determined according to the clinical and laboratory standards institute M27-A3 and M27-S4 documents. The concentration range for fluconazole was obtained as 0.063-64 μg/ml. In the resistant strains, ERG11 genes were amplified by specific primers. Subsequently, cycle sequencing reactions were performed on purified polymerase chain reaction (PCR) products in forward and reverse directions. Finally, the results were analyzed by MEGA (version 7) and Gene Runner software (version 6.5.30).

Results

Out of 216 strains, 100 (46.3%) species were identified as C. albicans. The MIC values for fluconazole had a range of 0.125-16 μg/ml with the MIC50 and MIC90 values of 0.5 and 1 μg/ml, respectively. Totally, 41 nucleotide changes were detected among 4 resistant isolates. In this regard, 4 out of 41 mutations in codons caused changes in ERG11p; however, these mutations did not lead to fluconazole resistance.

Conclusion

Fluconazole resistance among clinical isolates is not merely due to the changes in ERG11p. This resistance may be also related to some other mechanisms, such as the prevention of the intracellular accumulation of the antifungal agent and alteration of the target enzyme to diminish drug binding.

Fungal Lanosterol 14α-demethylase: A target for next-generation antifungal design

The cytochrome P450 enzyme lanosterol 14α-demethylase (LDM) is the target of the azole antifungals used widely in medicine and agriculture as prophylaxis or treatments of infections or diseases caused by fungal pathogens. These drugs and agrochemicals contain an imidazole, triazole or tetrazole substituent, with one of the nitrogens in the azole ring coordinating as the sixth axial ligand to the LDM heme iron. Structural studies show that this membrane bound enzyme contains a relatively rigid ligand binding pocket comprised of a deeply buried heme-containing active site together with a substrate entry channel and putative product exit channel that reach to the membrane. Within the ligand binding pocket the azole antifungals have additional affinity determining interactions with hydrophobic side-chains, the polypeptide backbone and via water-mediated hydrogen bond networks. This review will describe the tools that can be used to identify and characterise the next generation of antifungals targeting LDM, with the goal of obtaining highly potent broad-spectrum fungicides that will be able to avoid target and drug efflux mediated antifungal resistance.

Evolution of Fluconazole-Resistant Candida albicans Strains by Drug-Induced Mating Competence and Parasexual Recombination

Sexual reproduction is an important mechanism in the evolution of species, since it allows the combination of advantageous traits of individual members in a population. The pathogenic yeast Candida albicans is a diploid organism that normally propagates in a clonal fashion, because heterozygosity at the mating type locus (MTL) inhibits mating between cells. Here we show that C. albicans cells that have acquired drug resistance mutations during treatment with the commonly used antifungal agent fluconazole rapidly develop further increased resistance by genome rearrangements that result in simultaneous loss of heterozygosity for the mutated allele and the mating type locus. This enables the drug-resistant cells of a population to switch to the mating-competent opaque morphology and mate with each other to combine different individually acquired resistance mechanisms. The tetraploid mating products reassort their merged genomes and, under selective pressure by the drug, generate highly resistant progeny that have retained the advantageous mutated alleles. Parasexual propagation, promoted by stress-induced genome rearrangements that result in the acquisition of mating competence in cells with adaptive mutations, may therefore be an important mechanism in the evolution of C. albicans populations.

The clonal population structure of Candida albicans suggests that (para)sexual recombination does not play an important role in the lifestyle of this opportunistic fungal pathogen, an assumption that is strengthened by the fact that most C. albicans strains are heterozygous at the mating type locus (MTL) and therefore mating-incompetent. On the other hand, mating might occur within clonal populations and allow the combination of advantageous traits that were acquired by individual cells to adapt to adverse conditions. We have investigated if parasexual recombination may be involved in the evolution of highly drug-resistant strains exhibiting multiple resistance mechanisms against fluconazole, an antifungal drug that is commonly used to treat infections by C. albicans. Growth of strains that were heterozygous for MTL and different fluconazole resistance mutations in the presence of the drug resulted in the emergence of derivatives that had become homozygous for the mutated allele and the mating type locus and exhibited increased drug resistance. When MTLa/a and MTLα/α cells of these strains were mixed in all possible combinations, we could isolate mating products containing the genetic material from both parents. The initial mating products did not exhibit higher drug resistance than their parental strains, but further propagation under selective pressure resulted in the loss of the wild-type alleles and increased fluconazole resistance. Therefore, fluconazole treatment not only selects for resistance mutations but also promotes genomic alterations that confer mating competence, which allows cells in an originally clonal population to exchange individually acquired resistance mechanisms and generate highly drug-resistant progeny.

Dissection of the regulatory role for the N-terminal domain in Candida albicans protein phosphatase Z1

The novel type, fungus specific protein phosphatase Z1 of the opportunistic pathogen, Candida albicans (CaPpz1) has several important physiological roles. It consists of a conserved C-terminal catalytic domain and a variable, intrinsically disordered, N-terminal regulatory domain. To test the function of these domains we modified the structure of CaPpz1 by in vitro mutagenesis. The two main domains were separated, four potential protein binding regions were deleted, and the myristoylation site as well as the active site of the enzyme was crippled by point mutations G2A and R262L, respectively. The in vitro phosphatase activity assay of the bacterially expressed recombinant proteins indicated that the N-terminal domain was inactive, while the C-terminal domain became highly active against myosin light chain substrate. The deletion of the N-terminal 1-16 amino acids and the G2A mutation significantly decreased the specific activity of the enzyme. Complementation of the ppz1 Saccharomyces cerevisiae deletion mutant strain with the different CaPpz1 forms demonstrated that the scission of the main domains, the two point mutations and the N-terminal 1-16 deletion rendered the phosphatase incompetent in the in vivo assays of LiCl tolerance and caffeine sensitivity. Thus our results confirmed the functional role of the N-terminal domain and highlighted the significance of the very N-terminal part of the protein in the regulation of CaPpz1.