Candida auris Forms High-Burden Biofilms in Skin Niche Conditions and on Porcine Skin

Dual function of Candida auris mannosyltransferase, MNT5, in biofilm community protection from antifungal therapy and the host

Screen of mutants from a mannosyltransferase family identified the importance of MNT5 for C. auris biofilm drug resistance and neutrophil evasion. Biochemical analysis of the mnt5∆ mutant matrix and cell wall identified alterations in the mannan structures. Resistance and matrix for mnt5∆ were restored with delivery of wild-type matrix via extracellular vesicles. Analysis of the mnt5∆ cell wall revealed a reduction in mannan and compensatory increase in cell surface glucan and chitin, suggesting a role for MNT5 in mannan masking of pathogen-associated molecular patterns.

IMPORTANCE

C. auris recalcitrance is linked to biofilm drug resistance and immune evasion. The mannosyltransferase encoded by MNT5 is necessary for both phenotypes and may serve as a useful therapeutic target.

Impact of Candida auris on Critically Ill Patients: A Three-Year Observational Study in a Greek Intensive Care Unit

Candida auris has emerged as a multidrug-resistant yeast implicated in healthcare-associated invasive infections and hospital outbreaks. The aim of the current 38-month period observational study in a multidisciplinary Intensive Care Unit (ICU) was to analyze the epidemiology, potential risk factors, management strategies, and patient outcomes of patients with C. auris. During the study period, 32 patients were identified with C. auris infection (6 patients) or colonization (26 patients) and their clinical characteristics and treatment-related factors were compared. Identification of C. auris isolates was confirmed by MALDI-TOF spectrometry. According to our results, regarding patient-related factors, no significant differences were identified. Regarding treatment-related factors, the proportion of patients already receiving corticosteroids (34.6% vs. 83.3%, p = 0.064) or being on renal replacement treatment (7.7% vs. 33.3%) was higher in infected patients. Median time elapsed from ICU admission to first positive culture was 7 (1-21) days and half of cases were ICU-imported. All strains were resistant to fluconazole and susceptible to echinocandines and amphotericin B. Crude mortality of the study population was 43.75%, similar to other previously reported candidemias. Rapid identification of C. auris, continued surveillance, and infection control practices are important elements for controlling successfully its spread in the hospital setting and for establishing promptly its transition from commensalism to infection.

Candida Infections: The Role of Saliva in Oral Health-A Narrative Review

Candida species, particularly Candida albicans, are causative agents of oral infections to which immunocompromised patients are especially susceptible. Reduced saliva flow (xerostomia) can lead to Candida overgrowth, as saliva contains antibacterial components such as histatins and β-defensins that inhibit fungal growth and adhesion to the oral mucosa. Candida adheres to host tissues, forms biofilms, and secretes enzymes required for tissue invasion and immune evasion. Secretory asparaginyl proteinases (Saps) and candidalysin, a cytolytic peptide toxin, are vital to Candida virulence, and agglutinin-like sequence (Als) proteins are crucial for adhesion, invasion, and biofilm formation. C. albicans is a risk factor for dental caries and may increase periodontal disease virulence when it coexists with Porphyromonas gingivalis. Candida infections have been suggested to heighten the risk of oral cancer based on a relationship between Candida species and oral squamous cell carcinoma (OSCC) or oral potentially malignant disorder (OPMD). Meanwhile, β-glucan in the Candida cell wall has antitumor effects. In addition, Candida biofilms protect viruses such as herpesviruses and coxsackieviruses. Understanding the intricate interactions between Candida species, host immune responses, and coexisting microbial communities is essential for developing preventive and therapeutic strategies against oral Candida infections, particularly in immunocompromised individuals.

Candida auris: A Continuing Threat

Candida auris is a World Health Organization critical-priority fungal pathogen that has variable resistance to antifungal treatments. Multiple clades have been identified through genomic analysis and have appeared in different geographic locations simultaneously. Due to a combination of factors including antifungal resistance, ability to colonize and persist in the environment, and thermotolerance, it can thrive. Infected patients are associated with a high mortality rate, especially those with multiple health risk factors like those associated with other Candida species. This review highlights the current situation of this pathogen to help provide guidance for future work.

Candida auris Outbreak and Epidemiologic Response in Burn Intensive Care Unit, Illinois, USA, 2021-2023

Candida auris is an emerging fungal pathogen associated with outbreaks in healthcare settings. We report a multiyear outbreak of C. auris in a burn intensive care unit in Illinois, USA, during 2021-2023. We identified 28 C. auris cases in the unit over a 2-year period, despite outbreak response and multimodal mitigation measures. Of the 28 case-patients, 15 (53.6%) were considered colonized and 13 (46.4%) had clinical infections. Phylogenetic analysis of whole-genome sequences revealed 4 distinct clusters of closely related (0-6 SNP differences) genomes containing 3-6 cases. Clusters generally contained temporally related isolates from patients with epidemiologic links; this finding suggests that multiple introductions and within-unit spread over a limited time were responsible for the outbreak, rather than transmission from a long-term source (e.g., persistent environmental contamination or staff carriage). Here, integrated traditional and genomic epidemiology supported C. auris outbreak investigation and response and informed targeted interventions.

A Novel and Robust Method for Investigating Fungal Biofilm

Candida auris, labeled an urgent threat by the CDC, shows significant resilience to treatments and disinfectants via biofilm formation, complicating treatment/disease management. The inconsistencies in biofilm architecture observed across studies hinder the understanding of its role in pathogenesis. Our novel in vitro technique cultivates C. auris biofilms on gelatin-coated coverslips, reliably producing multilayer biofilms with extracellular polymeric substances (EPS). This method, applicable to other Candida species like C. glabrata and C. albicans, is cost-effective and mimics the niche of biofilm formation. It is suitable for high-throughput drug screening and repurposing efforts, aiding in the development of new therapeutics. Our technique represents a significant advancement in Candida biofilm research, addressing the need for consistent, reproducible biofilm models. We detail a step-by-step procedure for creating a substratum for biofilm growth and measuring biofilm thickness using confocal laser scanning microscopy (CLSM) and ultrastructure by scanning electron microscopy (SEM). This method provides consistent outcomes across various Candida species. Key features • The biofilm formed on gelatin surfaces mimics host conditions, replicating the multilayered structure and EPS, offering a more accurate model for studying C. auris biofilms. • This method is highly reproducible and suitable for drug screening and biofilm analysis through three-dimensional (3D) reconstruction. • This in vitro technique aids in studying biofilm formation, related virulence properties, and drug tolerance of C. auris and other Candida species. • The simple, cost-effective technique is ideal for screening novel inhibitors and repurposed drug libraries, facilitating the design/identification of new therapeutics against Candida species.

Alkaloids solenopsins from fire ants display in vitro and in vivo activity against the yeast Candida auris

The urgency surrounding Candida auris as a public health threat is highlighted by both the Center for Disease Control (CDC) and World Health Organization (WHO) that categorized this species as a priority fungal pathogen. Given the current limitations of antifungal therapy for C. auris, particularly due to its multiple resistance to the current antifungals, the identification of new drugs is of paramount importance. Some alkaloids abundant in the venom of the red invasive fire ant (Solenopsis invicta), known as solenopsins, have garnered attention as potent inhibitors of bacterial biofilms, and there are no studies demonstrating such effects against fungal pathogens. Thus, we herein investigated the antibiotic efficacy of solenopsin alkaloids against C. auris biofilms and planktonic cells. Both natural and synthetic solenopsins inhibited the growth of C. auris strains from different clades, including fluconazole and amphotericin B-resistant isolates. Such alkaloids also inhibited matrix deposition and altered cellular metabolic activity of C. auris in biofilm conditions. Mechanistically, the alkaloids compromised membrane integrity as measured by propidium iodide uptake in exposed planktonic cells. Additionally, combining the alkaloids with AMB yielded an additive antifungal effect, even against AMB-resistant strains. Finally, both extracted solenopsins and the synthetic analogues demonstrated protective effect in vivo against C. auris infection in the invertebrate model Galleria mellonella. These findings underscore the potent antifungal activities of solenopsins against C. auris and suggest their inclusion in future drug development. Furthermore, exploring derivatives of solenopsins could reveal novel compounds with therapeutic promise.

