Candida parapsilosis, Candida orthopsilosis, and Candida metapsilosis virulence in the non-conventional host Galleria mellonella

In vitro photodynamic therapy of Candida albicans, the cause of vulvovaginal candidiasis, is enhanced by Bacillus and Enterococcus probiotics

BACKGROUND

Candida albicans is the primary cause of vulvovaginal candidiasis, a worldwide health concern for women. The use of supplemental methods, such as antimicrobial photodynamic therapy (aPDT) and probiotics, was promoted by the ineffectiveness of the existing antifungal drugs.

METHODS

This study examines the combined effects of probiotics (Bacillus and Enterococcus isolated from the fermented pickles) and PDT (using red laser (655 nm, 18 J/cm2) as a light source and methylene blue dye (30 mg/mL) as a photosensitizer) on the in vitro virulence activity of C. albicans including growth, biofilm formation, antifungal resistance, biofilm elimination, and biofilm dispersion.

RESULTS

The probiotic strains demonstrated a higher resistance to PDT compared to the fungal cell. Bacillus and Enterococcus enhanced the antifungal effects of PDT on planktonic Candida cells in both pre-PDT and post-PDT interactions. The inhibition of biofilm formation by PDT was improved upon interaction with Bacillus (70 %) and Enterococcus (58 %). The eradication of Candida biofilm using PDT was increased after a combination with Bacillus (67 %) and Enterococcus (46 %). The nystatin resistance of the fungal biofilm following PDT treatment was decreased from (µg/ml) 25 to 6.25 due to the interaction with both probiotic strains. Fungal cell dispersion from the biofilm after PDT treatment diminished by 18 % and 25 % in the presence of Bacillus and Enterococcus strains. Galleria mellonella mortality was significantly changed following the PDT of the fungi/probiotic-injected larvae.

CONCLUSIONS

This synergistic activity suggests the use of probiotics/PDT as a supplemental treatment for vulvovaginal candidiasis.

Mortality patterns in candidemia: Insights from a multispecies analysis using a global research network

Understanding the impact of different Candida species on patient outcomes is crucial for effective management and treatment strategies. This study aims to comprehensively analyze the association between Candida species and mortality in documented candidemia. We queried TriNetX, a global research network database, to identify patients diagnosed with candidemia through polymerase chain reaction from 2020 to 2023. The primary outcome was mortality in candidemia patients, categorized by Candida species at 90 days and 1 year. The time to death was assessed using Kaplan-Meier plots. Cox proportional hazard (PH) models were also used for comparative analysis, unadjusted and adjusted for demographic and comorbidity covariates. We captured 1234 candidemia episodes during the study period. The 90-day and 1-year mortality rates for the various Candida species were as follows: C. tropicalis (33.9% and 35.6%), C. glabrata (28.3% and 34%), multispecies (27.7% and 36.4%), C. parapsilosis (25.8% and 31.8%), C. krusei (21.4% and 28.6%), C. albicans (21.1% and 23.9%), and C. auris (13.3% and 15.9%). The unadjusted Kaplan-Meier Survival analysis showed that multispecies candidemia, followed by C. tropicalis, had the lowest survival. The adjusted multivariable Cox PH model found that C.albicans, C. glabrata, C. parapsilosis, C. tropicalis, and multispecies candidemia had significantly higher mortality rates than C. auris. Age and a higher Charlson comorbidity index value emerged as independent predictors of increased mortality. Among patients with candidemia, we found an overall 1-year mortality of 28%. Multispecies candidemia, C. tropicalis, older age, and a higher comorbidity burden were associated with the highest mortality rates.

Characterising phagocytes and measuring phagocytosis from live Galleria mellonella larvae

Over the last 20 years, the larva of the greater waxmoth, Galleria mellonella, has rapidly increased in popularity as an in vivo mammalian replacement model organism for the study of human pathogens. Experimental readouts of response to infection are most often limited to observing the melanization cascade and quantifying larval death and, whilst transcriptomic and proteomic approaches, and methods to determine microbial load are also used, a more comprehensive toolkit of profiling infection over time could transform the applicability of this model. As an invertebrate, Galleria harbour an innate immune system comprised of both humoral components and a repertoire of innate immune cells - termed haemocytes. Although information on subtypes of haemocytes exists, there are conflicting reports on their exact number and function. Flow cytometry has previously been used to assay Galleria haemocytes, but protocols include both centrifugation and fixation - physical methods which have the potential to affect haemocyte morphology prior to analysis. Here, we present a method for live haemocyte analysis by flow cytometry, revealing that Galleria haemocytes constitute only a single resolvable population, based on relative size or internal complexity. Using fluorescent zymosan particles, we extend our method to show that up to 80% of the Galleria haemocyte population display phagocytic capability. Finally, we demonstrate that the developed assay reliably replicates in vitro data, showing that cell wall β-1,3-glucan masking by Candida albicans subverts phagocytic responses. As such, our method provides a new tool with which to rapidly assess phagocytosis and understand live infection dynamics in Galleria.

Hybrids unleashed: exploring the emergence and genomic insights of pathogenic yeast hybrids

Hybridisation is the crossing of two divergent lineages that give rise to offspring carrying an admixture of both parental genomes. Genome sequencing has revealed that this process is common in the Saccharomycotina, where a growing number of hybrid strains or species, including many pathogenic ones, have been recently described. Hybrids can display unique traits that may drive adaptation to new niches, and some pathogenic hybrids have been shown to have higher prevalence over their parents in human and environmental niches, suggesting a higher fitness and potential to colonise humans. Here, we discuss how hybridisation and its genomic and phenotypic outcomes can shape the evolution of fungal species and may play a role in the emergence of new pathogens.

Humoral immune response of Galleria mellonella after mono- and co-injection with Hypericum perforatum extract and Candida albicans

Galleria mellonella is used as a model organism to study the innate immune response of insects. In this study, the humoral immune response was assessed by examining phenoloxidase activity, fungal burden, and the expression of phenoloxidase and antimicrobial peptide genes at different time point following separate and combined injections of Hypericum perforatum extract and a nonlethal dose of Candida albicans. The administration of a plant extract at low doses increased phenoloxidase activity, while higher doses had no effect. Similarly, co-injection of a low dose of the extract with the pathogen allowed half of the yeast cells to survive after 24 h. Co-injection of plant extract with the pathogen decreased the phenoloxidase activity at the end of 4 h compared to C. albicans mono-injection. The phenoloxidase gene expressions was reduced in all experimental conditions with respect to the control. When plant extracts and the pathogen were administered together, gallerimycin and hemolin gene expressions were considerably higher compared to mono-injections of plant extracts and the pathogen. The results of this study reveal that gene activation and regulatory mechanisms may change for each immune gene, and that recognition and signaling pathways may differ depending on the involved immunoregulator.

The Emerging Pathogen Candida metapsilosis: Biological Aspects, Virulence Factors, Diagnosis, and Treatment

Fungal infections represent a constant and growing menace to public health. This concern is due to the emergence of new fungal species and the increase in antifungal drug resistance. Mycoses caused by Candida species are among the most common nosocomial infections and are associated with high mortality rates when the infection affects deep-seated organs. Candida metapsilosis is part of the Candida parapsilosis complex and has been described as part of the oral microbiota of healthy individuals. Within the complex, this species is considered the least virulent; however, the prevalence has been increasing in recent years, as well as an increment in the resistance to some antifungal drugs. One of the main concerns of candidiasis caused by this species is the wide range of clinical manifestations, ranging from tissue colonization to superficial infections, and in more severe cases it can spread, which makes diagnosis and treatment difficult. The study of virulence factors of this species is limited, however, proteomic comparisons between species indicate that virulence factors in this species could be similar to those already described for C. albicans. However, differences may exist, taking into account changes in the lifestyle of the species. Here, we provide a detailed review of the current literature about this organism, the caused disease, and some sharing aspects with other members of the complex, focusing on its biology, virulence factors, the host-fungus interaction, the identification, diagnosis, and treatment of infection.

