Killing of Caenorhabditis elegans by Cryptococcus neoformans as a model of yeast pathogenesis

Isobavachalcone confers protection against Cryptococcus neoformans-induced ferroptosis in Caenorhabditis elegans via lifespan extension and GSH-GPX-1 axis modulation

The recent designation of Cryptococcus neoformans as a critical-priority fungal pathogen by the World Health Organization highlights the imperative need for novel antifungal agents with distinct mechanisms of action. This study elucidates the novel ferroptotic pathway underlying C. neoformans-induced cell death in Caenorhabditis elegans and investigates the therapeutic potential of isobavachalcone (IBC) through comprehensive evaluation of core biochemical markers: total glutathione (GSH), malondialdehyde, ferrous iron content, and lipid reactive oxygen species (ROS). Integrated transcriptomic analysis via RNA-seq and subsequent RT-qPCR validation revealed critical gene expression patterns associated with antiferroptotic regulation. Our findings demonstrate that C. neoformans infection initiates ferroptosis in C. elegans through iron-dependent lipid peroxidation cascades. Remarkably, IBC administration conferred significant protection against fungal-induced ferroptosis by restoring redox homeostasis-evidenced by elevated GSH levels, attenuated ROS accumulation, and decreased ferrous iron content. Mechanistic investigations identified IBC-mediated upregulation of SKN-1 and GSH biosynthesis genes, coupled with suppression of GPX-1 activity. These coordinated effects disrupted the iron-ROS amplification loop through modulation of the GSH-GPX-1 axis, ultimately extending host lifespan in C. neoformans-challenged models. Our results position IBC as a ferroptosis inhibitor with dual antioxidant and iron-chelating properties, offering a therapeutic strategy against cryptococcal infections through targeting of evolutionary conserved cell death pathways.

ER-mitochondria encounter structure connections determine drug sensitivity and virulence of Cryptococcus neoformans

Cryptococcus neoformans is a common fungal pathogen, causing fatal meningoencephalitis in immunocompromised individuals. The limited availability of antifungals and increasing resistance in pathogens including C. neoformans emphasize the need to find new drugs. Mitochondria have long been associated with drug resistance in fungi. They are connected to the endoplasmic reticulum (ER) via a multiprotein complex, the ER-mitochondria encounter structure (ERMES), which is unique in the fungal kingdom. In this study on C. neoformans, the four subunits of the ERMES complex, namely, Mmm1, Mdm12, Mdm10 and Mdm34, were deleted to generate the strains Δmmm1, Δmdm12, Δmdm10 and Δmdm34, respectively. These mutants had impaired mitochondria and were sensitive to antifungals, including echinocandins, due to lower chitin content. Virulence factors, including capsule formation and melanin production, were debilitated in the mutants. The partner organelle ER was also affected by compromised ERMES contact, as the activity of several ER-synthesized enzymes involved in virulence was impacted. The in vivo studies in Caenorhabditis elegans model of cryptococcosis confirmed the reduced virulence of the mutants. These results indicate that the impairment of the ERMES complex is crucial for the virulence and pathogenesis of C. neoformans.

hmuSTUV operon positively regulates the alginate gene cluster to mediate the pathogenicity of Pseudomonas donghuensis HYS

Pseudomonas donghuensis HYS is highly virulent to Caenorhabditis elegans, but with mechanistic details that are not fully understood. The hmuSTUV operon was reported to participate in the synthesis of heme in Pseudomonas. However, the exact role of the hmuSTUV operon in Pseudomonas virulence has not been elucidated. In this study, we report for the first time that the hmuSTUV operon in P. donghuensis HYS causes host virulence, and that hmuS was a key gene for the toxicity of this operon. Furthermore, RNA-seq data showed that hmuS deletion inhibited alginate gene expression, thereby inhibiting biofilm formation. The hmuSTUV operon and alginate gene cluster are conserved in Pseudomonas. By constructing mutant strains carrying GFP, we found that the hmuS deletion reduced colonisation of HYS to the host gut. Moreover, the expression of the alginate gene cluster was controlled by the construction of a L-arabinose-inducible promoter. hmuS positively regulated alginate gene cluster expression, mediating bacterial virulence against C. elegans. In addition, HYS originating from the East Lake of Wuhan City was more pathogenic to zebrafish than any other pathogenic Pseudomonas, through impairment of zebrafish neurodevelopment and locomotor ability, by colonizing to the zebrafish brain. In conclusion, the hmuSTUV operon positively regulated the alg gene cluster, thereby disabling bacterial biofilm formation and colonisation to mediate bacterial pathogenicity to the host. These novel findings revealed the critical interaction between the hmuSTUV operon and the alg gene cluster in the bacterial virulence of Pseudomonas, providing new insights into Pseudomonas pathogenicity.

The Roles of Distinct Transcriptional Factors in the Innate Immunity of C. elegans

Deleterious molecules or factors produced by pathogens can hinder the normal physiological functioning of organisms. In response to these survival challenges, organisms rely on innate immune signaling as their first line of defense, which regulates immune-responsive genes and antimicrobial peptides to protect against pathogenic infections. These genes are under the control of transcription factors, which are known to regulate the transcriptional activity of genes after binding to their regulatory sequences. Previous studies have employed Caenorhabditis elegans as a host-pathogen interaction model to demonstrate the essential role of different transcription factors in the innate immunity of worms. In this review, we summarize the advances made regarding the functioning of distinct transcription factors in the innate immune response upon pathogen infection. Finally, we discuss the open questions in the field, whose resolutions have the potential to expand our understanding of the mechanisms underlying the innate immunity of organisms.

Microbial adaptive pathogenicity strategies to the host inflammatory environment

Pathogenic microorganisms can infect a variety of niches in the human body. During infection, these microbes can only persist if they adapt adequately to the dynamic host environment and the stresses imposed by the immune system. While viruses entirely rely on host cells to replicate, bacteria and fungi use their pathogenicity mechanisms for the acquisition of essential nutrients that lie under host restriction. An inappropriate deployment of pathogenicity mechanisms will alert host defence mechanisms that aim to eradicate the pathogen. Thus, these adaptations require tight regulation to guarantee nutritional access without eliciting strong immune activation. To work efficiently, the immune system relies on a complex signalling network, involving a myriad of immune mediators, some of which are quite directly associated with imminent danger for the pathogen. To manipulate the host immune system, viruses have evolved cytokine receptors and viral cytokines. However, among bacteria and fungi, selected pathogens have evolved the capacity to use these inflammatory response-specific signals to regulate their pathogenicity. In this review, we explore how bacterial and fungal pathogens can sense the immune system and use adaptive pathogenicity strategies to evade and escape host defence to ensure their persistence in the host.

Peptides from Galleria mellonella against Cryptococcus spp: toxicity in three-dimensional cell cultures and G. mellonella

Aim: This work aimed to test peptides against the planktonic and biofilm form of Cryptococcus spp. and in vitro toxicity using three-dimensional (3D) cells characterized and evaluate in vivo toxicity in Galleria mellonella.Materials & methods: Susceptibility tests were conducted on the planktonic form and biofilm formation. The toxicity of the peptides was evaluated in lung and brain cells in monolayer (2D) and 3D mono- and co-culture, in addition to in vivo analysis with G. mellonella.Results: Susceptibility values ranged from 31.25 to over 250 µg/ml with a fungicidal profile. Regarding toxicity, the PepM2 peptide was not toxic in 3D culture (500 µg/ml). G. mellonella, showed a survival rate of more than 85% In assays with brain and lung cell lines, concentrations ranged from 4 × 104 to 4 × 103 cells/well for brain cells and 1 × 103 cells/well for lung cells. Cocultures used 1 × 105 brain and 1 × 103 lung cells.Conclusion: This study shows that the peptides have great potential against cryptococcosis, and all spheroids were characterized as having a spheroidal and compact structure.

