Complementary adhesin function in C. albicans biofilm formation

Candida species covered from traditional cheeses: Characterization of C. albicans regarding virulence factors, biofilm formation, caseinase activity, antifungal resistance and phylogeny

This study has provided characterization data (carriage of virulence, antifungal resistance, caseinase activity, biofilm-forming ability and genotyping) of Candida albicans isolates and the occurrence of Candida species in traditional cheeses collected from Kayseri, Türkiye. Phenotypic (E-test, Congo red agar and microtiter plate tests) and molecular tests (identification, virulence factors, biofilm-formation, antifungal susceptibility) were carried out. The phylogenetic relatedness of C. albicans isolates was obtained by constructing the PCA dendrogram from the mass spectra data. Of 102 samples, 13 (12.7%) were found to be contaminated with C. albicans, 15 (14.7%), 10 (9.8%) and five (4.9%) were found to be contaminated with C. krusei, C. lusitane and C. paraplosis, respectively. While seven (16.2%) of 43 Candida spp. isolates were obtained from cheese collected from villages, 36 (83.7%) belonged to cheeses collected from traditional retail stores. The carriage rate of C. albicans isolates belonging to virulence factors HSP90 and PLB1 genes was 30.7%. ALST1, ALST3, BCR, ECE, andHWP (virulence and biofilm-associated) genes were harbored by 30.7%, 23%, 38.4%, 53.8%, and 38.4% of the 13 isolates. According to the microplate test, eight (61.5%) of 13 isolates had strong biofilm production. ERG11 and FKS1 (antifungal resistance genes) were found in 46.1% and 23% of 13 isolates, respectively. Due to missense mutations, K128T, E266D and V488I amino acid changes were detected for some isolates regarding azole resistance. As a result of the E-test, of the 13 isolates, one (7.6%) was resistant to flucytosine, four (30.7%) were resistant to caspofungin, and nine (69.2%) were resistant to fluconazole. The PCA analysis clustered the studied isolates into two major clades. C. albicans isolates of traditional cheese collected from villages were grouped in the same cluster. Among the C. albicans isolates from village cheese, there were those obtained from the same dairy milk at different times. Samples from the same sales points produced at different dairy farms were also contaminated with C. albicans. Concerning food safety standards applied from farm to fork, in order to prevent these pathogenic agents from contaminating cheeses, attention to the hygiene conditions of the sale points, conscious personnel, prevention of cross contamination will greatly reduce public health threats in addition to the application of animal health control, milking hygiene, pasteurization parameters in traditional cheese production.

In Silico and In Vitro Studies to Explore the Effect of Thymoquinone on Isocitrate Lyase, Biofilm Formation, and the Expression of Some Virulence Genes in Candida albicans

Thymoquinone (TQ), a bioactive compound from black cumin (Nigella sativa), has demonstrated a broad range of therapeutic effects. The aim of this study is to evaluate the antifungal efficacy of TQ by targeting key virulence factors in Candida albicans, specifically focusing on isocitrate lyase (ICL) activity, biofilm formation, and gene expression. This study explored TQ's impact on ICL, a decisive enzyme in the glyoxylate cycle, along with its effect on hyphal formation, biofilm development, and the virulent gene expression of C. albicans through in silico and in vitro studies. Molecular docking revealed a binding energy of -6.4 kcal/mol between TQ and ICL, indicating moderate affinity. The stability of the ICL-TQ complex was validated through 50 ns molecular dynamics simulations, showing the root mean square deviation (RMSD) values of 0.35 nm for ICL and 0.38 nm for the complex. In vitro studies further validated these findings, showing a dose-dependent inhibition of ICL activity. TQ at 2 µg/mL reduced enzyme activity by 57%, and at 4 µg/mL, by 91.4%. Additionally, TQ disrupted the yeast-to-hyphae switch, a key virulence factor, with 1 and 2 µg/mL doses significantly inhibiting hyphal formation. The biofilm formation was similarly affected, with a 58% reduction at 2 µg/mL and an 83% reduction at 4 µg/mL. TQ also downregulated the ALS1 and HWP1 genes that are associated with adhesion and biofilm development, demonstrating its broad-spectrum antifungal activity. These findings suggest that TQ is a promising candidate for antifungal therapies, targeting multiple virulence factors in C. albicans and potentially overcoming biofilm-associated drug resistance. Future research should focus on in vivo validation, optimization for clinical applications, and expanding its spectrum against other drug-resistant fungal species.

Functional redundancy in Candida auris cell surface adhesins crucial for cell-cell interaction and aggregation

Candida auris is an emerging nosocomial fungal pathogen associated with life-threatening invasive disease due to its persistent colonization, high level of transmissibility and multi-drug resistance. Aggregative and non-aggregative growth phenotypes for C. auris strains with different biofilm forming abilities, drug susceptibilities and virulence characteristics have been described. Using comprehensive transcriptional analysis we identified key cell surface adhesins that were highly upregulated in the aggregative phenotype during in vitro and in vivo grown biofilms using a mouse model of catheter infection. Phenotypic and functional evaluations of generated null mutants demonstrated crucial roles for the adhesins Als4112 and Scf1 in mediating cell-cell adherence, coaggregation and biofilm formation. While individual mutants were largely non-aggregative, in combination cells were able to co-adhere and aggregate, as directly demonstrated by measuring cell adhesion forces using single-cell atomic force spectroscopy. This co-adherence indicates their role as complementary adhesins, which despite their limited similarity, may function redundantly to promote cell-cell interaction and biofilm formation. Functional diversity of cell wall proteins may be a form of regulation that provides the aggregative phenotype of C. auris with flexibility and rapid adaptation to the environment, potentially impacting persistence and virulence.

Fungal biofilm formation and its regulatory mechanism

Fungal biofilm is a microbial community composed of fungal cells and extracellular polymeric substances (EPS). In recent years, fungal biofilms have played an increasingly important role in many fields. However, there are few studies on fungal biofilms and their related applications and development are still far from enough. Therefore, this review summarizes the composition and function of EPS in fungal biofilms, and improves and refines the formation process of fungal biofilms according to the latest viewpoints. Moreover, based on the study of Saccharomyces cerevisiae and Candida albicans, this review summarizes the gene regulation network of fungal biofilm synthesis, which is crucial for systematically understanding the molecular mechanism of fungal biofilm formation. It is of great significance to further develop effective methods at the molecular level to control harmful biofilms or enhance and regulate the formation of beneficial biofilms. Finally, the quorum sensing factors and mixed biofilms formed by fungi in the current research of fungal biofilms are summarized. These results will help to deepen the understanding of the formation process and internal regulation mechanism of fungal biofilm, provide reference for the study of EPS composition and structure, formation, regulation, group behavior and mixed biofilm formation of other fungal biofilms, and provide strategies and theoretical basis for the control, development and utilization of fungal biofilms.

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

Introduction

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

Methods

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

Results

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

Conclusion

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

Elucidating the structural basis for the enhanced antifungal activity of amide derivative against Candida albicans: a comprehensive computational investigation

The continuous search for more effective options against well-known pathogens such as Candida albicans remains the rationale for the search for novel lead compounds from various sources. This study aims to investigate the chemical structure, chemical properties, of 5-(2-((5-(((1S,3R) -3-(5-acetamido-1,3,4-thiadiazolidin-2-yl) cyclopentyl) methyl)-1,3,4-thiadiazolidin-2-yl)amino)-2-oxoethyl)-2-methyl-2,3-dihydro-1H-pyrazol-3-ide designated ATCTP using DFT method ωB97XD/-311 +  + g(2d, 2p) and the biological potential of compound ATCTP against Candida albicans using molecular docking and ADMET studies. Geometry optimization was carried out in DMSO, ethanol. gas and water revealing minute discrepancies in bond length and wider differences in bond angles. Frontier molecular orbital investigations reveal HOMO-LUMO energy gap magnitude in decreasing order of ATCTP_Gas > ATCTP_Water > ATCTP_ethanol > ATCTP_DMSO inferring that water influences chemical stability of the compound the most compared to ethanol and DMSO. Density of state investigations have revealed electron density contributions at corresponding energy peaks. In silico pharmacokinetic predicts ATCTP not to be cytotoxic, hepatotoxic, immunotoxic or mutagenic but probable mutagen. Molecular docking investigation of ATCTP against aspartic proteinase of Candida albicans (ID: 2QZX) in comparison with standard drug Fluconazole. Compound ATCTP had higher binding affinity (- 8.1 kcal/mol) compared to that of the standard drug fluconazole (- 5.6 kcal/mol) which records 4 conventional hydrogen interactions compared to 2 formed in the interaction of ATCTP + 2QZX. ATCTP also reports binding affinity of - 7.2 kcal/mol which reportedly surpassed that of 2QZX interaction with fluconazole (- 5.7 kcal/mol). ATCTP binds with lanosterol14-α-demethylase (5v5z) with binding affinity of - 9.7 kcal/mol binding to active site amino acid residues of the protein compared to fluconazole + 5v5z (- 8.0 kcal/mol). ATCTP is therefore recommended to be a lead compound for the possible design of a new and more effective anti-candida therapeutic compound.

