Persisting Cryptococcus yeast species Vishniacozyma victoriae and Cryptococcus neoformans elicit unique airway inflammation in mice following repeated exposure

Background

Allergic airway disease (AAD) is a growing concern in industrialized nations and can be influenced by fungal exposures. Basidiomycota yeast species such as Cryptococcus neoformans are known to exacerbate allergic airway disease; however, recent indoor assessments have identified other Basidiomycota yeasts, including Vishniacozyma victoriae (syn. Cryptococcus victoriae), to be prevalent and potentially associated with asthma. Until now, the murine pulmonary immune response to repeated V. victoriae exposure was previously unexplored.

Objective

This study aimed to compare the immunological impact of repeated pulmonary exposure to Cryptococcus yeasts.

Methods

Mice were repeatedly exposed to an immunogenic dose of C. neoformans or V. victoriae via oropharyngeal aspiration. Bronchoalveolar lavage fluid (BALF) and lungs were collected to examine airway remodeling, inflammation, mucous production, cellular influx, and cytokine responses at 1 day and 21 days post final exposure. The responses to C. neoformans and V. victoriae were analyzed and compared.

Results

Following repeated exposure, both C. neoformans and V. victoriae cells were still detectable in the lungs 21 days post final exposure. Repeated C. neoformans exposure initiated myeloid and lymphoid cellular infiltration into the lung that worsened over time, as well as an IL-4 and IL-5 response compared to PBS-exposed controls. In contrast, repeated V. victoriae exposure induced a strong CD4+ T cell-driven lymphoid response that started to resolve by 21 days post final exposure.

Discussion

C. neoformans remained in the lungs and exacerbated the pulmonary immune responses as expected following repeated exposure. The persistence of V. victoriae in the lung and strong lymphoid response following repeated exposure were unexpected given its lack of reported involvement in AAD. Given the abundance in indoor environments and industrial utilization of V. victoriae, these results highlight the importance to investigate the impact of frequently detected fungal organisms on the pulmonary response following inhalational exposure. Moreover, it is important to continue to address the knowledge gap involving Basidiomycota yeasts and their impact on AAD.

Immunological Analysis of Cryptococcal Meningoencephalitis in a Murine Model

Cryptococcal meningoencephalitis (CM), caused by the fungal pathogen Cryptococcus neoformans species complex, can lead to high mortality or severe neurological sequelae in survivors that are associated with excessive inflammation in the central nervous system (CNS), especially in those who develop immune reconstitution inflammatory syndrome (IRIS) or postinfectious immune response syndrome (PIIRS). While the means to establish a cause-and-effect relationship of a specific pathogenic immune pathway during CM by human studies are limited, mouse models allow dissection of the potential mechanistic links within the CNS immunological network. In particular, these models are useful for separating pathways contributing predominantly to immunopathology from those important for fungal clearance. In this protocol, we described methods to induce a robust, physiologically relevant murine model of C. neoformans CNS infection that reproduces multiple aspects of human cryptococcal disease immunopathology and subsequent detailed immunological analysis. Combined with tools including gene knockout mice, antibody blockade, cell adoptive transfer, as well as high throughput techniques such as single-cell RNA sequencing, studies using this model will provide new insights regarding the cellular and molecular processes that elucidate the pathogenesis of cryptococcal CNS diseases in order to develop more effective therapeutic strategies.

Drug Target Elucidation Through Isolation and Analysis of Drug-Resistant Mutants in Cryptococcus neoformans

Drug target identification is an essential component to antifungal drug development. Many methods, including large chemical library screening, natural product screening, and drug repurposing efforts, can identify compounds with favorable in vitro antifungal activity. However, these approaches will often identify compounds with no known mechanism of action. Herein, we describe a method utilizing the human fungal pathogen Cryptococcus neoformans to identify antifungal drug targets through the isolation of spontaneous resistant mutants, antifungal testing, whole-genome sequencing, and variant analysis.

