The Cryptococcus wall: A different wall for a unique lifestyle

The pathobiology of human fungal infections

Human fungal infections are a historically neglected area of disease research, yet they cause more than 1.5 million deaths every year. Our understanding of the pathophysiology of these infections has increased considerably over the past decade, through major insights into both the host and pathogen factors that contribute to the phenotype and severity of these diseases. Recent studies are revealing multiple mechanisms by which fungi modify and manipulate the host, escape immune surveillance and generate complex comorbidities. Although the emergence of fungal strains that are less susceptible to antifungal drugs or that rapidly evolve drug resistance is posing new threats, greater understanding of immune mechanisms and host susceptibility factors is beginning to offer novel immunotherapeutic options for the future. In this Review, we provide a broad and comprehensive overview of the pathobiology of human fungal infections, focusing specifically on pathogens that can cause invasive life-threatening infections, highlighting recent discoveries from the pathogen, host and clinical perspectives. We conclude by discussing key future challenges including antifungal drug resistance, the emergence of new pathogens and new developments in modern medicine that are promoting susceptibility to infection.

Natural compounds from freshwater mussels disrupt fungal virulence determinants and influence fluconazole susceptibility in the presence of macrophages in Cryptococcus neoformans

Cryptococcus neoformans is a human fungal pathogen responsible for fatal infections, especially in patients with a depressed immune system. Overexposure to antifungal drugs due to prolonged treatment regimens and structure-similar applications in agriculture have weakened the efficacy of current antifungals in the clinic. The rapid evolution of antifungal resistance urges the discovery of new compounds that inhibit fungal virulence determinants, rather than directly killing the pathogen, as alternative strategies to overcome disease and reduce selective pressure toward resistance. Here, we evaluated the efficacy of freshwater mussel extracts (crude and clarified) against the production of well-defined virulence determinants (i.e., thermotolerance, melanin, capsule, and biofilm) and fluconazole resistance in C. neoformans. We demonstrated the extracts' influence on fungal thermotolerance, capsule production, and biofilm formation, as well as susceptibility to fluconazole in the presence of macrophages. Additionally, we measured the inhibitory activity of extracts against commercial peptidases (family representatives of cryptococcal orthologs) related to fungal virulence determinants and fluconazole resistance, and integrated these phenotypic findings with quantitative proteomics profiling. Our approach defined distinct signatures of each treatment and validated a new mechanism of anti-virulence action toward the polysaccharide capsule from a selected extract following fractionation. By understanding the mechanisms driving the antifungal activity of mussels, we may develop innovative treatment options to overcome fungal infections and promote susceptibility to fluconazole in resistant strains.

IMPORTANCE

As the prevalence and severity of global fungal infections rise, along with an increasing incidence of antifungal resistance, new strategies to combat fungal pathogens and overcome resistance are urgently needed. Critically, our current methods to overcome fungal infections are limited and drive the evolution of resistance forward; however, an anti-virulence approach to disarm virulence factors of the pathogen and promote host cell clearance is promising. Here, we explore the efficacy of natural compounds derived from freshwater mussels against classical fungal virulence determinants, including thermotolerance, capsule production, stress response, and biofilm formation. We integrate our phenotypic discoveries with state-of-the-art mass spectrometry-based proteomics to identify mechanistic drivers of these antifungal properties and propose innovative avenues to reduce infection and support the treatment of resistant strains.