Graphical abstract

Estimating the expression levels of genes controlling biofilm formation and evaluating the effects of different conditions on biofilm formation and secreted aspartic proteinase activity in Candida albicans and Saccharomyces cerevisiae: a comparative study

Background

Characterization of yeast virulence genes is an important tool for identifying the molecular pathways involved in switching yeast virulence. Biofilm formation (BF) and secreted aspartic proteinase (SAP) activity are essential virulence factors that contribute to yeast pathogenicity.

Results

Four Candida albicans and two Saccharomyces cerevisiae strains were tested for BF and SAP activity under optimum conditions, and the expression levels of several genes controlling BF were quantified under the optimal conditions. Biofilm formation was assessed by the microplate method at different pH values, incubation times and culture media. Similarly, SAP activity was assessed at different pH values and incubation periods. The expression levels of nine genes were determined via qRT-PCR technique. All tests were carried out in triplicate, and the values presented as the means ± standard deviations and were analysed with the SPSS programme. Only C. albicans (1), C. albicans (2) and S. cerevisiae 43 formed biofilms. The optimal BF was obtained after culture in sabouraud dextrose broth with 8% glucose at pH 7.5, 4 and 6, respectively, for 48h. Candida albicans biofilm production was more significant than that of S. cerevisiae 43. Moreover, the SAP activity was estimated under the optimum conditions. All yeasts showed optimal SAP activity at pH 4, but astonishingly the SAP activity of S. cerevisiae 44 was higher than that of C. albicans. The expression levels of EFG1 and ZAP1 (transcription factors); ALS3, HWP1and YWP1 (adhesion genes); SAP1 and SAP4 (aspartic proteinase) in C. albicans (1); and FLO11 (adhesion gene) and YPS3 (aspartic proteinase) in S. cerevisiae 43 were quantified during biofilm development at different time intervals. The expression levels of EFG1, ALS3, YWP1, SAP1, SAP4, FLO11 and YPS3 were upregulated at 8 h, while that of ZAP1 was upregulated at 48 h. Only HWP1 was downregulated.

Conclusions

The findings of the present study may provide information for overcoming yeast BF and pathogenicity by regulating specific genes at specific times. Additionally, this study revealed the virulence of the commensal S. cerevisiae, which may take the pathogenicity direction as C. albicans.

Antimicrobial and anti-biofilm properties of oleuropein against Escherichia coli and fluconazole-resistant isolates of Candida albicans and Candida glabrata

BACKGROUND

Side effects associated with antimicrobial drugs, as well as their high cost, have prompted a search for low-cost herbal medicinal substances with fewer side effects. These substances can be used as supplements to medicine or to strengthen their effects. The current study investigated the effect of oleuropein on the inhibition of fungal and bacterial biofilm in-vitro and at the molecular level.

MATERIALS AND METHODS

In this experimental study, antimicrobial properties were evaluated using microbroth dilution method. The effect of oleuropein on the formation and eradication of biofilm was assessed on 96-well flat bottom microtiter plates and their effects were observed through scanning electron microscopy (SEM). Its effect on key genes (Hwp1, Als3, Epa1, Epa6, LuxS, Pfs) involved in biofilm formation was investigated using the quantitative reverse transcriptase-polymerase chain reaction (RT-qPCR) method.

RESULTS

The minimum inhibitory concentration (MIC) and minimum fungicidal/bactericidal concentration (MFC/MBC) for oleuropein were found to be 65 mg/ml and 130 mg/ml, respectively. Oleuropein significantly inhibited biofilm formation at MIC/2 (32.5 mg/ml), MIC/4 (16.25 mg/ml), MIC/8 (8.125 mg/ml) and MIC/16 (4.062 mg/ml) (p < 0.0001). The anti-biofilm effect of oleuropein was confirmed by SEM. RT-qPCR indicated significant down regulation of expression genes involved in biofilm formation in Candida albicans (Hwp1, Als3) and Candida glabrata (Epa1, Epa6) as well as Escherichia coli (LuxS, Pfs) genes after culture with a MIC/2 of oleuropein (p < 0.0001).

CONCLUSIONS

The results indicate that oleuropein has antifungal and antibacterial properties that enable it to inhibit or destroy the formation of fungal and bacterial biofilm.

Biofilm-associated metabolism via ERG251 in Candida albicans

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

Functional Redundancy in Candida auris Cell Surface Adhesins Crucial for Cell-Cell Interaction and Aggregation

Candida auris is an emerging nosocomial fungal pathogen associated with life-threatening invasive disease due to its persistent colonization, high level of transmissibility and multi-drug resistance. Aggregative and non-aggregative growth phenotypes for C. auris strains with different biofilm forming abilities, drug susceptibilities and virulence characteristics have been described. Using comprehensive transcriptional analysis we identified key cell surface adhesins that were highly upregulated in the aggregative phenotype during in vitro and in vivo grown biofilms using a mouse model of catheter infection. Phenotypic and functional evaluations of generated null mutants demonstrated crucial roles for the adhesins Als5 and Scf1 in mediating cell-cell adherence, coaggregation and biofilm formation. While individual mutants were largely non-aggregative, in combination cells were able to co-adhere and aggregate, as directly demonstrated by measuring cell adhesion forces using single-cell atomic force spectroscopy. This co-adherence indicates their role as complementary adhesins, which despite their limited similarity, may function redundantly to promote cell-cell interaction and biofilm formation. Functional diversity of cell wall proteins may be a form of regulation that provides the aggregative phenotype of C. auris with flexibility and rapid adaptation to the environment, potentially impacting persistence and virulence.

Functional Redundancy in Candida auris Cell Surface Adhesins Crucial for Cell-Cell Interaction and Aggregation

Candida auris is an emerging nosocomial fungal pathogen associated with life-threatening invasive disease due to its persistent colonization, high level of transmissibility and multi-drug resistance. Aggregative and non-aggregative growth phenotypes for C. auris strains with different biofilm forming abilities, drug susceptibilities and virulence characteristics have been described. Using comprehensive transcriptional analysis we identified key cell surface adhesins that were highly upregulated in the aggregative phenotype during in vitro and in vivo grown biofilms using a mouse model of catheter infection. Phenotypic and functional evaluations of generated null mutants demonstrated crucial roles for the adhesins Als5 and Scf1 in mediating cell-cell adherence, coaggregation and biofilm formation. While individual mutants were largely non-aggregative, in combination cells were able to co-adhere and aggregate, as directly demonstrated by measuring cell adhesion forces using single-cell atomic force spectroscopy. This co-adherence indicates their role as complementary adhesins, which despite their limited similarity, may function redundantly to promote cell-cell interaction and biofilm formation. Functional diversity of cell wall proteins may be a form of regulation that provides the aggregative phenotype of C. auris with flexibility and rapid adaptation to the environment, potentially impacting persistence and virulence.

Transcriptomic meta-analysis to identify potential antifungal targets in Candida albicans

BACKGROUND

Candida albicans is a fungal pathogen causing human infections. Here we investigated differential gene expression patterns and functional enrichment in C. albicans strains grown under different conditions.

