Candida auris-macrophage cellular interactions and transcriptional response

Evolutionary accumulation of FKS1 mutations from clinical echinocandin-resistant Candida auris

INTRODUCTION

Drug resistance to echinocandins, first-line drugs used to treat Candida auris infection, is rapidly emerging. However, the accumulation of mutations in genes other than FKS1 (before an isolate develops to resistance via FKS1 mutations), remains poorly understood. Methods: Four clinical cases and 29 isolates associated with the incremental process of echinocandin resistance were collected and analyzed using antifungal drug susceptibility testing and genome sequencing to assess the evolution of echinocandin resistance.

FINDINGS

Six echinocandin minimum inhibitory concentration (MIC)-elevated C. auris strains and seven resistant strains were isolated from the urinary system of patients receiving echinocandin treatment. Meanwhile, phylogenetic analyses illustrated that the echinocandin-resistant strains were closely related to other strains in the same patient. Genomic data revealed that the echinocandin-resistant strains had FKS1 mutations. Furthermore, three categories (ECN-S/E/R) of non-synonymous mutant SNP genes (such as RBR3, IFF6, MKC1, MPH1, RAD2, and MYO1) in C. auris appeared to be associated with the three-stage-evolutionary model of echinocandin resistance in C. glabrata: cell wall stress, drug adaptation, and genetic escape (FKS mutation).

INTERPRETATION

Echinocandin-resistant C. auris undergoes spatial and temporal phase changes closely related to echinocandin exposure, particularly in the urinary system. These findings suggest that FKS1 mutations mediate an evolutionary accumulation of echinocandin resistance followed by modulation of chromosome remodelling and DNA repair processes that ultimately lead to FKS1 hot spot mutations and the development of drug resistance. This study provides an in-depth exploration of the molecular pathways involved in the evolution of Candida auris echinocandin resistance.

Cell aggregation mediated by ACE2 deletion in Candida auris modulates fungal colonization and host immune responses in the skin

Candida auris is an emerging multi-drug-resistant fungal pathogen that colonizes the skin and causes invasive infections in hospitalized patients. Multi-cellular aggregative phenotype is widely reported in the C. auris isolates, but its role in skin colonization and host immune response is not yet known. In this study, we generated aggregative phenotype by deleting the ACE2 gene in C. auris and determined the fungal colonization and host immune response using an intradermal mouse model of C. auris skin infection. Our results indicate that mice infected with ace2Δ strain had significantly lower fungal load after 3 and 14 days post-infections compared to the non-aggregative wild-type and the ACE2 reintegrated strain. The colonization of ace2Δ is associated with increased recruitment of CD11b+ Ly6G+ neutrophils and decreased accumulation of CD11b+ Ly6 Chi inflammatory monocytes and CD11b+ MHCII+ CD64+ macrophages. Furthermore, Th17 cells and type 3 innate lymphoid cells (ILCs) were significantly increased in the skin tissue of ace2Δ infected mice. Our findings suggest that aggregative phenotype mediated by ACE2 deletion in C. auris induces potent neutrophil and IL-17-mediated immune response and reduces fungal colonization in the skin.IMPORTANCEC. auris is a rapidly emerging fungal pathogen that can colonize hospitalized patients, especially in skin tissue, and cause invasive infections. C. auris isolates exhibit morphological heterogeneity, and the multicellular aggregative phenotype of C. auris is reported frequently in clinical settings. Understanding the role of fungal morphotypes in colonization, persistence, and immune response in the skin microenvironment will have potential applications in clinical diagnosis and novel preventive and therapeutic measures. Here, we utilized the murine model of intradermal infection and determined that the aggregative phenotype of C. auris as the result of ACE2 gene deletion elicits potential innate and adaptive immune responses in mice. These observations will help explain the differences in the skin colonization and immune responses of the aggregative morphotype of C. auris and open the door to developing novel antifungal therapeutics.

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.

Antimicrobial Efficacy of GS-2 on Reusable Food Packaging Materials for Specialty Crops

The European Union (EU) regulations mandate 10% of all food packaging to be reusable by 2030. United States (U.S.) exporters of specialty crops face new challenges in ensuring microbiological food safety using reusable packaging. A novel antimicrobial formulation consisting of ammonium carboxylate salt of capric acid and L-arginine (GS-2) was recently developed as a spray coating chemical for food packaging materials. In this study, we evaluated the antimicrobial efficacy of GS-2 against microbial strains representing three foodborne bacterial pathogens (Escherichia coli O157:H7, Listeria monocytogenes, Salmonella enterica), one fungal spoilage organism (Aspergillus niger), and one surrogate viral pathogen (murine norovirus) on three reusable plastic materials (acrylonitrile butadiene styrene, high-density polyethylene, and polypropylene) and one cardboard packaging material, respectively. Different chemical concentrations, exposure times, and storage conditions were individually evaluated for the relative antimicrobial efficacies of GS-2 against these microorganisms. Our results showed that GS-2 was highly effective for inactivating bacterial pathogens on both plastic and cardboard surfaces. For instance, 3% GS-2 achieved a >5 log CFU/in2 reduction in E. coli O157:H7, L. monocytogenes, and S. enterica on tested plastic surfaces at an exposure time of 60 min. However, its efficacy against A. niger and murine norovirus was less optimal, resulting in a ≤1 log CFU/in2 reduction on all tested surfaces. Based on our study, GS-2 demonstrated a strong potential as an antibacterial coating reagent for reusable food packaging materials to minimize pathogen contamination and ensure the safety of the specialty crops.

