Impact of glucocorticoids and rapamycin on autophagy in Candida glabrata-infected macrophages from BALB/c mice

Objective

In the defense against microorganisms like Candida albicans, macrophages recruit LC3(Microtubule-associated protein 1A/1B-light chain 3) to the periplasm, engaging in the elimination process through the formation of a single-membrane phagosome known as LC3-associated phagocytosis (LAP). Building on this, we propose the hypothesis that glucocorticoids may hinder macrophage phagocytosis of Candida glabrata by suppressing LAP, and rapamycin could potentially reverse this inhibitory effect.

Methods

RAW264.7 cells were employed for investigating the immune response to Candida glabrata infection. Various reagents, including dexamethasone, rapamycin, and specific antibodies, were utilized in experimental setups. Assays, such as fluorescence microscopy, flow cytometry, ELISA (Enzyme-Linked Immunosorbent Assay), Western blot, and confocal microscopy, were conducted to assess phagocytosis, cytokine levels, protein expression, viability, and autophagy dynamics.

Results

Glucocorticoids significantly inhibited macrophage autophagy, impairing the cells' ability to combat Candida glabrata. Conversely, rapamycin exhibited a dual role, initially inhibiting and subsequently promoting phagocytosis of Candida glabrata by macrophages. Glucocorticoids hinder macrophage autophagy in Candida glabrata infection by suppressing the MTOR pathway(mammalian target of rapamycin pathway), while the activation of MTOR pathway by Candida glabrata diminishes over time.

Conclusion

Our study elucidates the intricate interplay between glucocorticoids, rapamycin, and macrophage autophagy during Candida glabrata infection. Understanding the implications of these interactions not only sheds light on the host immune response dynamics but also unveils potential therapeutic avenues for managing fungal infections.

Calcineurin-dependent contributions to fitness in the opportunistic pathogen Candida glabrata

The protein phosphatase calcineurin is vital for the virulence of the opportunistic fungal pathogen Candida glabrata. The host-induced stresses that activate calcineurin signaling are unknown, as are the targets of calcineurin relevant to virulence. To potentially shed light on these processes, millions of transposon insertion mutants throughout the genome of C. glabrata were profiled en masse for fitness defects in the presence of FK506, a specific inhibitor of calcineurin. Eighty-seven specific gene deficiencies depended on calcineurin signaling for full viability in vitro both in wild-type and pdr1∆ null strains lacking pleiotropic drug resistance. Three genes involved in cell wall biosynthesis (FKS1, DCW1, FLC1) possess co-essential paralogs whose expression depended on calcineurin and Crz1 in response to micafungin, a clinical antifungal that interferes with cell wall biogenesis. Interestingly, 80% of the FK506-sensitive mutants were deficient in different aspects of vesicular trafficking, such as endocytosis, exocytosis, sorting, and biogenesis of secretory proteins in the endoplasmic reticulum (ER). In response to the experimental antifungal manogepix that blocks GPI-anchor biosynthesis in the ER, calcineurin signaling increased and strongly prevented cell death independent of Crz1, one of its major targets. Comparisons between manogepix, micafungin, and the ER-stressing tunicamycin reveal a correlation between the degree of calcineurin signaling and the degree of cell survival. These findings suggest that calcineurin plays major roles in mitigating stresses of vesicular trafficking. Such stresses may arise during host infection and in response to antifungal therapies.IMPORTANCECalcineurin plays critical roles in the virulence of most pathogenic fungi. This study sheds light on those roles in the opportunistic pathogen Candida glabrata using a genome-wide analysis in vitro. The findings could lead to antifungal developments that also avoid immunosuppression.