METHODS

A systematic GEO database search identified 239 "Candida albicans" datasets, of which 14 were selected after rigorous criteria application. Retrieval of raw sequencing data from the ENA database was accompanied by essential metadata extraction from dataset descriptions and original articles. Pre-processing via the tailored nf-core pipeline for C. albicans involved alignment, gene/transcript quantification, and diverse quality control measures. Quality assessment via PCA and DESeq2 identified significant genes (FDR < = 0.05, log2-fold change > = 1 or <= -1), while topGO conducted GO term enrichment analysis. Exclusions were made based on data quality and strain relevance, resulting in the selection of seven datasets from the SC5314 strain background for in-depth investigation.

RESULTS

The meta-analysis of seven selected studies unveiled a substantial number of genes exhibiting significant up-regulation (24,689) and down-regulation (18,074). These differentially expressed genes were further categorized into 2,497 significantly up-regulated and 2,573 significantly down-regulated Gene Ontology (GO) IDs. GO term enrichment analysis clustered these terms into distinct groups, providing insights into the functional implications. Three target gene lists were compiled based on previous studies, focusing on central metabolism, ion homeostasis, and pathogenicity. Frequency analysis revealed genes with higher occurrence within the identified GO clusters, suggesting their potential as antifungal targets. Notably, the genes TPS2, TPS1, RIM21, PRA1, SAP4, and SAP6 exhibited higher frequencies within the clusters. Through frequency analysis within the GO clusters, several key genes emerged as potential targets for antifungal therapies. These include RSP5, GLC7, SOD2, SOD5, SOD1, SOD6, SOD4, SOD3, and RIM101 which exhibited higher occurrence within the identified clusters.

CONCLUSION

This comprehensive study significantly advances our understanding of the dynamic nature of gene expression in C. albicans. The identification of genes with enhanced potential as antifungal drug targets underpins their value for future interventions. The highlighted genes, including TPS2, TPS1, RIM21, PRA1, SAP4, SAP6, RSP5, GLC7, SOD2, SOD5, SOD1, SOD6, SOD4, SOD3, and RIM101, hold promise for the development of targeted antifungal therapies.

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

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

DNase improves the efficacy of antimicrobial photodynamic therapy in the treatment of candidiasis induced with Candida albicans

The study evaluated the association of DNase I enzyme with antimicrobial photodynamic therapy (aPDT) in the treatment of oral candidiasis in mice infected with fluconazole-susceptible (CaS) and -resistant (CaR) Candida albicans strains. Mice were inoculated with C. albicans, and after the infection had been established, the tongues were exposed to DNase for 5 min, followed by photosensitizer [Photodithazine®(PDZ)] and light (LED), either singly or combined. The treatments were performed for 5 consecutive days. Treatment efficacy was evaluated by assessing the tongues via fungal viable population, clinical evaluation, histopathological and fluorescence microscopy methods immediately after finishing treatments, and 7 days of follow-up. The combination of DNase with PDZ-aPDT reduced the fungal viability in mice tongues immediately after the treatments by around 4.26 and 2.89 log10 for CaS and CaR, respectively (versus animals only inoculated). In the fluorescence microscopy, the polysaccharides produced by C. albicans and fungal cells were less labeled in animals treated with the combination of DNase with PDZ-aPDT, similar to the healthy animals. After 7 days of the treatment, DNase associated with PDZ-aPDT maintained a lower count, but not as pronounced as immediately after the intervention. For both strains, mice treated with the combination of DNase with PDZ-aPDT showed remission of oral lesions and mild inflammatory infiltrate in both periods assessed, while animals treated only with PDZ-aPDT presented partial remission of oral lesions. DNase I enzyme improved the efficacy of photodynamic treatment.

Polystyrene Microplastics Exacerbate Candida albicans Infection Ability In Vitro and In Vivo

Plastic pollution is an important environmental problem, and microplastics have been shown to have harmful effects on human and animal health, affecting immune and metabolic physiological functions. Further, microplastics can interfere with commensal microorganisms and exert deleterious effects on exposure to pathogens. Here, we compared the effects of 1 µm diameter polystyrene microplastic (PSMPs) on Candida albicans infection in both in vitro and in vivo models by using HT29 cells and Galleria mellonella larvae, respectively. The results demonstrated that PSMPs could promote Candida infection in HT29 cells and larvae of G. mellonella, which show immune responses similar to vertebrates. In this study, we provide new experimental evidence for the risk to human health posed by PSMPs in conjunction with Candida infections.

Biofilm Formation and Aspartyl Proteinase Activity and Their Association with Azole Resistance Among Candida albicans Causing Vulvovaginal Candidiasis, Egypt

Background

Candida albicans (C. albicans) is a major cause of vulvovaginal candidiasis (VVC), a condition that is commonly treated with azole agents. Biofilm formation and aspartyl proteinase production are important virulence factors that could be linked to azole resistance in C. albicans impeding therapy.

Aim

To find out the association of both factors with azole resistance among C. albicans isolated from VVC cases in Egyptian nonpregnant women of childbearing age.

Patients and Methods

In a cross-sectional study, C. albicans was isolated from nonpregnant females diagnosed clinically as having VVC during a 1-year study period. Susceptibility to azole agents was tested using the disc diffusion method. Biofilm formation and aspartyl proteinase production were assessed phenotypically. Additionally, two biofilm-related genes (ALS1 and HWP1) and three proteinase genes (SAP2, SAP4, and SAP6) were screened for using polymerase chain reaction (PCR).

Results

Among 204 C. albicans isolates, azole resistance ratios were as follows: voriconazole (30.4%), itraconazole (17.6%), fluconazole (11.3%) and econazole (6.4%). Biofilm-producing capacity was detected in 63.2% of isolates, and 63.2% were proteinase producers. The frequencies of ALS1 and HWP1 were 69.6% and 74.5%, respectively, while SAP2, SAP4, and SAP6 were 69.2%, 88.7%, and 64.7%, respectively. Biofilm formation was significantly associated with azole resistance (P < 0.001 for each tested azole agent) as was proteinase production (P < 0.001 for fluconazole, voriconazole, and econazole resistance and P = 0.047 for itraconazole).

Conclusion

Among nonpregnant Egyptian women of childbearing age, azole resistance in C. albicans causing VVC is significantly associated with biofilm formation and proteinase production. The development of new therapeutic agents that can target these factors is warranted.

Candida albicans Adhesins Als1 and Hwp1 Modulate Interactions with Streptococcus mutans

Candida albicans and Streptococcus mutans are known to synergistically interact with each other in the oral cavity. For example, glucosyltransferase B (GtfB), secreted by S. mutans, can bind to the C. albicans cell surface, promoting dual-species biofilm formation. However, the fungal factors mediating interactions with S. mutans are unknown. The C. albicans adhesins Als1, Als3, and Hwp1 are key players in C. albicans single-species biofilm formation, but their roles, if any, in interacting with S. mutans have not been assessed. Here, we investigated the roles of the C. albicans cell wall adhesins Als1, Als3, and Hwp1 on forming dual-species biofilms with S. mutans. We assessed the abilities of the C. albicans wild-type als1Δ/Δ, als3Δ/Δ, als1Δ/Δ/als3Δ/Δ, and hwp1Δ/Δ strains to form dual-species biofilms with S. mutans by measuring optical density, metabolic activity, cell enumeration, biomass, thickness, and architecture of the biofilms. We observed that the C. albicans wild-type strain formed enhanced dual-species biofilms in the presence of S. mutans in these different biofilm assays, confirming that C. albicans and S. mutans synergistically interact in the context of biofilms. Our results reveal that C. albicans Als1 and Hwp1 are major players in interacting with S. mutans, since dual-species biofilm formation was not enhanced when the als1Δ/Δ or hwp1Δ/Δ strains were cultured with S. mutans in dual-species biofilms. Als3, however, does not seem to play a clear role in interacting with S. mutans in dual-species biofilm formation. Overall, our data suggest that the C. albicans adhesins Als1 and Hwp1 function to modulate interactions with S. mutans and could be potential targets for future therapeutics.

