Comparative adherence of Candida albicans and Candida dubliniensis to human buccal epithelial cells and extracellular matrix proteins

Candida albicans and Candida glabrata triosephosphate isomerase - a moonlighting protein that can be exposed on the candidal cell surface and bind to human extracellular matrix proteins

Background

Triosephosphate isomerase (Tpi1) is a glycolytic enzyme that has recently been reported also to be an atypical proteinaceous component of the Candida yeast cell wall. Similar to other known candidal “moonlighting proteins”, surface-exposed Tpi1 is likely to contribute to fungal adhesion during the colonization and infection of a human host. The aim of our present study was to directly prove the presence of Tpi1 on C. albicans and C. glabrata cells under various growth conditions and characterize the interactions of native Tpi1, isolated and purified from the candidal cell wall, with human extracellular matrix proteins.

Results

Surface plasmon resonance measurements were used to determine the dissociation constants for the complexes of Tpi1 with host proteins and these values were found to fall within a relatively narrow range of 10^− 8-10^− 7 M. Using a chemical cross-linking method, two motifs of the Tpi1 molecule (aa 4–17 and aa 224–247) were identified to be directly involved in the interaction with vitronectin. A proposed structural model for Tpi1 confirmed that these interaction sites were at a considerable distance from the catalytic active site. Synthetic peptides with these sequences significantly inhibited Tpi1 binding to several extracellular matrix proteins suggesting that a common region on the surface of Tpi1 molecule is involved in the interactions with the host proteins.

Conclusions

The current study provided structural insights into the interactions of human extracellular matrix proteins with Tpi1 that can occur at the cell surface of Candida yeasts and contribute to the host infection by these fungal pathogens.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12866-021-02235-w.

Lineage-specific selection and the evolution of virulence in the Candida clade

Of the many microbial species on earth, only a small number are able to thrive in humans and cause disease. Comparison of closely related pathogenic and nonpathogenic species can therefore be useful in identifying key features that contribute to virulence. We created interspecies hybrids between Candida albicans, a prevalent fungal pathogen of humans, and Candida dubliniensis, a close, but much less pathogenic, relative. By comparing genome-wide expression differences between the two genomes in the same cell, we surmised that since the two species diverged from a common ancestor, natural selection has acted upon the expression level of an ancient metabolic pathway, illustrating that pathogenicity traits can arise over evolutionary timescales through small expression changes in deeply conserved proteins.

Candida albicans is the most common cause of systemic fungal infections in humans and is considerably more virulent than its closest known relative, Candida dubliniensis. To investigate this difference, we constructed interspecies hybrids and quantified mRNA levels produced from each genome in the hybrid. This approach systematically identified expression differences in orthologous genes arising from cis-regulatory sequence changes that accumulated since the two species last shared a common ancestor, some 10 million y ago. We documented many orthologous gene-expression differences between the two species, and we pursued one striking observation: All 15 genes coding for the enzymes of glycolysis showed higher expression from the C. albicans genome than the C. dubliniensis genome in the interspecies hybrid. This pattern requires evolutionary changes to have occurred at each gene; the fact that they all act in the same direction strongly indicates lineage-specific natural selection as the underlying cause. To test whether these expression differences contribute to virulence, we created a C. dubliniensis strain in which all 15 glycolysis genes were produced at modestly elevated levels and found that this strain had significantly increased virulence in the standard mouse model of systemic infection. These results indicate that small expression differences across a deeply conserved set of metabolism enzymes can play a significant role in the evolution of virulence in fungal pathogens.

Different expression levels of ALS and SAP genes contribute to recurrent vulvovaginal candidiasis by Candida albicans

Aim: To study the behavior of Candida albicans in women with vulvovaginal candidiasis (VVC), recurrent VVC (RVVC) and asymptomatic (AS), regarding adhesion on HeLa cells and their ability to express secreted aspartic proteinases (SAP) genes, agglutinin-like sequence (ALS) genes and HWP1. Materials & methods: The adhesion of Candida albicans to HeLa cells was evaluated by colony-forming units, and the expressed genes were evaluated by qRT-PCR. Results: AS and VVC isolates showed greater ability to adhere HeLa cells when compared with RVVC isolate. Nevertheless, RVVC isolate exhibited upregulation of a large number of genes of ALS and SAP gene families and HWP1 gene. Conclusion: The results demonstrated that RVVC isolate expressed significantly important genes for invasion and yeast-host interactions.

Antifungal efficacy of atorvastatin-containing emulgel in the treatment of oral and vulvovaginal candidiasis

Drug repositioning has been an important ally in the search for new antifungal drugs. Statins are drugs that act to prevent sterol synthesis in both humans and fungi and for this reason they are promissory candidates to be repositioned to treat mycoses. In this study we evaluated the antifungal activity of atorvastatin by in vitro tests to determine the minimum inhibitory concentration against azole resistant Candida albicans and its mechanisms of action. Moreover, the efficacy of both atorvastatin-loaded oral and vaginal emulgels (0.75%, 1.5% and 3% w/w) was evaluated by means of in vivo experimental models of oral and vulvovaginal candidiasis, respectively. The results showed that atorvastatin minimal inhibitory concentration against C. albicans was 31.25 μg/ml. In oral candidiasis experiments, the group treated with oral emulgel containing 3.0% atorvastatin showcased total reduction in fungal load after nine days of treatment. Intravaginal delivery atorvastatin emulgel showed considerable effectiveness at the concentration of 3% (65% of fungal burden reduction) after nine days of treatment. From these findings, it is possible to assert that atorvastatin may be promising for drug repositioning towards the treatment of these opportunistic mycoses.