The Candida auris Hog1 MAP kinase is essential for the colonization of murine skin and intradermal persistence

Candida auris, a multidrug-resistant human fungal pathogen, was first identified in 2009 in Japan. Since then, systemic C. auris infections have now been reported in more than 50 countries, with mortality rates of 30%-60%. A major contributing factor to its high inter- and intrahospital clonal transmission is that C. auris, unlike most Candida species, displays unique skin tropism and can stay on human skin for a prolonged period. However, the molecular mechanisms responsible for C. auris skin colonization, intradermal persistence, and systemic virulence are poorly understood. Here, we report that C. auris Hog1 mitogen-activated protein kinase is essential for efficient skin colonization, intradermal persistence as well as systemic virulence. RNA-seq analysis of wild-type parental and hog1Δ mutant strains revealed marked downregulation of genes involved in processes such as cell adhesion, cell wall rearrangement, and pathogenesis in hog1Δ mutant compared to the wild-type parent. Consistent with these data, we found a prominent role for Hog1 in maintaining cell wall architecture, as the hog1Δ mutant demonstrated a significant increase in cell-surface β-glucan exposure and a concomitant reduction in chitin content. Additionally, we observed that Hog1 was required for biofilm formation in vitro and fungal survival when challenged with primary murine macrophages and neutrophils ex vivo. Collectively, these findings have important implications for understanding the C. auris skin adherence mechanisms and penetration of skin epithelial layers preceding bloodstream infections.

IMPORTANCE

Candida auris is a World Health Organization fungal priority pathogen and an urgent public health threat recognized by the Centers for Disease Control and Prevention. C. auris has a unique ability to colonize human skin. It also persists on abiotic surfaces in healthcare environments for an extended period of time. These attributes facilitate the inter- and intrahospital clonal transmission of C. auris. Therefore, understanding C. auris skin colonization mechanisms is critical for infection control, especially in hospitals and nursing homes. However, despite its profound clinical relevance, the molecular and genetic basis of C. auris skin colonization mechanisms are poorly understood. Herein, we present data on the identification of the Hog1 MAP kinase as a key regulator of C. auris skin colonization. These findings lay the foundation for further characterization of unique mechanisms that promote fungal persistence on human skin.

Ume6-dependent pathways of morphogenesis and biofilm formation in Candida auris

Candida auris is a yeast pathogen causing nosocomial outbreaks of candidemia. Its ability to adhere to inert surfaces and to be transmitted from one patient to another via medical devices is of particular concern. Like other Candida spp., C. auris has the ability to transition from the yeast form to pseudohyphae and to build biofilms. Moreover, some isolates have a unique capacity to form aggregates. These morphogenetic changes may impact virulence. In this study, we demonstrated the role of the transcription factor Ume6 in C. auris morphogenesis. Genetic hyperactivation of Ume6 induced filamentation and aggregation. The Ume6-hyperactivated strain (UME6HA) also exhibited increased adhesion to inert surface and formed biofilms of higher biomass compared to the parental strain. Transcriptomic analyses of UME6HA revealed enrichment of genes encoding for adhesins, proteins involved in cell wall organization, sterol biosynthesis, and aspartic protease activities. The three most upregulated genes compared to wild-type were those encoding for the agglutin-like sequence adhesin Als4498, the C. auris-specific adhesin Scf1, and the hypha-specific G1 cyclin-related protein Hgc1. The deletion of these genes in the UME6HA background showed that Ume6 controls filamentation via Hgc1 and aggregation via Als4498 and Scf1. Adhesion to inert surface was essentially triggered by Scf1. However, Als4498 and Hgc1 were also crucial for biofilm formation. Our data show that Ume6 is a universal regulator of C. auris morphogenesis via distinct modulators.IMPORTANCEC. auris represents a public health threat because of its ability to cause difficult-to-treat infections and hospital outbreaks. The morphogenetic plasticity of C. auris, including its ability to filament, to form aggregates or biofilms on inert surfaces, is important to the fungus for interhuman transmission, skin or catheter colonization, tissue invasion, antifungal resistance, and escape of the host immune system. This work deciphered the importance of Ume6 in the control of distinct pathways involved in filamentation, aggregation, adhesion, and biofilm formation of C. auris. A better understanding of the mechanisms of C. auris morphogenesis may help identify novel antifungal targets.

Metabolic homeostasis in fungal infections from the perspective of pathogens, immune cells, and whole-body systems

SUMMARYThe ability to overcome metabolic stress is a major determinant of outcomes during infections. Pathogens face nutrient and oxygen deprivation in host niches and during their encounter with immune cells. Immune cells require metabolic adaptations for producing antimicrobial compounds and mounting antifungal inflammation. Infection also triggers systemic changes in organ metabolism and energy expenditure that range from an enhanced metabolism to produce energy for a robust immune response to reduced metabolism as infection progresses, which coincides with immune and organ dysfunction. Competition for energy and nutrients between hosts and pathogens means that successful survival and recovery from an infection require a balance between elimination of the pathogen by the immune systems (resistance), and doing so with minimal damage to host tissues and organs (tolerance). Here, we discuss our current knowledge of pathogen, immune cell and systemic metabolism in fungal infections, and the impact of metabolic disorders, such as obesity and diabetes. We put forward the idea that, while our knowledge of the use of metabolic regulation for fungal proliferation and antifungal immune responses (i.e., resistance) has been growing over the years, we also need to study the metabolic mechanisms that control tolerance of fungal pathogens. A comprehensive understanding of how to balance resistance and tolerance by metabolic interventions may provide insights into therapeutic strategies that could be used adjunctly with antifungal drugs to improve patient outcomes.

Vertebrate and invertebrate animal infection models of Candida auris pathogenicity

Candida auris is an emerging fungal pathogen with several concerning qualities. First recognized in 2009, it has arisen in multiple geographically distinct genomic clades nearly simultaneously. C. auris strains are typically multidrug resistant and colonize the skin much better than most other pathogenic fungi; it also persists on abiotic surfaces, enabling outbreaks due to transmission in health care facilities. All these suggest a biology substantially different from the 'model' fungal pathogen, Candida albicans and support intensive investigation of C. auris biology directly. To uncover novel virulence mechanisms in this species requires the development of appropriate animal infection models. Various studies using mice, the definitive model, are inconsistent due to differences in mouse and fungal strains, immunosuppressive regimes, doses, and outcome metrics. At the same time, developing models of skin colonization present a route to new insights into an aspect of fungal pathogenesis that has not been well studied in other species. We also discuss the growing use of nonmammalian model systems, including both vertebrates and invertebrates, such as zebrafish, C. elegans, Drosophila, and Galleria mellonella, that have been productively employed in virulence studies with other fungal species. This review will discuss progress in developing appropriate animal models, outline current challenges, and highlight opportunities in demystifying this curious species.

Suppressing the virulence factors of Candida auris with baicalein through multifaceted mechanisms

Candida auris, a rapidly spreading multi-drug-resistant fungus, is causing lethal infections under certain conditions globally. Baicalin (BE), an active ingredient extracted from the dried root of Scutellaria baicalensis Georgi, exhibits antifungal activity. However, studies have shown the distinctive advantages of Traditional Chinese medicine in combating fungal infections, while the effect of BE, an active ingredient extracted from the dried roots of Scutellaria baicalensis Georgi, on C. auris, remains unknown. Therefore, this study aims to evaluate the potential of BE as an antifungal agent against the emerging multidrug-resistant C. auris. Various assays and models, including microbroth dilution, time growth curve analysis, spot assays, adhesion tests, flocculation test, cell surface hydrophobicity assay, hydrolase activity assays, XTT assay, violet crystal assay, scanning electron microscope (SEM), confocal laser scanning microscope (CLSM), flow cytometry, Live/dead fluorescent staining, reactive oxygen species (ROS), cell wall assay, aggregation assay, porcine skin model, Galleria mellonella larvae (G. mellonella larvae) infection model, and reverse transcription-quantitative polymerase chain reaction (RT-PCR) were utilized to investigate how baicalein suppresses C. auris through possible multifaceted mechanisms. The findings indicate that BE strongly inhibited C. auris growth, adhesion, and biofilm formation. It also effectively reduced drug resistance and aggregation by disrupting the cell membrane and cell wall while reducing colonization and invasion of the host. Transcriptome analysis showed significant modulation in gene expression related to different virulence factors post-BE treatment. In conclusion, BE exhibits significant effectiveness against C. auris, suggesting its potential as a viable treatment option due to its multifaceted suppression mechanisms.