Zerumbone Disturbs the Extracellular Matrix of Fluconazole-Resistant Candida albicans Biofilms

This study assessed the effect of zerumbone (ZER) against fluconazole-resistant (CaR) and -susceptible Candida albicans (CaS) biofilms and verified the influence of ZER on extracellular matrix components. Initially, to determine the treatment conditions, the minimum inhibitory concentration (MIC), the minimum fungicidal concentration (MFC) and the survival curve were evaluated. Biofilms were formed for 48 h and exposed to ZER at concentrations of 128 and 256 µg/mL for 5, 10 and 20 min (n = 12). One group of biofilms did not receive the treatment in order to monitor the effects. The biofilms were evaluated to determine the microbial population (CFU/mL), and the extracellular matrix components (water-soluble polysaccharides (WSP), alkali-soluble polysaccharides (ASPs), proteins and extracellular DNA (eDNA), as well as the biomass (total and insoluble) were quantified. The MIC value of ZER for CaS was 256 μg/mL, and for CaR, it was 64 μg/mL. The survival curve and the MFC value coincided for CaS (256 μg/mL) and CaR (128 μg/mL). ZER reduced the cellular viability by 38.51% for CaS and by 36.99% for CaR. ZER at 256 µg/mL also reduced the total biomass (57%), insoluble biomass (45%), WSP (65%), proteins (18%) and eDNA (78%) of CaS biofilms. In addition, a reduction in insoluble biomass (13%), proteins (18%), WSP (65%), ASP (10%) and eDNA (23%) was also observed in the CaR biofilms. ZER was effective against fluconazole-resistant and -susceptible C. albicans biofilms and disturbed the extracellular matrix.

Sticking to the Subject: Multifunctionality in Microbial Adhesins

Bacterial and fungal adhesins mediate microbial aggregation, biofilm formation, and adhesion to host. We divide these proteins into two major classes: professional adhesins and moonlighting adhesins that have a non-adhesive activity that is evolutionarily conserved. A fundamental difference between the two classes is the dissociation rate. Whereas moonlighters, including cytoplasmic enzymes and chaperones, can bind with high affinity, they usually dissociate quickly. Professional adhesins often have unusually long dissociation rates: minutes or hours. Each adhesin has at least three activities: cell surface association, binding to a ligand or adhesive partner protein, and as a microbial surface pattern for host recognition. We briefly discuss Bacillus subtilis TasA, pilin adhesins, gram positive MSCRAMMs, and yeast mating adhesins, lectins and flocculins, and Candida Awp and Als families. For these professional adhesins, multiple activities include binding to diverse ligands and binding partners, assembly into molecular complexes, maintenance of cell wall integrity, signaling for cellular differentiation in biofilms and in mating, surface amyloid formation, and anchorage of moonlighting adhesins. We summarize the structural features that lead to these diverse activities. We conclude that adhesins resemble other proteins with multiple activities, but they have unique structural features to facilitate multifunctionality.

Development and applications of a CRISPR activation system for facile genetic overexpression in Candida albicans

For the fungal pathogen Candida albicans, genetic overexpression readily occurs via a diversity of genomic alterations, such as aneuploidy and gain-of-function mutations, with important consequences for host adaptation, virulence, and evolution of antifungal drug resistance. Given the important role of overexpression on C. albicans biology, it is critical to develop and harness tools that enable the analysis of genes expressed at high levels in the fungal cell. Here, we describe the development, optimization, and application of a novel, single-plasmid-based CRISPR activation (CRISPRa) platform for targeted genetic overexpression in C. albicans, which employs a guide RNA to target an activator complex to the promoter region of a gene of interest, thus driving transcriptional expression of that gene. Using this system, we demonstrate the ability of CRISPRa to drive high levels of gene expression in C. albicans, and we assess optimal guide RNA targeting for robust and constitutive overexpression. We further demonstrate the specificity of the system via RNA sequencing. We highlight the application of CRISPR activation to overexpress genes involved in pathogenesis and drug susceptibility, and contribute toward the identification of novel phenotypes. Consequently, this tool will facilitate a broad range of applications for the study of C. albicans genetic overexpression.

Analysis of Candida Antifungal Resistance Using Animal Infection Models

Candida frequently produces three general disease states, including mucosal candidiasis, disseminated candidiasis, and biofilm infection (which can be present with either of the other disease states). Antifungal drug resistance is intrinsic to biofilm growth and has emerged in other disease states. Mechanistic studies have uncovered the genetic pathways governing resistance to a number of antifungal agents. However, analyzing the clinical relevance of distinct mechanisms is fundamental for broadening our knowledge of antifungal drug resistance and for delineating the potential impact of targeting these pathways medically. Also, as drug-resistant strains and biofilms represent important nosocomial problems, preclinical animal models to assess the activity of novel antifungals are of great interest. Here we describe two rodent models that mimic the most common biofilm device and disseminated candidiasis states in patients. The model systems incorporate the anatomical site, immune components, and antifungal exposures relevant for the study of antifungal resistance. The models can be used to analyze mutant strains, assess the extent of drug resistance, examine biofilm formation, test new antimicrobials, and help determine drug exposures that may be linked with clinical failure.

The Landscape of Gene Expression during Hyperfilamentous Biofilm Development in Oral Candida albicans Isolated from a Lung Cancer Patient

The filamentation ability of Candida albicans represents one of the main virulence factors allowing for host tissue penetration and biofilm formation. The aim of this paper was to study the genetic background of the hyperfilamentous biofilm development in vitro in C. albicans isolated from the oral cavity of a lung cancer patient. Analyzed C. albicans isolates (CA1, CA2, CA3) were chosen based on their different structures of mature biofilm. The CA3 isolate possessing hyperfilamentation properties and forming high biofilm was compared with CA1 and CA2 isolates exhibiting low or average biofilm-forming ability, respectively. The detailed biofilm organization was studied with the use of confocal scanning laser microscopy. The whole transcriptome analysis was conducted during three stages of biofilm development (24 h, 48 h, 72 h). In contrast to CA1 and/or CA2 isolate, the CA3 isolate was characterized by a significant upregulation of genes encoding for cell wall proteins (HWP1, PGA13, PGA44, ALS3) and candidalysin (ECE1), as well as being involved in iron metabolism (FRE1, ALS3), sulfur metabolism (HAL21), the degradation of aromatic compounds (HQD2), and membrane transport (DIP5, PHO89, TNA1). In contrast, some genes (SCW11, FGR41, RBE1) in the CA3 were downregulated. We also observed the overexpression of a few genes over time-mainly FRE1, ATX1, CSA2 involved in iron metabolism. This is the first insight into the potential function of multiple genes in the hyperfilamentous biofilm formation in C. albicans, primarily isolated from host tissue, which may have an important clinical impact on cancer patients. Moreover, the presented data can lay the foundation for further research on novel pathogen-specific targets for antifungal drugs.

From intestinal colonization to systemic infections: Candida albicans translocation and dissemination

Candida species are the most prevalent cause of invasive fungal infections, of which Candida albicans is the most common. Translocation across the epithelial barrier into the bloodstream by intestinal-colonizing C. albicans cells serves as the main source for systemic infections. Understanding the fungal mechanisms behind this process will give valuable insights on how to prevent such infections and keep C. albicans in the commensal state in patients with predisposing conditions. This review will focus on recent developments in characterizing fungal translocation mechanisms, compare what we know about enteric bacterial pathogens with C. albicans, and discuss the different proposed hypotheses for how C. albicans enters and disseminates through the bloodstream immediately following translocation.

Interkingdom assemblages in human saliva display group-level surface mobility and disease-promoting emergent functions

Fungi and bacteria form multicellular biofilms causing many human infections. How such distinctive microbes act in concert spatiotemporally to coordinate disease-promoting functionality remains understudied. Using multiscale real-time microscopy and computational analysis, we investigate the dynamics of fungal and bacterial interactions in human saliva and their biofilm development on tooth surfaces. We discovered structured interkingdom assemblages displaying emergent functionalities to enhance collective surface colonization, survival, and growth. Further analyses revealed an unexpected group-level surface mobility with coordinated “leaping-like” and “walking-like” motions while continuously growing. These mobile groups of growing cells promote rapid spatial spreading of both species across surfaces, causing more extensive tooth decay. Our findings show multicellular interkingdom assemblages acting like supraorganisms with functionalities that cannot be achieved without coassembly.