New tools to monitor Pseudomonas aeruginosa infection and biofilms in vivo in C. elegans

Introduction

Antimicrobial resistance is a growing health problem. Pseudomonas aeruginosa is a pathogen of major concern because of its multidrug resistance and global threat, especially in health-care settings. The pathogenesis and drug resistance of P. aeruginosa depends on its ability to form biofilms, making infections chronic and untreatable as the biofilm protects against antibiotics and host immunity. A major barrier to developing new antimicrobials is the lack of in vivo biofilm models. Standard microbiological testing is usually performed in vitro using planktonic bacteria, without representation of biofilms, reducing translatability. Here we develop tools to study both infection and biofilm formation by P. aeruginosa in vivo to accelerate development of strategies targeting infection and pathogenic biofilms.

Methods

Biofilms were quantified in vitro using Crystal Violet staining and fluorescence biofilm assays. For in vivo assays, C. elegans were infected with P. aeruginosa strains. Pathogenicity was quantified by measuring healthspan, survival and GFP fluorescence. Healthspan assays were performed using the WormGazerTM automated imaging technology.

Results

Using the nematode Caenorhabditis elegans and P. aeruginosa reporters combined with in vivo imaging we show that fluorescent P. aeruginosa reporters that form biofilms in vitro can be used to visualize tissue infection. Using automated tracking of C. elegans movement, we find that that the timing of this infection corresponds with a decline in health endpoints. In a mutant strain of P. aeruginosa lacking RhlR, a transcription factor that controls quorum sensing and biofilm formation, we find reduced capacity of P. aeruginosa to form biofilms, invade host tissues and negatively impact healthspan and survival.

Discussion

Our findings suggest that RhlR could be a new antimicrobial target to reduce P. aeruginosa biofilms and virulence in vivo and C. elegans could be used to more effectively screen for new drugs to combat antimicrobial resistance.

Cryptococcus neoformans: plant-microbe interactions and ecology

While the opportunistic human pathogens Cryptococcus neoformans and Cryptococcus gattii are often isolated from plants and plant-related material, evidence suggests that these Cryptococcus species do not directly infect plants. Studies find that plants are important for Cryptococcus mating and dispersal. However, these studies have not provided enough detail about how plants and these fungi interact, especially in ways that could show the fungi are capable of causing disease. This review synthesizes recent findings from studies utilizing different plant models associated with the ecology of C. neoformans and C. gattii. Unanswered questions about their environmental role are highlighted. Overall, current research indicates that Cryptococcus utilizes plants as a substrate rather than harming them, arguing against Cryptococcus as a genuine plant pathogen. We hypothesize that plants represent reservoirs that aid dispersal, not hosts vulnerable to infection.

SICKO: Systematic Imaging of Caenorhabditis Killing Organisms

Caenorhabditis elegans are an important model system for research on host-microbe interaction. Their rapid life cycle, short lifespan, and transparent body structure allow simple quantification of microbial load and the influence of microbial exposure on host survival. C. elegans host-microbe interaction studies typically examine group survival and infection severity at fixed timepoints. Here we present an imaging pipeline, Systematic Imaging of Caenorhabditis Killing Organisms (SICKO), that allows longitudinal characterization of microbes colonizing isolated C. elegans, enabling dynamic tracking of tissue colonization and host survival in the same animals. Using SICKO, we show that Escherichia coli or Pseudomonas aeruginosa gut colonization dramatically shortens C. elegans lifespan and that immunodeficient animals lacking pmk-1 are more susceptible to colonization but display similar colony growth relative to wild type. SICKO opens new avenues for detailed research into bacterial pathogenesis, the benefits of probiotics, and the role of the microbiome in host health.

Novel combinatorial approach: Harnessing HIV protease inhibitors to enhance amphotericin B's antifungal efficacy in cryptococcosis

Cryptococcosis is a fungal infection that is becoming increasingly prevalent worldwide, particularly among individuals with compromised immune systems, such as HIV patients. Amphotericin B (AmB) is the first-line treatment mainly combined with flucytosine. The scarcity and the prohibitive cost of this regimen urge the use of fluconazole as an alternative, leading to increased rates of treatment failure and relapses. Therefore, there is a critical need for efficient and cost-effective therapy to enhance the efficacy of AmB. In this study, we evaluated the efficacy of the HIV protease inhibitors (PIs) to synergize the activity of AmB in the treatment of cryptococcosis. Five PIs (ritonavir, atazanavir, saquinavir, lopinavir, and nelfinavir) were found to synergistically potentiate the killing activity of AmB against Cryptococcus strains with ƩFICI ranging between 0.09 and 0.5 against 20 clinical isolates. This synergistic activity was further confirmed in a time-kill assay, where different AmB/PIs combinations exhibited fungicidal activity within 24 hrs. Additionally, PIs in combination with AmB exhibited an extended post-antifungal effect on treated cryptococcal cells for approximately 10 hrs compared to 4 hours with AmB alone. This promising activity against cryptococcal cells did not exhibit increased cytotoxicity towards treated kidney cells, ruling out the risk of drug combination-induced nephrotoxicity. Finally, we evaluated the efficacy of AmB/PIs combinations in the Caenorhabditis elegans model of cryptococcosis, where these combinations significantly reduced the fungal burden of the treated nematodes by approximately 2.44 Log10 CFU (92.4%) compared to the untreated worms and 1.40 Log10 ((39.4%) compared to AmB alone. The cost-effectiveness and accessibility of PIs in resource-limited geographical areas compared to other antifungal agents, such as flucytosine, make them an appealing choice for combination therapy.

HemN2 Regulates the Virulence of Pseudomonas donghuensis HYS through 7-Hydroxytropolone Synthesis and Oxidative Stress

Compared to pathogens Pseudomonas aeruginosa and P. putida, P. donghuensis HYS has stronger virulence towards Caenorhabditis elegans. However, the underlying mechanisms haven't been fully understood. The heme synthesis system is essential for Pseudomonas virulence, and former studies of HemN have focused on the synthesis of heme, while the relationship between HemN and Pseudomonas virulence were barely pursued. In this study, we hypothesized that hemN2 deficiency affected 7-hydroxytropolone (7-HT) biosynthesis and redox levels, thereby reducing bacterial virulence. There are four hemN genes in P. donghuensis HYS, and we reported for the first time that deletion of hemN2 significantly reduced the virulence of HYS towards C. elegans, whereas the reduction in virulence by the other three genes was not significant. Interestingly, hemN2 deletion significantly reduced colonization of P. donghuensis HYS in the gut of C. elegans. Further studies showed that HemN2 was regulated by GacS and participated in the virulence of P. donghuensis HYS towards C. elegans by mediating the synthesis of the virulence factor 7-HT. In addition, HemN2 and GacS regulated the virulence of P. donghuensis HYS by affecting antioxidant capacity and nitrative stress. In short, the findings that HemN2 was regulated by the Gac system and that it was involved in bacterial virulence via regulating 7-HT synthesis and redox levels were reported for the first time. These insights may enlighten further understanding of HemN-based virulence in the genus Pseudomonas.