Culture media influences Candida parapsilosis growth, susceptibility, and virulence

Introduction

Candida parapsilosis, a pathogenic yeast associated with systemic infections, exhibits metabolic adaptability in response to nutrient availability.

Methods

We investigated the impact of RPMI glucose supplemented (RPMId), TSB, BHI and YPD media on C. parapsilosis growth, morphology, susceptibility (caspofungin and amphotericin B), and in vivo virulence (Galleria mellonella) in planktonic and biofilm states.

Results

High-glucose media favors growth but hinders metabolic activity and filamentation. Media promoting carbohydrate production reduces biofilm susceptibility. Virulence differences between planktonic cells and biofilm suspensions from the same media shows that biofilm-related factors influence infection outcome depending on nutrient availability. Pseudohyphal growth occurred in biofilms under low oxygen and shear stress, but its presence is not exclusively correlated with virulence.

Discussion

This study provides valuable insights into the intricate interplay between nutrient availability and C. parapsilosis pathogenicity. It emphasizes the importance of considering pathogen behavior in diverse conditions when designing research protocols and therapeutic strategies.

Detection and Characterization of Two Phenotypes of Candida parapsilosis in South Korea: Clinical Features and Microbiological Findings

We newly detected two (sinking and floating) phenotypes of Candida parapsilosis among bloodstream infection (BSI) isolates from Korean hospitals and assessed their microbiological and clinical characteristics. During the performance of a Clinical and Laboratory Standards Institute (CLSI) broth microdilution antifungal susceptibility testing, the sinking phenotype had a characteristic smaller button-like appearance because all yeast cells sank to the bottoms of the CLSI U-shaped round-bottom wells, whereas the floating phenotype comprised dispersed cells. Phenotypic analysis, antifungal susceptibility testing, ERG11 sequencing, microsatellite genotyping, and clinical analysis were performed on C. parapsilosis isolates from 197 patients with BSI at a university hospital during 2006 to 2018. The sinking phenotype was detected in 86.7% (65/75) of the fluconazole-nonsusceptible (FNS) isolates, 92.9% (65/70) of the isolates harboring the Y132F ERG11 gene substitution, and 49.7% (98/197) of all isolates. Clonality was more frequently observed for the Y132F-sinking isolates (84.6% [55/65]) than for all other isolates (26.5% [35/132]; P < 0.0001). Annual incidence of Y132F-sinking isolates increased 4.5-fold after 2014, and two dominant genotypes, persistently recovered for 6 and 10 years, accounted for 69.2% of all Y132F-sinking isolates. Azole breakthrough fungemia (odds ratio [OR], 6.540), admission to the intensive care unit (OR, 5.044), and urinary catheter placement (OR, 6.918) were independent risk factors for BSIs with Y132F-sinking isolates. The Y132F-sinking isolates exhibited fewer pseudohyphae, a higher chitin content, and lower virulence in the Galleria mellonella model than the floating isolates. These long-term results illustrate the increasing BSIs caused by clonal transmission of the Y132F-sinking isolates of C. parapsilosis. IMPORTANCE We believe that this is the first study describe the microbiological and molecular characteristics of bloodstream isolates of C. parapsilosis in Korea exhibiting two phenotypes (sinking and floating). An important aspect of our findings is that the sinking phenotype was observed predominantly in isolates harboring a Y132F substitution in the ERG11 gene (92.9%), fluconazole-nonsusceptible (FNS) isolates (86.7%), and clonal BSI isolates (74.4%) of C. parapsilosis. Although the increase in the prevalence of FNS C. parapsilosis isolates has been a major threat in developing countries, in which the vast majority of candidemia cases are treated with fluconazole, our long-term results show increasing numbers of BSIs caused by clonal transmission of Y132F-sinking isolates of C. parapsilosis in the period with an increased echinocandin use for candidemia treatment in Korea, which suggests that C. parapsilosis isolates with the sinking phenotype continue to be a nosocomial threat in the era of echinocandin therapy.

Whole-Genome Sequence Analysis of Candida glabrata Isolates from a Patient with Persistent Fungemia and Determination of the Molecular Mechanisms of Multidrug Resistance

Whole-genome sequencing (WGS) was used to determine the molecular mechanisms of multidrug resistance for 10 serial Candida glabrata bloodstream isolates obtained from a neutropenic patient during 82 days of amphotericin B (AMB) or echinocandin therapy. For WGS, a library was prepared and sequenced using a Nextera DNA Flex Kit (Illumina) and the MiseqDx (Illumina) instrument. All isolates harbored the same Msh2p substitution, V239L, associated with multilocus sequence type 7 and a Pdr1p substitution, L825P, that caused azole resistance. Of six isolates with increased AMB MICs (≥2 mg/L), three harboring the Erg6p A158fs mutation had AMB MICs ≥ 8 mg/L, and three harboring the Erg6p R314K, Erg3p G236D, or Erg3p F226fs mutation had AMB MICs of 2-3 mg/L. Four isolates harboring the Erg6p A158fs or R314K mutation had fluconazole MICs of 4-8 mg/L while the remaining six had fluconazole MICs ≥ 256 mg/L. Two isolates with micafungin MICs > 8 mg/L harbored Fks2p (I661_L662insF) and Fks1p (C499fs) mutations, while six isolates with micafungin MICs of 0.25-2 mg/L harbored an Fks2p K1357E substitution. Using WGS, we detected novel mechanisms of AMB and echinocandin resistance; we explored mechanisms that may explain the complex relationship between AMB and azole resistance.

A case of Candida metapsilosis conjunctivitis in a neonate admitted to the cardiac heart intensive care unit

Harmless commensal Candida species, especially uncommon and rare ones may rarely cause a serious infection. Candida metapsilosis is a recently described yeast that is phenotypically indistinguishable from Candida parapsilosis and molecular methods are essential for its identification. We report the first case of Candida conjunctivitis due to C. metapsilosis obtained from the eye discharge of a 40-day-old girl with congenital heart disease admitted to the cardiac intensive care unit (CICU). The yeast isolate was identified by sequencing the entire ITS1-5.8 rRNA-ITS2 region. Antifungal susceptibility testing performed according to the CLSI M27-A3 showed that the isolate was susceptible to amphotericin B, fluconazole, itraconazole, voriconazole, clotrimazole, nystatin, terbinafine, 5-fluorocytosine, and caspofungin. Differentiation of the fungal new species allows us the accurate diagnosis and treatment, and a better understanding the microbial epidemiology.

Host-pathogen interactions upon Candida auris infection: fungal behaviour and immune response in Galleria mellonella

Candida auris has globally emerged as a multidrug-resistant fungus linked to healthcare-associated outbreaks. There is still limited evidence on its virulence, pathogenicity determinants, and complex host-pathogen interactions. This study analyzes the in vivo fungal behaviour, immune response, and host-pathogen interactions upon C. auris infection compared to C. albicans and C. parapsilosis in G. mellonella. This was performed by immunolabelling fungal structures and larval plasmatocytes and using a quantitative approach incorporating bioinformatic morphometric techniques into the study of microbial pathogenesis. C. auris presents a remarkably higher immunogenic activity than expected at its moderate degree of tissue invasion. It induces a greater inflammatory response than C. albicans and C. parapsilosis at the expense of plasmatocyte nodule formation, especially in non-aggregative strains. It specifically invades the larval respiratory system, in a pattern not previously observed in other Candida species, and presents inter-phenotypic tissue tropism differences. C. auris filaments in vivo less frequently than C. albicans or C. parapsilosis mostly through pseudohyphal growth. Filamentation might not be a major pathogenic determinant in C. auris, as less virulent aggregative phenotypes form pseudohyphae to a greater extent. C. auris has important both interspecific and intraspecific virulence and phenotype heterogeneity, with aggregative phenotypes of C. auris sharing characteristics with low pathogenic species such as C. parapsilosis. Our work suggests that C. auris owns an important morphogenetic plasticity that distinguishes it from other yeasts of the genus. Routine phenotypic identification of aggregative or non-aggregative phenotypes should be performed in the clinical setting as it may impact patient management.

