Evaluation of Biofilm Formation in Candida tropicalis Using a Silicone-Based Platform with Synthetic Urine Medium

Gold nanorods non-functionalised and associated with gallic acid exhibit activity against non-albicans Candida species

Strategies focusing on natural compounds and nanotechnology have been explored to overcome the limitations of conventional therapies in managing Candida infections. In this context, metal nanoparticles, both non-functionalised and combined with gallic acid, may offer a promising alternative. This study investigated the effects of gold nanoparticles non-functionalised (AuNp) and associated with gallic acid (AuNpGA) against planktonic cells and biofilms of Nakaseomyces glabratus, Pichia kudriavzevii, Candida parapsilosis, and Candida tropicalis. Both AuNp and AuNpGA inhibited the growth of all strains at 1.56 µg/mL and exhibited fungicidal effects at concentrations ranging from 1.56 to 3.12 µg/mL. The time-kill curve revealed that AuNpGA and AuNp completely inhibited the viability of all strains in planktonic cultures at 8 and 24 h, respectively, exhibiting greater antifungal activity compared to fluconazole. Treatment with AuNp increased ROS production against N. glabratus and P. kudriavzevii. Oxidative stress was enhanced against all strains after treatment with AuNpGA, and exposure to this compound reduced ergosterol levels of P. kudriavzevii and C. parapsilosis. Furthermore, AuNpGA and AuNp significantly decreased the viability of all Candida biofilms at 7.8 and 15.6 µg/mL, respectively. In summary, both gold nanoparticles exhibited activity against planktonic cells and biofilms, suggesting their potential as agents for treating Candida infections.

Features of the rare pathogen Meyerozyma guilliermondii strain SO and comprehensive in silico analyses of its adherence-contributing virulence factor agglutinin-like sequences

Meyerozyma guilliermondii is a rare yeast pathogen contributing to the deadly invasive candidiasis. M. guilliermondii strain SO, as a promising protein expression host, showed 99% proteome similarity with the clinically isolated ATCC 6260 (type strain) in a recent comparative genomic analysis. However, their in vitro virulence features and in vivo pathogenicity were uncharacterized. This study aimed to characterize the in vitro and in vivo pathogenicity of M. guilliermondii strain SO and analyze its Als proteins (MgAls) via comprehensive bioinformatics approaches. M. guilliermondii strain SO showed lower and higher sensitivity towards β-mercaptoethanol and lithium, respectively than the avirulent S. cerevisiae but exhibited the same tolerance towards cell wall-perturbing Congo Red with C. albicans. With 7.5× higher biofilm mass, M. guilliermondii strain SO also demonstrated 75% higher mortality rate in the zebrafish embryos with a thicker biofilm layer on the chorion compared to the avirulent S. cerevisiae. Being one of the most important Candida adhesins, sequence and structural analyses of four statistically identified MgAls showed that MgAls1056 was predicted to exhibit the most conserved amyloid-forming regions, tandem repeat domain and peptide binding cavity (PBC) compared to C. albicans Als3. Favoured from the predicted largest ligand binding site and druggable pockets, it showed the highest affinity towards hepta-threonine. Non-PBC druggable pockets in the most potent virulence contributing MgAls1056 provide new insights into developing antifungal drugs targeting non-albicans Candida spp. Virtual screening of available synthetic or natural bioactive compounds and MgAls1056 deletion from the fungal genome should be further performed and validated experimentally.

The Anti-candidal and Absorbtion Performance of PVA/PVP-Based Jania rubens Hydrogel on Candida tropicalis and Some Physicochemical Properties of the Hydrogel

This study was aimed to create a bioactive hydrogel form with PVA/PVP (polyvinyl alcohol/poly(N-vinylpyrrolidone) polymer using acetone and ethanol extractions of Jania rubens red algae and investigate some pharmaceutical properties. The anti-candidal activity and some inhibition performance of J. rubens/PVA/PVP hydrogel were investigated on Candida tropicalis which is one of the important causes of bloodstream infections. The physicochemical properties of J. rubens/PVA/PVP hydrogel were revealed using FTIR and swelling-absorption tests. The volatile compounds of J. rubens extracts were examined by GCMS. By mixing the extracts in equal proportions, PVA/PVP-based hydrogel was prepared. According to the results, Cumulative Drug Release was stable at 25 °C for the first 5 h. The IZ (inhibition zone) and MIC (minimum inhibitory concentration) of J. rubens/PVA/PVP hydrogel were 9.01 mm and 80.20 mg/mL, respectively. It was found that logarithmic reduction and percent reduction were seen as 1.5 CFU/mL and 97.5%, respectively, on C. tropicalis exposed to J. rubens/PVA/PVP hydrogel in the first 5 min of the incubation. After exposure of C. tropicalis to J. rubens/PVA/PVP, the number of viable cells transferred from the gel to water was between 76.1 and 73.1% in high glucose medium, while it was between 92.2 and 80.8% for the PVA/PVP hydrogel under the same conditions. As a result, PVA/PVP hydrogel was made bioactive with J. rubens extracts for the first time in this study, and its potential for use as a functional anticandidal hydrogel on C. tropicalis has been demonstrated.