Transcriptome Analysis of Human Dermal Cells Infected with Candida auris Identified Unique Pathogenesis/Defensive Mechanisms Particularly Ferroptosis

Candida auris is an emerging multi-drug resistant yeast that can cause life-threatening infections. A recent report clarified the ability of C. auris to form a biofilm with enhanced drug resistance properties in the host skin's deep layers. The formed biofilm may initiate further bloodstream spread and immune escape. Therefore, we propose that secreted chemicals from the biofilm may facilitate fungal pathogenesis. In response to this interaction, the host skin may develop potential defensive mechanisms. Comparative transcriptomics was performed on the host dermal cells in response to indirect interaction with C. auris biofilm through Transwell inserts compared to planktonic cells. Furthermore, the effect of antifungals including caspofungin and fluconazole was studied. The obtained data showed that the dermal cells exhibited different transcriptional responses. Kyoto Encyclopedia of Genes and Genomes and Reactome analyses identified potential defensive responses employed by the dermal cells and potential toxicity induced by C. auris. Additionally, our data indicated that the dominating toxic effect was mediated by ferroptosis; which was validated by qRT-PCR, cytotoxicity assay, and flow cytometry. On the other hand, the viability of C. auris biofilm was enhanced and accompanied by upregulation of MDR1, and KRE6 upon interaction with dermal cells; both genes play significant roles in drug resistance and biofilm maturation, respectively. This study for the first-time shed light on the dominating defensive responses of human dermal cells, microbe colonization site, to C. auris biofilm and its toxic effects. Further, it demonstrates how C. auris biofilm responds to the defensive mechanisms developed by the human dermal cells.

A lateral flow immunoassay for the rapid identification of Candida auris from isolates or directly from surveillance enrichment broths

Introduction

Candida auris is a recently discovered yeast with a multi-drug resistant profile associated with high mortality rates. The rapid identification of Candida auris in hospital settings is crucial to allow appropriate therapeutic and rapid implementation of infection management measures. The aim of this study was to develop a lateral flow immunoassay (LFIA) for the rapid identification of Candida auris.

Methods

Highly specific monoclonal antibodies were obtained by immunizing mice with membrane proteins from Candida auris which were then used to develop a LFIA whose performance was assessed by testing 12 strains of Candida auris and 37 strains of other Candida species. Isolates were grown on either Sabouraud dextrose, CHROMagarTM Candida Plus or HardyCHROMTM Candida + auris agar plates. The strains were also cultured on salt sabouraud-dextrose with chloramphenicol or a commercially available Salt-Sabouraud Dulcitol Broth with chloramphenicol and gentamicin, and processed using a simple centrifugation protocol to recover a pellet. Finally, the colonies or yeast extract were transferred to the LFIA to determine the specificity and sensitivity of the assay.

Results

The LFIA reached 100% specificity and sensitivity from solid agar plates. For both enrichment broths, some Candida non-auris species were able to grow, but the LFIA remained 100% specific. The use of a dextrose-based sabouraud broth resulted in earlier identification with the LFIA, with most of the Candida auris strains detected at 24 h.

Conclusion

The developed LFIA prototype represents a powerful tool to fight the emerging threat of Candida auris. Clinical validation represents the next step.

A single gene mutation underpins metabolic adaptation and acquisition of filamentous competence in the emerging fungal pathogen Candida auris

Filamentous cell growth is a vital property of fungal pathogens. The mechanisms of filamentation in the emerging multidrug-resistant fungal pathogen Candida auris are poorly understood. Here, we show that exposure of C. auris to glycerol triggers a rod-like filamentation-competent (RL-FC) phenotype, which forms elongated filamentous cells after a prolonged culture period. Whole-genome sequencing analysis reveals that all RL-FC isolates harbor a mutation in the C2H2 zinc finger transcription factor-encoding gene GFC1 (Gfc1 variants). Deletion of GFC1 leads to an RL-FC phenotype similar to that observed in Gfc1 variants. We further demonstrate that GFC1 mutation causes enhanced fatty acid β-oxidation metabolism and thereby promotes RL-FC/filamentous growth. This regulation is achieved through a Multiple Carbon source Utilizer (Mcu1)-dependent mechanism. Interestingly, both the evolved RL-FC isolates and the gfc1Δ mutant exhibit an enhanced ability to colonize the skin. Our results reveal that glycerol-mediated GFC1 mutations are beneficial during C. auris skin colonization and infection.

Comparative fitness trade-offs associated with azole resistance in Candida auris clinical isolates

Multidrug-resistant yeast Candida auris is a serious threat to public health with documented survival in various hospital niches. The dynamics of this survival benefit and its trade off with drug resistance are still unknown for this pathogen. In this study we investigate the oxidative stress response (OSR) in fluconazole-resistant C. auris and compare its relative fitness with fluconazole-susceptible strains. A total of 351 C. auris clinical isolates (61 fluconazole-susceptible and 290 fluconazole-resistant) were screened for stress tolerance by spot assay and 95.08 % fluconazole-susceptible isolates were hyper-resistant to oxidative stress while majority (94.5 %) fluconazole-resistant isolates had lower oxidative tolerance. Expression of Hog1 and Cta1 gene transcript levels and cellular catalase levels were significantly higher in fluconazole-susceptible isolates and a corresponding higher intracellular reactive oxygen species level (iROS) was accumulated in the fluconazole-resistant isolates. Biofilm formation and cell viability under oxidative stress revealed higher biofilm formation and better viability in fluconazole-susceptible isolates. Fluconazole-resistant isolates had higher basal cell wall chitin. On comparison of virulence, the % cytotoxicity in A549 cell line was higher in fluconazole-susceptible isolates and the median survival of the infected larvae in G. mellonella infection model was higher in fluconazole-resistant (5; IQR:4.5-5 days) vs. fluconazole-susceptible C. auris (2; IQR:1.5-2.5 days). All organisms evolve with changes in their environmental conditions, to ensure an optimal balance between proliferation and survival. Development of tolerance to a certain kind of stress example antifungal exposure in yeast can leads to a compensatory decrease in tolerance for other stresses. This study provides useful insights into the comparative fitness and antifungal susceptibility trade off in C. auris. We report a negative association between H2O2 tolerance and fluconazole susceptibility. Using in-vitro cell cytotoxicity and in-vivo survival assays we also demonstrate the higher virulence potential of fluconazole-susceptible C. auris isolates corroborating the negative correlation between susceptibility and pathogen survival or virulence. These findings could also be translated to clinical practice by investigating the possibility of using molecules targeting stress response and fitness regulating pathways for management of this serious infection.