Anthraquinones against Cryptococcus neoformans sensu stricto: antifungal interaction, biofilm inhibition and pathogenicity in the Caenorhabditis elegans model

Introduction. Cryptococcal biofilms have been associated with persistent infections and antifungal resistance. Therefore, strategies, such as the association of natural compounds and antifungal drugs, have been applied for the prevention of biofilm growth. Moreover, the Caenorhabditis elegans pathogenicity model has been used to investigate the capacity to inhibit the pathogenicity of Cryptococcus neoformans sensu stricto.Hypothesis. Anthraquinones and antifungals are associated with preventing C. neoformans sensu stricto biofilm formation and disrupting these communities. Antraquinones reduced the C. neoformans sensu stricto pathogenicity in the C. elegans model.Aim. This study aimed to evaluate the in vitro interaction between aloe emodin, barbaloin or chrysophanol and itraconazole or amphotericin B against growing and mature biofilms of C. neoformans sensu stricto.Methodology. Compounds and antifungal drugs were added during biofilm formation or after 72 h of growth. Then, the metabolic activity was evaluated by the MTT reduction assay, the biomass by crystal-violet staining and the biofilm morphology by confocal laser scanning microscopy. C. neoformans sensu stricto's pathogenicity was investigated using the nematode C. elegans. Finally, pathogenicity inhibition by aloe emodin, barbarloin and chrysophanol was investigated using this model.Results. Anthraquinone-antifungal combinations affected the development of biofilms with a reduction of over 60 % in metabolic activity and above 50 % in biomass. Aloe emodin and barbaloin increased the anti-biofilm activity of antifungal drugs. Chrysophanol potentiated the effect of itraconazole against C. neoformans sensu stricto biofilms. The C. elegans mortality rate reached 76.7 % after the worms were exposed to C. neoformans sensu stricto for 96 h. Aloe emodin, barbaloin and chrysophanol reduced the C. elegans pathogenicity with mortality rates of 61.12 %, 65 % and 53.34 %, respectively, after the worms were exposed for 96 h to C. neoformans sensu stricto and these compounds at same time.Conclusion. These results highlight the potential activity of anthraquinones to increase the effectiveness of antifungal drugs against cryptococcal biofilms.

Accumulation of endogenous free radicals is required to induce titan-like cell formation in Cryptococcus neoformans

IMPORTANCE

Cryptococcus neoformans is an excellent model to investigate fungal pathogenesis. This yeast can produce "titan cells," which are cells of an abnormally larger size that contribute to the persistence of the yeast in the host. In this work, we have used a new approach to characterize them by identifying drugs that inhibit this process. We have used a repurposing off-patent drug library, combined with an automatic method to image and analyze fungal cell size. In this way, we have identified many compounds that inhibit this transition. Interestingly, several compounds were antioxidants, allowing us to confirm that endogenous ROS and mitochondrial changes are important for titan cell formation. This work provides new evidence of the mechanisms required for titanization. Furthermore, the future characterization of the inhibitory mechanisms of the identified compounds by the scientific community will contribute to better understand the role of titan cells in virulence.

Models for Inducing Experimental Cryptococcosis in Mice

Cryptococcus neoformans and Cryptococcus gattii are the predominant etiological agents of cryptococcosis, a particularly problematic disease in immunocompromised individuals. The increased clinical use of immunosuppressive drugs, the inherent ability of Cryptococcus species to suppress and evade host immune responses, and the emergence of drug-resistant yeast support the need for model systems that facilitate the design of novel immunotherapies and antifungals to combat disease progression. The mouse model of cryptococcosis is a widely used system to study Cryptococcus pathogenesis and the efficacy of antifungal drugs in vivo. In this chapter, we describe three commonly used strategies to establish cryptococcosis in mice: intranasal, intratracheal, and intravenous inoculations. Also, we discuss the methodology for delivering drugs to mice via intraperitoneal injection.

Alternative Non-Mammalian Animal and Cellular Methods for the Study of Host-Fungal Interactions

In the study of fungal pathogenesis, alternative methods have gained prominence due to recent global legislation restricting the use of mammalian animals in research. The principle of the 3 Rs (replacement, reduction, and refinement) is integrated into regulations and guidelines governing animal experimentation in nearly all countries. This principle advocates substituting vertebrate animals with other invertebrate organisms, embryos, microorganisms, or cell cultures. This review addresses host-fungus interactions by employing three-dimensional (3D) cultures, which offer more faithful replication of the in vivo environment, and by utilizing alternative animal models to replace traditional mammals. Among these alternative models, species like Caenorhabditis elegans and Danio rerio share approximately 75% of their genes with humans. Furthermore, models such as Galleria mellonella and Tenebrio molitor demonstrate similarities in their innate immune systems as well as anatomical and physiological barriers, resembling those found in mammalian organisms.

Amphid sensory neurons of Caenorhabditis elegans orchestrate its survival from infection with broad classes of pathogens

The survival of a host during infection relies on its ability to rapidly sense the invading pathogen and mount an appropriate response. The bacterivorous nematode Caenorhabditis elegans lacks most of the traditional pattern recognition mechanisms. In this study, we hypothesized that the 12 pairs of amphid sensory neurons in the heads of worms provide sensing capability and thus affect survival during infection. We tested animals lacking amphid neurons to three major classes of pathogens, namely-a Gram-negative bacterium Pseudomonas aeruginosa, a Gram-positive bacterium Enterococcus faecalis, and a pathogenic yeast Cryptococcus neoformans By using individual neuronal ablation lines or mutants lacking specific neurons, we demonstrate that some neurons broadly suppress the survival of the host and colonization of all pathogens, whereas other amphid neurons differentially regulate host survival during infection. We also show that the roles of some of these neurons are pathogen-specific, as seen with the AWB odor sensory neurons that promote survival only during infections with P aeruginosa Overall, our study reveals broad and specific roles for amphid neurons during infections.

Infections of Cryptococcus species induce degeneration of dopaminergic neurons and accumulation of α-Synuclein in Caenorhabditis elegans

Cryptococcosis in the central nervous system (CNS) can present with motor declines described as Parkinsonism. Although several lines of evidence indicate that dopaminergic (DA) neuron degeneration and α-synuclein accumulation contribute to the hallmark of Parkinsonism and Parkinson’s disease (PD), little is known about cryptococcal infections associated with neuronal degeneration. In this study, the effects of Cryptococcus neoformans and C. gattii infections on dopaminergic neuron degeneration, α-synuclein accumulation, and lifespan in Caenorhabditis elegans were investigated. The results showed that cryptococcal infections significantly (P<0.05) induced DA neuron degeneration similar to a selective cathecholamine neurotoxin 6-hydroxydopamine (6-OHDA) in C. elegans (BZ555 strain) when compared to mock infected controls. Cryptococcal infections also significantly (P< 0.05) induced α-synuclein aggregation in C. elegans (NL5901 strain). Moreover, lifespan of the infected worms was significantly decreased (P<0.0001). In conclusion, DA neurodegeneration and α-synuclein accumulation are associated with lifespan reduction during cryptococcal infection in C elegans.

Interaction of Talaromyces marneffei with free living soil amoeba as a model of fungal pathogenesis

Talaromyces (Penicillium) marneffei is an important dimorphic mycosis endemic in Southeast Asia and Southern China, but the origin and maintenance of virulence traits in this organism remains obscure. Several pathogenic fungi, including Cryptococcus neoformans, Aspergillus fumigatus, Blastomyces dermatitidis, Sporothrix schenckii, Histoplasma capsulatum and Paracoccidioides spp. interact with free living soil amoebae and data suggests that fungal pathogenic strategies may emerge from environmental interactions of these fungi with ubiquitous phagocytic microorganisms. In this study, we examined the interactions of T. marneffei with the soil amoeba Acanthamoeba castellanii. T. marneffei was rapidly ingested by A. castellanii and phagocytosis of fungal cells resulted in amoeba death after 24 h of contact. Co-culture also resulted in a rapid transition for conidia to the fission-yeast form. In addition, well-established virulence factors such as melanin and a yeast specific mannoprotein of T. marneffei were expressed during interaction with A. castellanii at 37°C. Our findings support the assumption that soil amoebae environmental predators play a role in the selection and maintenance of particular features in T. marneffei that impart virulence to this clinically important dimorphic fungus in mammalian hosts.

