Candida glabrata is a successful pathogen: an artist manipulating the immune response

Exploring the effects of culture conditions on Yapsin (YPS) gene expression in Nakaseomyces glabratus

Nakaseomyces glabratus, previously known as Candida glabrata, has the great potential to cause systemic fungal infections despite its similarity to baker's yeast. Its pathogenicity is attributed to the production of numerous virulence factors, among which the YPS genes (YPS1-YPS11) encoding aspartyl proteases have yet to be sufficiently characterized, and limited studies suggest their involvement in cellular homeostasis. The study's novelty is an investigation of the role of YPS in N. glabratus's ability to adapt to different host environments. For this purpose, we isolated RNA from N. glabratus cells grown in both host niche-mimicking culture media, such as artificial saliva (AS) and vagina-simulating media (VS), as well as standard yeast media (RPMI 1640 and YPDA). We then performed quantitative real-time PCR to evaluate YPS gene expression at different growth phases. At the early logarithmic phase, we observed a general increase in the expression levels of YPS genes; however, at the stationary phase, high expression levels were maintained for YPS7 in RPMI 1640 and YPDA media and YPS6 in RPMI 1640 and AS media. In addition, although the VS medium does not promote the proliferation of N. glabratus, the yeast can survive in an acidic environment, and the significantly overexpressed gene is YPS7. These findings underscore the significant modulation of N. glabratus YPS gene expression in response to external environmental conditions. This research provides insights into the molecular basis of N. glabratus pathogenicity and highlights new potential targets for antifungal therapy.

The Antifungal Potential of Ozonated Extra-Virgin Olive Oil Against Candida albicans: Mechanisms and Efficacy

The growing emergence of resistance mechanisms and side effects associated with antifungal agents highlight the need for alternative therapies. This study aims to investigate the antifungal potential of ozonated extra-virgin olive oil (EOO) against Candida albicans, with the goal of developing eco-friendly and highly effective treatments based on natural products. Antifungal activity was evaluated via cell viability and biofilm formation assays using Crystal Violet and Sytox green staining. The results showed that EOO reduced C. albicans viability in a dose-dependent manner, achieving over 90% cell death at a 3% (v/v) concentration. Transmission Electron Microscopy (TEM) revealed cell wall structural damage, and ROS levels increased by approximately 60% compared to untreated controls within 10 min of treatment. Additionally, the expression of autophagy-related genes atg-7 and atg-13was upregulated by 2- and 3.5-fold, respectively, after 15 min, suggesting a stress-induced cell death response. EOO also significantly inhibited hyphal formation and biofilm development, thus reducing C. albicans pathogenicity while preserving cell biocompatibility. EOO antifungal activity was also observed in the case of Candida glabrata. In conclusion, ozonated olive oil demonstrates potent antifungal activity against C. albicans by reducing cell viability, inhibiting hyphal and biofilm formation, and triggering oxidative stress and autophagy pathways. These findings position EOO as a promising alternative therapy for fungal infections.

Genomic characterisation of an extended-spectrum β-Lactamase-producing Klebsiella pneumoniae isolate assigned to a novel sequence type (6914)

BACKGROUND

Cow milk, which is sometimes consumed raw, hosts a plethora of microorganisms, some of which are beneficial, while others raise food safety concerns. In this study, the draft genome of an extended-spectrum β-lactamase-producing Klebsiella pneumoniae subsp. pneumoniae strain Cow102, isolated from raw cow milk used to produce traditional foods in Nigeria, is reported.

RESULT

The genome has a total length of 5,359,907 bp, with 70 contigs and a GC content of 57.35%. A total of 5,244 protein coding sequences were detected with 31% mapped to a subsystem, and genes coding for amino acids and derivatives being the most prevalent. Multilocus sequence typing revealed that the strain had new allelic profile assigned to the novel 6914 sequence type possessing capsular and lipopolysaccharide antigen K locus 122 with an unknown K type (KL122) and O locus O1/O2v2 with type O2afg, respectively. A total of 28 resistance-related genes, 98 virulence-related genes, two plasmids and five phages were identified in the genome. The resistance genes oqxA, oqxB and an IS3 belonging to cluster 204 were traced to bacteriophage Escher 500,465. Comparative analysis predicted one strain specific orthologous group comprising three genes.