Protective interaction of human phagocytic APC subsets with Cryptococcus neoformans induces genes associated with metabolism and antigen presentation

Cryptococcal meningitis is the most common cause of meningitis among HIV/AIDS patients in sub-Saharan Africa, and worldwide causes over 223,000 cases leading to more than 181,000 annual deaths. Usually, the fungus gets inhaled into the lungs where the initial interactions occur with pulmonary phagocytes such as dendritic cells and macrophages. Following phagocytosis, the pathogen can be killed or can replicate intracellularly. Previous studies in mice showed that different subsets of these innate immune cells can either be antifungal or permissive for intracellular fungal growth. Our studies tested phagocytic antigen-presenting cell (APC) subsets from the human lung against C. neoformans. Human bronchoalveolar lavage was processed for phagocytic APCs and incubated with C. neoformans for two hours to analyze the initial interactions and fate of the fungus, living or killed. Results showed all subsets (3 macrophage and 3 dendritic cell subsets) interacted with the fungus, and both living and killed morphologies were discernable within the subsets using imaging flow cytometry. Single cell RNA-seq identified several different clusters of cells which more closely related to interactions with C. neoformans and its protective capacity against the pathogen rather than discrete cellular subsets. Differential gene expression analyses identified several changes in the innate immune cell's transcriptome as it kills the fungus including increases of TNF-α (TNF) and the switch to using fatty acid metabolism by upregulation of the gene FABP4. Also, increases of TNF-α correlated to cryptococcal interactions and uptake. Together, these analyses implicated signaling networks that regulate expression of many different genes - both metabolic and immune - as certain clusters of cells mount a protective response and kill the pathogen. Future studies will examine these genes and networks to understand the exact mechanism(s) these phagocytic APC subsets use to kill C. neoformans in order to develop immunotherapeutic strategies to combat this deadly disease.

Engineered Fluorescent Strains of Cryptococcus neoformans: a Versatile Toolbox for Studies of Host-Pathogen Interactions and Fungal Biology, Including the Viable but Nonculturable State

Cryptococcus neoformans is an opportunistic fungal pathogen known for its remarkable ability to infect and subvert phagocytes. This ability provides survival and persistence within the host and relies on phenotypic plasticity. The viable but nonculturable (VBNC) phenotype was recently described in C. neoformans, whose study is promising in understanding the pathophysiology of cryptococcosis. The use of fluorescent strains is improving host interaction research, but it is still underexploited. Here, we fused histone H3 or the poly(A) binding protein (Pab) to enhanced green fluorescent protein (eGFP) or mCherry, obtaining a set of C. neoformans transformants with different colors, patterns of fluorescence, and selective markers (hygromycin B resistance [Hygr] or neomycin resistance [Neor]). We validated their similarity to the parental strain in the stress response, the expression of virulence-related phenotypes, mating, virulence in Galleria mellonella, and survival within murine macrophages. PAB-GFP, the brightest transformant, was successfully applied for the analysis of phagocytosis by flow cytometry and fluorescence microscopy. Moreover, we demonstrated that an engineered fluorescent strain of C. neoformans was able to generate VBNC cells. GFP-tagged Pab1, a key regulator of the stress response, evidenced nuclear retention of Pab1 and the assembly of cytoplasmic stress granules, unveiling posttranscriptional mechanisms associated with dormant C. neoformans cells. Our results support that the PAB-GFP strain is a useful tool for research on C. neoformans. IMPORTANCE Cryptococcus neoformans is a human-pathogenic yeast that can undergo a dormant state and is responsible for over 180,000 deaths annually worldwide. We engineered a set of fluorescent transformants to aid in research on C. neoformans. A mutant with GFP-tagged Pab1 improved fluorescence-based techniques used in host interaction studies. Moreover, this mutant induced a viable but nonculturable phenotype and uncovered posttranscriptional mechanisms associated with dormant C. neoformans. The experimental use of fluorescent mutants may shed light on C. neoformans-host interactions and fungal biology, including dormant phenotypes.