High-throughput small molecule screen identifies inhibitors of microsporidia invasion and proliferation in C. elegans

Microsporidia are a diverse group of fungal-related obligate intracellular parasites that infect most animal phyla. Despite the emerging threat that microsporidia represent to humans and agricultural animals, few reliable treatment options exist. Here, we develop a high-throughput screening method for the identification of chemical inhibitors of microsporidia infection, using liquid cultures of Caenorhabditis elegans infected with the microsporidia species Nematocida parisii. We screen a collection of 2560 FDA-approved compounds and natural products, and identify 11 candidate microsporidia inhibitors. Five compounds prevent microsporidia infection by inhibiting spore firing, whereas one compound, dexrazoxane, slows infection progression. The compounds have in vitro activity against several other microsporidia species, including those known to infect humans. Together, our results highlight the effectiveness of C. elegans as a model host for drug discovery against intracellular pathogens, and provide a scalable high-throughput system for the identification and characterization of microsporidia inhibitors.

The p38 MAPK/PMK-1 Pathway Is Required for Resistance to Nocardia farcinica Infection in Caenorhabditis elegance

Nocardia farcinica is an opportunistic pathogen that causes nocardiosis primarily in patients with compromised immune systems. In this study, we used the genetically tractable organism Caenorhabditis elegans as a model to study the innate immune responses to N. farcinica infection. We found that unlike other pathogenic bacteria such as Pseudomonas aeruginosa and Staphylococcus aureus, N. farcinica failed to kill adult worms. In another words, adult worms exposed to N. farcinica exhibited a normal lifespan, compared with those fed the standard laboratory food bacterium Escherichia coli OP50. Interestingly, deletion of three core genes (pmk-1, nsy-1 and sek-1) in the p38 MAPK/PMK-1 pathway reduced the survival of worm exposure to N. farcinica, highlighting a crucial role of this pathway for C. elegans in resistance to N. farcinica. Furthermore, our results revealed that N. farcinica exposure up-regulated the level of PMK-1 phosphorylation. The activation of PMK-1 promoted nuclear translocation of a transcription factor SKN-1/Nrf2, which in turn mediated N. farcinica infection resistance in C. elegans. Our results provide an excellent example that the integrity of immune system is key aspect for counteract with pathogenesis of N. farcinica.

Caenorhabditis elegans DAF-16 regulates lifespan and immune responses to Cryptococcus neoformans and Cryptococcus gattii infections

Background

Cryptococcosis is a life-threatening infection is primarily caused by two sibling species Cryptococcus neoformans and Cryptococcus gattii. Several virulence-related factors of these cryptococci have been widely investigated in Caenorhabditis elegans, representing a facile in vivo model of host–pathogen interaction. While recent studies elucidated cryptococcal virulence factors, intrinsic host factors that affect susceptibility to infections by cryptococci remain unclear and poorly investigated.

Results

Here, we showed that defects in C. elegans insulin/insulin-like growth factor-1 (IGF-1) signaling (IIS) pathway influenced animal lifespan and mechanisms of host resistance in cryptococcal infections, which required the activation of aging regulator DAF-16/Forkhead box O transcription factor. Moreover, accumulation of lipofuscin, DAF-16 nuclear localization, and expression of superoxide dismutase (SOD-3) were elevated in C. elegans due to host defenses during cryptococcal infections.

Conclusion

The present study demonstrated the relationship between longevity and immunity, which may provide a possibility for novel therapeutic intervention to improve host resistance against cryptococcal infections.

Experimental models for pharmacokinetic and pharmacodynamic studies of antifungals used in cryptococcosis treatment

Studies on cryptococcosis in the mammal animal model have demonstrated the occurrence of central nervous system infection and similarities in fungal pathogenicity with clinical and immunological features of the human infection. Although there is still a lack of studies involving pharmacokinetics (PK) and pharmacodynamics (PD) in animal models of cryptococcosis in the literature, these experimental models are useful for understanding this mycosis and antifungal effectiveness in improving the therapeutic schemes. The scope of this review is to describe and discuss the main mammal animal models for PK and PD studies of antifungals used in cryptococcosis treatment. Alternative models and computational methods are also addressed. All approaches for PK/PD studies are relevant to investigating drug-infection interaction and improving cryptococcosis therapy.

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.

Cryptococcus spp. and Cryptococcosis: focusing on the infection in Brazil

Cryptococcosis is a global fungal infection caused by the Cryptococcus neoformans/Cryptococcus gattii yeast complex. This infection is acquired by inhalation of propagules such as basidiospores or dry yeast, initially causing lung infections with the possibility of progressing to the meninges. This infection mainly affects immunocompromised HIV and transplant patients; however, immunocompetent patients can also be affected. This review proposes to evaluate cryptococcosis focusing on studies of this mycosis in Brazilian territory; moreover, recent advances in the understanding of its virulence mechanism, animal models in research are also assessed. For this, literature review as realized in PubMed, Scielo, and Brazilian legislation. In Brazil, cryptococcosis has been identified as one of the most lethal fungal infections among HIV patients and C. neoformans VNI and C. gattii VGII are the most prevalent genotypes. Moreover, different clinical settings published in Brazil were described. As in other countries, cryptococcosis is difficult to treat due to a limited therapeutic arsenal, which is highly toxic and costly. The presence of a polysaccharide capsule, thermo-tolerance, production of melanin, biofilm formation, mechanisms for iron use, and morphological alterations is an important virulence mechanism of these yeasts. The introduction of cryptococcosis as a compulsory notification disease could improve data regarding incidence and help in the management of these infections.

The sat1 Gene Is Required for the Growth and Virulence of the Human Pathogenic Fungus Aspergillus fumigatus

Aspergillus fumigatus is an important opportunistic pathogenic fungus that causes invasive aspergillosis in immunocompromised humans. Regulated fungal growth is essential for disease development and progression. Thus, screening for genes that regulate fungal growth may lead to the identification of potential therapeutic targets for invasive aspergillosis (IA). Screening of the transfer DNA (T-DNA) random-insertion A. fumigatus mutants identified a severe growth deficiency mutant AFM2954 and featured sat1 as the mutated gene described as a putative intracellular protein transporter of unknown function. The deletion of sat1 exhibited severe growth defects and significantly increased the nematode and mouse survival rates and decreased the fungal loads and histopathological damages in mouse lungs. Transcriptomic analyses revealed expression changes associated with the cell wall synthesis, the tricarboxylic acid cycle (TCA cycle), and oxidative phosphorylation genes in the sat1 mutant. Deletion of the gene resulted in resistance to cell wall-perturbing agents and thickened cell wall as well as reduced ATP contents and mitochondrial membrane potential, suggested that sat1 affected the cell wall synthesis and mitochondrial function of A. fumigatus. All together, our study uncovered novel functions of sat1 in growth and virulence of A. fumigatus and provided a theoretical basis for the development of new therapeutic target for treating IA patients. IMPORTANCE Aspergillus fumigatus is the main causative agent of invasive aspergillosis in immunocompromised hosts, with up to 90% lethality. Nevertheless, the fungal factors that regulate the pathogenesis of A. fumigatus remain largely unknown. Better understanding of the mechanisms controlling growth of A. fumigatus may provide novel therapeutic targets. In the present study, we characterized sat1 in the opportunistic pathogen A. fumigatus. The function of sat1 remains unknown. We proved its important role in growth and virulence, likely because of its effects on cell wall synthesis and mitochondrial functions.