Fungi and bacteria often engage in complex interactions, such as the formation of multicellular biofilms within the human body. Knowledge about how interkingdom biofilms initiate and coalesce into higher-level communities and which functions the different species carry out during biofilm formation remain limited. We found native-state assemblages of Candida albicans (fungi) and Streptococcus mutans (bacteria) with highly structured arrangement in saliva from diseased patients with childhood tooth decay. Further analyses revealed that bacterial clusters are attached within a network of fungal yeasts, hyphae, and exopolysaccharides, which bind to surfaces as a preassembled cell group. The interkingdom assemblages exhibit emergent functions, including enhanced surface colonization and growth rate, stronger tolerance to antimicrobials, and improved shear resistance, compared to either species alone. Notably, we discovered that the interkingdom assemblages display a unique form of migratory spatial mobility that enables fast spreading of biofilms across surfaces and causes enhanced, more extensive tooth decay. Using mutants, selective inactivation of species, and selective matrix removal, we demonstrate that the enhanced stress resistance and surface mobility arise from the exopolymeric matrix and require the presence of both species in the assemblage. The mobility is directed by fungal filamentation as hyphae extend and contact the surface, lifting the assemblage with a “forward-leaping motion.” Bacterial cell clusters can “hitchhike” on this mobile unit while continuously growing, to spread across the surface three-dimensionally and merge with other assemblages, promoting community expansion. Together, our results reveal an interkingdom assemblage in human saliva that behaves like a supraorganism, with disease-causing emergent functionalities that cannot be achieved without coassembly.

A common vesicle proteome drives fungal biofilm development

Candida species are commensal organisms commonly interacting in the same host niche. In the pathogenic state, they frequently grow as a biofilm, often in mixed infections. The present studies observe a reliance upon common extracellular vesicle cargo for biofilm structure and function supporting interactions among species. The results reveal a vesicle cargo-driven coordination among Candida species during biofilm formation.

Extracellular vesicles mediate community interactions among cells ranging from unicellular microbes to complex vertebrates. Extracellular vesicles of the fungal pathogen Candida albicans are vital for biofilm communities to produce matrix, which confers environmental protection and modulates community dispersion. Infections are increasingly due to diverse Candida species, such as the emerging pathogen Candida auris, as well as mixed Candida communities. Here, we define the composition and function of biofilm-associated vesicles among five species across the Candida genus. We find similarities in vesicle size and release over the biofilm lifespan. Whereas overall cargo proteomes differ dramatically among species, a group of 36 common proteins is enriched for orthologs of C. albicans biofilm mediators. To understand the function of this set of proteins, we asked whether mutants in select components were important for key biofilm processes, including drug tolerance and dispersion. We found that the majority of these cargo components impact one or both biofilm processes across all five species. Exogenous delivery of wild-type vesicle cargo returned mutant phenotypes toward wild type. To assess the impact of vesicle cargo on interspecies interactions, we performed cross-species vesicle addition and observed functional complementation for both biofilm phenotypes. We explored the biologic relevance of this cross-species biofilm interaction in mixed species and mutant studies examining the drug-resistance phenotype. We found a majority of biofilm interactions among species restored the community’s wild-type behavior. Our studies indicate that vesicles influence the development of protective monomicrobial and mixed microbial biofilm communities.

Tachyplesin I Analogue Peptide as an Effective Antimicrobial Agent against Candida albicans-Staphylococcus aureus Poly-Biofilm Formation and Mixed Infection

Microbial biofilms are difficult to tackle in many infectious diseases. Candida albicans and Staphylococcus aureus are prevalent symbiotic strains in polymicrobial biofilms, which showed enhanced antimicrobial resistance and made identifying effective treatment techniques more difficult. The antibiofilm abilities of tachplesin I analogue peptide (TP11A) and tachplesin I were investigated quantitatively in this study. Both inhibited C. albicans monomicrobial, S. aureus monomicrobial, and C. albicans-S. aureus polymicrobial biofilms quite well. TP11A suppressed the biofilm- and virulence-related genes of C. albicans (hwp 1) and S. aureus (ica A, fnb B, agr A, hla, nor A, and sig B) in the mixed biofilm, according to quantitative reverse transcription polymerase chain reaction analysis. We created an injectable thermosensitive in situ PLEL@TP11A gel system by simply adding TP11A into poly(d,l-lactide)-poly(ethylene glycol)-poly(d,l-lactide) (PLEL). Using C. albicans-S. aureus mixed infected wound models of mice, the in vivo therapeutic effect of TP11A and PLEL@TP11A in polymicrobial infections was investigated. The findings revealed that TP11A and PLEL@TP11A could efficiently reduce bacterial and fungal burden in wound infections, as well as accelerated wound healing. Based on above findings, TP11A might be an effective antimicrobial against C. albicans-S. aureus poly-biofilm formation and mixed infection.

Development and Use of a Monoclonal Antibody Specific for the Candida albicans Cell-Surface Protein Hwp1

The Candida albicans cell-surface protein Hwp1 functions in adhesion to the host and in biofilm formation. A peptide from the Gln-Pro-rich adhesive domain of Hwp1 was used to raise monoclonal antibody (MAb) 2-E8. MAb 2-E8 specificity for Hwp1 was demonstrated using a hwp1/hwp1 C. albicans isolate and strains that expressed at least one HWP1 allele. Immunofluorescence and atomic force microscopy experiments using MAb 2-E8 confirmed C. albicans germ-tube-specific detection of the Hwp1 protein. MAb 2-E8 also immunolabeled the tips of some Candida dubliniensis germ tubes grown under conditions that maximized HWP1 expression. The phylogeny of HWP1 and closely related genes suggested that the Gln-Pro-rich adhesive domain was unique to C. albicans and C. dubliniensis focusing the utility of MAb 2-E8 on these species. This new reagent can be used to address unanswered questions about Hwp1 and its interactions with other proteins in the context of C. albicans biology and pathogenesis.

DNase enhances photodynamic therapy against fluconazole-resistant Candida albicans biofilms

OBJECTIVE

This study evaluated the effectiveness of DNase I combined with antimicrobial photodynamic therapy, mediated by Photodithazine^® and light-emitting diode light, against biofilms formed by a fluconazole-resistant Candida albicans strain (ATCC 96901) and two clinical isolates (R14 and R70).

MATERIALS AND METHODS

Biofilms were grown for 48 h and exposed to DNase for 5 min, followed by application of a photosensitizer (P) and light (L), either singly or combined (P+L+, P-L+, P+L-, P-L-, P-L-DNase, P+L+DNase, P+L-DNase, and P-L+DNase; n = 12). Biofilm analysis included quantification of extracellular matrix components (water-soluble and insoluble proteins and polysaccharides, and extracellular DNA), and biomass (total and insoluble), as well as enumeration of colony-forming units. The data were analyzed using three-way analysis of variance with Bonferroni's post-hoc test.

RESULTS

The DNase treatment combined with aPDT showed a reduction of 1.92, 1.65, and 1.29 log₁₀ of cell viability compared with untreated controls for ATCC 96901, R14, and R70 strains, respectively. It also reduced extracellular matrix contents of water-soluble polysaccharides (36.3%) and extracellular DNA (72.3%), as well as insoluble biomass content (43.3%).

CONCLUSION

The three strains showed similar behavior when treated with DNase, and the extracellular matrix components were affected, improving the effectiveness of antimicrobial photodynamic therapy.

Fungal commensalism modulated by a dual-action phosphate transceptor

Successful host colonization by fungi in fluctuating niches requires response and adaptation to multiple environmental stresses. However, our understanding about how fungal species thrive in the gastrointestinal (GI) ecosystem by combing multifaceted nutritional stress with respect to homeostatic host-commensal interactions is still in its infancy. Here, we discover that depletion of the phosphate transceptor Pho84 across multiple fungal species encountered a substantial cost in gastrointestinal colonization. Mechanistically, Pho84 enhances the gastrointestinal commensalism via a dual-action activity, coordinating both phosphate uptake and TOR activation by induction of the transcriptional regulator Try4 and downstream commensalism-related transcription. As such, Pho84 promotes Candida albicans commensalism, but this does not translate into enhanced pathogenicity. Thus, our study uncovers a specific nutrient-dependent dual-action regulatory pathway for Pho84 on fungal commensalism.