Cross-reactivity between vaccine antigens from the chitin deacetylase protein family improves survival in a mouse model of cryptococcosis

Meningitis due to the fungal pathogen Cryptococcus neoformans is estimated to cause nearly 200,000 deaths annually, mostly in resource-limited regions. We previously identified cryptococcal protein antigens which, when delivered in glucan particles, afford vaccine-mediated protection against an otherwise lethal infection. Many of these proteins exhibit significant homology to other similar cryptococcal proteins leading us to hypothesize that protection may be augmented by immunologic cross-reactivity to multiple members of a protein family. To examine the significance of protein cross-reactivity in vaccination, we utilized strains of Cryptococcus that are genetically deficient in select antigens, yet are still lethal in mice. Vaccination with a protein without homologs (e.g., Mep1 and Lhc1) protected against challenge with wild-type Cryptococcus, but not against a deletion strain lacking that protein. Contrastingly, vaccination with a single chitin deacetylase (Cda) protein protected against the corresponding deletion strain, presumably due to host recognition of one or more other family members still expressed in this strain. Vaccination with a single Cda protein induced cross-reactive antibody and interferon-gamma (IFNγ) immune responses to other Cda protein family members. Paradoxically, we saw no evidence of cross-protection within the carboxypeptidase family of proteins. Factors such as in vivo protein expression and the degree of homology across the family could inform the extent to which vaccine-mediated immunity is amplified. Together, these data suggest a role for prioritizing protein families in fungal vaccine design: increasing the number of immune targets generated by a single antigen may improve efficacy while diminishing the risk of vaccine-resistant strains arising from gene mutations.

Outcomes of flucytosine-containing combination treatment for cryptococcal meningitis in a South African national access programme: a cross-sectional observational study

BACKGROUND

Although flucytosine is a key component of WHO-recommended induction treatment for HIV-associated cryptococcal meningitis, this antifungal agent is not widely available in low-income and middle-income countries due to limited production and cost. In 2018, a national flucytosine access programme was initiated in South Africa. We aimed to determine the effectiveness of flucytosine-containing induction regimens in routine care to motivate for the urgent registration of flucytosine and its inclusion in treatment guidelines.

METHODS

In this cross-sectional study, we compared outcomes of adults aged 18 years and older with incident laboratory-confirmed cryptococcal meningitis treated with or without flucytosine-containing regimens at 19 sentinel hospitals in South Africa. A case of cryptococcosis was defined as illness in an adult with: (1) positive cerebrospinal fluid (CSF) India ink microscopy; (2) a positive CSF cryptococcal antigen test; or (3) culture of Cryptococcus neoformans or Cryptococcus gattii from CSF or any other specimen. We excluded patients without a case report form, those with an unknown or negative HIV serology result, those with a recurrent episode, and those who did not receive antifungal treatment in hospital. We assessed cumulative in-hospital mortality at 14 days and 30 days and calculated the overall crude in-hospital case-fatality ratio. We used random-effects logistic regression to examine the association between treatment group and in-hospital mortality.

FINDINGS

From July 1, 2018, to March 31, 2020, 10 668 individuals were diagnosed with laboratory-confirmed cryptococcal meningitis, 7787 cases diagnosed at non-enhanced surveillance sites and 567 cases from eight enhanced surveillance sites with no access to flucytosine were excluded. Of 2314 adults with a first episode of cryptococcosis diagnosed at 19 facilities with access to flucytosine, 1996 had a case report form and of these, 1539 received induction antifungal treatment and were confirmed HIV-seropositive first-episode cases. Of 1539 patients who received antifungal therapy, 596 (38·7%) individuals received a flucytosine-containing regimen and 943 (61·3%) received another regimen. The median age was 36 years (IQR 32-43) and 906 (58·9%) participants were male and 633 (41·1%) were female. The crude in-hospital case-fatality ratio was 23·9% (95% CI 20·0-27·0; 143 of 596) in those treated with flucytosine-containing regimens and 37·2% (95% CI 34·0-40·0; 351 of 943) in those treated with other regimens. Patients admitted to non-academic hospitals (adjusted odds ratio [aOR] 1·95 [95% CI 1·53-2·48]; p<0·0001) and those who were antiretroviral treatment-experienced (aOR 1·30 [1·02-1·67]; p=0·033) were more likely to receive flucytosine. After adjusting for relevant confounders, flucytosine treatment was associated with a 53% reduction in mortality (aOR 0·47 [95% CI 0·35-0·64]; p<0·0001). Among survivors, the median length of hospital admission in the flucytosine group was 11 days (IQR 8-15) versus 17 days (13-21) in the comparison group (p=0·0010).