A gain-of-function mutation in zinc cluster transcription factor Rob1 drives Candida albicans adaptive growth in the cystic fibrosis lung environment

Candida albicans chronically colonizes the respiratory tract of patients with Cystic Fibrosis (CF). It competes with CF-associated pathogens (e.g. Pseudomonas aeruginosa) and contributes to disease severity. We hypothesize that C. albicans undergoes specific adaptation mechanisms that explain its persistence in the CF lung environment. To identify the underlying genetic and phenotypic determinants, we serially recovered 146 C. albicans clinical isolates over a period of 30 months from the sputum of 25 antifungal-naive CF patients. Multilocus sequence typing analyses revealed that most patients were individually colonized with genetically close strains, facilitating comparative analyses between serial isolates. We strikingly observed differential ability to filament and form monospecies and dual-species biofilms with P. aeruginosa among 18 serial isolates sharing the same diploid sequence type, recovered within one year from a pediatric patient. Whole genome sequencing revealed that their genomes were highly heterozygous and similar to each other, displaying a highly clonal subpopulation structure. Data mining identified 34 non-synonymous heterozygous SNPs in 19 open reading frames differentiating the hyperfilamentous and strong biofilm-former strains from the remaining isolates. Among these, we detected a glycine-to-glutamate substitution at position 299 (G299E) in the deduced amino acid sequence of the zinc cluster transcription factor ROB1 (ROB1G299E), encoding a major regulator of filamentous growth and biofilm formation. Introduction of the G299E heterozygous mutation in a co-isolated weak biofilm-former CF strain was sufficient to confer hyperfilamentous growth, increased expression of hyphal-specific genes, increased monospecies biofilm formation and increased survival in dual-species biofilms formed with P. aeruginosa, indicating that ROB1G299E is a gain-of-function mutation. Disruption of ROB1 in a hyperfilamentous isolate carrying the ROB1G299E allele abolished hyperfilamentation and biofilm formation. Our study links a single heterozygous mutation to the ability of C. albicans to better survive during the interaction with other CF-associated microbes and illuminates how adaptive traits emerge in microbial pathogens to persistently colonize and/or infect the CF-patient airways.

Convergent and divergent roles of the glucose-responsive kinase SNF4 in Candida tropicalis

The sucrose non-fermenting 1 (SNF1) complex is a heterotrimeric protein kinase complex that is an ortholog of the mammalian AMPK complex and is evolutionally conserved in most eukaryotes. This complex contains a catalytic subunit (Snf1), a regulatory subunit (Snf4) and a scaffolding subunit (Sip1/Sip2/Gal73) in budding yeast. Although the function of AMPK has been well studied in Saccharomyces cerevisiae and Candida albicans, the role of AMPK in Candida tropicalis has never been investigated. In this study, we focused on SNF4 in C. tropicalis as this fungus cannot produce a snf1Δ mutant. We demonstrated that C. tropicalis SNF4 shares similar roles in glucose derepression and is necessary for cell wall integrity and virulence. The expression of both SNF1 and SNF4 was significantly induced when glucose was limited. Furthermore, snf4Δ strains exhibited high sensitivity to many surface-perturbing agents because the strains contained lower levels of glucan, chitin and mannan. Interestingly, in contrast to C. albicans sak1Δ and snf4Δ, C. tropicalis snf4Δ exhibited phenotypes for cell aggregation and pseudohypha production. These data indicate that SNF4 performs convergent and divergent roles in C. tropicalis and possibly other unknown roles in the C. tropicalis SNF1-SNF4 AMPK pathway.