Inhibitory effect of 405-nm blue LED light on the growth of Candida albicans and Streptococcus mutans dual-species biofilms on denture base resin

We investigated whether irradiation with 405-nm blue LED light could inhibit the growth of not only single- but dual-species biofilms formed by Candida albicans and Streptococcus mutans on denture base resin and cause the alteration in gene expression related to adhesion and biofilm formation. C. albicans and S. mutans single-/dual-species biofilms were formed on the denture base specimens. The biofilms were irradiated with 405-nm blue LED light (power density output: 280 mW/cm²) for 0 (control) and 40 min. Dual-species biofilms were analyzed using CFU assay and fluorescence microscopy, and single-/dual-species biofilms were analyzed using alamarBlue assays and gene expression analysis. To assess the inhibitory effect of irradiation on dual-species biofilms, specimens after irradiation were aerobically incubated for 12 h. After incubation, the inhibition of growth was assessed using CFU assays and fluorescence microscopy. Data were analyzed using the Mann-Whitney U or Student's t test (p < 0.05). Irradiation produced a significant inhibitory effect on biofilms. Fluorescence microscopy revealed that almost all C. albicans and S. mutans cells were killed by irradiation, and there was no notable difference in biofilm thickness immediately after irradiation and after irradiation and incubation for 12 h. alamarBlue assays indicated the growth of the biofilms was inhibited for 12-13 h. The expression of genes associated with adhesion and biofilm formation-als1 in C. albicans and ftf, gtfC, and gtfB in S. mutans-significantly reduced by irradiation. Irradiation with 405-nm blue LED light effectively inhibited the growth of C. albicans and S. mutans dual-species biofilms for 12 h.

Regulatory network controls microbial biofilm development, with Candida albicans as a representative: from adhesion to dispersal

Microorganisms mainly exist in the form of biofilm in nature. Biofilm can contaminate food and drinking water system, as well as cause chronic wound infections, thereby posing a potential threat to public health safety. In the last two decades, researchers have made efforts to investigate the genetic contributors control different stages of biofilm development (adherence, initiation, maturation, and dispersal). As an opportunistic pathogen, C. albicans causes severe superficial or systemic infections with high morbidity and mortality under conditions of immune dysfunction. It has been reported that 80% of C. albicans infections are directly or indirectly associated with biofilm formation on host or abiotic surfaces including indwelling medical devices, resulting in high morbidity and mortality. Significantly, the outcome of C. albicans biofilm development includes enhanced invasion, exacerbated inflammatory responses and intrinsic resistance to antimicrobial chemotherapy. Thus, this review aimed at providing a comprehensive overview of the regulatory network controls microbial biofilm development, with C. albicans as a representative, served as reference for therapeutic targets.

Adhesins in the virulence of opportunistic fungal pathogens of human

Aspergillosis, candidiasis, and cryptococcosis are the most common cause of mycoses-related disease and death among immune-compromised patients. Adhesins are cell-surface exposed proteins or glycoproteins of pathogens that bind to the extracellular matrix (ECM) constituents or mucosal epithelial surfaces of the host cells. The forces of interaction between fungal adhesins and host tissues are accompanied by ligand binding, hydrophobic interactions and protein-protein aggregation. Adherence is the primary and critical step involved in the pathogenesis; however, there is limited information on fungal adhesins compared to that on the bacterial adhesins. Except a few studies based on screening of proteome for adhesin identification, majority are based on characterization of individual adhesins. Recently, based on their characteristic signatures, many putative novel fungal adhesins have been predicted using bioinformatics algorithms. Some of these novel adhesin candidates have been validated by in-vitro studies; though, most of them are yet to be characterised experimentally. Morphotype specific adhesin expression as well as tissue tropism are the crucial determinants for a successful adhesion process. This review presents a comprehensive overview of various studies on fungal adhesins and discusses the targetability of the adhesins and adherence phenomenon, for combating the fungal infection in a preventive or therapeutic mode.

Ozone ultrafine bubble water inhibits the early formation of Candida albicans biofilms

This study aimed to investigate the effect of ozone ultrafine bubble water (OUFBW) on the formation and growth of Candida albicans (C. albicans) biofilms and surface properties of denture base resins. OUFBWs were prepared under concentrations of 6 (OUFBW6), 9 (OUFBW9), and 11 ppm (OUFBW11). Phosphate buffered saline and ozone-free electrolyte aqueous solutions (OFEAS) were used as controls. Acrylic resin discs were made according to manufacturer instructions, and C. albicans was initially cultured on the discs for 1.5 h. A colony forming unit (CFU) assay was performed by soaking the discs in OUFBW for 5 min after forming a 24-h C. albicans biofilm. The discs after initial attachment for 1.5 h were immersed in OUFBW and then cultured for 0, 3, and 5 h. CFUs were subsequently evaluated at each time point. Moreover, a viability assay, scanning electron microscopy (SEM), Alamar Blue assay, and quantitative real-time polymerase chain reaction (qRT-PCR) test were performed. To investigate the long-term effects of OUFBW on acrylic resin surface properties, Vickers hardness (VH) and surface roughness (Ra) were measured. We found that OUFBW9 and OUFBW11 significantly degraded the formed 24-h biofilm. The time point CFU assay showed that C. albicans biofilm formation was significantly inhibited due to OUFBW11 exposure. Interestingly, fluorescence microscopy revealed that almost living cells were observed in all groups. In SEM images, the OUFBW group had lesser number of fungi and the amount of non-three-dimensional biofilm than the control group. In the Alamar Blue assay, OUFBW11 was found to suppress Candida metabolic function. The qRT-PCR test showed that OUFBW down-regulated ALS1 and ALS3 expression regarding cell-cell, cell-material adhesion, and biofilm formation. Additionally, VH and Ra were not significantly different between the two groups. Overall, our data suggest that OUFBW suppressed C. albicans growth and biofilm formation on polymethyl methacrylate without impairing surface properties.

Genotyping, drug resistance and virulence factors of Candida species isolated from patients using long-term inhaled steroids

AIMS

In this study, it was aimed to determine the isolation frequency and species distribution of Candida species isolated from asthmatic patients using long-term inhaled steroids. It was also aimed to determine the drug resistance patterns and the frequency of erg11, HWP1, ALS1, INT1, SAP1 PLB1 genes in isolates.

METHODS

Genotyping of Candida strains isolated from patients and healthy control group was performed by PCR-RFLP method. Drug resistance was investigated phenotypically, and the presence of erg11 resistance genes and HWP1, ALS1, INT1, SAP1 PLB1 virulence genes were investigated by PCR method.

RESULTS

C albicans was the most isolated species in steroid-using patients and healthy control groups (patients: 44.2%; control group: 30.8%). C tropicalis and C glabrata were found to have the highest rates of non-albicans Candida in patients with 17.4% and 13.77%, respectively. Azole resistance was found to be significantly higher in isolates isolated from patients compared to the control group. Similarly, the presence of erg11 resistance gene was highest in C albicans (17.65%), C glabrata (12.5%) and C tropicalis (8.3%) strains in the control group, while C parapsilosis was highest in patients. (57.1%) and C glabrata (54.2%) strains. Compared to the control group, the virulence of Candida strains isolated from the patients was found to be higher. Presence of HWP1, ALS1, INT1, SAP1 and PLB1 genes in patients were determined as 72.1%, 63.9%, 68.9%, 57.38% and 54.5%, respectively. These rates were 29.4%, 35.3%, 25.5%, 17.7% and 23.5% in the healthy control group, respectively.

CONCLUSIONS

In asthma patients using long-term inhaled steroids, both Isolation rates of Candida species, drug resistance rates, presence of virulence genes were found to be significantly higher in patients than in the control group. We think that this may be due to the suppression of cellular immunity by long-term steroid use.