INTERPRETATION

In-hospital mortality among patients treated with a flucytosine-containing regimen was comparable to reduced mortality reported in patients receiving a flucytosine-containing regimen in a recent multicentre African clinical trial. Flucytosine-based treatment can be delivered in routine care in a middle-income country with a substantial survival benefit.

FUNDING

National Institute for Communicable Diseases, a Division of the National Health Laboratory Service.

TRANSLATION

For the Zulu translation of the abstract see Supplementary Materials section.

Membrane Integrity Contributes to Resistance of Cryptococcus neoformans to the Cell Wall Inhibitor Caspofungin

The fungal pathogen Cryptococcus neoformans causes up to 278 000 infections each year globally, resulting in up to 180,000 deaths annually, mostly impacting immunocompromised people. Therapeutic options for C. neoformans infections are very limited. Caspofungin, a member of the echinocandin class of antifungals, is generally well tolerated but clinically ineffective against C. neoformans. We sought to identify biological processes that can be targeted to render the cell more susceptible to echinocandins by screening the available libraries of gene deletion mutants made in the KN99α background for caspofungin sensitivity. We adapted a Candida albicans fungal biofilm assay for the growth characteristics of C. neoformans and systematically screened 4,030 individual gene deletion mutants in triplicate plate assays. We identified 25 strains that showed caspofungin sensitivity. We followed up with a dose dependence assay, and 17 of the 25 were confirmed sensitive, 5 of which were also sensitive in an agar plate assay. We made new deletion mutant strains for four of these genes: CFT1, encoding an iron transporter; ERG4, encoding a sterol desaturase; MYO1, encoding a myosin heavy chain; and YSP2, encoding a sterol transporter. All were more sensitive to membrane stress and showed significantly increased sensitivity to caspofungin at higher temperatures. Surprisingly, none showed any obvious cell wall defects such as would be expected for caspofungin-sensitive strains. Our microscopy analyses suggested that loss of membrane integrity contributed to the caspofungin sensitivity, either by allowing more caspofungin to enter or remain in the cell or by altering the location or orientation of the enzyme target to render it more susceptible to inhibition. IMPORTANCE The intrinsic resistance of Cryptococcus neoformans to the cell wall inhibitor caspofungin limits the available therapies for treating cryptococcal infections. We screened a collection of more than 4,000 gene deletion strains for altered caspofungin sensitivity to identify biological processes that could be targeted to render the cell more susceptible to caspofungin. We identified multiple genes with an effect on caspofungin susceptibility and found that they were associated with altered membrane permeability rather than the expected cell wall defects. This suggests that targeting these genes or other genes affecting membrane permeability is a viable path for developing novel therapies for treating this global fungal pathogen.

Cerebrospinal fluid cytokine and chemokine patterns correlate with prognosis of HIV-uninfected cryptococcal meningitis: A prospective observational study

The cerebrospinal fluid (CSF) immune responses in HIV-uninfected cryptococcal meningitis (CM) have not been well studied. In this study, we aimed to explore the phenotype of CSF immune response during the course of disease and to examine relationships between phenotypes and disease severity. We profiled the CSF immune response in 128 HIV-uninfected CM and 30 pulmonary cryptococcosis patients using a 27-plex Luminex cytokine kit. Principal component analyses (PCA) and logistic regression model were performed. Concentrations of 23 out of 27 cytokines and chemokines in baseline CSF were significantly elevated in CM patients compared with pulmonary cryptococcosis cases. In CM patients with Cryptococcus neoformans infection, IL-1ra, IL-9, and VEGF were significantly elevated in immunocompetent cases. Cytokine levels usually reached peaks within the first 2 weeks of antifungal treatment and gradually decreased over time. PCA demonstrated a co-correlated CSF cytokine and chemokine response consisting of Th1, Th2, and Th17 type cytokines. Prognostic analysis showed that higher scores for the PCs loading pro-inflammatory cytokines, IFN-γ, TNF-α, and IL-12; and anti-inflammatory cytokine, IL-4; and chemokines, Eotaxin, FGF-basis, and PDGF-bb; as well as lower scores for the PCs loading RANTES were associated with disease severity, as defined by a Glasgow Coma Scale of <15 or death. In conclusion, combined inflammatory responses in CSF involving both pro- and anti-inflammatory cytokines and chemokines are upregulated in HIV-uninfected CM, and associated with disease severity.