Tuning interdomain conjugation to enable in situ population modification in yeasts

The ability to modify and control natural and engineered microbiomes is essential for biotechnology and biomedicine. Fungi are critical members of most microbiomes, yet technology for modifying the fungal members of a microbiome has lagged far behind that for bacteria. Interdomain conjugation (IDC) is a promising approach, as DNA transfer from bacterial cells to yeast enables in situ modification. While such genetic transfers have been known to naturally occur in a wide range of eukaryotes and are thought to contribute to their evolution, IDC has been understudied as a technique to control fungal or fungal-bacterial consortia. One major obstacle to the widespread use of IDC is its limited efficiency. In this work, we manipulated metabolic and physical interactions between genetically tractable Escherichia coli and Saccharomyces cerevisiae to control the incidence of IDC. We test the landscape of population interactions between the bacterial donors and yeast recipients to find that bacterial commensalism leads to maximized IDC, both in culture and in mixed colonies. We demonstrate the capacity of cell-to-cell binding via mannoproteins to assist both IDC incidence and bacterial commensalism in culture and model how these tunable controls can predictably yield a range of IDC outcomes. Furthermore, we demonstrate that these controls can be utilized to irreversibly alter a recipient yeast population, by both "rescuing" a poor-growing recipient population and collapsing a stable population via a novel IDC-mediated CRISPR/Cas9 system.IMPORTANCEFungi are important but often unaddressed members of most natural and synthetic microbial communities. This work highlights opportunities for modifying yeast microbiome populations through bacterial conjugation. While conjugation has been recognized for its capacity to deliver engineerable DNA to a range of cells, its dependence on cell contact has limited its efficiency. Here, we find "knobs" to control DNA transfer, by engineering the metabolic dependence between bacterial donors and yeast recipients and by changing their ability to physically adhere to each other. Importantly, we functionally validate these "knobs" by irreversibly altering yeast populations. We use these controls to "rescue" a failing yeast population, demonstrate the capacity of conjugated CRISPR/Cas9 to depress or collapse populations, and show that conjugation can be easily interrupted by disrupting cell-to-cell binding. These results offer building blocks toward in situ mycobiome editing, with significant implications for clinical treatments of fungal pathogens and other fungal system engineering.

The Candida auris Hog1 MAP kinase is essential for the colonization of murine skin and intradermal persistence

Candida auris , a multidrug-resistant human fungal pathogen, was first identified in 2009 in Japan. Since then, systemic C. auris infections have now been reported in more than 50 countries, with mortality rates of 30-60%. A major contributing factor to its high inter- and intrahospital clonal transmission is that C. auris, unlike most Candida species, displays unique skin tropism and can stay on human skin for a prolonged period. However, the molecular mechanisms responsible for C. auris skin colonization, intradermal persistence, and systemic virulence are poorly understood. Here, we report that C. auris Hog1 mitogen-activated protein kinase (MAPK) is essential for efficient skin colonization, intradermal persistence, as well as systemic virulence. RNA-seq analysis of wildtype parental and hog1 Δ mutant strains revealed marked down-regulation of genes involved in processes such as cell adhesion, cell-wall rearrangement, and pathogenesis in hog1 Δ mutant compared to the wildtype parent. Consistent with these data, we found a prominent role for Hog1 in maintaining cell-wall architecture, as the hog1 Δ mutant demonstrated a significant increase in cell-surface β-glucan exposure and a concomitant reduction in chitin content. Additionally, we observed that Hog1 was required for biofilm formation in vitro and fungal survival when challenged with primary murine macrophages and neutrophils ex vivo . Collectively, these findings have important implications for understanding the C. auris skin adherence mechanisms and penetration of skin epithelial layers preceding bloodstream infections.

Importance

Candida auris is a World Health Organization (WHO) fungal priority pathogen and an urgent public health threat recognized by the Centers for Disease Control and Prevention (CDC). C. auris has a unique ability to colonize human skin. It also persists on abiotic surfaces in healthcare environments for an extended period of time. These attributes facilitate the inter- and intrahospital clonal transmission of C. auris . Therefore, understanding C. auris skin colonization mechanisms are critical for infection control, especially in hospitals and nursing homes. However, despite its profound clinical relevance, the molecular and genetic basis of C. auris skin colonization mechanisms are poorly understood. Herein, we present data on the identification of the Hog1 MAP kinase as a key regulator of C. auris skin colonization. These findings lay foundation for further characterization of unique mechanisms that promote fungal persistence on human skin.

Previously Uncharacterized Variants, OCF-E-OCF-J, of the Antifungal Occidiofungin Produced by Burkholderia contaminans MS14

The rise of multidrug resistant fungal infections highlights the need to identify and develop novel antifungal agents. Occidiofungin is a nonribosomally synthesized glycolipopeptide that has a unique mechanism of action, disrupting actin-mediated functions and inducing cellular apoptosis. Antifungal activity has been observed in vitro against various fungal species, including multidrug resistant Candida auris, and in vivo efficacy has been demonstrated in a murine vulvovaginal candidiasis model. Occidiofungin, a cyclic glycolipopeptide, is composed of eight amino acids and in previous studies, an asparagine residue was assigned at position 7 (ASN7). In this study, new structural variants of occidiofungin have been characterized which have aspartic acid (ASP7), glutamine (GLN7), or glutamic acid (GLU7) at position 7. The side chain of the ASP7 variant contains the only terminal carboxylic acid in the peptide and provides a useful site for selective chemical modifications. Analogues were synthesized at the ASP7 position and tested for antifungal activity. These analogues were shown to be more active as compared to the ASP7 variant against a panel of Candida species. The naturally occurring variants of occidiofungin with a side chain containing a carboxylic acid at the seventh amino acid position can be used to develop semisynthetic analogues with enhanced therapeutic properties.

Skin and hard surface disinfection against Candida auris - What we know today

Candida auris has emerged as a global healthcare threat, displaying resistance to important healthcare antifungal therapies. Infection prevention and control protocols have become paramount in reducing transmission of C. auris in healthcare, of which cleaning and disinfection plays an important role. Candida albicans is used as a surrogate yeast for yeasticidal claims of disinfection products, but reports have been made that sensitivity to disinfectants by C. auris differs from its surrogate. In this review, we aimed to compile the information reported for products used for skin and hard surface disinfection against C. auris in its planktonic or biofilm form. A comparison was made with other Candida species, and information were gathered from laboratory studies and observations made in healthcare settings.

Bacterial viability in dry-surface biofilms in healthcare facilities: a systematic review

BACKGROUND

Bacteria are known to live inside architectural structures called biofilms. Though standard biofilms have been studied extensively for more than 50 years, little is known about dry-surface biofilms (DSBs). Since 2012, DSBs have been described in several scientific papers, but basic knowledge about the viability and culturability of bacteria remains limited.

AIM

To conduct a systematic review to determine whether bacteria inside DSBs are viable, culturable, and enumerable.

METHODS

Eligible articles had to deal with DSBs containing at least one bacterial species involved in healthcare-associated infections, which developed in actual healthcare environments (in-situ) or with the help of any biofilm model (in-vitro).

FINDINGS

Twenty-four articles were included in the review. Whereas most of them isolated viable bacteria (87% in situ; 100% in vitro), no in-situ study quantified culturable bacteria in the biofilm per unit area. Conversely, 100% of in-vitro studies cultured the bacteria from controls and 94.4% supplied an enumeration of them. Culturable bacteria also grew after 78% of the cleaning, disinfection, or sterilization protocols tested. Microscopic observations after staining the samples with live/dead fluorescent probes (Baclight®) showed large amounts of viable cells in culture-negative samples.

CONCLUSION

Our study questions the efficacy of current methods for microbiological monitoring of surfaces, since these methods are only based on bacterial culturability. To improve both surface monitoring and cleaning and disinfection protocols, it is necessary to integrate the concept of DSBs which appears to contain a significant amount of viable but non-culturable bacteria.