Coordination of fungal biofilm development by extracellular vesicle cargo

The fungal pathogen Candida albicans can form biofilms that protect it from drugs and the immune system. The biofilm cells release extracellular vesicles (EVs) that promote extracellular matrix formation and resistance to antifungal drugs. Here, we define functions for numerous EV cargo proteins in biofilm matrix assembly and drug resistance, as well as in fungal cell adhesion and dissemination. We use a machine-learning analysis of cargo proteomic data from mutants with EV production defects to identify 63 candidate gene products for which we construct mutant and complemented strains for study. Among these, 17 mutants display reduced biofilm matrix accumulation and antifungal drug resistance. An additional subset of 8 cargo mutants exhibit defects in adhesion and/or dispersion. Representative cargo proteins are shown to function as EV cargo through the ability of exogenous wild-type EVs to complement mutant phenotypic defects. Most functionally assigned cargo proteins have roles in two or more of the biofilm phases. Our results support that EVs provide community coordination throughout biofilm development in C. albicans.

The fungal pathogen Candida albicans can release extracellular vesicles that promote biofilm formation and antifungal resistance. Here, Zarnowski et al. define functions for numerous vesicle cargo proteins in biofilm matrix assembly and drug resistance, as well as in fungal cell adhesion and dissemination.

The Flo Adhesin Family

The first step in the infection of fungal pathogens in humans is the adhesion of the pathogen to host tissue cells or abiotic surfaces such as catheters and implants. One of the main players involved in this are the expressed cell wall adhesins. Here, we review the Flo adhesin family and their involvement in the adhesion of these yeasts during human infections. Firstly, we redefined the Flo adhesin family based on the domain architectures that are present in the Flo adhesins and their functions, and set up a new classification of Flo adhesins. Next, the structure, function, and adhesion mechanisms of the Flo adhesins whose structure has been solved are discussed in detail. Finally, we identified from Pfam database datamining yeasts that could express Flo adhesins and are encountered in human infections and their adhesin architectures. These yeasts are discussed in relation to their adhesion characteristics and involvement in infections.

Fungal Cell Wall Proteins and Signaling Pathways Form a Cytoprotective Network to Combat Stresses

Candida species are part of the normal flora of humans, but once the immune system of the host is impaired and they escape from commensal niches, they shift from commensal to pathogen causing candidiasis. Candida albicans remains the primary cause of candidiasis, accounting for about 60% of the global candidiasis burden. The cell wall of C. albicans and related fungal pathogens forms the interface with the host, gives fungal cells their shape, and also provides protection against stresses. The cell wall is a dynamic organelle with great adaptive flexibility that allows remodeling, morphogenesis, and changes in its components in response to the environment. It is mainly composed of the inner polysaccharide rich layer (chitin, and β-glucan) and the outer protein coat (mannoproteins). The highly glycosylated protein coat mediates interactions between C. albicans cells and their environment, including reprograming of wall architecture in response to several conditions, such as carbon source, pH, high temperature, and morphogenesis. The mannoproteins are also associated with C. albicans adherence, drug resistance, and virulence. Vitally, the mannoproteins contribute to cell wall construction and especially cell wall remodeling when cells encounter physical and chemical stresses. This review describes the interconnected cell wall integrity (CWI) and stress-activated pathways (e.g., Hog1, Cek1, and Mkc1 mediated pathways) that regulates cell wall remodeling and the expression of some of the mannoproteins in C. albicans and other species. The mannoproteins of the surface coat is of great importance to pathogen survival, growth, and virulence, thus understanding their structure and function as well as regulatory mechanisms can pave the way for better management of candidiasis.

CO2 enhances the formation, nutrient scavenging and drug resistance properties of C. albicans biofilms

C. albicans is the predominant human fungal pathogen and frequently colonises medical devices, such as voice prostheses, as a biofilm. It is a dimorphic yeast that can switch between yeast and hyphal forms in response to environmental cues, a property that is essential during biofilm establishment and maturation. One such cue is the elevation of CO₂ levels, as observed in exhaled breath for example. However, despite the clear medical relevance, the effect of CO₂ on C. albicans biofilm growth has not been investigated to date. Here we show that physiologically relevant CO₂ elevation enhances each stage of the C. albicans biofilm-forming process: from attachment through maturation to dispersion. The effects of CO₂ are mediated via the Ras/cAMP/PKA signalling pathway and the central biofilm regulators Efg1, Brg1, Bcr1 and Ndt80. Biofilms grown under elevated CO₂ conditions also exhibit increased azole resistance, increased Sef1-dependent iron scavenging and enhanced glucose uptake to support their rapid growth. These findings suggest that C. albicans has evolved to utilise the CO₂ signal to promote biofilm formation within the host. We investigate the possibility of targeting CO₂-activated processes and propose 2-deoxyglucose as a drug that may be repurposed to prevent C. albicans biofilm formation on medical airway management implants. We thus characterise the mechanisms by which CO₂ promotes C. albicans biofilm formation and suggest new approaches for future preventative strategies.

Candida albicans Biofilm Inhibition by Two Vaccinium macrocarpon (Cranberry) Urinary Metabolites: 5-(3',4'-DihydroxyPhenyl)-γ-Valerolactone and 4-Hydroxybenzoic Acid

Candida spp. are pathobionts, as they can switch from commensals to pathogens, responsible for a variety of pathological processes. Adhesion to surfaces, morphological switch and biofilm-forming ability are the recognized virulence factors promoting yeast virulence. Sessile lifestyle also favors fungal persistence and antifungal tolerance. In this study, we investigated, in vitro, the efficacy of two urinary cranberry metabolites, 5-(3′,4′-dihydroxy phenyl)-γ-valerolactone (VAL) and 4-hydroxybenzoic acid (4-HBA), in inhibiting C. albicans adhesion and biofilm formation. Both the reference strain SC5314 and clinical isolates were used. We evaluated biomass reduction, by confocal microscopy and crystal violet assay, and the possible mechanisms mediating their inhibitory effects. Both VAL and 4-HBA were able to interfere with the yeast adhesion, by modulating the expression of key genes, HWP1 and ALS3. A significant dose-dependent reduction in biofilm biomass and metabolic activity was also recorded. Our data showed that the two cranberry metabolites VAL and 4-HBA could pave the way for drug development, for targeting the very early phases of biofilm formation and for preventing genitourinary Candida infections.

Where the infection is isolated rather than the specific species correlates with adherence strength, whereas biofilm density remains static in clinically isolated Candida and arthroconidial yeasts

To colonize and infect the host, arthroconidial yeasts must avoid being killed by the host's defenses. The formation of biofilms on implanted devices allows fungi to avoid host responses and to disseminate into the host. To better study the mechanisms of infection by arthroconidial yeasts, adherence and biofilm formation were assayed using patient samples collected over 10 years. In clinical samples, adherence varies within species, but the relative adherence is constant for those samples isolated from the same infection site. Herein we document, for the first time, in-vitro biofilm formation by Trichosporon dohaense, T. ovoides, T. japonicum, T. coremiiforme, Cutaneotrichosporon mucoides, Cutaneotrichosporon cutaneum, Galactomyces candidus, and Magnusiomyces capitatus on clinically relevant catheter material. Analysis of biofilm biomass assays indicated that biofilm mass changes less than 2-fold, regardless of the species. Our results support the hypothesis that most pathogenic fungi can form biofilms, and that biofilm formation is a source of systemic infections.

Risk factors and biofilm formation analyses of hospital-acquired infection of Candida pelliculosa in a neonatal intensive care unit

Background

Candida pelliculosa is an ecological fungal species that can cause infections in immunocompromised individuals. Numerous studies globally have shown that C. pelliculosa infects neonates. An outbreak recently occurred in our neonatal intensive care unit; therefore, we aimed to evaluate the risk factors in this hospital-acquired fungal infection.

Methods

We performed a case-control study, analysing the potential risk factors for neonatal infections of C. pelliculosa so that infection prevention and control could be implemented in our units. Isolated strains were tested for drug resistance and biofilm formation, important factors for fungal transmission that give rise to hospital-acquired infections.

Results

The use of three or more broad-spectrum antimicrobials or long hospital stays were associated with higher likelihoods of infection with C. pelliculosa. The fungus was not identified on the hands of healthcare workers or in the environment. All fungal isolates were susceptible to anti-fungal medications, and after anti-fungal treatment, all infected patients recovered. Strict infection prevention and control procedures efficiently suppressed infection transmission. Intact adhesin-encoding genes, shown by genome analysis, indicated possible routes for fungal transmission.