Exposure of Candida parapsilosis to the silver(I) compound SBC3 induces alterations in the proteome and reduced virulence

The antimicrobial properties of silver have been exploited for many centuries and continue to gain interest in the fight against antimicrobial drug resistance. The broad-spectrum activity and low toxicity of silver have led to its incorporation into a wide range of novel antimicrobial agents, including N-heterocyclic carbene (NHC) complexes. The antimicrobial activity and in vivo efficacy of the NHC silver(I) acetate complex SBC3, derived from 1,3-dibenzyl-4,5-diphenylimidazol-2-ylidene (NHC*), have previously been demonstrated, although the mode(s) of action of SBC3 remains to be fully elucidated. Label-free quantitative proteomics was applied to analyse changes in protein abundance in the pathogenic yeast Candida parapsilosis in response to SBC3 treatment. An increased abundance of proteins associated with detoxification and drug efflux were indicative of a cell stress response, whilst significant decreases in proteins required for protein and amino acid biosynthesis offer potential insight into the growth-inhibitory mechanisms of SBC3. Guided by the proteomic findings and the prolific biofilm and adherence capabilities of C. parapsilosis, our studies have shown the potential of SBC3 in reducing adherence to epithelial cells and biofilm formation and hence decrease fungal virulence.

Antifungal Exposure and Resistance Development: Defining Minimal Selective Antifungal Concentrations and Testing Methodologies

This scoping review aims to summarise the current understanding of selection for antifungal resistance (AFR) and to compare and contrast this with selection for antibacterial resistance, which has received more research attention. AFR is an emerging global threat to human health, associated with high mortality rates, absence of effective surveillance systems and with few alternative treatment options available. Clinical AFR is well documented, with additional settings increasingly being recognised to play a role in the evolution and spread of AFR. The environment, for example, harbours diverse fungal communities that are regularly exposed to antifungal micropollutants, potentially increasing AFR selection risk. The direct application of effect concentrations of azole fungicides to agricultural crops and the incomplete removal of pharmaceutical antifungals in wastewater treatment systems are of particular concern. Currently, environmental risk assessment (ERA) guidelines do not require assessment of antifungal agents in terms of their ability to drive AFR development, and there are no established experimental tools to determine antifungal selective concentrations. Without data to interpret the selective risk of antifungals, our ability to effectively inform safe environmental thresholds is severely limited. In this review, potential methods to generate antifungal selective concentration data are proposed, informed by approaches used to determine antibacterial minimal selective concentrations. Such data can be considered in the development of regulatory guidelines that aim to reduce selection for AFR.

Antifungal activity of 2-Chloro-N-phenylacetamide, docking and molecular dynamics studies against clinical isolates of Candida tropicalis and Candida parapsilosis

AIMS

This study evaluated the antifungal, antibiofilm, and molecular docking of 2-Chloro-N-phenylacetamide against clinical isolates of Candida tropicalis and Candida parapsilosis.

METHODS AND RESULTS

MIC of the test drugs was determined by microdilution. A1Cl obtained MIC values ranging from 16 and 256 μg/mL. Fluconazole MIC ranging from 16 and 512 μg/mL. MIC of A1Cl showed fungicide activity, emphasizing the solid antifungal potential of this drug. An association study was performed with A1Cl and fluconazole (checkerboard), revealing indifference by decreasing. Thus, we conducted this study using A1Cl isolated. In the micromorphological assay, the test drugs reduced the production of virulence structures compared to the control (concentration-dependent effect). A1Cl inhibited in vitro biofilm formation at all concentrations tested (1/4MIC to 8xMIC) (p<0.05) and reduced mature biofilm biomass (p<0.05) against C. tropicalis and C. parapsilosis. In the ex vivo biofilm susceptibility testing (human nails fragments), A1Cl inhibited biofilm formation and reduced mature biofilm biomass (p<0.05) more than 50% at MIC. Fluconazole had a similar effect at 4xMIC. In silico studies suggest that the mechanism of antifungal activity of A1Cl involves the inhibition of the enzyme dihydrofolate reductase rather than geranylgeranyltransferase-I.

CONCLUSIONS

The results suggest that A1Cl is a promising antifungal agent. Furthermore, this activity is related to attenuation of expression of virulence factors and antibiofilm effects against C. tropicalis and C. parapsilosis.

SIGNIFICANCE AND IMPACT OF THE STUDY

Our study provides the first evidence that A1Cl, a novel synthetic drug, has fungicidal effects against C. tropicalis and C. parapsilosis. Furthermore, in vitro and ex vivo biofilms assays have demonstrated the potential antibiofilm of A1Cl. The mechanism of action involves inhibiting the enzyme dihydrofolate reductase, which was supported by in silico analyses. Therefore, this potential can be explored as a therapeutic alternative for onychomycosis and, at the same time, contribute to decreasing the resistance of clinical isolates of C. tropicalis and C. parapsilosis.

Antifungal Effects and Potential Mechanisms of Benserazide Hydrochloride Alone and in Combination with Fluconazole Against Candida albicans

Purpose

The resistance of C. albicans to traditional antifungal drugs brings a great challenge to clinical treatment. To overcome the resistance, developing antifungal agent sensitizers has attracted considerable attention. This study aimed to determine the anti-Candida activity of BEH alone or BEH–FLC combination and to explore the underlying mechanisms.

Materials and Methods

In vitro antifungal effects were performed by broth microdilution assay and XTT reduction assay. Infected Galleria mellonella larvae model was used to determine the antifungal effects in vivo. Probes Fluo-3/AM, FITC-VAD-FMK and rhodamine 6G were used to study the influence of BEH and FLC on intracellular calcium concentration, metacaspase activity and drug efflux of C. albicans.

Results

BEH alone exhibited obvious antifungal activities against C. albicans. BEH plus FLC not only showed synergistic effects against planktonic cells and preformed biofilms within 8 h but also enhanced the antifungal activity in infected G. mellonella larvae. Mechanistic studies indicated that antifungal effects of drugs might be associated with the increasement of calcium concentration, activation of metacaspase activity to reduce virulence and anti-biofilms, but were not related to drug efflux.

Conclusion

BEH alone or combined with FLC displayed potent antifungal activity both in vitro and in vivo, and the underlying mechanisms were related to reduced virulence factors.

Candidiasis by Candida glabrata, Candida nivariensis and Candida bracarensis in Galleria mellonella: Virulence and Therapeutic Responses to Echinocandins

Candida albicans is the major etiological agent of invasive candidiasis but the increasing prevalence of emerging species of Candida, such as Candida glabrata and phylogenetically closely related species, Candida nivariensis and Candida bracarensis, requires special attention. Differences in virulence among these species and their therapeutic responses using in vivo non-mammalian models are scarcely analysed. The aim of this study was analyse the survival of G. mellonella and host-pathogen interactions during infection by C. glabrata, C. nivariensis and C. bracarensis. Moreover, therapeutic responses to echinocandins were also assessed in the G. mellonella model of candidiasis. These three species produced lethal infection in G. mellonella; C. glabrata was the most virulent species and C. bracarensis the less. Haemocytes of G. mellonella phagocytised C. bracarensis cells more effectively than those of the other two species. Treatment with caspofungin and micafungin was most effective to protect larvae during C. glabrata and C. nivariensis infections while anidulafungin was during C. bracarensis infection. The model of candidiasis in G. mellonella is simple and appropriate to assess the virulence and therapeutic response of these emerging Candida species. Moreover, it successfully allows for detecting differences in the immune system of the host depending on the virulence of pathogens.