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.

Innate immune response to Candida auris

Candida auris, a newly emergent fungal species, has been spreading in health care systems and causing life-threatening infections. Intact innate immunity is essential for protection against many invasive fungal infections, including candidiasis. Here, we highlight recent studies exploring immune interactions with C. auris, including investigations using animal models and ex vivo immune cells. We summarize innate immune studies comparing C. auris and the common fungal pathogen Candida albicans. We also discuss how structures of the C. auris cell wall influence immune recognition, the role of soluble host factors in immune recognition, and areas of future study.

Case report: From oral infection to life-threatening pneumonia: clinical considerations in Nocardia infection from a case

Nocardia is an anthropozoonotic bacteria that occurs widely in the natural environment. However, because it is a gram-positive aerobic opportunistic pathogen, it rarely occurs in patients with no prior history of immune function disease. Since the symptoms are nonspecific the diagnosis of Nocardia pneumonia is challenging. Previous studies have not reported that this anthropozoonotic bacteria colonizing the human body could cause severe pneumonia by gingival pain and pharyngeal discomfort. This case report describes a previously healthy 60-year-old female farmer who presented to the doctor with gingival pain and pharyngeal discomfort. She was treated with a dental cleaning and oral metronidazole. The patient rapidly progressed to breathing difficulties. Lung shadow was found by computerized tomography examination. The radiologist diagnosed pulmonary tuberculosis as image-based. Through laboratory examination and culture of pathogenic microorganisms in the sputum and blood of the patient, no obvious positive findings were found. The disease progressed rapidly to tracheal intubation ventilator assisted breathing. Subsequently, the patient underwent alveolar lavatory examination under endotracheal intubation fiberbronchoscopy, and the culture of alveolar lavage fluid indicated Nocardia. According to this result, the patient's disease was quickly controlled after selecting the targeted drug compound sulfamethoxazole and intravenous meropenem for treatment. In view of the reason for the high misdiagnosis rate due to the low positive rate of Nocardia culture in most cases, the clinical thinking of diagnosis and treatment from oral infection symptoms to fatal pneumonia reported in this case has certain clinical popularization and enlighten significance, not only improved the diagnosis and treatment of rare diseases, but also be reduced medical disputes.

Fungi of the order Mucorales express a "sealing-only" tRNA ligase

Some eukaryotic pre-tRNAs contain an intron that is removed by a dedicated set of enzymes. Intron-containing pre-tRNAs are cleaved by tRNA splicing endonuclease, followed by ligation of the two exons and release of the intron. Fungi use a "heal and seal" pathway that requires three distinct catalytic domains of the tRNA ligase enzyme, Trl1. In contrast, humans use a "direct ligation" pathway carried out by RTCB, an enzyme completely unrelated to Trl1. Because of these mechanistic differences, Trl1 has been proposed as a promising drug target for fungal infections. To validate Trl1 as a broad-spectrum drug target, we show that fungi from three different phyla contain Trl1 orthologs with all three domains. This includes the major invasive human fungal pathogens, and these proteins can each functionally replace yeast Trl1. In contrast, species from the order Mucorales, including the pathogens Rhizopus arrhizus and Mucor circinelloides, have an atypical Trl1 that contains the sealing domain but lacks both healing domains. Although these species contain fewer tRNA introns than other pathogenic fungi, they still require splicing to decode three of the 61 sense codons. These sealing-only Trl1 orthologs can functionally complement defects in the corresponding domain of yeast Trl1 and use a conserved catalytic lysine residue. We conclude that Mucorales use a sealing-only enzyme together with unidentified nonorthologous healing enzymes for their heal and seal pathway. This implies that drugs that target the sealing activity are more likely to be broader-spectrum antifungals than drugs that target the healing domains.

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.

Fungi of the order Mucorales express a "sealing-only" tRNA ligase

Some eukaryotic pre-tRNAs contain an intron that is removed by a dedicated set of enzymes. Intron-containing pre-tRNAs are cleaved by tRNA splicing endonuclease (TSEN), followed by ligation of the two exons and release of the intron. Fungi use a "heal and seal" pathway that requires three distinct catalytic domains of the tRNA ligase enzyme, Trl1. In contrast, humans use a "direct ligation" pathway carried out by RTCB, an enzyme completely unrelated to Trl1. Because of these mechanistic differences, Trl1 has been proposed as a promising drug target for fungal infections. To validate Trl1 as a broad-spectrum drug target, we show that fungi from three different phyla contain Trl1 orthologs with all three domains. This includes the major invasive human fungal pathogens, and these proteins each can functionally replace yeast Trl1. In contrast, species from the order Mucorales, including the pathogens Rhizopus arrhizus and Mucor circinelloides, contain an atypical Trl1 that contains the sealing domain, but lack both healing domains. Although these species contain fewer tRNA introns than other pathogenic fungi, they still require splicing to decode three of the 61 sense codons. These sealing-only Trl1 orthologs can functionally complement defects in the corresponding domain of yeast Trl1 and use a conserved catalytic lysine residue. We conclude that Mucorales use a sealing-only enzyme together with unidentified non-orthologous healing enzymes for their heal and seal pathway. This implies that drugs that target the sealing activity are more likely to be broader-spectrum antifungals than drugs that target the healing domains.