From the first touch to biofilm establishment by the human pathogen Candida glabrata: a genome-wide to nanoscale view

Candida glabrata is an opportunistic pathogen that adheres to human epithelial mucosa and forms biofilm to cause persistent infections. In this work, Single-cell Force Spectroscopy (SCFS) was used to glimpse at the adhesive properties of C. glabrata as it interacts with clinically relevant surfaces, the first step towards biofilm formation. Following a genetic screening, RNA-sequencing revealed that half of the entire transcriptome of C. glabrata is remodeled upon biofilm formation, around 40% of which under the control of the transcription factors CgEfg1 and CgTec1. Using SCFS, it was possible to observe that CgEfg1, but not CgTec1, is necessary for the initial interaction of C. glabrata cells with both abiotic surfaces and epithelial cells, while both transcription factors orchestrate biofilm maturation. Overall, this study characterizes the network of transcription factors controlling massive transcriptional remodelling occurring from the initial cell-surface interaction to mature biofilm formation.

Yeast cell fate control by temporal redundancy modulation of transcription factor paralogs

Recent single-cell studies have revealed that yeast stress response involves transcription factors that are activated in pulses. However, it remains unclear whether and how these dynamic transcription factors temporally interact to regulate stress survival. Here we show that budding yeast cells can exploit the temporal relationship between paralogous general stress regulators, Msn2 and Msn4, during stress response. We find that individual pulses of Msn2 and Msn4 are largely redundant, and cells can enhance the expression of their shared targets by increasing their temporal divergence. Thus, functional redundancy between these two paralogs is modulated in a dynamic manner to confer fitness advantages for yeast cells, which might feed back to promote the preservation of their redundancy. This evolutionary implication is supported by evidence from Msn2/Msn4 orthologs and analyses of other transcription factor paralogs. Together, we show a cell fate control mechanism through temporal redundancy modulation in yeast, which may represent an evolutionarily important strategy for maintaining functional redundancy between gene duplicates.

Emerging echinocandin-resistant Candida albicans and glabrata in Switzerland

Echinocandins represent the first-line therapy of candidemia. Echinocandin resistance among Candida spp. is mainly due to acquired FKS mutations. In this study, we report the emergence of FKS-mutant Candida albicans/glabrata in Switzerland and provide the microbiological and clinical characteristics of 9 candidemic episodes. All patients were previously exposed to echinocandins (median 26 days; range 15–77). Five patients received initial echinocandin therapy with persistent candidemia in 4 of them. Overall mortality was 33%.

A gain-of-function mutation in PDR1 of Candida glabrata decreases EPA1 expression and attenuates adherence to epithelial cells through enhancing recruitment of the Mediator subunit Gal11A

Genetic studies have revealed critical roles of transcription factor Pdr1 and the Mediator subunit Gal11A in regulating azole resistance in Candida glabrata. Recently, PDR1 gain-of-function (GOF) mutations have been shown to not only increase azole resistance but also enhance adherence during C. glabrata infection. However, mechanism of how Pdr1 regulates adherence, especially the implication of PDR1 GOF mutations in the regulation of the major adhesin gene EPA1, remains uncharacterized. Initially, we unexpectedly observed that expression of PDR1 harbouring GOF mutation G346D down-regulated EPA1 transcription and attenuated adherence to epithelial cells in different strain backgrounds. Given that PDR1 GOF mutations have been previously regarded as stimulators for adherence of this species, these findings prompted us to explore the regulation of EPA1 by wild-type Pdr1 and Pdr1 harbouring G346D mutation. Epitope tagged version of Pdr1 and Gal11A were utilized to determine the association of Pdr1 and Gal11A with EPA1 promoter. A combination of approaches including deletion, molecular, and biochemical assays showed that EPA1 is a direct target of Pdr1, and demonstrated for the first time that PDR1 G346D mutation decreases EPA1 expression and attenuates adherence to epithelial cells via enhancing recruitment of Gal11A. Taken together, our data propose a critical role of Gal11A in Pdr1-regulated EPA1 expression and adherence to epithelial cells, which could be utilized a novel therapeutic target for the treatment of hyper-adherent C. glabrata infection.