Rice Big Grain1 enhances biomass and plant growth-promoting traits in rhizospheric yeast Candida tropicalis

The Big Grain1 (BG1) gene of rice (Oryza sativa L.) is reported to increase the yield of rice crops; however, its molecular mechanism is largely concealed. To explore its functional prospects, we have taken a structure-function-based approach. In silico analyses suggest OsBG1 is a DNA- and phytohormone-binding protein. Heterologous expression of OsBG1 with galactose-inducible promoter GAL1p in the rhizospheric yeast Candida tropicalis SY005 revealed 7.9- and 1.5-fold higher expression of the gene at 12 and 24 h, respectively, compared to the expression at 36 h post-galactose induction. Functional activity of the induced OsBG1 in engineered yeast increased cell density, specific growth rate, and biomass by 28.5%, 29.8%, and 14.1%, respectively, and decreased the generation time by 21.25%. Flow cytometry-based cell cycle analysis of OsBG1-expressing yeast cells exhibited an increase in the cells of the G2/M population by 15.8% after 12 h of post-galactose induction. The gene expression study of yeast transformants disclosed that OsBG1 regulates cell division by upregulating the expression of the endogenous gene cyclin B1 (CtCYB1) by 1.3- and 1.9-folds at 10 and 12 h, respectively, compared to the control, and is positively influenced by the phytohormone indole acetic acid (IAA). Further, the study revealed that OsBG1 significantly increases biofilm formation, stress tolerance, and IAA production in C. tropicalis SY005, implying its prospective role in enhancing plant growth-promoting traits in microbes. OsBG1-expressing rhizospheric yeast cells significantly improved the germination and growth parameters of the bio-inoculated rice seeds. Altogether, this study suggests OsBG1 can be employed to genetically improve suitable bio-inoculants for their plant growth-promoting traits to augment crop productivity. KEY POINTS: • In silico analyses suggested OsBG1 is a phytohormone-binding transcription factor. • OsBG1 enhanced growth in rhizospheric Candida tropicalis by upregulating CtCYB1. • OsBG1 improved plant growth-promoting traits of the rhizospheric yeast C. tropicalis.

Biofilm Formation in Medically Important Candida Species

Worldwide, the number of infections caused by biofilm-forming fungal pathogens is very high. In human medicine, there is an increasing proportion of immunocompromised patients with prolonged hospitalization, and patients with long-term inserted drains, cannulas, catheters, tubes, or other artificial devices, that exhibit a predisposition for colonization by biofilm-forming yeasts. A high percentage of mortality is due to candidemia caused by medically important Candida species. Species of major clinical significance include C. albicans, C. glabrata, C. tropicalis, C. parapsilosis, C. krusei, and C. auris. The association of these pathogenic species in the biofilm structure is a serious therapeutic problem. Candida cells growing in the form of a biofilm are able to resist persistent therapy thanks to a combination of their protective mechanisms and their ability to disseminate to other parts of the body, thus representing a threat from the perspective of a permanent source of infection. The elucidation of the key mechanisms of biofilm formation is essential to progress in the understanding and treatment of invasive Candida infections.

Inhibitory effect of lactobacilli supernatants on biofilm and filamentation of Candida albicans, Candida tropicalis, and Candida parapsilosis

Introduction

Probiotic Lactobacillus strains had been investigated for the potential to protect against infection caused by the major fungal pathogen of human, Candida albicans. Besides antifungal activity, lactobacilli demonstrated a promising inhibitory effect on biofilm formation and filamentation of C. albicans. On the other hand, two commonly isolated non-albicans Candida species, C. tropicalis and C. parapsilosis, have similar characteristics in filamentation and biofilm formation with C. albicans. However, there is scant information of the effect of lactobacilli on the two species.

Methods

In this study, biofilm inhibitory effects of L. rhamnosus ATCC 53103, L. plantarum ATCC 8014, and L. acidophilus ATCC 4356 were tested on the reference strain C. albicans SC5314 and six bloodstream isolated clinical strains, two each of C. albicans, C. tropicalis, and C. parapsilosis.