Cell Wall Integrity Pathway Involved in Morphogenesis, Virulence and Antifungal Susceptibility in Cryptococcus neoformans

Due to its location, the fungal cell wall is the compartment that allows the interaction with the environment and/or the host, playing an important role during infection as well as in different biological functions such as cell morphology, cell permeability and protection against stress. All these processes involve the activation of signaling pathways within the cell. The cell wall integrity (CWI) pathway is the main route responsible for maintaining the functionality and proper structure of the cell wall. This pathway is highly conserved in the fungal kingdom and has been extensively characterized in Saccharomyces cerevisiae. However, there are still many unknown aspects of this pathway in the pathogenic fungi, such as Cryptococcus neoformans. This yeast is of particular interest because it is found in the environment, but can also behave as pathogen in multiple organisms, including vertebrates and invertebrates, so it has to adapt to multiple factors to survive in multiple niches. In this review, we summarize the components of the CWI pathway in C. neoformans as well as its involvement in different aspects such as virulence factors, morphological changes, and its role as target for antifungal therapies among others.

Tobacco Hornworm (Manduca sexta) caterpillars as a novel host model for the study of fungal virulence and drug efficacy

The two leading yeast pathogens of humans, Candida albicans and Cryptococcus neoformans, cause systemic infections in >1.4 million patients worldwide with mortality rates approaching 75%. It is thus imperative to study fungal virulence mechanisms, efficacy of antifungal drugs, and host response pathways. While this is commonly done in mammalian models, which are afflicted by ethical and practical concerns, invertebrate models, such as wax moth larvae and nematodes have been introduced over the last two decades. To complement existing invertebrate host models, we developed fifth instar caterpillars of the Tobacco Hornworm moth Manduca sexta as a novel host model. These caterpillars can be maintained at 37°C, are suitable for injections with defined amounts of yeast cells, and are susceptible to the most threatening yeast pathogens, including C. albicans, C. neoformans, C. auris, and C. glabrata. Importantly, fungal burden can be assessed daily throughout the course of infection in a single caterpillar’s feces and hemolymph. Infected caterpillars can be rescued by treatment with antifungal drugs. Notably, these animals are large enough for weight to provide a reliable and reproducible measure of fungal disease and to facilitate host tissue-specific expression analyses. M. sexta caterpillars combine a suite of parameters that make them suitable for the study of fungal virulence.

A mutation in C. neoformans mitochondrial NADH dehydrogenase results in increased virulence in mice

Cryptococcus neoformans: (H99W) was serially passaged in the invertebrate wax moth Galleria mellonella fifteen times to study how fungal virulence evolves under selection and whether those adaptations affect virulence. The G. mellonella passaged strain (P15) and the pre-passage H99W strains were used to infect three different host models of C. neoformans: C. elegans, G. mellonella, and Balb/c mice. While there was no difference in survival in the invertebrate models, P15 killed mice faster than H99W through both intratracheal and intravenous routes of infection and mice infected intravenously with P15 showed higher fungal burden in the brain. Characterization of the major virulence factors of C. neoformans found that P15 had increased capsule size, GXM release, and melanization. Whole genome sequencing of P15 and H99W revealed two mutations in P15, an insertion in the promoter region of NADH dehydrogenase (CNAG_09000) and an insertion in the LMP1 gene (CNAG_06765). Both ATP production and metabolic rate were higher in P15 compared to H99W. Quantitative RT-PCR suggested that the increased ATP was due to increased RNA levels of NADH dehydrogenase. Thus, adaptation to growth in hemocytes resulted in increased production of ATP, increased metabolic rate, and increased virulence in mice. This was likely due to differential expression of virulence factors, which skewed the host immune response to a less efficient Th2 response, with higher levels of IL-4, IL-10, and TNF-α in the brain. Overall, serial passage experiments have increased our understanding of how this yeast evolves under innate immune selection pressure.

A Simple Nematode Infection Model for Studying Candida albicans Pathogenesis

Candida albicans is an opportunistic fungal pathogen and a model organism to study fungal pathogenesis. It exists as a harmless commensal organism and member of the healthy human microbiome, but can cause life-threatening mucosal and systemic infections. A model host to study C. albicans infection and pathogenesis is the nematode Caenorhabditis elegans. C. elegans is frequently used as a model host to study microbial-host interactions because it can be infected by many human pathogens and there are also close morphological resemblances between the intestinal cells of C. elegans and mammals, where C. albicans infections can occur. This article outlines a detailed methodology for exploiting C. elegans as a host to study C. albicans infection, including a C. elegans egg preparation protocol and an agar-based C. elegans killing protocol to monitor fungal virulence. These protocols can additionally be used to study C. albicans genetic mutants in order to further our understanding of the genes involved in pathogenesis and virulence in C. albicans and the mechanisms of host-microbe interactions. © 2020 Wiley Periodicals LLC. Basic Protocol 1: Preparation of Caenorhabditis elegans eggs Support Protocol 1: Freezing and recovering Caenorhabditis elegans Support Protocol 2: Making superfood agar and OP50 plates Basic Protocol 2: Caenorhabditis elegans/Candida albicans agar killing assay Support Protocol 3: Constructing a worm pick.

C. elegans: A biosensor for host-microbe interactions

Microbes are an integral part of life on this planet. Microbes and their hosts influence each other in an endless dance that shapes how the meta-organism interacts with its environment. Although great advances have been made in microbiome research over the past 20 years, the mechanisms by which both hosts and their microbes interact with each other and the environment are still not well understood. The nematode Caenorhabditis elegans has been widely used as a model organism to study a remarkable number of human-like processes. Recent evidence shows that the worm is a powerful tool to investigate in fine detail the complexity that exists in microbe-host interactions. By combining the large array of genetic tools available for both organisms together with deep phenotyping approaches, it has been possible to uncover key effectors in the complex relationship between microbes and their hosts. In this perspective, we survey the literature for insightful discoveries in the microbiome field using the worm as a model. We discuss the latest conceptual and technological advances in the field and highlight the strengths that make C. elegans a valuable biosensor tool for the study of microbe-host interactions.

Comprehensive genetic analysis of adhesin proteins and their role in virulence of Candida albicans

Candida albicans is a microbial fungus that exists as a commensal member of the human microbiome and an opportunistic pathogen. Cell surface-associated adhesin proteins play a crucial role in C. albicans' ability to undergo cellular morphogenesis, develop robust biofilms, colonize, and cause infection in a host. However, a comprehensive analysis of the role and relationships between these adhesins has not been explored. We previously established a CRISPR-based platform for efficient generation of single- and double-gene deletions in C. albicans, which was used to construct a library of 144 mutants, comprising 12 unique adhesin genes deleted singly, and every possible combination of double deletions. Here, we exploit this adhesin mutant library to explore the role of adhesin proteins in C. albicans virulence. We perform a comprehensive, high-throughput screen of this library, using Caenorhabditis elegans as a simplified model host system, which identified mutants critical for virulence and significant genetic interactions. We perform follow-up analysis to assess the ability of high- and low-virulence strains to undergo cellular morphogenesis and form biofilms in vitro, as well as to colonize the C. elegans host. We further perform genetic interaction analysis to identify novel significant negative genetic interactions between adhesin mutants, whereby combinatorial perturbation of these genes significantly impairs virulence, more than expected based on virulence of the single mutant constituent strains. Together, this study yields important new insight into the role of adhesins, singly and in combinations, in mediating diverse facets of virulence of this critical fungal pathogen.