Transcriptional responses of Candida glabrata biofilm cells to fluconazole are modulated by the carbon source

Candida glabrata is an important human fungal pathogen known to trigger serious infections in immune-compromised individuals. Its ability to form biofilms, which exhibit high tolerance to antifungal treatments, has been considered as an important virulence factor. However, the mechanisms involving antifungal resistance in biofilms and the impact of host niche environments on these processes are still poorly defined. In this study, we performed a whole-transcriptome analysis of C. glabrata biofilm cells exposed to different environmental conditions and constraints in order to identify the molecular pathways involved in fluconazole resistance and understand how acidic pH niches, associated with the presence of acetic acid, are able to modulate these responses. We show that fluconazole treatment induces gene expression reprogramming in a carbon source and pH-dependent manner. This is particularly relevant for a set of genes involved in DNA replication, ergosterol, and ubiquinone biosynthesis. We also provide additional evidence that the loss of mitochondrial function is associated with fluconazole resistance, independently of the growth condition. Lastly, we propose that C. glabrata Mge1, a cochaperone involved in iron metabolism and protein import into the mitochondria, is a key regulator of fluconazole susceptibility during carbon and pH adaptation by reducing the metabolic flux towards toxic sterol formation. These new findings suggest that different host microenvironments influence directly the physiology of C. glabrata, with implications on how this pathogen responds to antifungal treatment. Our analyses identify several pathways that can be targeted and will potentially prove to be useful for developing new antifungals to treat biofilm-based infections.

Divergent Approaches to Virulence in C. albicans and C. glabrata: Two Sides of the Same Coin

Candida albicans and Candida glabrata are the two most prevalent etiologic agents of candidiasis worldwide. Although both are recognized as pathogenic, their choice of virulence traits is highly divergent. Indeed, it appears that these different approaches to fungal virulence may be equally successful in causing human candidiasis. In this review, the virulence mechanisms employed by C. albicans and C. glabrata are analyzed, with emphasis on the differences between the two systems. Pathogenesis features considered in this paper include dimorphic growth, secreted enzymes and signaling molecules, and stress resistance mechanisms. The consequences of these traits in tissue invasion, biofilm formation, immune system evasion, and macrophage escape, in a species dependent manner, are discussed. This review highlights the observation that C. albicans and C. glabrata follow different paths leading to a similar outcome. It also highlights the lack of knowledge on some of the specific mechanisms underlying C. glabrata pathogenesis, which deserve future scrutiny.

Competition of Candida glabrata against Lactobacillus is Hog1 dependent

Candida glabrata is a common human fungal commensal and opportunistic pathogen. This fungus shows remarkable resilience as it can form recalcitrant biofilms on indwelling catheters, has intrinsic resistance against azole antifungals, and is causing vulvovaginal candidiasis. As a nosocomial pathogen, it can cause life-threatening bloodstream infections in immune-compromised patients. Here, we investigate the potential role of the high osmolarity glycerol response (HOG) MAP kinase pathway for C. glabrata virulence. The C. glabrata MAP kinase CgHog1 becomes activated by a variety of environmental stress conditions such as osmotic stress, low pH, and carboxylic acids and subsequently accumulates in the nucleus. We found that CgHog1 allows C. glabrata to persist within murine macrophages, but it is not required for systemic infection in a mouse model. C. glabrata and Lactobacilli co-colonise mucosal surfaces. Lactic acid at a concentration produced by vaginal Lactobacillus spp. causes CgHog1 phosphorylation and accumulation in the nucleus. In addition, CgHog1 enables C. glabrata to tolerate different Lactobacillus spp. and their metabolites when grown in co-culture. Using a phenotypic diverse set of clinical C. glabrata isolates, we find that the HOG pathway is likely the main quantitative determinant of lactic acid stress resistance. Taken together, our data indicate that CgHog1 has an important role in the confrontation of C. glabrata with the common vaginal flora.

Short-Form Bomanins Mediate Humoral Immunity in Drosophila

The Bomanins (Boms) are a family of a dozen secreted peptides that mediate the innate immune response governed by the Drosophila Toll receptor. We recently showed that deleting a cluster of 10 Bom genes blocks Toll-mediated defenses against a range of fungi and gram-positive bacteria. Here, we characterize the activity of individual Bom family members. We provide evidence that the Boms overlap in function and that a single Bom gene encoding a mature peptide of just 16 amino acids can act largely or entirely independent of other family members to provide phenotypic rescue in vivo. We further demonstrate that the Boms function in Drosophila humoral immunity, mediating the killing of the fungal pathogen Candida glabrata in an in vitro assay of cell-free hemolymph. In addition, we find that the level of antifungal activity both in vivo and in vitro is linked to the level of Bom gene expression. Although Toll dictates expression of the antimicrobial peptides (AMPs) drosomycin and metchnikowin, we find no evidence that Boms act by modifying the expression of the mature forms of these antifungal AMPs.