CONCLUSION

This report of a novel sequence type (ST6914) in K. pneumoniae presents a new allelic profile, indicating ongoing evolution and diversification within the species. Its uniqueness suggests it may represent a locally evolved lineage, although further sampling would be necessary to confirm this hypothesis. The strain's multidrug resistance, virulence gene repertoire, and isolation from animal milk render it a potentially significant public health concern, underscoring the importance of genomic surveillance in non-clinical settings to detect emerging strains. Further research is required to fully characterise the capsular K type of ST6914.

Antibiofilm Activity of PDMS/TiO2 against Candida glabrata through Inhibited Hydrophobic Recovery

Coatings with antibiofilm properties are desirable for biomedical applications. Titanium dioxide (TiO2) has been explored as an antimicrobial agent in materials development primarily due to it being an excellent photocatalyst. Candida glabrata (C. glabrata) is an emerging human fungal pathogen with known high resistance to oxidative stress. Here, we fabricated a polydimethylsiloxane/titanium dioxide (PDMS/TiO2) nanocomposite coating and tested its antibiofilm activities against C. glabrata. The resulting nanocomposite exhibited >50% reduction in C. glabrata biofilm formation with 2.5 wt % TiO2 loading, even in the dark. Through ROS detection and surface characterization, the antibiofilm activity was attributed to the synergistic interaction of TiO2 nanoparticles with the PDMS matrix, which resulted in the impediment of hydrophobic recovery. This work provides a design strategy to develop antibiofilm coatings against C. glabrata.

Adhesive and biofilm-forming Candida glabrata Lebanese hospital isolates harbour mutations in subtelomeric silencers and adhesins

BACKGROUND

The prevalence of Candida glabrata healthcare-associated infections is on the rise worldwide and in Lebanon, Candida glabrata infections are difficult to treat as a result of their resistance to azole antifungals and their ability to form biofilms.

OBJECTIVES

The first objective of this study was to quantify biofilm biomass in the most virulent C. glabrata isolates detected in a Lebanese hospital. In addition, other pathogenicity attributes were evaluated. The second objective was to identify the mechanisms of azole resistance in those isolates.

METHODS

A mouse model of disseminated systemic infection was developed to evaluate the degree of virulence of 41 azole-resistant C. glabrata collected from a Lebanese hospital. The most virulent isolates were further evaluated alongside an isolate having attenuated virulence and a reference strain for comparative purposes. A DNA-sequencing approach was adopted to detect single nucleotide polymorphisms (SNPs) leading to amino acid changes in proteins involved in azole resistance and biofilm formation. This genomic approach was supported by several phenotypic assays.

RESULTS

All chosen virulent isolates exhibited increased adhesion and biofilm biomass compared to the isolate having attenuated virulence. The amino acid substitutions D679E and I739N detected in the subtelomeric silencer Sir3 are potentially involved- in increased adhesion. In all isolates, amino acid substitutions were detected in the ATP-binding cassette transporters Cdr1 and Pdh1 and their transcriptional regulator Pdr1.

CONCLUSIONS

In summary, increased adhesion led to stable biofilm formation since mutated Sir3 could de-repress adhesins, while decreased azole susceptibility could result from mutations in Cdr1, Pdh1 and Pdr1.