Liposomal formulation of a new antifungal hybrid compound provides protection against Candida auris in the ex vivo skin colonization model

The newly emerged pathogen, Candida auris, presents a serious threat to public health worldwide. This multidrug-resistant yeast often colonizes and persists on the skin of patients, can easily spread from person to person, and can cause life-threatening systemic infections. New antifungal therapies are therefore urgently needed to limit and control both superficial and systemic C. auris infections. In this study, we designed a novel antifungal agent, PQA-Az-13, that contains a combination of indazole, pyrrolidine, and arylpiperazine scaffolds substituted with a trifluoromethyl moiety. PQA-Az-13 demonstrated antifungal activity against biofilms of a set of 10 different C. auris clinical isolates, representing all four geographical clades distinguished within this species. This compound showed strong activity, with MIC values between 0.67 and 1.25 µg/mL. Cellular proteomics indicated that PQA-Az-13 partially or completely inhibited numerous enzymatic proteins in C. auris biofilms, particularly those involved in both amino acid biosynthesis and metabolism processes, as well as in general energy-producing processes. Due to its hydrophobic nature and limited aqueous solubility, PQA-Az-13 was encapsulated in cationic liposomes composed of soybean phosphatidylcholine (SPC), 1,2-dioleoyloxy-3-trimethylammonium-propane chloride (DOTAP), and N-(carbonyl-methoxypolyethylene glycol-2000)-1,2-distearoyl-sn-glycero-3-phosphoethanolamine, sodium salt (DSPE-PEG 2000), and characterized by biophysical and spectral techniques. These PQA-Az-13-loaded liposomes displayed a mean size of 76.4 nm, a positive charge of +45.0 mV, a high encapsulation efficiency of 97.2%, excellent stability, and no toxicity to normal human dermal fibroblasts. PQA-Az-13 liposomes demonstrated enhanced antifungal activity levels against both C. auris in in vitro biofilms and ex vivo skin colonization models. These initial results suggest that molecules like PQA-Az-13 warrant further study and development.

The adhesin SCF1 mediates Candida auris colonization

Candida auris is an emerging human fungal pathogen that can rapidly spread and cause outbreaks of invasive infections. Santana et al. discovered that a novel surface colonization factor (SCF1), and a conserved adhesin, Iff4109, mediates C. auris colonization on abiotic surfaces, skin, and virulence in vivo.

Native human and mouse skin infection models to study Candida auris-host interactions

The World Health Organization (WHO) declared certain fungal pathogens as global health threats for the next decade. Candida auris (C. auris) is a newly emerging skin-tropic multidrug-resistant fungal pathogen that can cause life-threatening infections of high mortality in hospitals and healthcare settings. Here, we address an unmet need and present novel native ex vivo skin models, thus extending previous C. auris-host interaction studies. We exploit histology and immunofluorescence analysis of ex vivo skin biopsies of human adult and fetal, as well as mouse origin infected with C. auris via distinct routes. We demonstrate that an intact skin barrier efficiently protects from C. auris penetration and invasion. Although C. auris readily grows on native human skin, it can reach deeper layers only upon physical disruption of the barrier by needling or through otherwise damaged skin. By contrast, a barrier disruption is not necessary for C. auris penetration of native mouse skin. Importantly, we show that C. auris undergoes morphogenetic changes upon skin penetration, as it acquires pseudohyphal growth phenotypes in deeper human and mouse dermis. Taken together, this new human and mouse skin model toolset yields new insights into C. auris colonization, adhesion, growth and invasion properties of native versus damaged human skin. The results form a crucial basis for future studies on skin immune defense to colonizing pathogens, and offer new options for testing the action and efficacy of topical antimicrobial compound formulations.

Plastic pollution as a novel reservoir for the environmental survival of the drug resistant fungal pathogen Candida auris

The WHO recently classified Candida auris as a fungal pathogen of "critical concern". Evidence suggests that C. auris emerged from the natural environment, yet the ability of this pathogenic yeast to survive in the natural environment is still poorly understood. The aim of this study, therefore, was to quantify the persistence of C. auris in simulated environmental matrices and explore the role of plastic pollution for facilitating survival and potential transfer of C. auris. Multi-drug resistant strains of C. auris persisted for over 30 days in river water or seawater, either planktonically, or in biofilms colonising high-density polyethylene (HDPE) or glass. C. auris could be transferred from plastic beads onto simulated beach sand, particularly when the sand was wet. Importantly, all C. auris cells recovered from plastics retained their pathogenicity; therefore, plastic pollution could play a significant role in the widescale environmental dissemination of this recently emerged pathogen.

Efficacy of biofilm disrupters against Candida auris and other Candida species in monomicrobial and polymicrobial biofilms

Candida species are now considered global threats by the CDC and WHO. Candida auris specifically is on the critical pathogen threat list along with Candida albicans. In addition, it is not uncommon to find Candida spp. in a mixed culture with bacterial organisms, especially Staphylococcus aureus producing polymicrobial infections. To eradicate these organisms from the environment and from patient surfaces, surface agents such as chlorhexidine (CHD) and Puracyn are used. Biofilm disrupters (BDs) are novel agents with a broad spectrum of antimicrobial activity and have been used in the management of chronic wounds and to sterilise environmental surfaces for the past several years. The goal of this study was to evaluate BDs (BlastX, Torrent, NSSD) and CHD against Candida spp. and S. aureus using zone of inhibition assays, biofilm and time-kill assays. All BDs and CHD inhibited C. auris growth effectively in a concentration-dependent manner. Additionally, CHD and the BDs showed excellent antimicrobial activity within polymicrobial biofilms. A comparative analysis of the BDs and CHD against C. auris and C. albicans using biofilm kill-curves showed at least 99.999% killing. All three BDs and CHD have excellent activity against different Candida species, including C. auris. However, one isolate of C. auris in a polymicrobial biofilm assay showed resistance/tolerance to CHD, but not to the BDs. The fungicidal activity of these novel agents will be valuable in eradicating surface colonisation of Candida spp, especially C. auris from colonised environmental surfaces and from wounds in colonised patients.

Preventing the spread of life-threatening gastrointestinal microbes on the surface of a continuously self-disinfecting block polymer

Highly persistent, drug-resistant and transmissible healthcare pathogens such as Clostridioides difficile (C. difficile) and Candida auris (C. auris) are responsible for causing antibiotic-associated fatal diarrhea and invasive candidiasis, respectively. In this study, we demonstrate that these potentially lethal gastrointestinal microbes can be rapidly inactivated on the solid surface of a self-disinfecting anionic block polymer that inherently generates a water surface layer that is highly acidic (pH < 1) upon hydration. Due to thermodynamic incompatibility between its chemical sequences, the polymer spontaneously self-organizes into a nanostructure that enables proton migration from the interior of a film to the surface via contiguous nanoscale hydrophilic channels, as discerned here by scanning electron and atomic force microscopies, as well as X-ray photoelectron spectroscopy. Here, we report that two strains of C. difficile in the vegetative state and two species of Candida, Candida albicans (C. albicans) and C. auris, are, in most cases, inactivated to the limit of minimum detection. Corresponding electron and optical microscopy images reveal that, upon exposure to the hydrated polymer, the outer microbial membranes display evidence of damage and intracellular material is expelled. Combined with our previous studies of rapid bacterial and viral inactivation, these antimicrobial results are highly encouraging and, if translatable to clinical conditions in the form of self-standing polymer films or coatings, are expected to benefit the welfare of patients in healthcare facilities by continuously preventing the spread of such potentially dangerous microbes.

The Gordian Knot of C. auris: If You Cannot Cut It, Prevent It

Since its first description in 2009, Candida auris has, so far, resulted in large hospital outbreaks worldwide and is considered an emerging global public health threat. Exceptionally for yeast, it is gifted with a profoundly worrying invasive potential and high inter-patient transmissibility. At the same time, it is capable of colonizing and persisting in both patients and hospital settings for prolonged periods of time, thus creating a vicious cycle of acquisition, spreading, and infection. It exhibits various virulence qualities and thermotolerance, osmotolerance, filamentation, biofilm formation and hydrolytic enzyme production, which are mainly implicated in its pathogenesis. Owing to its unfavorable profile of resistance to diverse antifungal agents and the lack of effective treatment options, the implementation of robust infection prevention and control (IPC) practices is crucial for controlling and minimizing intra-hospital transmission of C. auris. Rapid and accurate microbiological identification, adherence to hand hygiene, use of adequate personal protective equipment (PPE), proper handling of catheters and implantable devices, contact isolation, periodical environmental decontamination, targeted screening, implementation of antimicrobial stewardship (AMS) programs and communication between healthcare facilities about residents' C. auris colonization status are recognized as coherent strategies for preventing its spread. Current knowledge on C. auris epidemiology, clinical characteristics, and its mechanisms of pathogenicity are summarized in the present review and a comprehensive overview of IPC practices ensuring yeast prevention is also provided.