Mimicking Charged Host-Defense Peptides to Tune the Antifungal Activity and Biocompatibility of Amphiphilic Polymers

Invasive fungal infections impose a substantial global health burden. They cause more than 1.5 million deaths annually and are insufficiently met by the currently approved antifungal drugs. Antifungal peptides are a promising alternative to existing antifungal drugs; however, they can be challenging to synthesize, and are often susceptible to proteases in vivo. Synthetic polymers which mimic the properties of natural antifungal peptides can circumvent these limitations. In this study, we developed a library of 29 amphiphilic polyacrylamides with different charged units, namely, amines, guanidinium, imidazole, and carboxylic acid groups, representative of the natural amino acids lysine, arginine, histidine, and glutamic acid. Ternary polymers incorporating primary ammonium (lysine-like) or imidazole (histidine-like) groups demonstrated superior activity against Candida albicans and biocompatibility with mammalian cells compared to the polymers containing the other charged groups. Furthermore, a combination of primary ammonium, imidazole, and guanidinium (arginine-like) within the same polymer outperformed the antifungal drug amphotericin B in terms of therapeutic index and exhibited fast C. albicans-killing activity. The most promising polymer compositions showed synergistic effects in combination with caspofungin and fluconazole against C. albicans and additionally demonstrated activity against other clinically relevant fungi. Collectively, these results indicate the strong potential of these easily producible polymers to be used as antifungals.

Demographic profiles and risk factors for mortality in acute meningitis: A nationwide population-based observational study

Aim

Acute meningitis encompasses bacterial, viral (aseptic), fungal, tuberculous, and carcinomatous meningitis. The rate and risks of mortality in each type remain uncertain. This study aimed to elucidate these aspects in each type of meningitis.

Methods

This study utilized Japan's nationwide administrative Diagnosis Procedure Combination (DPC) database. Patients with acute meningitis, treated at 1132 DPC-covered hospitals from 2016 to 2022, were enrolled.

Results

Among 47,366,222 cumulative hospitalized patients, 48,758 (0.10%) were hospitalized with acute meningitis. The types of meningitis were as follows: 10,338 with bacterial, 29,486 with viral/aseptic, 965 with fungal, 678 with tuberculous, and 3790 with carcinomatous meningitis. Bacterial and viral meningitis exhibited bimodal age distributions, with the first peak occurring at 0-9 years. The median onset age was below 50 years only in viral meningitis. The mortality rate was the highest in carcinomatous meningitis (39%), followed by fungal meningitis (21%), and the lowest in viral meningitis (0.61%). Mortality rates increased with age across all meningitis types, but this trend was less prominent in carcinomatous meningitis. The duration from admission to mortality was longer in fungal and tuberculous meningitis compared with other types. Staphylococcus aureus in bacterial meningitis (adjusted odds ratio 1.71; p = 0.0016) and herpes simplex virus in viral meningitis (adjusted odds ratio 1.53; p = 0.0467) exhibited elevated mortality rates.

Conclusion

Distinct demographic profiles and mortality rates were observed among different meningitis types. The high mortality rates in less common types of meningitis emphasize the necessity to further optimize the required diagnostic and treatment strategies.

Metals and the cell surface of Cryptococcus neoformans

Recent studies in pathogenic yeasts reinforce our appreciation of the influence of metal homeostasis on the fungal cell surface. To illustrate this influence, we focus on recent studies on Cryptococcus neoformans, a fungal pathogen with a complex surface of a cell wall with embedded melanin and an attached polysaccharide capsule. Copper and iron are essential yet toxic metals, and current efforts demonstrate the importance of these metals for modulating the surface structure of C. neoformans cells in ways that contribute to fungal-host interactions during disease in vertebrate hosts. In this review, we briefly summarize mechanisms of acquisition and regulation for copper and iron, and then discuss recent insights into the connections between the metals and the cell surface.

Importance of Clinical Isolates in Cryptococcus neoformans Research

The human pathogenic fungus Cryptococcus neoformans is a global health concern. Previous research in the field has focused on studies using reference strains to identify virulence factors, generate mutant libraries, define genomic structures, and perform functional studies. In this review, we discuss the benefits and drawbacks of using reference strains to study C. neoformans, describe how the study of clinical isolates has expanded our understanding of pathogenesis, and highlight how studies using clinical isolates can further develop our understanding of the host-pathogen interaction during C. neoformans infection.