Anti-biofilm activity of antibody directed against surface antigen complement receptor 3-related protein-comparison of Candida albicans and Candida dubliniensis

Candida albicans and C. dubliniensis are related yeasts that differ in the expression of virulence-associated proteins involved in adherence and biofilm development. CR3-RP (complement receptor 3-related protein) is one of the surface antigens expressed by Candida species. The main objective of this research was to elucidate the effect of the polyclonal anti-CR3-RP antibody (Ab) on adherence and the biofilm formed by C. albicans SC5314 and C. dubliniensis CBS 7987 and two clinical isolates in vitro, ex vivo and in vivo. A comparison of species, and of treated vs. non-treated with the anti-CR3-RP Ab showed a reduction in adherence (22%-41%) that was dependent on the time point of evaluation (60, 90 or 120 min), but did not prove to be species-dependent. Confocal microscopy revealed a decreased thickness in biofilms formed by both species after pre-treatment with the anti-CR3-RP Ab. This observation was confirmed ex vivo by immunohistochemistry analysis of biofilms formed on mouse tongues. Moreover, anti-CR3-RP Ab administration, 1 h post-infection, has been shown to promote larval survival compared to the control group in a Galleria mellonella infection model. Our data suggest a potential activity of the anti-CR3-RP Ab relevant to immunotherapy or vaccine development against biofilm-associated Candida infections.

Population structure and molecular genetic characterization of 5-flucytosine-susceptible and -resistant clinical Candida dubliniensis isolates from Kuwait

Candida dubliniensis and Candida albicans are two closely related species. Although C. dubliniensis is less pathogenic, it has a higher propensity to develop resistance to fluconazole and some strains exhibit intrinsic resistance to 5-flucytosine (5-FC). All 5-FC-resistant isolates from Kuwait were previously shown to belong to one of seven internal transcribed spacer (ITS) region of rDNA-based haplotypes. This study performed fingerprinting of C. dubliniensis isolates by multilocus sequence typing (MLST) to determine population structure of 5-FC-resistant and -susceptible strains and compared the results with data from a global collection of isolates. Fifty-two C. dubliniensis isolates previously analyzed and 58 additional isolates mostly collected during 2010–2013 and characterized by phenotypic and molecular methods were used. ITS-based haplotypes were identified by haplotype-specific PCR and/or by PCR-DNA sequencing of rDNA. Population structure was determined by 8-loci-based MLST. E-test was used to determine susceptibility to 5-FC, fluconazole, voriconazole and amphotericin B. Five ITS haplotypes (ITSH) were detected among 110 C. dubliniensis isolates. The ITSH1 was most common (n = 80 isolates) followed by ITSH4 (n = 25 isolates). Two isolates each belonged to ITSH5 and ITSH8 while one isolate belonged to ITSH7. MLST identified 16 diploid sequence types (DSTs) including six new DSTs. DST11 (n = 52) and DST14 (n = 25) were dominant genotypes and were confined (together with DST21) to Middle-Eastern countries. Other DSTs (excluding some new DSTs) had a wider global distribution as they were identified from various other countries. Only ITSH4 isolates (n = 25) belonged to DST14, were resistant to 5-FC and contained S29L mutation in CdFCA1. ITSH5, ITSH7 and ITSH8 isolates belonged to different DSTs. Thus, clinical C. dubliniensis isolates in Kuwait exhibited limited genotypic heterogeneity and most isolates belonged to region-specific DSTs. All 5-FC-resistant C. dubliniensis isolates belonged to ITSH4 and MLST-based DST14 genotype. Placement of some isolates into additional ITS haplotypes is also supported by MLST data.

Conserved Patterns of Microbial Immune Escape: Pathogenic Microbes of Diverse Origin Target the Human Terminal Complement Inhibitor Vitronectin via a Single Common Motif

Pathogenicity of many microbes relies on their capacity to resist innate immunity, and to survive and persist in an immunocompetent human host microbes have developed highly efficient and sophisticated complement evasion strategies. Here we show that different human pathogens including Gram-negative and Gram-positive bacteria, as well as the fungal pathogen Candida albicans, acquire the human terminal complement regulator vitronectin to their surface. By using truncated vitronectin fragments we found that all analyzed microbial pathogens (n = 13) bound human vitronectin via the same C-terminal heparin-binding domain (amino acids 352-374). This specific interaction leaves the terminal complement complex (TCC) regulatory region of vitronectin accessible, allowing inhibition of C5b-7 membrane insertion and C9 polymerization. Vitronectin complexed with the various microbes and corresponding proteins was thus functionally active and inhibited complement-mediated C5b-9 deposition. Taken together, diverse microbial pathogens expressing different structurally unrelated vitronectin-binding molecules interact with host vitronectin via the same conserved region to allow versatile control of the host innate immune response.