What Do We Know about Candida auris? State of the Art, Knowledge Gaps, and Future Directions

Candida auris has unprecedently emerged as a multidrug resistant fungal pathogen, considered a serious global threat due to its potential to cause nosocomial outbreaks and deep-seated infections with staggering transmissibility and mortality, that has put health authorities and institutions worldwide in check for more than a decade now. Due to its unique features not observed in other yeasts, it has been categorised as an urgent threat by the Centers for Disease Control and Prevention and other international agencies. Moreover, epidemiological alerts have been released in view of the increase of healthcare-associated C. auris outbreaks in the context of the COVID-19 pandemic. This review summarises the current evidence on C. auris since its first description, from virulence to treatment and outbreak control, and highlights the knowledge gaps and future directions for research efforts.

Activation of cellular immune response in insect model host Galleria mellonella by fungal α-1,3-glucan

Alpha-1,3-glucan, in addition to β-1,3-glucan, is an important polysaccharide component of fungal cell walls. It is reported for many fungal species, including human pathogenic genera: Aspergillus, Blastomyces, Coccidioides, Cryptococcus, Histoplasma and Pneumocystis, plant pathogens, e.g. Magnaporthe oryzae and entomopathogens, e.g. Metarhizium acridum. In human and plant pathogenic fungi, α-1,3-glucan is considered as a shield for the β-1,3-glucan layer preventing recognition of the pathogen by the host. However, its role in induction of immune response is not clear. In the present study, the cellular immune response of the greater wax moth Galleria mellonella to Aspergillus niger α-1,3-glucan was investigated for the first time. The changes detected in the total hemocyte count (THC) and differential hemocyte count (DHC), formation of hemocyte aggregates and changes in apolipophorin III localization indicated activation of G. mellonella cellular mechanisms in response to immunization with A. niger α-1,3-glucan. Our results, which have clearly demonstrated the response of the insect immune system to this fungal cell wall component, will help in understanding the α-1,3-glucan role in immune response against fungal pathogens not only in insects but also in mammals, including humans.

Culture Degeneration Reduces Sex-Related Gene Expression, Alters Metabolite Production and Reduces Insect Pathogenic Response in Cordyceps militaris

Cordyceps militaris is an entomopathogenic ascomycete, known primarily for infecting lepidopteran larval (caterpillars) and pupal hosts. Cordycepin, a secondary metabolite produced by this fungus has anti-inflammatory properties and other pharmacological activities. However, little is known about the biological role of this adenosine derivate and its stabilising compound pentostatin in the context of insect infection the life cycle of C. militaris. During repeated subcultivation under laboratory conditions a degeneration of C. militaris marked by decreasing levels of cordycepin production can occur. Here, using degenerated and parental control strains of an isolate of C. militaris, we found that lower cordycepin production coincides with the decline in the production of various other metabolites as well as the reduced expression of genes related to sexual development. Additionally, infection of Galleria mellonella (greater wax moth) caterpillars indicated that cordycepin inhibits the immune response in host haemocytes. Accordingly, the pathogenic response to the degenerated strain was reduced. These data indicate that there are simultaneous changes in sexual reproduction, secondary metabolite production, insect immunity and infection by C. militaris. This study may have implications for biological control of insect crop pests by fungi.

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.

Characterization of the Differential Pathogenicity of Candida auris in a Galleria mellonella Infection Model

Candida auris is an emergent multidrug-resistant fungal pathogen considered a severe global threat due to its capacity to cause nosocomial outbreaks and deep-seated infections with high transmissibility and mortality. However, evidence on its pathogenicity and the complex host-pathogen interactions is still limited. This study used the in vivo invertebrate model in Galleria mellonella to assess its virulence, exploring the mortality kinetics, melanization response, and morphological changes after fungal infection compared to Candida albicans and Candida parapsilosis, with known high and low pathogenicity, respectively. All C. auris isolates presented less virulence than C. albicans strains but higher than that induced by C. parapsilosis isolates. Increased pathogenicity was observed in nonaggregative phenotypes of C. auris, while the melanization response of the larvae to fungal infection was homogeneous and independent of the causing species. C. auris was able to filament in the in vivo animal model G. mellonella, with aggregative and nonaggregative phenotypes presenting various pseudohyphal formation degrees as pathogenicity determinants in a strain-dependent manner. Histological invasiveness of C. auris mimicked that observed for C. albicans, with effective dissemination since the early stages of infection both in yeast and filamented forms, except for a remarkable respiratory tropism not previously observed in other yeasts. These characteristics widely differ between strains and advocate the hypothesis that the morphogenetic variability of C. auris is an indicator of its flexibility and adaptability, contributing to its emergence and rising worldwide prevalence.

IMPORTANCECandida auris is an emergent fungus that has become a global threat due to its multidrug resistance, mortality, and transmissibility. These unique features make it different from other Candida species, but we still do not fully know the degree of virulence and, especially, the host-pathogen interactions. In this in vivo insect model, we found that it presents an intermediate degree of virulence compared to known high- and low-virulence Candida species but with significant variability between aggregative and nonaggregative strains. Although it was previously considered unable to filament, we documented in vivo filamentation as an important pathogenic determinant. We also found that it is able to disseminate early through the host, invading both the circulatory system and many different tissues with a remarkable respiratory tropism not previously described for other yeasts. Our study provides new insights into the pathogenicity of an emergent fungal pathogen and its interaction with the host and supports the hypothesis that its morphogenetic variability contributes to its rising global prevalence.

Azole Susceptibility Profiles of More than 9,000 Clinical Yeast Isolates Belonging to 40 Common and Rare Species

Invasive yeast infections represent a major global public health issue, and only few antifungal agents are available. Azoles are one of the classes of antifungals used for treatment of invasive candidiasis. The determination of antifungal susceptibility profiles using standardized methods is important to identify resistant isolates and to uncover the potential emergence of intrinsically resistant species. Here, we report data on 9,319 clinical isolates belonging to 40 pathogenic yeast species recovered in France over 17 years. The antifungal susceptibility profiles were all determined at the National Reference Center for Invasive Mycoses and Antifungals based on the EUCAST broth microdilution method. The centralized collection and analysis allowed us to describe the trends of azole susceptibility of isolates belonging to common species, confirming the high susceptibility for Candida albicans (n = 3,295), Candida tropicalis (n = 641), and Candida parapsilosis (n = 820) and decreased susceptibility for Candida glabrata (n = 1,274) and Pichia kudriavzevii (n = 343). These profiles also provide interesting data concerning azole susceptibility of Cryptococcus neoformans species complex, showing comparable MIC distributions for the three species but lower MIC₅₀s and MIC₉₀s for serotype D (n = 208) compared to serotype A (n = 949) and AD hybrids (n = 177). Finally, these data provide useful information for rare and/or emerging species, such as Clavispora lusitaniae (n = 221), Saprochaete clavata (n = 184), Meyerozyma guilliermondii complex (n = 150), Candida haemulonii complex (n = 87), Rhodotorula mucilaginosa (n = 55), and Wickerhamomyces anomalus (n = 36).