Susceptibility of Candida glabrata biofilms to echinocandins: alterations in the matrix composition

Candidiases are the most recurrent fungal infections, especially among immunosuppressed patients. Although Candida albicans is still the most widespread isolated species, non-Candida albicans Candida species have been increasing. The goal of this work was to determine the susceptibility of C. glabrata biofilms to echinocandins and to evaluate their effect on the biofilm matrix composition, comparing the results with other Candida species. Drug susceptibilities were assessed through the determination of minimum inhibitory concentration (MIC), minimum fungicidal concentration (MFC) and minimum biofilm eradication concentration (MBEC) of caspofungin (Csf) and micafugin (Mcf). The β-1,3 glucans content of the matrices was assessed after contact with the drugs. The data suggest that, generally, after contact with echinocandins, the concentration of β-1,3 glucans increased. These adjustments in the matrix composition of C. glabrata biofilms and the chemical differences between Csf and Mcf, seem responsible and may determine the effectivity of the drug responses.

Quantitative Simulations Predict Treatment Strategies Against Fungal Infections in Virtual Neutropenic Patients

The condition of neutropenia, i.e., a reduced absolute neutrophil count in blood, constitutes a major risk factor for severe infections in the affected patients. Candida albicans and Candida glabrata are opportunistic pathogens and the most prevalent fungal species in the human microbiota. In immunocompromised patients, they can become pathogenic and cause infections with high mortality rates. In this study, we use a previously established approach that combines experiments and computational models to investigate the innate immune response during blood stream infections with the two fungal pathogens C. albicans and C. glabrata. First, we determine immune-reaction rates and migration parameters under healthy conditions. Based on these findings, we simulate virtual patients and investigate the impact of neutropenic conditions on the infection outcome with the respective pathogen. Furthermore, we perform in silico treatments of these virtual patients by simulating a medical treatment that enhances neutrophil activity in terms of phagocytosis and migration. We quantify the infection outcome by comparing the response to the two fungal pathogens relative to non-neutropenic individuals. The analysis reveals that these fungal infections in neutropenic patients can be successfully cleared by cytokine treatment of the remaining neutrophils; and that this treatment is more effective for C. glabrata than for C. albicans.

In vitro activity of micafungin against biofilms of Candida albicans, Candida glabrata, and Candida parapsilosis at different stages of maturation

Candida spp. is able to form a biofilm, which is considered resistant to the majority of antifungals used in medicine. The aim of this study was to evaluate the in vitro activity of micafungin against Candida spp. biofilms at different stages of their maturation (2, 6, and 24 h). We assessed the inhibitory effect of micafungin against 78 clinical isolates of Candida spp., growing as planktonic or sessile cells, by widely recommended broth microdilution method. The in vitro effect on sessile cells viability was evaluated by colorimetric reduction assay. All examined strains were susceptible or intermediate to micafungin when growing as planktonic cells. At the early stages of biofilm maturation, from 11 (39.3%) to 20 (100%), tested strains, depending on the species, exhibited sessile minimal inhibitory concentrations (SMICs) of micafungin at ≤ 2 mg/L. For 24-h-old Candida spp. biofilms, from 3 (10.7%) to 20 (100%) of the tested strains displayed SMICs of micafungin at ≤ 2 mg/L. Our findings confirm that micafungin exhibits high potential anti-Candida-biofilm activity. However, this effect does not comprise all Candida species and strains. All strains were susceptible or intermediate to micafungin when growing as planktonic cells, but for biofilms, micafungin displays species- and strain-specific activity. Paradoxical growth of C. albicans and C. parapsilosis was observed. Antifungal susceptibility testing of Candida spp. biofilms would be the best solution, but to date, no reference method is available. The strongest antibiofilm activity of micafungin is observed at early stages of biofilm formation. Possibly, micafungin could be considered as an effective agent for prevention of biofilm-associated candidiasis, especially catheter-related candidaemia.