Global characteristics and trends in research on Candida auris

Introduction

Candida auris, a fungal pathogen first reported in 2009, has shown strong resistance to azole antifungal drugs and has caused severe nosocomial outbreaks. It can also form biofilms, which can colonize patients' skin and transmit to others. Despite numerous reports of C. auris isolation in various countries, many studies have reported contradictory results.

Method

A bibliometric analysis was conducted using VOSviewer to summarize research trends and provide guidance for future research on controlling C. auris infection. The analysis revealed that the United States and the US CDC were the most influential countries and research institutions, respectively. For the researchers, Jacques F. Meis published the highest amount of related articles, and Anastasia P. Litvintseva's articles with the highest average citation rate. The most cited publications focused on clade classification, accurate identification technologies, nosocomial outbreaks, drug resistance, and biofilm formation. Keyword co-occurrence analysis revealed that the top five highest frequencies were for 'drug resistance,' 'antifungal susceptibility test,' 'infection,' 'Candida auris,' and 'identification.' The high-frequency keywords clustered into four groups: rapid and precise identification, drug resistance research, pathogenicity, and nosocomial transmission epidemiology studies. These clusters represent different study fields and current research hotspots of C. auris.

Conclusion

The bibliometric analysis identified the most influential country, research institution, and researcher, indicating current research trends and hotspots for controlling C. auris.

The rapid emergence of antifungal-resistant human-pathogenic fungi

During recent decades, the emergence of pathogenic fungi has posed an increasing public health threat, particularly given the limited number of antifungal drugs available to treat invasive infections. In this Review, we discuss the global emergence and spread of three emerging antifungal-resistant fungi: Candida auris, driven by global health-care transmission and possibly facilitated by climate change; azole-resistant Aspergillus fumigatus, driven by the selection facilitated by azole fungicide use in agricultural and other settings; and Trichophyton indotineae, driven by the under-regulated use of over-the-counter high-potency corticosteroid-containing antifungal creams. The diversity of the fungi themselves and the drivers of their emergence make it clear that we cannot predict what might emerge next. Therefore, vigilance is critical to monitoring fungal emergence, as well as the rise in overall antifungal resistance.

Mechanisms of pathogenicity for the emerging fungus Candida auris

Candida auris recently emerged as an urgent public health threat, causing outbreaks of invasive infections in healthcare settings throughout the world. This fungal pathogen persists on the skin of patients and on abiotic surfaces despite antiseptic and decolonization attempts. The heightened capacity for skin colonization and environmental persistence promotes rapid nosocomial spread. Following skin colonization, C. auris can gain entrance to the bloodstream and deeper tissues, often through a wound or an inserted medical device, such as a catheter. C. auris possesses a variety of virulence traits, including the capacity for biofilm formation, production of adhesins and proteases, and evasion of innate immune responses. In this review, we highlight the interactions of C. auris with the host, emphasizing the intersection of laboratory studies and clinical observations.

The skin mycobiome and intermicrobial interactions in the cutaneous niche

Mammalian microbiomes have coevolved with their host to establish a stable homeostatic relationship. Multifaceted commensal-host and commensal-commensal interactions contribute to the maintenance of the equilibrium with an impact on diverse host physiological processes. Despite constant exposure to physical and chemical insults from the environment, the skin harbors a surprisingly stable microbiome. The fungal compartment of the skin microbiome, the skin mycobiome, is unique in that it is dominated by a single fungus, Malassezia. The lack in diversity suggests that the skin may provide a unique niche for this fungal genus and that Malassezia may efficiently outcompete other fungi from the skin. This opinion article examines aspects in support of this hypothesis, discusses how changes in niche conditions associate with skin mycobiome dysregulation, and highlights an emerging example of Malassezia being displaced from the skin by the emerging fungal pathogen C. auris, thereby generating a predisposing situation for fatal-invasive infection.

Candida auris from colonisation to candidemia: A four-year study

BACKGROUND

Candida auris has become a worrisome multi-drug resistant healthcare-associated pathogen due to its capacity to colonise patients and surfaces and to cause outbreaks of invasive infections in critically ill patients.

OBJECTIVES

This study evaluated the outbreak in our setting in a 4-year period, reporting the risk factors for developing candidemia in previously colonised patients, the therapeutic measures for candidemia and the outcome of candidemia and colonisation cases among all C. auris isolates and their susceptibility to antifungals.

METHODS

Data were retrospectively collected from patients admitted to Consorcio Hospital General Universitario de Valencia (Spain) from September 2017 to September 2021. A retrospective case-control study was designed to identify risk factors for developing C. auris candidemia in previously colonised patients.

RESULTS

C. auris affected 550 patients, of which 210 (38.2%) had some clinical sample positive. Isolates were uniformly resistant to fluconazole, 20 isolates were resistant to echinocandins (2.8%) and four isolates were resistant to ampfotericin B (0.6%). There were 86 candidemia cases. APACHE II, digestive disease and catheter isolate were proven to be independent risk factors for developing candidemia in previously colonised patients. Thirty-day mortality rate for C. auris candidemia cases was 32.6%, while for colonisation cases was 33.7%.

CONCLUSIONS

Candidemia was one of the most frequent and severe infections caused by C. auris. The risk factors identified in this study should help to detect patients who are at more risk of developing candidemia, as long as an adequate surveillance of C. auris colonisation is performed.

Tools and techniques to identify, study, and control Candida auris

Candida auris, is an emerging fungal pathogen that can cause life-threatening infections in humans. Unlike many other Candida species that colonize the intestine, C. auris most efficiently colonizes the skin. Such colonization contaminates the patient's environment and can result in rapid nosocomial transmission. In addition, this transmission can lead to outbreaks of systemic infections that have mortality rates between 40% and 60%. C. auris isolates resistant to all known classes of antifungals have been identified and as such, understanding the underlying biochemical mechanisms of how skin colonization initiates and progresses is critical to developing better therapeutic options. With this review, we briefly summarize what is known about horizontal transmission and current tools used to identify, understand, and control C. auris infections.

A Candida auris-specific adhesin, Scf1, governs surface association, colonization, and virulence

Candida auris is an emerging fungal pathogen responsible for health care-associated outbreaks that arise from persistent surface and skin colonization. We characterized the arsenal of adhesins used by C. auris and discovered an uncharacterized adhesin, Surface Colonization Factor (Scf1), and a conserved adhesin, Iff4109, that are essential for the colonization of inert surfaces and mammalian hosts. SCF1 is apparently specific to C. auris, and its expression mediates adhesion to inert and biological surfaces across isolates from all five clades. Unlike canonical fungal adhesins, which function through hydrophobic interactions, Scf1 relies on exposed cationic residues for surface association. SCF1 is required for C. auris biofilm formation, skin colonization, virulence in systemic infection, and colonization of inserted medical devices.

A Novel Robust Method Mimicking Human Substratum To Dissect the Heterogeneity of Candida auris Biofilm Formation

Candida auris is a pathogen of urgent threat level as marked by the CDC. The formation of biofilms is an essential property of this fungus to establish infection and escape drug treatment. However, our understanding of pathogenesis through biofilm is hampered by heterogeneity in C. auris biofilms observed in different studies. It is imperative to replicate in vivo conditions for studying C. auris biofilm formation in vitro. Different methods are standardized, but the surface used to form biofilms lacks consistency as well as the architecture of a typical biofilm. Here, we report an in vitro technique to grow C. auris biofilms on gelatin-coated coverslips. Interestingly, C. auris cells grown on gelatin-coated coverslips either on modified synthetic sweat media or RPMI 1640 resulted in similar multilayer biofilm formation with extracellular polymeric substances (EPS). This method is also consistent with the biofilm formation of other Candida species, such as Candida glabrata and Candida albicans. Biofilms of C. glabrata developed through this method show pseudohyphae and EPS. This method can be used to understand the molecular basis of biofilm formation, associated pathogenesis, and drug tolerance. The technique is cost-effective and would thus serve in rightful screening and repurposing drug libraries for designing new therapeutics against the less-studied high-alarm pathogen C. auris. IMPORTANCE Heterogeneity is seen when multidrug-resistant C. auris biofilm is cultured using different reported methods. Biofilm formed on the gelatin surface mimics the condition of a host environment that has multilayers and EPS. This method has feasibility for drug screening and analyzing biofilms through three-dimensional (3D) reconstruction. This in vitro biofilm formation technique is also exploited to study the formation of biofilm of other Candida species. The biofilms of C. glabrata and C. albicans can also be correctly mimicked using gelatin in the biofilm-forming environment. Thus, the novel in vitro method for biofilm formation reported here can be widely used to understand the mechanism of biofilm formation, related virulence properties, and drug tolerance of C. auris and other Candida species. This simple and low-cost technique is highly suitable for screening novel inhibitors and repurposed libraries and to design new therapeutics against Candida species.