Virulence of Candida auris from different clinical origins in Caenorhabditis elegans and Galleria mellonella host models

Candida auris is an emerging multidrug-resistant fungal pathogen responsible for nosocomial outbreaks of invasive candidiasis. Although several studies on the pathogenicity of this species have been reported, the knowledge on C. auris virulence is still limited. This study aims to analyze the pathogenicity of C. auris, using one aggregating isolate and eleven non-aggregating isolates from different clinical origins (blood, urine and oropharyngeal specimens) in two alternative host models of candidiasis: Caenorhabditis elegans and Galleria mellonella. Furthermore, possible associations between virulence, aggregation, biofilm-forming capacity, and clinical origin were assessed. The aggregating phenotype isolate was less virulent in both in vivo invertebrate infection models than non-aggregating isolates but showed higher capacity to form biofilms. Blood isolates were significantly more virulent than those isolated from urine and respiratory specimens in the G. mellonella model of candidiasis. We conclude that both models of candidiasis present pros and cons but prove useful to evaluate the virulence of C. auris in vivo. Both models also evidence the heterogeneity in virulence that this species can develop, which may be influenced by the aggregative phenotype and clinical origin.

Fungal immunity and pathogenesis in mammals versus the invertebrate model organism Galleria mellonella

In recent decades, Galleria mellonella (Lepidoptera: Pyralidae) have emerged as a model system to explore experimental aspects of fungal pathogenesis. The benefits of the G. mellonella model include being faster, cheaper, higher throughput and easier compared with vertebrate models. Additionally, as invertebrates, their use is subject to fewer ethical and regulatory issues. However, for G. mellonella models to provide meaningful insight into fungal pathogenesis, the G. mellonella-fungal interactions must be comparable to mammalian-fungal interactions. Indeed, as discussed in the review, studies suggest that G. mellonella and mammalian immune systems share many similarities, and fungal virulence factors show conserved functions in both hosts. While the moth model has opened novel research areas, many comparisons are superficial and leave large gaps of knowledge that need to be addressed concerning specific mechanisms underlying G. mellonella-fungal interactions. Closing these gaps in understanding will strengthen G. mellonella as a model for fungal virulence in the upcoming years. In this review, we provide comprehensive comparisons between fungal pathogenesis in mammals and G. mellonella from immunological and virulence perspectives. When information on an antifungal immune component is unknown in G. mellonella, we include findings from other well-studied Lepidoptera. We hope that by outlining this information available in related species, we highlight areas of needed research and provide a framework for understanding G. mellonella immunity and fungal interactions.

In Vitro and In Vivo Effect of Peptides Derived from 14-3-3 Paracoccidioides spp. Protein

Background: Paracoccidioidomycosis (PCM) is a chronic disease that causes sequelae and requires prolonged treatment; therefore, new therapeutic approaches are necessary. In view of this, three peptides from Paracoccidioides brasiliensis 14-3-3 protein were selected based on its immunogenicity and therapeutic potential. Methods: The in vitro antifungal activity and cytotoxicity of the 14-3-3 peptides were evaluated. The influence of the peptides in immunological and survival aspects was evaluated in vivo, using Galleria mellonella and the expression of antimicrobial peptide genes in Caenorhabditis elegans. Results: None of the peptides were toxic to HaCaT (skin keratinocyte), MRC-5 (lung fibroblast), and A549 (pneumocyte) cell lines, and only P1 exhibited antifungal activity against Paracoccidioides spp. The peptides could induce an immune response in G. mellonella. Moreover, the peptides caused a delay in the death of Paracoccidioides spp. infected larvae. Regarding C. elegans, the three peptides were able to increase the expression of the antimicrobial peptides. These peptides had essential effects on different aspects of Paracoccidioides spp. infection showing potential for a therapeutic vaccine. Future studies using mammalian methods are necessary to validate our findings.

Prevalence and Antifungal Susceptibility of Candida parapsilosis Species Complex in Eastern China: A 15-Year Retrospective Study by ECIFIG

Candida parapsilosis complex is one of the most common non-albicans Candida species that cause candidemia, especially invasive candidiasis. The purpose of this study was to evaluate the antifungal susceptibilities of both colonized and invasive clinical C. parapsilosis complex isolates to 10 drugs: amphotericin (AMB), anidulafungin (AFG), caspofungin (CAS), micafungin (MFG), fluconazole (FLZ), voriconazole (VRZ), itraconazole (ITZ), posaconazole (POZ), 5-flucytosine (FCY), and isaconazole (ISA). In total, 884 C. parapsilosis species complex isolates were gathered between January 2005 and December 2020. C. parapsilosis, Candida metapsilosis, and Candida orthopsilosis accounted for 86.3, 8.1, and 5.5% of the cryptic species, respectively. The resistance/non-wild-type rate of bloodstream C. parapsilosis to the drugs was 3.5%, of C. metapsilosis to AFG and CAS was 7.7%, and of C. orthopsilosis to FLZ and VRZ was 15% and to CAS, MFG, and POZ was 5%. The geometric mean (GM) minimum inhibitory concentrations (MICs) of non-bloodstream C. parapsilosis for CAS (0.555 mg/L), MFG (0.853 mg/L), FLZ (0.816 mg/L), VRZ (0.017 mg/L), ITZ (0.076 mg/L), and POZ (0.042 mg/L) were significantly higher than those of bloodstream C. parapsilosis, for which the GM MICs were 0.464, 0.745, 0.704, 0.015, 0.061, and 0.033 mg/L, respectively (P < 0.05). The MIC distribution of the bloodstream C. parapsilosis strains collected from 2019 to 2020 for VRZ, POZ, and ITZ were 0.018, 0.040, and 0.073 mg/L, significantly higher than those from 2005 to 2018, which were 0.013, 0.028, and 0.052 mg/L (P < 0.05). Additionally, MIC distributions of C. parapsilosis with FLZ and the distributions of C. orthopsilosis with ITZ and POZ might be higher than those in Clinical and Laboratory Standards Institute studies. Furthermore, a total of 143 C. parapsilosis complex isolates showed great susceptibility to ISA. Overall, antifungal treatment of the non-bloodstream C. parapsilosis complex isolates should be managed and improved. The clinicians are suggested to pay more attention on azoles usage for the C. parapsilosis complex isolates. In addition, establishing the epidemiological cutoff values (ECVs) for azoles used in Eastern China may offer better guidance for clinical treatments. Although ISA acts on the same target as other azoles, it may be used as an alternative therapy for cases caused by FLZ- or VRZ-resistant C. parapsilosis complex strains.

Early Virulence Predictors during the Candida Species-Galleria mellonella Interaction

Fungal infections are a serious and increasing threat for human health, and one of the most frequent etiological agents for systemic mycoses is Candida spp. The gold standard to assess Candida virulence is the mouse model of systemic candidiasis, a restrictive, expensive, and time-consuming approach; therefore, invertebrate models have been proposed as alternatives. Galleria mellonella larvae have several traits that make them good candidates to study the fungal virulence. Here, we showed that a reduction in circulating hemocytes, increased melanin production, phenoloxidase, and lactate dehydrogenase activities were observed at 12 and 24 h postinoculation of highly virulent Candidatropicalis strains, while minimal changes in these parameters were observed in low-virulent strains. Similarly, the most virulent species Candida albicans, Candida tropicalis, Candida auris, Candida parapsilosis, and Candida orthopsilosis have led to significant changes in those parameters; while the low virulent species Candida guilliermondii, Candida krusei, and Candida metapsilosis induced modest variations in these immunological and cytotoxicity parameters. Since changes in circulating hemocytes, melanin production, phenoloxidase and lactate dehydrogenase activities showed a correlation with the larval median survival rates at 12 and 24 h postinoculation, we proposed them as candidates for early virulence predictors in G. mellonella.