Complement receptor 3-dependent engagement by Candida glabrata β-glucan modulates dendritic cells to induce regulatory T-cell expansion

Candida glabrata is an important pathogen causing invasive infection associated with a high mortality rate. One mechanism that causes the failure of Candida eradication is an increase in regulatory T cells (Treg), which play a major role in immune suppression and promoting Candida pathogenicity. To date, how C. glabrata induces a Treg response remains unclear. Dendritic cells (DCs) recognition of fungi provides the fundamental signal determining the fate of the T-cell response. This study investigated the interplay between C. glabrata and DCs and its effect on Treg induction. We found that C. glabrata β-glucan was a major component that interacted with DCs and consequently mediated the Treg response. Blocking the binding of C. glabrata β-glucan to dectin-1 and complement receptor 3 (CR3) showed that CR3 activation in DCs was crucial for the induction of Treg. Furthermore, a ligand-receptor binding assay showed the preferential binding of C. glabrata β-glucan to CR3. Our data suggest that C. glabrata β-glucan potentially mediates the Treg response, probably through CR3-dependent activation in DCs. This study contributes new insights into immune modulation by C. glabrata that may lead to a better design of novel immunotherapeutic strategies for invasive C. glabrata infection.

Invasive candidiasis

Invasive candidiasis is an important fungal disease caused by Candida albicans and, increasingly, non-albicans Candida pathogens. Invasive Candida infections originate most frequently from endogenous human reservoirs and are triggered by impaired host defences. Signs and symptoms of invasive candidiasis are non-specific; candidaemia is the most diagnosed manifestation, with disseminated candidiasis affecting single or multiple organs. Diagnosis poses many challenges, and conventional culture techniques are frequently supplemented by non-culture-based assays. The attributable mortality from candidaemia and disseminated infections is ~30%. Fluconazole resistance is a concern for Nakaseomyces glabratus, Candida parapsilosis, and Candida auris and less so in Candida tropicalis infection; acquired echinocandin resistance remains uncommon. The epidemiology of invasive candidiasis varies in different geographical areas and within various patient populations. Risk factors include intensive care unit stay, central venous catheter use, broad-spectrum antibiotics use, abdominal surgery and immune suppression. Early antifungal treatment and central venous catheter removal form the cornerstones to decrease mortality. The landscape of novel therapeutics is growing; however, the application of new drugs requires careful selection of eligible patients as the spectrum of activity is limited to a few fungal species. Unanswered questions and knowledge gaps define future research priorities and a personalized approach to diagnosis and treatment of invasive candidiasis is of paramount importance.

Thiamine-Starved Lactococcus lactis for Producing Food-Grade Pyruvate

Lactococcus lactis is a safe lactic acid bacterium widely used in dairy fermentations. Normally, its main fermentation product is lactic acid; however, L. lactis can be persuaded into producing other compounds, e.g., through genetic engineering. Here, we have explored the possibility of rewiring the metabolism of L. lactis into producing pyruvate without using genetic tools. Depriving the thiamine-auxotrophic and lactate dehydrogenase-deficient L. lactis strain RD1M5 of thiamine efficiently shut down two enzymes at the pyruvate branch, the thiamine pyrophosphate (TPP) dependent pyruvate dehydrogenase (PDHc) and α-acetolactate synthase (ALS). After eliminating the remaining enzyme acting on pyruvate, the highly oxygen-sensitive pyruvate formate lyase (PFL), by simple aeration, the outcome was pyruvate production. Pyruvate could be generated by nongrowing cells and cells growing in a substrate low in thiamine, e.g., Florisil-treated milk. Pyruvate is a precursor for the butter aroma compound diacetyl. Using an α-acetolactate decarboxylase deficient L. lactis strain, pyruvate could be converted to α-acetolactate and diacetyl. Summing up, by starving L. lactis for thiamine, secretion of pyruvate could be attained. The food-grade pyruvate produced has many applications, e.g., as an antioxidant or be used to make butter aroma.

The regulatory subunits of CK2 complex mediate DNA damage response and virulence in Candida Glabrata

BACKGROUND

Candida glabrata which belongs to normal microbiota, has caused significant concern worldwide due to its high prevalence and drug resistance in recent years. C. glabrata has developed many strategies to evade the clearance of the host immune system, thereby causing persistent infection. Although coping with the induced DNA damage is widely acknowledged to be important, the underlying mechanisms remain unclear.