Prevalence of Cryptococcus gattii in Ugandan HIV-infected patients presenting with cryptococcal meningitis

Introduction

Cryptococcal meningitis (CM) is a life threatening disease and leading cause of opportunistic fungal-related mortality in HIV/AIDS. Most CM infections are caused by C. neoformans species complexes but the prevalence of Cryptococcus gattii species complexes in Uganda is unknown however, it is known in a few other parts of Africa. We estimated the prevalence of C. gattii in patients living with HIV and a diagnosis of cryptococcal meningitis in Uganda.

Methods

Cryptococcus isolates (n = 200) obtained from cerebrospinal fluid of patients with CM recruited at the Infectious Diseases Institute, Kampala, Uganda, were tested by phenotypic methods. The Cryptococcus isolates were sub-cultured on Sabouraud Dextrose Agar plates for 48 hours. The yeast colonies were examined by India ink stain, urea hydrolysis, and C. gattii was identified by blue pigmentation on CGB agar. The results were analyzed for frequency of C. gattii. Patient demographic characteristics were collected from the case record forms.

Results

From the 200 patients’ case record forms, 87 (43.5%) were female and 113 (56.5%) were male. The median age was 35 (19–64) years. Most patients, 93% (187/200) were from Central Uganda in the districts of Kampala and Wakiso. 97.51% (157/161) of the patients had absolute CD4 lymphocyte counts of less than 200 cells per cubic millimeter; 1.86% (3/161) 200–350 cells per cubic millimeter and 0.62% (1/161) above 500 cells per cubic millimeter. 45.4% (74/163) were not yet on HAART and 54.6% (89/163) were on HAART. 66.7% (58/87) had poor adherence to HAART treatment and 33.3% (29/87) had reported good adherence to HAART treatment. A total of 200 clinical isolates of Cryptococcus isolates were tested. No (0% (0/200) C. gattii was identified among the Cryptococcus isolates.

Conclusion

In this study among patients living with HIV and a diagnosis of cryptococcal meningitis in Uganda, we found no C. gattii infections.

Synergistic Antifungal Effect of a Combination of Iron Deficiency and Calcium Supplementation

Fungal diseases have become a major public health issue worldwide. Increasing drug resistance and the limited number of available antifungals result in high morbidity and mortality. Metal-based drugs have been reported to be therapeutic agents against major protozoan diseases, but knowledge of their ability to function as antifungals is limited. In this study, we found that calcium supplementation combined with iron deficiency causes dramatic growth inhibition of the human fungal pathogens Aspergillus fumigatus, Candida albicans, and Cryptococcus neoformans. Calcium induces the downregulation of iron uptake-related genes and, in particular, causes a decrease in the expression of the transcription factor HapX, which tends to transcriptionally activate siderophore-mediated iron acquisition under iron-deficient conditions. Iron deficiency causes calcium overload and the overproduction of intracellular reactive oxygen species (ROS), and perturbed ion homeostasis suppresses fungal growth. These phenomena are consistently identified in azole-resistant A. fumigatus isolates. The findings here imply that low iron availability lets cells mistakenly absorb calcium as a substitute, causing calcium abnormalities. Thus, there is a mutual effect between iron and calcium in fungal pathogens, and the combination of calcium with an iron chelator could serve to improve antifungal therapy. IMPORTANCE Millions of immunocompromised people are at a higher risk of developing different types of severe fungal diseases. The limited number of antifungals and the emergence of antimicrobial resistance highlight an urgent need for new strategies against invasive fungal infections. Here, we report that calcium can interfere with iron absorption of fungal pathogens, especially in iron-limited environments. Thus, a combination of calcium supplementation with an iron chelator inhibits the growth of human fungal pathogens, including Aspergillus fumigatus, Candida albicans, and Cryptococcus neoformans. Moreover, we demonstrate that iron deficiency induces a nonspecific calcium uptake response, which results in toxic levels of metal. Findings in this study suggest that a microenvironment with excess calcium and limited iron is an efficient strategy to curb the growth of fungal pathogens, especially for drug-resistant isolates.