The Antifungal and Synergistic Effect of Bisphosphonates in Cryptococcus

New treatment strategies are required for cryptococcosis, a leading mycosis in HIV-AIDS patients. Following the identification of Cryptococcus proteins differentially expressed in response to fluconazole, we targeted farnesyl pryrophosphate synthetase (FPPS), an enzyme in the squalene biosynthesis pathway, using nitrogenous bisphosphonates. We hypothesized that these would disrupt squalene synthesis and thereby produce synergy with fluconazole, which acts on a downstream pathway that requires squalene. The susceptibilities of 39 clinical isolates from 6 different species of Cryptococcus were assessed for bisphosphonates and fluconazole, used both independently and in combination. Effective fluconazole-bisphosphonate combinations were then assessed for fungicidal activity, efficacy against biofilms, and ability to resolve cryptococcosis in an invertebrate model. The nitrogenous bisphosphonates risedronate, alendronate, and zoledronate were antifungal against all strains tested. Zoledronate was the most effective (geometric mean MIC = 113.03 mg/liter; risedronate = 378.49 mg/liter; alendronate = 158.4 mg/liter) and was broadly synergistic when combined with fluconazole, with a fractional inhibitory concentration index (FICI) of ≤0.5 in 92% of isolates. Fluconazole and zoledronate in combination were fungicidal in a time-kill assay, inhibited Cryptococcus biofilms, prevented the development of fluconazole resistance, and resolved infection in a nematode model. Supplementation with squalene eliminated bisphosphonate-mediated synergy, demonstrating that synergy was due to the inhibition of squalene biosynthesis. This study demonstrates the utility of targeting squalene synthesis for improving the efficacy of azole-based antifungal drugs and suggests bisphosphonates are promising lead compounds for further antifungal development.

Facilitating Drug Discovery in Human Disease Models Using Insects

Drugs are developed through basic studies and clinical trials. In basic studies, researchers seek drug candidates using in vitro evaluation systems and subsequently examine their effectiveness in animal experiments as in vivo evaluations. Drug candidates identified in basic studies are tested to determine whether they are effective against human diseases in clinical trials. However, most drug candidates identified in in vitro evaluation systems do not show therapeutic effects in animal experiments due to pharmacokinetics and toxicity problems in the in vivo evaluations. This review outlines drug discovery using insect disease models that allow us to perform in vivo screening. Since insects have various advantages as experimental animals such as low cost for rearing and few ethical concerns, researchers can perform large-scale in vivo screening to find drug candidates. Silkworms are insects frequently used for studies of drug efficacy, pharmacokinetics, and toxicity. Based on silkworm research, I describe the benefits of using insect disease models for drug discovery. The use of insect disease models for in vivo screening is expected to facilitate drug discovery.

The molecular tug of war between immunity and fertility: Emergence of conserved signaling pathways and regulatory mechanisms

Reproduction and immunity are energy intensive, intimately linked processes in most organisms. In women, pregnancy is associated with widespread immunological adaptations that alter immunity to many diseases, whereas, immune dysfunction has emerged as a major cause for infertility in both men and women. Deciphering the molecular bases of this dynamic association is inherently challenging in mammals. This relationship has been traditionally studied in fast-living, invertebrate species, often in the context of resource allocation between life history traits. More recently, these studies have advanced our understanding of the mechanistic underpinnings of the immunity-fertility dialogue. Here, we review the molecular connections between reproduction and immunity from the perspective of human pregnancy to mechanistic discoveries in laboratory organisms. We focus particularly on recent invertebrate studies identifying conserved signaling pathways and transcription factors that regulate resource allocation and shape the balance between reproductive status and immune health.

Antifungal activity of marine-derived actinomycetes against Talaromyces marneffei

AIMS

This study aimed to isolate actinomycetes from marine environments and examine their antifungal activity against Talaromyces marneffei both in vitro and in vivo.

METHODS AND RESULTS

Nineteen out of 101 actinomycete extracts were active and further determined for their minimum inhibitory concentrations (MIC). Three extracts of AMA50 that isolated from sediment showed strong antifungal activity against T. marneffei yeast (MICs ≤0·03-0·25 µg ml^-1 ) and mould (MICs 0·5-16 µg ml^-1 ) forms. The hexane extract from the cells of AMA50 (AMA50CH) exhibited the best activity against both the forms (MIC ≤ 1 µg ml^-1 ). Three extracts from AMA50 killed the melanized yeast cells at 0·5 µg ml^-1 . The AMA50CH was further tested for protective effects in Caenorhabditis elegans model. At concentrations of 1-8 µg ml^-1 , the AMA50CH prolonged survival of T. marneffei-infected C. elegans with a 60-70% survival rate. The composition of AMA50CH was determined by gas chromatography-mass spectrometry. The major components were n-hexadecanoic acid, tetradecanoic acid and pentadecanoic acid. Sequencing analysis revealed that isolate AMA50 belonged to the genus Streptomyces.

CONCLUSIONS

The AMA50CH from Streptomyces sp. AMA50 was the most effective extract against T. marneffei.

SIGNIFICANCE AND IMPACT OF THE STUDY

Talaromyces marneffei is one of the most important thermally dimorphic pathogenic fungi. These results indicated the potency of marine-derived actinomycete extracts against T. marneffei both in vitro and in vivo.

Animal Models of Cryptococcus neoformans in Identifying Immune Parameters Associated With Primary Infection and Reactivation of Latent Infection

Cryptococcus species are environmental fungal pathogens and the causative agents of cryptococcosis. Infection occurs upon inhalation of infectious particles, which proliferate in the lung causing a primary infection. From this primary lung infection, fungal cells can eventually disseminate to other organs, particularly the brain, causing lethal meningoencephalitis. However, in most cases, the primary infection resolves with the formation of a lung granuloma. Upon severe immunodeficiency, dormant cryptococcal cells will start proliferating in the lung granuloma and eventually will disseminate to the brain. Many investigators have sought to study the protective host immune response to this pathogen in search of host parameters that keep the proliferation of cryptococcal cells under control. The majority of the work assimilates research carried out using the primary infection animal model, mainly because a reactivation model has been available only very recently. This review will focus on anti-cryptococcal immunity in both the primary and reactivation models. An understanding of the differences in host immunity between the primary and reactivation models will help to define the key host parameters that control the infections and are important for the research and development of new therapeutic and vaccine strategies against cryptococcosis.

In Vitro or In Vivo Models, the Next Frontier for Unraveling Interactions between Malassezia spp. and Hosts. How Much Do We Know?

Malassezia is a lipid-dependent genus of yeasts known for being an important part of the skin mycobiota. These yeasts have been associated with the development of skin disorders and cataloged as a causal agent of systemic infections under specific conditions, making them opportunistic pathogens. Little is known about the host-microbe interactions of Malassezia spp., and unraveling this implies the implementation of infection models. In this mini review, we present different models that have been implemented in fungal infections studies with greater attention to Malassezia spp. infections. These models range from in vitro (cell cultures and ex vivo tissue), to in vivo (murine models, rabbits, guinea pigs, insects, nematodes, and amoebas). We additionally highlight the alternative models that reduce the use of mammals as model organisms, which have been gaining importance in the study of fungal host-microbe interactions. This is due to the fact that these systems have been shown to have reliable results, which correlate with those obtained from mammalian models. Examples of alternative models are Caenorhabditis elegans, Drosophila melanogaster, Tenebrio molitor, and Galleria mellonella. These are invertebrates that have been implemented in the study of Malassezia spp. infections in order to identify differences in virulence between Malassezia species.