RESULTS

The present study provides hitherto undocumented evidence of the importance of the regulatory subunits of CgCK2 (CgCkb1 and CgCkb2) in response to DNA damage. Deletion of CgCKB1 or CgCKB2 enhanced cellular apoptosis and DNA breaks and led to cell cycle delay. In addition, deficiencies in survival upon phagocytosis were observed in Δckb1 and Δckb2 strains. Consistently, disruption of CgCKB1 and CgCKB2 attenuated the virulence of C. glabrata in mouse models of invasive candidiasis. Furthermore, global transcriptional profiling analysis revealed that CgCkb1 and CgCkb2 participate in cell cycle resumption and genomic stability.

CONCLUSIONS

Overall, our findings suggest that the response to DNA damage stress is crucial for C. glabrata to survive in macrophages, leading to full virulence in vivo. The significance of this work lies in providing a better understanding of pathogenicity in C. glabrata-related candidiasis and expanding ideas for clinical therapies.

Molecular investigations on Candida glabrata clinical isolates for pharmacological targeting

Prevalence of drug resistant C. glabrata strains in hospitalized immune-compromised patients with invasive fungal infections has increased at an unexpected pace. This has greatly pushed researchers in identification of mutations/variations in clinical isolates for better assessment of the prevailing drug resistance trends and also for updating of antifungal therapy regime. In the present investigation, the clinical isolates of C. glabrata were comprehensively characterized at a molecular level using metabolic profiling and transcriptional expression analysis approaches in combination with biochemical, morphological and chemical profiling methods. Biochemically, significant variations in azole susceptibility, surface hydrophobicity, and oxidative stress generation were observed among the isolates as compared to wild-type. The 1H NMR profiling identified 18 differential metabolites in clinical strains compared to wild-type and were classified into five categories, that include: sugars (7), amino acids and their derivatives (7), nitrogen bases (3) and coenzymes (1). Transcriptional analysis of selective metabolic and regulatory enzymes established that the major differences were found in cell membrane stress, carbohydrate metabolism, amino acid biosynthesis, ergosterol pathway and turnover of nitrogen bases. This detailed molecular level/metabolic fingerprint study is a useful approach for differentiating pathogenic/clinical isolates to that of wild-type. This study comprehensively delineated the differential cellular pathways at a molecular level that have been re-wired by the pathogenic clinical isolates for enhanced pathogenicity and virulence traits.

Evaluating the Typing Power of Six Isoenzymatic Systems for Differentiation of Clinical and Standard Isolates of Candida Species

Background

Due to the increasing prevalence of candidiasis, early detection of the causative agents may pave the way for the management of this infection. The present study aimed to assess the discriminative power of the six isoenzymatic systems for differentiating the Candida species.

Materials and Methods

Sixteen standard Candida albicans and Candida dubliniensis strains and 30 fluconazole-sensitive and fluconazole-resistant clinical strains of Candida albicans were analyzed using a Multilocus Enzyme Electrophoresis (MLEE) method, including six enzymatic systems consisting of malate dehydrogenase (MDH), phosphoglucomutase (PGM), glucose-phosphate isomerase (GPI), glucose-6-phosphate dehydrogenase (G6PDH), 6-phosphogluconate dehydrogenase (6PGD), and malic enzyme (ME).

Results

Among the six enzymatic systems, ME showed no diagnostic activity, whereas MDH provided the best species-specific pattern for species discrimination. In addition, the MDH and G6PD systems provided a discriminatory pattern for differentiating C. dubliniensis from C. albicans isolates. The same isoenzymatic activity was detected in all 36 standard and clinical isolates. Moreover, the results showed no correlation between the isoenzymatic profiles and drug resistance.

Conclusion

Among the investigated MLEE systems, MDH was able to differentiate between Candida albicans and Candida dubliniensis. Although no association was detected between isoenzyme patterns and fluconazole resistance in this investigation, isoenzyme patterns are likely correlated with virulence factors between species and even within species. To answer these questions, additional studies should be done on more strains.