Conclusions

The use of three or more broad-spectrum antimicrobials or a lengthy hospital stay is theoretically associated with the risk of infection with C. pelliculosa. Strains that we isolated are susceptible to anti-fungal medications, and these were eliminated by treating all patients with an antifungal. Transmission is likely via adhesion to the cell surface and biofilm formation.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12879-021-06295-1.

The inhibitory activity of 5-aminolevulinic acid photodynamic therapy (ALA-PDT) on Candida albicans biofilms

BACKGROUND

Biofilm-associated Candida albicans (C. albicans) infections are hard to cure due to their high levels of resistance to antifungal agents. Photodynamic therapy (PDT) is a promising approach for controlling infections caused by C. albicans. This study was designed to explore the inhibitory activity of PDT using 5-aminolevulinic acid (ALA) as photosensitizer against C. albicans biofilms.

METHODS

C. albicans cell suspensions were incubated for 48 h to form mature biofilms. ALA solution was diluted to 15 mM and incubated with C. albicans biofilms for 5 h before irradiated by red light semiconductor laser under the light intensity of 300 J/cm² and fluence rate of 100 mW/cm² for 50 min. The inhibitory activity was evaluated from subcellular level, molecular level and transcriptional level using transmission electron microscopy (TEM) observation, flow cytometry analysis and quantitative Real-Time Polymerase Chain Reaction (qRT-PCR) assays, respectively.

RESULTS

From subcellular level, the degraded content of the cytoplasm, nuclear condensation and mitochondrial swelling were observed after ALA-PDT. From molecular level, ALA-PDT resulted in 19.4 % cell apoptosis. From transcriptional level, ALA-PDT significantly reduced the mRNA expressions of hyphae-specific genes (HWP1 and ALS3) and long-term biofilm maintenance genes (UME6 and HGC1), whereas ALA or red light alone had no significant effect.

CONCLUSIONS

The inhibitory activity indicated that ALA-PDT may have the potential to serve as an antifungal strategy in eliminatingC. albicans biofilms.

Gene expression of Candida albicans strains isolates from patients with denture stomatitis submitted to treatments with photodynamic therapy and nystatin

The study evaluated the effect of antimicrobial photodynamic therapy (aPDT) and nystatin (NYS) in the expression of genes (ACT1, ALS1, CAP1, CAT1, EFG1, HWP1, LIP3, PLB1, SAP1, and SOD1) involved in the virulence of Candida albicans strains recovered from patients with denture stomatitis (DS). These strains were isolated from the patients before (initial) and after treatment (final), and 45 days after the treatments (follow-up). For gene expression analyses, RNA was isolated from the clinical strains, followed by cDNA synthesis and qPCR using specific primers for each target gene. The samples that present integrity were pooled to increase the RNA yield. In the end, four patients treated with aPDT and five patients treated with NYS had the clinical isolates of C. albicans submitted to gene expression evaluation. The data demonstrated a statistical difference in the expression of PLB1 and ACT1 for the different therapies (aPDT versus NYS). Also, there was a statistical difference in the expression of CAT1, SOD1, and LIP3 at the time intervals assessed (initial, final, and follow-up). In contrast, no statistical difference was found in the expression of ALS1, HWP1, EFG1, CAP1, CAT1, SOD1, LIP3, and SAP1 between the therapies, while no significant difference was detected at the time intervals evaluated for ALS1, HWP1, EFG1, CAP1, and SAP1. Therefore, the topical treatments for DS with aPDT or NYS did not effect the expression of most C. albicans virulence genes evaluated.

In-silico design of a multivalent epitope-based vaccine against Candida auris

Candida auris is a rapidly emerging human pathogenic fungus with a high mortality rate. Recent report suggests that the new clinical isolates are showing resistance to the major classes of antifungal drugs. Due to the emergence of drug resistance, it becomes imperative to seek novel therapies for the treatment of C. auris. The potent vaccine could be one of the promising strategies for recalcitrant and multidrug-resistant pathogens. Using in silico approach we designed a novel multivalent vaccine against C. auris. We have selected the agglutinin-like sequence-3 (Als3) an adhesion protein, involved in virulence. The Als3p protein of C. auris was targeted to predict T cell and B cell epitopes. Epitopes which were found to be non-toxic, non-allergenic, highly conserved, and antigenic and could induce interferon-γ synthesis were selected for vaccine design. The selected epitopes were linked with suitable adjuvants to construct the final vaccine. The vaccine construct was predicted to be stable, soluble, antigenic, non-allergic with desirable physicochemical properties. We also constructed the 3D model of the vaccine and validated it with the Ramachandran plot. The ability of the vaccine construct to interact with Toll-like receptor (TLR) and major histocompatibility complex (MHC) was determined by molecular docking experiments. The binding energy of the vaccine construct with the TLR and MHC were found to be stable as predicted by molecular dynamics simulation. Further, in-silico cloning analysis showed that the vaccine construct can be successfully cloned and expressed in E. coli. Based on the results, we surmise that our candidate vaccine can be used as an alternative therapy for the treatment of C. auris. However, the efficacy and the safety of the vaccine model need to be determined by performing in vivo studies.

Comprehensive genetic analysis of adhesin proteins and their role in virulence of Candida albicans

Candida albicans is a microbial fungus that exists as a commensal member of the human microbiome and an opportunistic pathogen. Cell surface-associated adhesin proteins play a crucial role in C. albicans' ability to undergo cellular morphogenesis, develop robust biofilms, colonize, and cause infection in a host. However, a comprehensive analysis of the role and relationships between these adhesins has not been explored. We previously established a CRISPR-based platform for efficient generation of single- and double-gene deletions in C. albicans, which was used to construct a library of 144 mutants, comprising 12 unique adhesin genes deleted singly, and every possible combination of double deletions. Here, we exploit this adhesin mutant library to explore the role of adhesin proteins in C. albicans virulence. We perform a comprehensive, high-throughput screen of this library, using Caenorhabditis elegans as a simplified model host system, which identified mutants critical for virulence and significant genetic interactions. We perform follow-up analysis to assess the ability of high- and low-virulence strains to undergo cellular morphogenesis and form biofilms in vitro, as well as to colonize the C. elegans host. We further perform genetic interaction analysis to identify novel significant negative genetic interactions between adhesin mutants, whereby combinatorial perturbation of these genes significantly impairs virulence, more than expected based on virulence of the single mutant constituent strains. Together, this study yields important new insight into the role of adhesins, singly and in combinations, in mediating diverse facets of virulence of this critical fungal pathogen.

The transcription factor Ndt80 is a repressor of Candida parapsilosis virulence attributes

Candida parapsilosis is an emergent opportunistic yeast among hospital settings that affects mainly neonates and immunocompromised patients. Its most remarkable virulence traits are the ability to adhere to prosthetic materials, as well as the formation of biofilm on abiotic surfaces. The Ndt80 transcription factor was identified as one of the regulators of biofilm formation by C. parapsilosis; however, its function in this process was not yet clarified. By knocking out NDT80 (CPAR2-213640) gene, or even just one single copy of the gene, we observed substantial alterations of virulence attributes, including morphogenetic changes, adhesion and biofilm growth profiles. Both ndt80Δ and ndt80ΔΔ mutants changed colony and cell morphologies from smooth, yeast-shaped to crepe and pseudohyphal elongated forms, exhibiting promoted adherence to polystyrene microspheres and notably, forming a higher amount of biofilm compared to wild-type strain. Interestingly, we identified transcription factors Ume6, Cph2, Cwh41, Ace2, Bcr1, protein kinase Mkc1 and adhesin Als7 to be under Ndt80 negative regulation, partially explaining the phenotypes displayed by the ndt80ΔΔ mutant. Furthermore, ndt80ΔΔ pseudohyphae adhered more rapidly and were more resistant to murine macrophage attack, becoming deleterious to such cells after phagocytosis. Unexpectedly, our findings provide the first evidence for a direct role of Ndt80 as a repressor of C. parapsilosis virulence attributes. This finding shows that C. parapsilosis Ndt80 functionally diverges from its homolog in the close related fungal pathogen C. albicans.