The design and implementation of restraint devices for the injection of pathogenic microorganisms into Galleria mellonella

The injection of laboratory animals with pathogenic microorganisms poses a significant safety risk because of the potential for injury by accidental needlestick. This is especially true for researchers using invertebrate models of disease due to the required precision and accuracy of the injection. The restraint of the greater wax moth larvae (Galleria mellonella) is often achieved by grasping a larva firmly between finger and thumb. Needle resistant gloves or forceps can be used to reduce the risk of a needlestick but can result in animal injury, a loss of throughput, and inconsistencies in experimental data. Restraint devices are commonly used for the manipulation of small mammals, and in this manuscript, we describe the construction of two devices that can be used to entrap and restrain G. mellonella larvae prior to injection with pathogenic microbes. These devices reduce the manual handling of larvae and provide an engineering control to protect against accidental needlestick injury while maintaining a high rate of injection.

Pathogenicity Levels of Colombian Strains of Candida auris and Brazilian Strains of Candida haemulonii Species Complex in Both Murine and Galleria mellonella Experimental Models

Candida auris and Candida haemulonii complex (C. haemulonii, C. haemulonii var. vulnera and C. duobushaemulonii) are phylogenetically related species that share some physiological features and habits. In the present study, we compared the virulence of these yeast species using two different experimental models: (i) Galleria mellonella larvae to evaluate the survival rate, fungal burden, histopathology and phagocytosis index and (ii) BALB/c mice to evaluate the survival. In addition, the fungal capacity to form biofilm over an inert surface was analyzed. Our results showed that in both experimental models, the animal survival rate was lower when infected with C. auris strains than the C. haemulonii species complex. The hemocytes of G. mellonella showed a significantly reduced ability to phagocytize the most virulent strains forming the C. haemulonii species complex. Interestingly, for C. auris, it was impossible to measure the phagocytosis index due to a general lysis of the hemocytes. Moreover, it was observed a greater capability of biofilm formation by C. auris compared to C. haemulonii species complex. In conclusion, we observed that C. auris and C. haemulonii complex have different levels of pathogenicity in the experimental models employed in the present study.

Candida isolates causing candidemia show different degrees of virulence in Galleria mellonella

We aim to assess intra- and interspecies differences in the virulence of Candida spp. strains causing candidemia using the invertebrate Galleria mellonella model. We studied 739 Candida spp. isolates (C. albicans [n = 373], C. parapsilosis [n = 203], C. glabrata [n = 92], C. tropicalis [n = 53], and C. krusei [n = 18]) collected from patients with candidemia admitted to Gregorio Marañon Hospital (Madrid, Spain). Species-specific infecting inocula (yeast cells/larva) were adjusted (5 × 105 [C. albicans, and C. tropicalis], 2 × 106-5 × 106 [C. parapsilosis, C. glabrata, and C. krusei]) and used to infect 10 larvae per isolate; percentage of survival and median survival per isolate were calculated. According to the interquartile range of the median survival, isolates with a median survival under P25 were classified as of high-virulence and isolates with a median survival over P75 as of low virulence. The median survival of larvae infected with different species was variable: C. albicans (n = 2 days, IQR <1-3 days), C. tropicalis (n = 2 days, IQR 1.5-4 days), C. parapsilosis (n = 2 days, IQR 2-3.5 days), C. glabrata (n = 3 days, IQR 2-3 days), and C. krusei (n = 7 days, 6.5->8 days) (P < .001). Differences in virulence among species were validated by histological examination (day +1 post-infection) in the larvae infected by the isolates of each virulence category and species. Virulence-related gene expression in C. albicans isolates did not reach statistical significance. We report species-specific virulence patterns of Candida spp. and show that isolates within a given species have different degrees of virulence in the animal model.

The effect of Ginkgolide B combined with fluconazole against drug-resistant Candida albicans based on common resistance mechanisms

The number of invasive fungal infections has increased dramatically over recent years, leading to high morbidity and mortality of immunocompromised patients. Candida albicans is the most common cause of life-threatening disseminated candidiasis among invasive fungal infections. Resistance of C. albicans against conventional antifungals is frequently reported. Treatment with a combination of antifungal and non-antifungal agents is often considered in the aim to overcome drug resistance. This study shows for the first time that the combination of ginkgolide B (GB) and fluconazole (FLC) increases the sensitivity of resistant C. albicans to FLC. In vitro studies indicated that the drug combination had a synergistic effect on C. albicans in both planktonic cells and biofilms within 12 h. In vivo efficacy of this drug combination was evaluated using the Galleria mellonella infection model. Survival rate, fungal burden, and histological examination were determined. Studies indicated that the antifungal effects of GB in combination with FLC might be associated with inhibition of hyphal growth, disruption of intracellular calcium, and inhibition of drug efflux pumps. The results indicate a promising solution for overcoming drug resistance of C. albicans and expanding the clinical application of existing drugs.

Molecular Identification, Genotypic Diversity, Antifungal Susceptibility, and Clinical Outcomes of Infections Caused by Clinically Underrated Yeasts, Candida orthopsilosis, and Candida metapsilosis: An Iranian Multicenter Study (2014-2019)

Despite the increasing occurrence of Candida orthopsilosis and Candida metapsilosis in clinical settings, little is known about their microbiological and clinical properties. Herein, we conducted a national retrospective study (2014–2019) from multiple centers in Iran. Among the 1,770 Candida isolates collected, we identified 600 Candida parapsilosis species complex isolates. Isolate identification was performed by 9-plex PCR, matrix-assisted laser desorption-time of flight mass spectrometry (MALDI-TOF MS), and rDNA sequencing, and antifungal susceptibility testing (AFST) followed CLSI M27-A3/S4; genotyping was performed by amplified fragment length polymorphism (AFLP) analysis; and clinical information was mined. Thirty-one isolates of C. orthopsilosis from various clinical sources, one mixed sample (blood) concurrently containing C. orthopsilosis and C. parapsilosis and one isolate of C. metapsilosis from a nail sample were identified. Although both 9-plex PCR and MALDI-TOF successfully identified all isolates, only 9-plex PCR could identify the agents in a mixed sample. For the C. orthopsilosis isolates, resistance (non-wild type) was noted only for itraconazole (n = 4; 12.5%). Anidulafungin and fluconazole showed the highest and voriconazole had the lowest geometric mean values. AFLP analysis showed three main and four minor genotypes. Interestingly, 90% of nail isolates clustered with 80% of the blood isolates within two clusters, and four blood isolates recovered from four patients admitted to a hospital clustered into two genotypes and showed a high degree of similarity (>99.2%), which suggests that C. orthopsilosis disseminates horizontally. Supported by our data and published case studies, C. orthopsilosis and C. metapsilosis can be linked to challenging clinical failures, and successful outcomes are not always mirrored by in vitro susceptibility. Accordingly, conducting nationwide studies may provide more comprehensive data, which is required for a better prognosis and clinical management of patients.

Virulence of Candida haemulonii complex in Galleria mellonella and efficacy of classical antifungal drugs: a comparative study with other clinically relevant non-albicans Candida species

Candida haemulonii complex has emerged as notorious yeasts causing invasive infections with high rates of treatment failures. Since there is a particular interest in the development of non-mammalian host models to study microbial virulence, with the aim to evade the ethical impact of animal tests, herein we compared the virulence of C. haemulonii, C. duobushaemulonii and C. haemulonii var. vulnera with non-albicans Candida species (C. tropicalis, C. krusei and C. lusitaniae) on Galleria mellonella and the efficacy of antifungal drugs. All these fungi induced a dose-dependent effect on larvae killing, a decrease in hemocyte density and fungi were phagocytozed by hemocytes in equal proportions. Fungal inoculation caused early larvae melanization after some minutes of injection, followed by an augmented pigmentation after 24 h. Differences among species virulence can be explained, in part, by differences in growth rate and production of hydrolytic enzymes. First-line antifungals were tested with equivalent therapeutic doses and MIC profile in vitro was correlated with in vivo antifungal efficacy. Additionally, fungal burden increased in infected larvae along time and only caspofungin reduced the number of CFUs of C. haemulonii species complex. So, G. mellonella offers a simple and feasible model to study C. haemulonii complex virulence and drug efficacy.