Brazilian Copaifera Species: Antifungal Activity against Clinically Relevant Candida Species, Cellular Target, and In Vivo Toxicity

Plants belonging to the genus Copaifera are widely used in Brazil due to their antimicrobial properties, among others. The re-emergence of classic fungal diseases as a consequence of antifungal resistance to available drugs has stimulated the search for plant-based compounds with antifungal activity, especially against Candida. The Candida-infected Caenorhabditis elegans model was used to evaluate the in vitro antifungal potential of Copaifera leaf extracts and trunk oleoresins against Candida species. The Copaifera leaf extracts exhibited good antifungal activity against all Candida species, with MIC values ranging from 5.86 to 93.75 µg/mL. Both the Copaifera paupera and Copaifera reticulata leaf extracts at 46.87 µg/mL inhibited Candida glabrata biofilm formation and showed no toxicity to C. elegans. The survival of C. glabrata-infected nematodes increased at all the tested extract concentrations. Exposure to Copaifera leaf extracts markedly increased C. glabrata cell vacuolization and cell membrane damage. Therefore, Copaifera leaf extracts are potential candidates for the development of new and safe antifungal agents.

Honeydew Deposition by the Giant Willow Aphid (Tuberolachnus salignus) Affects Soil Biota and Soil Biochemical Properties

Infestation of willow plants by the giant willow aphid Tuberolachnus salignus (Hemiptera: Aphididae) is associated with copious deposition of sugar-rich honeydew under the plant canopy. We explored the effect of aphid honeydew on the soil biota and biochemical indicators in a two-year field trial. Soil samples from under aphid-infested and control willow trees, as well as samples from black sooty mould spots under the aphid-infested willows were compared; soil samples before aphid inoculation were used as a baseline. The honeydew deposition had a positive effect on the total soil carbon (C), but not on the total soil nitrogen content or soil pH. Microbial biomass C, basal respiration, number of yeast colony forming units, and the geometric mean of activities for six enzymes were significantly higher in honeydew-affected soils than in the control treatment on both years. The honeydew deposition also increased soil meso-fauna abundance, especially in the black sooty mould spots. The soil biochemical properties, which differed before and after aphid infestation, showed considerable overlap between the first and second year post-infestation. The results highlight the cascading effects of T. salignus on soil biological activity and the importance of using a multitrophic approach to explore similar scenarios.

Caenorhabditis elegans-Based Aspergillus fumigatus Infection Model for Evaluating Pathogenicity and Drug Efficacy

Aspergillus fumigatus is the most reported causative pathogen associated with the increasing global incidences of aspergilloses, with the health of immunocompromised individuals mostly at risk. Monitoring the pathogenicity of A. fumigatus strains to identify virulence factors and evaluating the efficacy of potent active agents against this fungus in animal models are indispensable in current research effort. Caenorhabditis elegans has been successfully utilized as an infection model for bacterial and dimorphic fungal pathogens because of the advantages of being time-efficient, and less costly. However, application of this model to the filamentous fungus A. fumigatus is less investigated. In this study, we developed and optimized a stable and reliable C. elegans model for A. fumigatus infection, and demonstrated the infection process with a fluorescent strain. Virulence results of several mutant strains in our nematode model demonstrated high consistency with the already reported pathogenicity pattern in other models. Furthermore, this C. elegans-A. fumigatus infection model was optimized for evaluating the efficacy of current antifungal drugs. Interestingly, the azole drugs in nematode model prevented conidial germination to a higher extent than amphotericin B. Overall, our established C. elegans infection model for A. fumigatus has potential applications in pathogenicity evaluation, antifungal agents screening, drug efficacy evaluation as well as host-pathogen interaction studies.

Investigation into In Vitro and In Vivo Caenorhabditis elegans Models to Select Cheese Yeasts as Probiotic Candidates for their Preventive Effects against Salmonella Typhimurium

The design of multiscale strategies integrating in vitro and in vivo models is necessary for the selection of new probiotics. In this regard, we developed a screening assay based on the investigation of the potential of yeasts from cheese as probiotics against the pathogen Salmonella Typhimurium UPsm1 (ST). Two yeasts isolated from raw-milk cheese (Saccharomyces cerevisiae 16, Sc16; Debaryomyces hansenii 25, Dh25), as well as S. cerevisiae subspecies boulardii (CNCM I-1079, Sb1079), were tested against ST by applying in vitro and in vivo tests. Adherence measurements to Caco-2 and HT29-MTX intestinal cells indicated that the two tested cheese yeasts presented a better adhesion than the probiotic Sb1079 as the control strain. Further, the Dh25 was the cheese yeast most likely to survive in the gastrointestinal tract. What is more, the modulation of the TransEpithelial Electrical Resistance (TEER) of differentiated Caco-2 cell monolayers showed the ability of Dh25 to delay the deleterious effects of ST. The influence of microorganisms on the in vivo model Caenorhabditis elegans was evaluated by measuring the longevity of the worm. This in vivo approach revealed that this yeast increased the worm’s lifespan and protected it against ST infection, confirming that this in vivo model can be useful for screening probiotic cheese yeasts.

Variation in Cell Surface Hydrophobicity among Cryptococcus neoformans Strains Influences Interactions with Amoebas

Cryptococcus neoformans and Cryptococcus gattii are pathogenic fungi that cause significant morbidity and mortality. Cell surface hydrophobicity (CSH) is a biophysical parameter that influences the adhesion of fungal cells or spores to biotic and abiotic surfaces. C. neoformans is encased by polysaccharide capsule that is highly hydrophilic and is a critical determinant of virulence. In this study, we report large differences in the CSH of some C. neoformans and C. gattii strains. The capsular polysaccharides of C. neoformans strains differ in repeating motifs and therefore vary in the number of hydroxyl groups, which, along with higher-order structure of the capsule, may contribute to the variation in hydrophobicity that we observed. We found that cell wall composition, in the context of chitin-chitosan content, does not influence CSH. For C. neoformans, CSH correlated with phagocytosis by natural soil predator Acanthamoeba castellanii Furthermore, capsular binding of the protective antibody (18B7), but not the nonprotective antibody (13F1), altered the CSH of C. neoformans strains. Variability in CSH could be an important characteristic in comparing the biological properties of cryptococcal strains.IMPORTANCE The interaction of a microbial cell with its environment is influenced by the biophysical properties of a cell. The affinity of the cell surface for water, defined by the cell surface hydrophobicity (CSH), is a biophysical parameter that varies among different strains of Cryptococcus neoformans The CSH influences the phagocytosis of the yeast by its natural predator in the soil, the amoeba. Studying variation in biophysical properties like CSH gives us insight into the dynamic host-predator interaction and host-pathogen interaction in a damage-response framework.

Caenorhabditis elegans: a model to understand host-microbe interactions

Host-microbe interactions within the gut are fundamental to all higher organisms. Caenorhabditis elegans has been in use as a surrogate model to understand the conserved mechanisms in host-microbe interactions. Morphological and functional similarities of C. elegans gut with the human have allowed the mechanistic investigation of gut microbes and their effects on metabolism, development, reproduction, behavior, pathogenesis, immune responses and lifespan. Recent reports suggest their suitability for functional investigations of human gut bacteria, such as gut microbiota of healthy and diseased individuals. Our knowledge on the gut microbial diversity of C. elegans in their natural environment and the effect of host genetics on their core gut microbiota is important. Caenorhabditis elegans, as a model, is continuously bridging the gap in our understanding the role of genetics, environment, and dietary factors on physiology of the host.