On the relationship between Pathogenic Potential and Infective Inoculum

Pathogenic Potential (PP) is a mathematical description of an individual microbe, virus, or parasite's ability to cause disease in a host, given the variables of inoculum, signs of disease, mortality, and in some instances, median survival time of the host. We investigated the relationship between pathogenic potential (PP) and infective inoculum (I) using two pathogenic fungi in the wax moth Galleria mellonella with mortality as the relevant outcome. Our analysis for C. neoformans infection revealed negative exponential relationship between PP and I. Plotting the log(I) versus the Fraction of animals with signs or symptoms (Fs) over median host survival time (T) revealed a linear relationship, with a slope that varied between the different fungi studied and a y-intercept corresponding to the inoculum that produced no signs of disease. The I vs Fs/T slope provided a measure of the pathogenicity of each microbial species, which we call the pathogenicity constant or kPath. The kPath provides a new parameter to quantitatively compare the relative virulence and pathogenicity of microbial species for a given host. In addition, we investigated the PP and Fs/T from values found in preexisting literature. Overall, the relationship between Fs/T and PP versus inoculum varied among microbial species and extrapolation to zero signs of disease allowed the calculation of the lowest pathogenic inoculum (LPI) of a microbe. Microbes tended to fall into two groups: those with positive linear relationships between PP and Fs/T vs I, and those that had a negative exponential PP vs I relationship with a positive logarithmic Fs/T vs I relationship. The microbes with linear relationships tended to be bacteria, whereas the exponential-based relationships tended to be fungi or higher order eukaryotes. Differences in the type and sign of the PP vs I and Fs/T vs I relationships for pathogenic microbes suggest fundamental differences in host-microbe interactions leading to disease.

Antifungal and Antibiofilm Efficacy of Paeonol Treatment Against Biofilms Comprising Candida albicans and/or Cryptococcus neoformans

Fungal populations are commonly found in natural environments and present enormous health care challenges, due to increased resistance to antifungal agents. Paeonol exhibits antifungal activities; nevertheless, the antifungal and antibiofilm activities of paeonol against Candida albicans and Cryptococcus neoformans remain largely unexplored. Here, we aimed to evaluate the antifungal and antibiofilm activities of paeonol against C. albicans and/or C. neoformans (i.e., against mono- or dual-species). The minimum inhibitory concentrations (MICs) of paeonol for mono-species comprising C. albicans or C. neoformans were 250 μg ml⁻¹, whereas the MIC values of paeonol for dual-species were 500 μg ml⁻¹. Paeonol disrupted cell membrane integrity and increased the influx of gatifloxacin into cells of mono- and dual-species cells, indicating an antifungal mode of action. Moreover, paeonol at 8 times the MIC damaged mono- and dual-species cells within C. albicans and C. neoformans biofilms, as it did planktonic cells. In particular, at 4 and 8 mg ml⁻¹, paeonol efficiently dispersed preformed 48-h biofilms formed by mono- and dual-species cells, respectively. Paeonol inhibited effectively the yeast-to-hyphal-form transition of C. albicans and impaired capsule and melanin production of C. neoformans. The addition of 10 MIC paeonol to the medium did not shorten the lifespan of C. elegans, and 2 MIC paeonol could effectively protect the growth of C. albicans and C. neoformans-infected C. elegans. Furthermore, RNA sequencing was employed to examine the transcript profiling of C. albicans and C. neoformans biofilm cells in response to 1/2 MIC paeonol. RNA sequencing data revealed that paeonol treatment impaired biofilm formation of C. albicans by presumably downregulating the expression level of initial filamentation, adhesion, and growth-related genes, as well as biofilm biosynthesis genes, whereas paeonol inhibited biofilm formation of C. neoformans by presumably upregulating the expression level of ergosterol biosynthesis-related genes. Together, the findings of this study indicate that paeonol can be explored as a candidate antifungal agent for combating serious single and mixed infections caused by C. albicans and C. neoformans.