In Vitro and In Vivo Evaluation of Voriconazole-Containing Antifungal Combinations against Mucorales Using a Galleria mellonella Model of Mucormycosis

Mucorales are resistant to most antifungals. Mucormycosis associated mortality is unacceptable and new treatment approaches are needed. The objectives of this work were (i) to evaluate the nature and intensity of the in vitro effect of three drugs combinations which included voriconazole (plus amphotericin B, posaconazole and caspofungin) against 25 strains of six different Mucorales species; (ii) to evaluate a Galleria mellonella mucormycosis model; and (iii) to establish if any in vitro⁻in vivo correlation exists. As expected, amphotericin B and posaconazole were the most active drugs when tested alone. However, species-specific differences were found. The ΣFICs varied according to the used combination. Only five strains showed synergism when voriconazole was combined with posaconazole and three strains when combined with amphotericin B. Microscopic hyphae alteration were observed for some isolates when confronted against drugs combinations. Using a Galleria mellonella mucormycosis model, better survival was seen in voriconazole plus amphotericin B and plus caspofungin combined treatments when compared with AMB alone for R. microsporus. These survival improvements were obtained using a 32-fold lower amphotericin B doses when combined with VRC than when treated with the polyene alone. These lower antifungal doses emulate the antifungal concentrations where the microscopic hyphae alterations were seen.

Mating type (MAT) locus and possible sexuality of the opportunistic pathogen Exophiala dermatitidis

Sexual reproduction among the black yeasts is generally limited to environmental saprobic species and is rarely observed among opportunists in humans. To date, a complete sexual cycle has not been observed in Exophiala dermatitidis. In this study, we aimed to gain insight into the reproductive mode of E. dermatitidis by characterizing its mating type (MAT) locus, conducting MAT screening of environmental and clinical isolates, examining the expression of the MAT genes and analyzing the virulence of the isolates of different mating types. Similar to other members of the Pezizomycotina, the E. dermatitidis genome harbors a high mobility group (HMG) domain gene (MAT1-2-1) in the vicinity of the SLA2 and APN2 genes. The MAT loci of 74 E. dermatitidis isolates (11 clinical and 63 environmental) were screened by PCR, and the surrounding region was amplified using long-range PCR. Sequencing of the ∼ 12-kb PCR product of a MAT1-1 isolate revealed an α-box gene (MAT1-1-1). The MAT1-1 idiomorph was 3544-bp long and harbored the MAT1-1-1 and MAT1-1-4 genes. The MAT1-2 idiomorph was longer, 3771-bp, and harbored only the MAT1-2-1 gene. This structure suggests a heterothallic reproduction mode. The distribution of MAT among 74 isolates was ∼ 1:1 with a MAT1-1:MAT1-2 ratio of 35:39. RT-PCR analysis indicated that the MAT genes are transcribed. No significant difference was detected in the virulence of isolates representing different mating types using a Galleria mellonella model (P > 0.05). Collectively, E. dermatitidis is the first opportunistic black yeast in which both MAT idiomorphs have been characterized. The occurrence of isolates bearing both idiomorphs, their approximately equal distribution, and the expression of the MAT genes suggest that E. dermatitidis might reproduce sexually.

Recent Advances in the Use of Galleria mellonella Model to Study Immune Responses against Human Pathogens

The use of invertebrates for in vivo studies in microbiology is well established in the scientific community. Larvae of Galleria mellonella are a widely used model for studying pathogenesis, the efficacy of new antimicrobial compounds, and immune responses. The immune system of G. mellonella larvae is structurally and functionally similar to the innate immune response of mammals, which makes this model suitable for such studies. In this review, cellular responses (hemocytes activity: phagocytosis, nodulation, and encapsulation) and humoral responses (reactions or soluble molecules released in the hemolymph as antimicrobial peptides, melanization, clotting, free radical production, and primary immunization) are discussed, highlighting the use of G. mellonella as a model of immune response to different human pathogenic microorganisms.

Standardization of G. mellonella Larvae to Provide Reliable and Reproducible Results in the Study of Fungal Pathogens

In the past decade, Galleria mellonella (wax moth) larvae have become widely used as a non-mammalian infection model. However, the full potential of this infection model has yet to be realised, limited by the variable quality of larvae used and the lack of standardised procedures. Here, we review larvae suitable for research, protocols for dosing larvae, and methods for scoring illness in larvae infected with fungal pathogens. The development of standardised protocols for carrying out our experimental work will allow high throughput screens to be developed, changing the way in which we evaluate panels of mutants and strains. It will also enable the in vivo screening of potential antimicrobials at an earlier stage in the research and development cycle.

Pathogenesis of the Candida parapsilosis Complex in the Model Host Caenorhabditis elegans

Caenorhabditiselegans is a valuable tool as an infection model toward the study of Candida species. In this work, we endeavored to develop a C. elegans-Candidaparapsilosis infection model by using the fungi as a food source. Three species of the C. parapsilosis complex (C. parapsilosis (sensu stricto), Candida orthopsilosis and Candida metapsilosis) caused infection resulting in C. elegans killing. All three strains that comprised the complex significantly diminished the nematode lifespan, indicating the virulence of the pathogens against the host. The infection process included invasion of the intestine and vulva which resulted in organ protrusion and hyphae formation. Importantly, hyphae formation at the vulva opening was not previously reported in C. elegans-Candida infections. Fungal infected worms in the liquid assay were susceptible to fluconazole and caspofungin and could be found to mount an immune response mediated through increased expression of cnc-4, cnc-7, and fipr-22/23. Overall, the C. elegans-C. parapsilosis infection model can be used to model C. parapsilosis host-pathogen interactions.

Fungal infection dynamics in response to temperature in the lepidopteran insect Galleria mellonella

This study examines how the dynamics of fungus-insect interactions can be modulated by temperature. The wax moth, Galleria mellonella, is a well-studied and important model insect whose larvae in the wild develop optimally at around 34 °C in beehives. However, surprisingly little research on wax moths has been conducted at relevant temperatures. In this study, the entomopathogenic fungus Metarhizium robertsii inflicted rapid and substantial mortality on wax moth larvae maintained at a constant temperature of 24 °C, but at 34 °C a 10 fold higher dose was required to achieve an equivalent mortality. The cooler temperature favored fungal pathogenicity, with condial adhesion to the cuticle, germination and hemocoel invasion all significantly enhanced at 24 °C, compared with 34 °C. The wax moth larvae immune responses altered with the temperature, and with the infective dose of the fungus. Enzyme-based immune defenses (lysozyme and phenoloxidase) exhibited enhanced activity at the warmer temperature. A dramatic upregulation in the basal expression of galiomicin and gallerimycin was triggered by cooling, and this was augmented in the presence of the fungus. Profiling of the predominant insect epicuticular fatty acids revealed a 4-7 fold increase in palmetic, oleic and linoleic acids in larvae maintained at 24 °C compared with those at 34 °C, but these failed to exert fungistatic effects on topically applied fungus. This study demonstrates the importance of choosing environmental conditions relevant to the habitat of the insect host when determining the dynamics and outcome of insect/fungus interactions, and has particular significance for the application of entomopathogens as biocontrol agents.

Antifungal susceptibility and virulence of Candida parapsilosis species complex: an overview of their pathogenic potential

PURPOSE

Antifungal resistance and several putative virulence factors have been associated with the pathogenicity of the Candida parapsilosis species complex. The objective of this study was to evaluate the antifungal susceptibility, the production of virulence factors and the pathogenicity of the C. parapsilosis complex.