Nanotechnology-Based Strategies to Combat Multidrug-Resistant Candida auris Infections

An emerging multidrug-resistant pathogenic yeast called Candida auris has a high potential to spread quickly among hospitalized patients and immunodeficient patients causing nosocomial outbreaks. It has the potential to cause pandemic outbreaks in about 45 nations with high mortality rates. Additionally, the fungus has become resistant to decontamination techniques and can survive for weeks in a hospital environment. Nanoparticles might be a good substitute to treat illnesses brought on by this newly discovered pathogen. Nanoparticles have become a trend and hot topic in recent years to combat this fatal fungus. This review gives a general insight into the epidemiology of C. auris and infection. It discusses the current conventional therapy and mechanism of resistance development. Furthermore, it focuses on nanoparticles, their different types, and up-to-date trials to evaluate the promising efficacy of nanoparticles with respect to C. auris.

Public Health Research Priorities for Fungal Diseases: A Multidisciplinary Approach to Save Lives

Fungal infections can cause severe disease and death and impose a substantial economic burden on healthcare systems. Public health research requires a multidisciplinary approach and is essential to help save lives and prevent disability from fungal diseases. In this manuscript, we outline the main public health research priorities for fungal diseases, including the measurement of the fungal disease burden and distribution and the need for improved diagnostics, therapeutics, and vaccines. Characterizing the public health, economic, health system, and individual burden caused by fungal diseases can provide critical insights to promote better prevention and treatment. The development and validation of fungal diagnostic tests that are rapid, accurate, and cost-effective can improve testing practices. Understanding best practices for antifungal prophylaxis can optimize prevention in at-risk populations, while research on antifungal resistance can improve patient outcomes. Investment in vaccines may eliminate certain fungal diseases or lower incidence and mortality. Public health research priorities and approaches may vary by fungal pathogen.

Host defense mechanisms against Candida auris

INTRODUCTION

Candida auris is a pathogen of growing public health concern given its rapid spread across the globe, its propensity for long-term skin colonization and healthcare-related outbreaks, its resistance to a variety of antifungal medications, and the high morbidity and mortality associated with invasive disease. Despite that, the host immune response mechanisms that operate during C. auris skin colonization and invasive infection remains poorly understood.

AREAS COVERED

In this manuscript, we review the available literature in the growing research field pertaining to C. auris host defenses and we discuss what is known about the ability of C. auris to thrive on mammalian skin, the role of lymphoid cell-mediated, IL-17-dependent defenses in controlling cutaneous colonization, and the contribution of myeloid phagocytes in curtailing systemic infection.

EXPERT OPINION

Understanding the mechanisms by which the host immune system responds to and controls colonization and infection with C. auris and developing a deeper knowledge of tissue-specific host-C. auris interactions and of C. auris immune-evading mechanisms may help devise improved strategies for decolonization, prognostication, prevention, vaccination, and/or directed antifungal treatment in vulnerable patient populations.

Efficacy of chlorhexidine in advanced performance technology formulation in decolonizing the skin using Candida auris skin colonization mouse model

The incidence of Candida auris, an emerging multidrug resistant fungal species, is increasing. The ability of this yeast to colonize the human skin could lead to infections. Identifying agents to reduce the skin fungal burden is critical. Chlorhexidine formulated in a new Advanced Performance Technology formulation (APT-CH) was significantly more effective than untreated controls. Additional studies are warranted.

Synergistic Antifungal Interaction between Pseudomonas aeruginosa LV Strain Metabolites and Biogenic Silver Nanoparticles against Candida auris

Candida auris has been found to be a persistent colonizer of human skin and a successful pathogen capable of causing potentially fatal infection, especially in immunocompromised individuals. This fungal species is usually resistant to most antifungal agents and has the ability to form biofilms on different surfaces, representing a significant therapeutic challenge. Herein, the effect of metabolites of Pseudomonas aeruginosa LV strain, alone and combined with biologically synthesized silver nanoparticles (bioAgNP), was evaluated in planktonic and sessile (biofilm) cells of C. auris. First, the minimal inhibitory and fungicidal concentration values of 3.12 and 6.25 μg/mL, respectively, were determined for F4a, a semi-purified bacterial fraction. Fluopsin C and indolin-3-one seem to be the active components of F4a. Like the semi-purified fraction, they showed a time- and dose-dependent fungicidal activity. F4a and bioAgNP caused severe changes in the morphology and ultrastructure of fungal cells. F4a and indolin-3-one combined with bioAgNP exhibited synergistic fungicidal activity against planktonic cells. F4a, alone or combined with bioAgNP, also caused a significant decrease in the number of viable cells within the biofilms. No cytotoxicity to mammalian cells was detected for bacterial metabolites combined with bioAgNP at synergistic concentrations that presented antifungal activity. These results indicate the potential of F4a combined with bioAgNP as a new strategy for controlling C. auris infections.

One population, multiple lifestyles: Commensalism and pathogenesis in the human mycobiome

Candida auris and Candida albicans can result in invasive fungal diseases. And yet, these species can stably and asymptomatically colonize human skin and gastrointestinal tracts. To consider these disparate microbial lifestyles, we first review factors shown to influence the underlying microbiome. Structured by the damage response framework, we then consider the molecular mechanisms deployed by C. albicans to switch between commensal and pathogenic lifestyles. Next, we explore this framework with C. auris to highlight how host physiology, immunity, and/or antibiotic receipt are associated with progression from colonization to infection. While treatment with antibiotics increases the risk that an individual will succumb to invasive candidiasis, the underlying mechanisms remain unclear. Here, we describe several hypotheses that may explain this phenomenon. We conclude by highlighting future directions integrating genomics with immunology to advance our understanding of invasive candidiasis and human fungal disease.

Environmental reservoirs of the drug-resistant pathogenic yeast Candida auris

Candia auris is an emerging human pathogenic yeast; yet, despite phenotypic attributes and genomic evidence suggesting that it probably emerged from a natural reservoir, we know nothing about the environmental phase of its life cycle and the transmission pathways associated with it. The thermotolerant characteristics of C. auris have been hypothesised to be an environmental adaptation to increasing temperatures due to global warming (which may have facilitated its ability to tolerate the mammalian thermal barrier that is considered a protective strategy for humans against colonisation by environmental fungi with pathogenic potential). Thus, C. auris may be the first human pathogenic fungus to have emerged as a result of climate change. In addition, the release of antifungal chemicals, such as azoles, into the environment (from both pharmaceutical and agricultural sources) is likely to be responsible for the environmental enrichment of resistant strains of C. auris; however, the survival and dissemination of C. auris in the natural environment is poorly understood. In this paper, we critically review the possible pathways through which C. auris can be introduced into the environment and evaluate the environmental characteristics that can influence its persistence and transmission in natural environments. Identifying potential environmental niches and reservoirs of C. auris and understanding its emergence against a backdrop of climate change and environmental pollution will be crucial for the development of effective epidemiological and environmental management responses.

The Mortality Attributable to Candidemia in C. auris Is Higher than That in Other Candida Species: Myth or Reality?