Gluconate Kinase Is Required for Gluconate Assimilation and Sporulation in Cryptococcus neoformans

Cryptococcus neoformans is an environmental yeast and an opportunistic human pathogen. The ability to cause disease depends on the ability to adapt to the human host. Previous studies implicated infectivity-related kinase 3 (IRK3, CNAG_03048) as required for establishing an infection. We genetically and biochemically characterized IRK3 as a gluconate kinase and propose the name GNK1. This metabolic enzyme utilizes gluconate to produce 6-phosphogluconate as part of the alternative oxidative phase of the pentose phosphate pathway (AOXPPP). The presence of GNK1 confirms that the AOXPPP is present and able to compensate for loss of the traditional OXPPP, providing an explanation for its nonessentiality. C. neoformans can utilize gluconate as an alternative carbon source in a GNK1-dependent manner. In our efforts to understand the role of GNK1 in host adaptation and virulence, we found that GNK1-deficient mutants have variable virulence and carbon dioxide tolerance across multiple strains, suggesting that second site mutations frequently interact with GNK1 deletion mutations. In our effort to isolate these genetic loci by backcrossing experiments, we discovered that GNK1-deficient strains are unable to sporulate. These data suggest that gluconate metabolism is critical for sporulation of C. neoformans. IMPORTANCE Cryptococcus neoformans is a fungal pathogen that contributes to nearly 180,000 deaths annually. We characterized a gene named GNK1 that appears to interact with other genetic loci involved with the ability of C. neoformans to act as a pathogen. While these interacting genetic loci remain elusive, we discovered that GNK1 plays roles in both metabolism and mating/sporulation. Further interrogation of the mechanistic role for GNK1 in sexual reproduction may uncover a larger network of genes that are important for host adaptation and virulence.

Performance of Metagenomic Next-Generation Sequencing for the Diagnosis of Cryptococcal Meningitis in HIV-Negative Patients

Objectives

Metagenomic next-generation sequencing (mNGS) has been applied more and more widely for the diagnosis of infectious diseases, but its performance in the diagnosis of cryptococcal meningitis (CM) remains unclear.

Methods

Cerebrospinal fluid (CSF) samples from 197 HIV-negative patients with suspected central nervous system infections were tested simultaneously by mNGS and routine methods [India ink staining, fungal culture, or cryptococcal antigen (CrAg) tests]. The performance of mNGS was evaluated.

Results

Of the 197 enrolled cases, 46 (23.4%) cases were finally diagnosed with CM, including 43 (93.5%) Cryptococcus neoformans infections and 3 (6.5%) Cryptococcus gattii infections. The sensitivity, specificity, positive predictive value, negative predictive value, and concordance rate of mNGS were 93.5% [95% confidence interval (CI) at 86.4%~100.0%], 96.0% (95% CI at 92.9%~99.1%), 87.8%, 98.0%, and 95.4%, respectively. Comparing to the conventional diagnostic methods, the sensitivity and concordance rate of mNGS were slightly lower than those of CrAg tests (97.4%) but higher than those of India ink (63.0%) and culture (76.7%). Besides, mNGS had a sensitivity of 100.0% against culture. It should be noted that mNGS could identify Cryptococcus at species level; C. gattii of the 3 cases was only distinguished by mNGS.

Conclusions

CSF mNGS can be considered as a supplementary test to diagnose CM and directly distinguish C. gattii from C. neoformans in clinical specimens.

Parkinsonism and prolonged cognitive decline as a manifestation of cryptococcal meningitis in a renal transplant patient

We report a case of a 67-year-old male recipient of a second renal allograft, presenting with a 9-month history of progressive cognitive and physical decline with features of Parkinsonism. He was HIV-negative. Serum and cerebrospinal fluid (CSF) cryptococcal antigen was positive though CSF culture was sterile. He had progressive deterioration despite induction and consolidation antifungal treatment. Postmortem brain examination confirmed a large burden of yeast forms in the substantia nigra with widespread chronic meningitis. The significant delay in presentation and diagnosis owing to the atypical, subacute neurocognitive features serves as a timely reminder of the variety of neurological presentations that may be associated with cryptococcal infection in solid organ transplant recipients.