Results and Discussion

Cell-free culture supernatants (CFSs) of L. rhamnosus and L. plantarum significantly inhibited in vitro biofilm growth of C. albicans and C. tropicalis. L. acidophilus, conversely, had little effect on C. albicans and C. tropicalis but was more effective on inhibiting C. parapsilosis biofilms. Neutralized L. rhamnosus CFS at pH 7 retained the inhibitory effect, suggesting that exometabolites other than lactic acid produced by the Lactobacillus strain might be accounted for the effect. Furthermore, we evaluated the inhibitory effects of L. rhamnosus and L. plantarum CFSs on the filamentation of C. albicans and C. tropicalis strains. Significantly less Candida filaments were observed after co-incubating with CFSs under hyphae-inducing conditions. Expressions of six biofilm-related genes (ALS1, ALS3, BCR1, EFG1, TEC1, and UME6 in C. albicans and corresponding orthologs in C. tropicalis) in biofilms co-incubated with CFSs were analyzed using quantitative real-time PCR. When compared to untreated control, the expressions of ALS1, ALS3, EFG1, and TEC1 genes were downregulated in C. albicans biofilm. In C. tropicalis biofilms, ALS3 and UME6 were downregulated while TEC1 was upregulated. Taken together, the L. rhamnosus and L. plantarum strains demonstrated an inhibitory effect, which is likely mediated by the metabolites secreted into culture medium, on filamentation and biofilm formation of C. albicans and C. tropicalis. Our finding suggested an alternative to antifungals for controlling Candida biofilm.

Growing importance of urogenital candidiasis in individuals with diabetes: A narrative review

Both diabetes and fungal infections contribute significantly to the global disease burden, with increasing trends seen in most developed and developing countries during recent decades. This is reflected in urogenital infections caused by Candida species that are becoming ever more pervasive in diabetic patients, particularly those that present with unsatisfactory glycemic control. In addition, a relatively new group of anti-hyperglycemic drugs, known as sodium glucose cotransporter 2 inhibitors, has been linked with an increased risk for colonization of the urogenital region with Candida spp., which can subsequently lead to an infectious process. In this review paper, we have highlighted notable virulence factors of Candida species (with an emphasis on Candida albicans) and shown how the interplay of many pathophysiological factors can give rise to vulvovaginal candidiasis, potentially complicated with recurrences and dire pregnancy outcomes. We have also addressed an increased risk of candiduria and urinary tract infections caused by species of Candida in females and males with diabetes, further highlighting possible complications such as emphysematous cystitis as well as the risk for the development of balanitis and balanoposthitis in (primarily uncircumcised) males. With a steadily increasing global burden of diabetes, urogenital mycotic infections will undoubtedly become more prevalent in the future; hence, there is a need for an evidence-based approach from both clinical and public health perspectives.

Candida Albicans Virulence Factors and Its Pathogenicity

Candida albicans lives as commensal on the skin and mucosal surfaces of the genital, intestinal, vaginal, urinary, and oral tracts of 80% of healthy individuals [...].

Candida tropicalis RON1 is required for hyphal formation, biofilm development, and virulence but is dispensable for N-acetylglucosamine catabolism

NDT80-like family genes are highly conserved across a large group of fungi, but the functions of each Ndt80 protein are diverse and have evolved differently among yeasts and pathogens. The unique NDT80 gene in budding yeast is required for sexual reproduction, whereas three NDT80-like genes, namely, NDT80, REP1, and RON1, found in Candida albicans exhibit distinct functions. Notably, it was suggested that REP1, rather than RON1, is required for N-acetylglucosamine (GlcNAc) catabolism. Although Candida tropicalis, a widely dispersed fungal pathogen in tropical and subtropical areas, is closely related to Candida albicans, its phenotypic, pathogenic and environmental adaptation characteristics are remarkably divergent. In this study, we focused on the Ron1 transcription factor in C. tropicalis. Protein alignment showed that C. tropicalis Ron1 (CtRon1) shares 39.7% identity with C. albicans Ron1 (CaRon1). Compared to the wild-type strain, the C. tropicalis ron1Δ strains exhibited normal growth in different carbon sources and had similar expression levels of several GlcNAc catabolic genes during GlcNAc treatment. In contrast, C. tropicalis REP1 is responsible for GlcNAc catabolism and is involved in GlcNAc catabolic gene expressions, similar to C. albicans Rep1. However, REP1 deletion strains in C. tropicalis promote hyphal development in GlcNAc with low glucose content. Interestingly, CtRON1, but not CaRON1, deletion mutants exhibited significantly impaired hyphal growth and biofilm formation. As expected, CtRON1 was required for full virulence. Together, the results of this study showed divergent functions of CtRon1 compared to CaRon1; CtRon1 plays a key role in yeast-hyphal dimorphism, biofilm formation and virulence.

LAY ABSTRACT

In this study, we identified the role of RON1, an NDT80-like gene, in Candida tropicalis. Unlike the gene in Candida albicans, our studies showed that RON1 is a key regulator of hyphal formation, biofilm development and virulence but is dispensable for N-acetylglucosamine catabolism in C. tropicalis.