METHODOLOGY

Overall, 49 isolates of C. parapsilosis sensu stricto, 19 C. orthopsilosis and nine C. metapsilosis were used. The planktonic and biofilm susceptibility to fluconazole, itraconazole, voriconazole, amphotericin B and caspofungin was assessed using a broth microdilution assay. Finally, the production of biofilm and hydrolytic enzymes and the fungal pathogenicity against Caenorhabditis elegans were investigated.Results/Key findings. Overall, one C. orthopsilosis was resistant to caspofungin and susceptible-dose-dependent to itraconazole, the other two C. orthopsilosis were susceptible-dose-dependent to fluconazole and itraconazole, and one C. metapsilosis was susceptible-dose-dependent to azoles. A total of 67.5 % of the isolates were biofilm producers. Amphotericin B and caspofungin caused the greatest reduction in the metabolic activity and biomass of mature biofilms. Phospholipase and protease production was observed in 55.1 % of C. parapsilosis sensu stricto, 42.1 % of C. orthopsilosis and 33.3 % of C. metapsilosis isolates. Moreover, 57.9 % of C. orthopsilosis and 20.4 % of C. parapsilosis sensu stricto isolates were β-haemolytic, and all C. metapsilosis were α-haemolytic. Finally, the C. parapsilosis complex caused high mortality of C. elegans after 96 h of exposure.

CONCLUSION

These results reinforce the heterogeneity of these cryptic species for their antifungal susceptibility, virulence and pathogenic potential, emphasizing the relevance of monitoring these emerging pathogens.

Analysis of the early cellular and humoral responses of Galleria mellonella larvae to infection by Candida albicans

Galleria mellonella larvae were administered an inoculum of Candida albicans and the response to infection over 24 hours was monitored. The yeast cell density in infected larvae declined initially but replication commenced six hours post-infection. The hemocyte density decreased from 5.2 × 10⁶/ml to 2.5 × 10⁶/ml at 2 hours but increased to 4.2 × 106 at 6 hours and decreased subsequently. Administration of β – glucan to larvae also caused a fluctuation in hemocyte density (5.1 ± 0.22 × 10⁶/ml (0 hour) to 6.25 ± 0.25 × 106/ml (6 hour) (p < 0.05) to 5 ± 2.7 × 106 (24 hour)) and the population showed an increase in the density of small, granular cells at 24 hours (p < 0.05). Hemocytes from larvae inoculated with β – glucan for 6 or 24 hours showed faster killing of C. albicans cells (53 ± 4.1% (p < 0.01), 64 ± 3.7%, (p < 0.01), respectively) than hemocytes from control larvae (24 ± 11%) at 60 min. Proteomic analysis indicated increased abundance of immune related proteins cecropin-A (5 fold) and prophenoloxidase-activating proteinase-1 (5 fold) 6 hours post infection but by 24 hours there was elevated abundance of muscle (tropomyosin 2 (141 fold), calponin (66 fold), troponin I (62 fold)) and proteins indicative of cellular stress (glutathione-S-transferase-like protein (114 fold)), fungal dissemination (muscle protein 20-like protein (174 fold)) and tissue breakdown (mitochondrial cytochrome c (10 fold)). Proteins decreased in abundance at 24 hour included β – 1,3 – glucan recognition protein precursor (29 fold) and prophenoloxidase subunit 2 (25 fold).

MTL genotypes, phenotypic switching, and susceptibility profiles of Candida parapsilosis species group compared to Lodderomyces elongisporus

Reference isolates of Candida parapsilosis (n = 8), Candida metapsilosis (n = 6), Candida orthopsilosis (n = 7), and Lodderomyces elongisporus (n = 11) were analyzed to gain insight into their pathobiology and virulence mechanisms. Initial evaluation using BBL Chromagar Candida medium misidentified L. elongisporus isolates as C. albicans. Polymerase chain reaction analysis of isolate MTL idiomorphs revealed that all C. parapsilosis isolates were MTLa homozygous and no MTL α1, α2, a1, or a2 gene was detected in L. elongisporus isolates. For C. orthopsilosis, two isolates were MTLa homozygous and five were MTL-heterozygous. Similarly, one C. metapsilosis isolate was MTLα homozygous whereas five were MTL-heterozygous. Isolate phenotypic switching analysis revealed potential phenotypic switching in the MTLα homozygous C. metapsilosis isolate, resulting in concomitant elongated cell formation. Minimum inhibitory concentrations of fluconazole (FLC) and FK506, alone or in combination, were determined by checkerboard assay, with data analyzed using the fractional inhibitory concentration index model. Synergistic or additive effects of these compounds were commonly observed in C. parapsilosis and L. elongisporus isolates. No killer activity was observed in the studied isolates, as determined phenotypically. No significant difference in virulence was seen for the four species in a Galleria mellonella model (P > 0.05). In conclusion, our results demonstrated phenotypic switching of C. metapsilosis CBS 2315 and that FLC and FK506 represent a promising drug combination against C. parapsilosis and L. elongisporus. The findings of the present study contribute to our understanding of the biology, diagnosis, and new possible treatments of the C. parapsilosis species group and L. elongisporus.

Usefulness of the Non-conventional Caenorhabditis elegans Model to Assess Candida Virulence

Invasive candidiasis is caused mainly by Candida albicans, but other Candida species have increasing etiologies. These species show different virulence and susceptibility levels to antifungal drugs. The aims of this study were to evaluate the usefulness of the non-conventional model Caenorhabditis elegans to assess the in vivo virulence of seven different Candida species and to compare the virulence in vivo with the in vitro production of proteinases and phospholipases, hemolytic activity and biofilm development capacity. One culture collection strain of each of seven Candida species (C. albicans, Candida dubliniensis, Candida glabrata, Candida krusei, Candida metapsilosis, Candida orthopsilosis and Candida parapsilosis) was studied. A double mutant C. elegans AU37 strain (glp-4;sek-1) was infected with Candida by ingestion, and the analysis of nematode survival was performed in liquid medium every 24 h until 120 h. Candida establishes a persistent lethal infection in the C. elegans intestinal tract. C. albicans and C. krusei were the most pathogenic species, whereas C. dubliniensis infection showed the lowest mortality. C. albicans was the only species with phospholipase activity, was the greatest producer of aspartyl proteinase and had a higher hemolytic activity. C. albicans and C. krusei caused higher mortality than the rest of the Candida species studied in the C. elegans model of candidiasis.

Hyphal wall protein 1 gene: A potential marker for the identification of different Candida species and phylogenetic analysis

BACKGROUND AND PURPOSE

Hyphal wall protein 1 (HWP1) is an important adhesin which usually is expressed on the germ tube and hyphal surface produced by different Candida species. The hyphal wall protein-coding gene (HWP1) was evaluated as a novel identification and phylogenetic marker in Candida tropicalis, C. orthopsilosis, C. parapsilosis and C. glabrata.

MATERIALS AND METHODS

Initially, four specific primer pairs were designed, and the target was amplified and finally sequenced. A total of 77 Candida isolates from four different species were included in the study. Consensus sequences were used for the evaluation of phylogenetic tree using the CLC Genome Workbench, GENEIOUS, and MEGA softwares and the levels of nucleotide and amino acid polymorphism were assessed.

RESULTS

According to the results, the specific amplified fragments of HWP1 gene were useful for the differentiation of four species. Intra-species variation was observed only in C. tropicalis with two DNA types. The phylogenetic tree of Candida species based on the HWP1 gene showed consistency in topology with those inferred from other gene sequences.

CONCLUSION

We found that HWP1 gene was an excellent marker for the identification of non-albicansCandida species as well as the phylogenetic analysis of the most clinically significant Candida species.