Induction of signal transduction pathways related to the pathogenicity of Cryptococcus neoformans in the host environment

Cryptococcus neoformans, a human pathogenic fungus, infects immunocompromised humans and causes serious diseases such as cerebral meningitis. C. neoformans controls the expression of virulence factors in response to the host environment via various signal transduction pathways. Understanding the molecular mechanisms involved in C. neoformans infection will contribute to the development of methods to prevent and treat C. neoformans-related diseases. C. neoformans produces virulence factors, such as a polysaccharide capsule and melanin, to escape host immunity. Several proteins of C. neoformans are reported to regulate production of the virulence factors. In this review, on the basis of studies using gene-deficient mutants of C. neoformans and animal infection models, we outline the signal transduction pathways involved in the regulation of virulence factors.

A hidden battle in the dirt: Soil amoebae interactions with Paracoccidioides spp

Paracoccidioides spp. are thermodimorphic fungi that cause a neglected tropical disease (paracoccidioidomycosis) that is endemic to Latin America. These fungi inhabit the soil, where they live as saprophytes with no need for a mammalian host to complete their life cycle. Despite this, they developed sophisticated virulence attributes allowing them not only to survive in host tissues but also to cause disease. A hypothesis for selective pressures driving the emergence or maintenance of virulence of soil fungi is their interaction with soil predators such as amoebae and helminths. We evaluated the presence of environmental amoeboid predators in soil from armadillo burrows where Paracoccidioides had been previously detected and tested if the interaction of Paracoccidioides with amoebae selects for fungi with increased virulence. Nematodes, ciliates, and amoebae-all potential predators of fungi-grew in cultures from soil samples. Microscopical observation and ITS sequencing identified the amoebae as Acanthamoeba spp, Allovahlkampfia spelaea, and Vermamoeba vermiformis. These three amoebae efficiently ingested, killed and digested Paracoccidioides spp. yeast cells, as did laboratory adapted axenic Acanthamoeba castellanii. Sequential co-cultivation of Paracoccidioides with A. castellanii selected for phenotypical traits related to the survival of the fungus within a natural predator as well as in murine macrophages and in vivo (Galleria mellonella and mice). These changes in virulence were linked to the accumulation of cell wall alpha-glucans, polysaccharides that mask recognition of fungal molecular patterns by host pattern recognition receptors. Altogether, our results indicate that Paracoccidioides inhabits a complex environment with multiple amoeboid predators that can exert selective pressure to guide the evolution of virulence traits.

Caenorhabditis elegans as a model animal for investigating fungal pathogenesis

The morbidity and mortality associated with systemic fungal infections in humans cannot be underestimated. The nematode Caenorhabditis elegans has become popular for the in vivo study of the pathogenesis of human fungal pathogens and as an antifungal drug-screening tool. C. elegans offers many advantages as a model organism for the study of human fungal diseases, including lack of ethics requirements, easy maintenance in the laboratory, fully sequenced genome, availability of genetic mutants, and the possibility of liquid assays for high-throughput antifungal screening. Its major drawbacks include the inability to grow at 37 °C and absence of an adaptive immune response. However, several virulence factors involved in the pathogenesis of medically important fungal pathogens have been identified using the C. elegans model, consequently providing new leads for drug discovery and potential drug targets. We review the use of C. elegans as a model animal to understand the pathogenesis of medically important human fungal pathogens and the discovery of novel antifungal compounds. The review makes a case for C. elegans as a suitable invertebrate model for a plethora of practical applications in the investigation of fungal pathogenesis as well as its amenability for liquid-based high-throughput screening of potential antifungal compounds.

Characterization of the atypical Ppz/Hal3 phosphatase system from the pathogenic fungus Cryptococcus neoformans

Ppz Ser/Thr protein phosphatases (PPases) are found only in fungi and have been proposed as potential antifungal targets. In Saccharomyces cerevisiae Ppz1 (ScPpz1) is involved in regulation of monovalent cation homeostasis. ScPpz1 is inhibited by two regulatory proteins, Hal3 and Vhs3, which have moonlighting properties, contributing to the formation of an unusual heterotrimeric PPC decarboxylase (PPCDC) complex crucial for CoA biosynthesis. Here we report the functional characterization of CnPpz1 (CNAG_03673) and two possible Hal3-like proteins, CnHal3a (CNAG_00909) and CnHal3b (CNAG_07348) from the pathogenic fungus Cryptococcus neoformans. Deletion of CnPpz1 or CnHal3b led to phenotypes unrelated to those observed in the equivalent S. cerevisiae mutants, and the CnHal3b-deficient strain was less virulent. CnPpz1 is a functional PPase and partially replaced endogenous ScPpz1. Both CnHal3a and CnHal3b interact with ScPpz1 and CnPpz1 in vitro but do not inhibit their phosphatase activity. Consistently, when expressed in S. cerevisiae, they poorly reproduced the Ppz1-regulatory properties of ScHal3. In contrast, both proteins were functional monogenic PPCDCs. The CnHal3b isoform was crystallized and, for the first time, the 3D-structure of a fungal PPCDC elucidated. Therefore, our work provides the foundations for understanding the regulation and functional role of the Ppz1-Hal3 system in this important pathogenic fungus.

Fungal Lanosterol 14α-demethylase: A target for next-generation antifungal design

The cytochrome P450 enzyme lanosterol 14α-demethylase (LDM) is the target of the azole antifungals used widely in medicine and agriculture as prophylaxis or treatments of infections or diseases caused by fungal pathogens. These drugs and agrochemicals contain an imidazole, triazole or tetrazole substituent, with one of the nitrogens in the azole ring coordinating as the sixth axial ligand to the LDM heme iron. Structural studies show that this membrane bound enzyme contains a relatively rigid ligand binding pocket comprised of a deeply buried heme-containing active site together with a substrate entry channel and putative product exit channel that reach to the membrane. Within the ligand binding pocket the azole antifungals have additional affinity determining interactions with hydrophobic side-chains, the polypeptide backbone and via water-mediated hydrogen bond networks. This review will describe the tools that can be used to identify and characterise the next generation of antifungals targeting LDM, with the goal of obtaining highly potent broad-spectrum fungicides that will be able to avoid target and drug efflux mediated antifungal resistance.

Silkworm as an experimental animal for research on fungal infections

Silkworm, Bombyx mori, has various advantages as an experimental animal, such as the low cost for rearing and fewer ethical problems. Models utilizing silkworms of infection with pathogenic bacteria have been established for identification of genes encoding virulence factors by large-scale in vivo screening. In this review, we describe recent progress in the study of silkworm infection models for elucidating the mechanisms of fungi infection. Silkworm infection models have been established for Candida albicans, Candida tropicalis, Candida glabrata and Cryptococcus neoformans, which are yeast type fungi, and Aspergillus fumigatus, Arthroderma vanbreuseghemii, Arthroderma benhamiae, Microsporum canis, Trichophyton rubrum, and Rhizopus oryzae, which are filamentous fungi. Novel genes encoding virulence factors in C. albicans and C. glabrata have been identified by using the silkworm infection models. We here outline the benefits of using silkworm infection models and a strategy for identifying the genes responsible for pathogenicity of microorganisms such as fungi. © 2019 The Authors. Microbiology and Immunology Published by The Societies and John Wiley & Sons Australia, Ltd.