Cryptococcal Meningitis in a Patient with Sjogren's Syndrome: a Case Report

BACKGROUND

Cryptococcal meningitis (CM) is a life-threatening infectious disease and causes high morbidity and mortality. No information about Cryptococcal meningitis in populations with Sjogren's syndrome (SS) was available.

METHODS

This report details the first case of Cryptococcal meningitis in a 75-year-old female patient with 10-years history of Sjogren's syndrome.

RESULTS

Detailed findings of C. neoformans from CSF examinations, including routine examination, India ink stain, immunological test, culturing, mass spectrum analysis and molecular biology identification were all delineated in this case, which facilitated understanding of detection methods in C. neoformans infection. The etiological exploration was initiated from a positive finding of yeast cells in routine examination of unstained CSF in the present case. Morphology description of C. neoformans in unstained CSF was depicted for the first time.

CONCLUSIONS

Clinicians should consider the possible complication of Cryptococcal meningitis when patients with Sjogren's syndrome show neurological symptoms. Importance of screening yeast cells from unstained CSF for routine examination was emphasized, which may reduce errors in cell counting and trigger further etiological ex-ploration of C. neoformans infection in laboratory and clinical practice.

The monothiol glutaredoxin Grx4 influences thermotolerance, cell wall integrity, and Mpk1 signaling in Cryptococcus neoformans

Monothiol glutaredoxins are important regulators of iron homeostasis that play conserved roles in the sensing and trafficking of iron-sulfur clusters. We previously characterized the role of the monothiol glutaredoxin Grx4 in iron homeostasis, the interaction with the iron regulator Cir1, and virulence in Cryptococcus neoformans. This important fungal pathogen causes cryptococcal meningoencephalitis in immunocompromised individuals worldwide. Here, we demonstrate that Grx4 is required for proliferation at elevated temperatures (both 37°C and 39°C) and under stress conditions. In particular, the grx4Δ mutant was hypersensitive to SDS, calcofluor white (CFW), and caffeine, suggesting that Grx4 is required for membrane and cell wall integrity (CWI). In this context, we found that Grx4 regulated the phosphorylation of the Mpk1 mitogen-activated protein kinase (MAPK) of the CWI pathway in cells grown at elevated temperature or upon treatment with CFW, caffeine, or SDS. The grx4Δ mutant also displayed increased sensitivity to FK506 and cyclosporin A, two inhibitors of the calcineurin pathway, indicating that Grx4 may influence growth at higher temperatures in parallel with calcineurin signaling. Upon thermal stress or calcium treatment, loss of Grx4 also caused partial mis-localization of Crz1, the transcription factor that is a calcineurin substrate. The phenotypes of the grx4Δ, crz1Δ, and cna1Δ (calcineurin) mutants suggest shared contributions to the regulation of temperature, cell wall, and other stresses. In summary, we show that Grx4 is also a key regulator of the responses to a variety of stress conditions in addition to its roles in iron homeostasis in C. neoformans.

Cryptococcal meningoencephalitis: time for action

Cryptococcal meningoencephalitis was first described over a century ago. This fungal infection is preventable and treatable yet continues to be associated with excessive morbidity and mortality. The largest burden of disease resides in people living with HIV in low-income and middle-income countries. In this group, mortality with the best antifungal induction regimen (7 days of amphotericin B deoxycholate [1·0 mg/kg per day] and flucytosine [100·0 mg/kg per day]) in a clinical trial setting was 24% at 10 weeks. The world is now at an inflection point in terms of recognition, research, and action to address the burden of morbidity and mortality from cryptococcal meningoencephalitis. However, the scope of interventional programmes needs to increase, with particular attention to implementation science that is specific to individual countries. This Review summarises causes of excessive mortality, interventions with proven survival benefit, and gaps in knowledge and practice that contribute to the ongoing high death toll from cryptococcal meningoencephalitis. TRANSLATIONS: For the Vietnamese and Chichewa translations of the abstract see Supplementary Materials section.