Candida auris has become a major health threat due to its transmissibility, multidrug resistance and severe outcomes. In a case-control design, 74 hospitalised patients with candidemia were enrolled. In total, 22 cases (29.7%) and 52 controls (C. albicans, 21.6%; C. parapsilosis, 21.6%; C. tropicalis, 21.6%; C. glabrata, 1.4%) were included and analysed in this study. Risk factors, clinical and microbiological characteristics and outcomes of patients with C. auris and non-auris Candida species (NACS) candidemia were compared. Previous fluconazole exposure was significantly higher in C. auris candidemia patients (OR 3.3; 1.15–9.5). Most C. auris isolates were resistant to fluconazole (86.3%) and amphotericin B (59%) whilst NACS isolates were generally susceptible. No isolates resistant to echinocandins were detected. The average time to start antifungal therapy was 3.6 days. Sixty-three (85.1%) patients received adequate antifungal therapy, without significant differences between the two groups. The crude mortality at 30 and 90 days of candidemia was up to 37.8% and 40.5%, respectively. However, there was no difference in mortality both at 30 and 90 days between the group with candidemia by C. auris (31.8%) and by NACS (42.3%) (OR 0.6; 95% IC 0.24–1.97) and 36.4% and 42.3% (0.77; 0.27–2.1), respectively. In this study, mortality due to candidemia between C. auris and NACS was similar. Appropriate antifungal therapy in both groups may have contributed to finding no differences in outcomes.

Candida auris biofilm: a review on model to mechanism conservation

INTRODUCTION

Candida auris is included in the fungal infection category 'critical' by WHO because of associated high drug tolerance and spread at an alarming rate which if remains untouched may result in serious outbreaks. Since its discovery in 2009, several assiduous efforts by mycologists across the world have deciphered its biology including growth physiology, drug tolerance, biofilm formation, etc. The differential response of various strains from different clades poses a hurdle in drawing a final conclusion.

AREAS COVERED

This review provides brief insights into the understanding of C. auris biofilm. It includes information on various models developed to understand the biofilms and conservation of different signaling pathways. Significant development has been made in the recent past with the generation of relevant in vivo and ex vivo models. The role of signaling pathways in the development of biofilm is largely unknown.

EXPERT OPINION

The selection of an appropriate model system is a must for the accuracy and reproducibility of results. The conservation of major signaling pathways in C. auris with respect to C. albicans and S. cerevisiae highlights that initial inputs acquired from orthologs will be valuable in getting insights into the mechanism of biofilm formation and associated pathogenesis.

Clonal Dissemination of Antifungal-Resistant Candida haemulonii, China

Candida haemulonii, a relative of C. auris, frequently shows antifungal resistance and is transmissible. However, molecular tools for genotyping and investigating outbreaks are not yet established. We performed genome-based population analysis on 94 C. haemulonii strains, including 58 isolates from China and 36 other published strains. Phylogenetic analysis revealed that C. haemulonii can be divided into 4 clades. Clade 1 comprised strains from China and other global strains; clades 2-4 contained only isolates from China, were more recently evolved, and showed higher antifungal resistance. Four regional epidemic clusters (A, B, C, and D) were identified in China, each comprising ≥5 cases (largest intracluster pairwise single-nucleotide polymorphism differences <50 bp). Cluster A was identified in 2 hospitals located in the same city, suggesting potential intracity transmissions. Cluster D was resistant to 3 classes of antifungals. The emergence of more resistant phylogenetic clades and regional dissemination of antifungal-resistant C. haemulonii warrants further monitoring.

Sweat and Sebum Preferences of the Human Skin Microbiota

The microorganisms inhabiting human skin must overcome numerous challenges that typically impede microbial growth, including low pH, osmotic pressure, and low nutrient availability. Yet the skin microbiota thrive on the skin and have adapted to these stressful conditions. The limited nutrients available for microbial use in this unique niche include those from host-derived sweat, sebum, and corneocytes. Here, we have developed physiologically relevant, synthetic skin-like growth media composed of compounds present in sweat and sebum. We find that skin-associated bacterial species exhibit unique growth profiles at different concentrations of artificial sweat and sebum. Most strains evaluated demonstrate a preference for high sweat concentrations, while the sebum preference is highly variable, suggesting that the capacity for sebum utilization may be a driver of the skin microbial community structure. In particular, the prominent skin commensal Staphylococcus epidermidis exhibits the strongest preference for sweat while growing equally well across sebum concentrations. Conversely, the growth of Corynebacterium kefirresidentii, another dominant skin microbiome member, is dependent on increasing concentrations of both sweat and sebum but only when sebum is available, suggesting a lipid requirement of this species. Furthermore, we observe that strains with similar growth profiles in the artificial media cluster by phylum, suggesting that phylogeny is a key factor in sweat and sebum use. Importantly, these findings provide an experimental rationale for why different skin microenvironments harbor distinct microbiome communities. In all, our study further emphasizes the importance of studying microorganisms in an ecologically relevant context, which is critical for our understanding of their physiology, ecology, and function on the skin. IMPORTANCE The human skin microbiome is adapted to survive and thrive in the harsh environment of the skin, which is low in nutrient availability. To study skin microorganisms in a system that mimics the natural skin environment, we developed and tested a physiologically relevant, synthetic skin-like growth medium that is composed of compounds found in the human skin secretions sweat and sebum. We find that most skin-associated bacterial species tested prefer high concentrations of artificial sweat but that artificial sebum concentration preference varies from species to species, suggesting that sebum utilization may be an important contributor to skin microbiome composition. This study demonstrates the utility of a skin-like growth medium, which can be applied to diverse microbiological systems, and underscores the importance of studying microorganisms in an ecologically relevant context.

Extracellular Vesicles Contribute to Mixed-Fungal Species Competition during Biofilm Initiation

Extracellular vesicles commonly modulate interactions among cellular communities. Recent studies demonstrate that biofilm maturation features, including matrix production, drug resistance, and dispersion, require the delivery of a core protein and carbohydrate vesicle cargo in Candida species. The function of the vesicle cargo for these advanced-phase biofilm characteristics appears to be conserved across Candida species. Mixed-species interactions in mature biofilms indicate that vesicle cargo serves a cooperative role in preserving the community. Here, we define the function of biofilm-associated vesicles for biofilm initiation both within and among five species across the Candida genus. We found similar vesicle cargo functions for several conserved proteins across species, based on the behavior of mutants. Repletion of the adhesion environment with wild-type vesicles returned the community phenotype toward reference levels in intraspecies experiments. However, cross-species vesicle complementation did not restore the wild-type biology and in fact drove the phenotype in the opposite direction for most cross-species interactions. Further study of mixed-species biofilm adhesion and exogenous wild-type vesicle administration similarly demonstrated competitive interactions. Our studies indicate that similar vesicle cargoes contribute to biofilm initiation. However, vesicles from disparate species serve an interference competitive role in mixed-Candida species scenarios. IMPORTANCE Candida species commonly form mixed-species biofilms with other Candida species and bacteria. In the established biofilm state, vesicle cargo delivers public goods to support the mature community. At biofilm initiation, however, vesicles play a negative role in cross-species interactions, presumably to allow species to gain a survival advantage. These observations and recent reports reveal that vesicle cargo has both cooperative and competitive roles among Candida species, depending on the needs of the community biofilm formation.

Forgotten fungi: the importance of the skin mycobiome

The mosaic ecosystems of microbes that live on our skin encompass not only bacteria but also fungi, microeukaryotes, and viruses. As the second most prevalent group, unique fungal communities are found across the dry, moist, and oily microenvironments of human skin, and alterations of these communities are largely driven by changes in skin physiology throughout an individual's lifespan. Fungi have also been associated with infection and dermatological disorders, resulting from the disrupted balance between fungal-bacterial networks on the skin. Mechanisms of colonization resistance toward fungi in the skin microbiome of animals have advanced our understanding in conservation strategies, yet in the human skin, the fungal microbiome (mycobiome) remains vastly unexplored. Here, we review recent studies on the role of fungi in the skin microbiome, emphasizing how fungal-bacterial interactions at the skin surface play an important ecological function in vertebrate hosts.