Generational distribution of a Candida glabrata population: Resilient old cells prevail, while younger cells dominate in the vulnerable host

Similar to other yeasts, the human pathogen Candida glabrata ages when it undergoes asymmetric, finite cell divisions, which determines its replicative lifespan. We sought to investigate if and how aging changes resilience of C. glabrata populations in the host environment. Our data demonstrate that old C. glabrata are more resistant to hydrogen peroxide and neutrophil killing, whereas young cells adhere better to epithelial cell layers. Consequently, virulence of old compared to younger C. glabrata cells is enhanced in the Galleria mellonella infection model. Electron microscopy images of old C. glabrata cells indicate a marked increase in cell wall thickness. Comparison of transcriptomes of old and young C. glabrata cells reveals differential regulation of ergosterol and Hog pathway associated genes as well as adhesion proteins, and suggests that aging is accompanied by remodeling of the fungal cell wall. Biochemical analysis supports this conclusion as older cells exhibit a qualitatively different lipid composition, leading to the observed increased emergence of fluconazole resistance when grown in the presence of fluconazole selection pressure. Older C. glabrata cells accumulate during murine and human infection, which is statistically unlikely without very strong selection. Therefore, we tested the hypothesis that neutrophils constitute the predominant selection pressure in vivo. When we altered experimentally the selection pressure by antibody-mediated removal of neutrophils, we observed a significantly younger pathogen population in mice. Mathematical modeling confirmed that differential selection of older cells is sufficient to cause the observed demographic shift in the fungal population. Hence our data support the concept that pathogenesis is affected by the generational age distribution of the infecting C. glabrata population in a host. We conclude that replicative aging constitutes an emerging trait, which is selected by the host and may even play an unanticipated role in the transition from a commensal to a pathogen state.

The Effectiveness of Voriconazole in Therapy of Candida glabrata's Biofilms Oral Infections and Its Influence on the Matrix Composition and Gene Expression

Candida glabrata is one of most prevalent yeast in fungal infections, especially in immunocompromised patients. Its azole resistance results in a low therapeutic response, particularly when associated with biofilms. The main goal of this work was to study the effectiveness of voriconazole (Vcz) against C. glabrata biofilms oral pathologies, as esophageal or oropharyngeal candidiasis. Antifungal susceptibilities were determined in pre-formed 24-h-biofilms and ERG genes expression was determined by qRT-PCR. Protein quantification was performed using BCA^® Kit, carbohydrate was estimated according to the Dubois assay and β-1,3 glucans concentration were determined using Glucatell^® kit. Finally, ergosterol, Vcz, and fluconazole (Flu) concentrations within the biofilm matrices were determined by RP-HPLC. Results showed that C. glabrata biofilms were more susceptible to Vcz than to Flu and that ERG genes expression evidenced an overexpression of the three ERG genes in the presence of both azoles. The matrix content presented a remarked decrease in proteins and an increase in carbohydrates, namely β-1,3 glucans. Ergosterol was successfully detected and quantified in the biofilm matrices, with no differences in all the considered conditions. Vcz demonstrated better diffusion through the biofilms and better cell penetration capacities, than Flu, indicating that the structure of the drug molecule fully influences its dissemination through the biofilm matrices. This work showed that Vcz is notably more effective than Flu for the treatment of resistant C. glabrata oral biofilms, which demonstrates a clinical relevance in its future use for the treatment of oropharyngeal/esophageal candidiasis caused by this species.

P2X7 from j774 murine macrophages acts as a scavenger receptor for bacteria but not yeast

We studied the effects of extracellular ATP and Ca²⁺ on uptake of bacteria (Staphylococcus aureus or Escherichia coli) and live yeast (Candida glabrata) by J774 macrophages to determine the role of endogenous P2X7 receptors in phagocytosis. Our findings show that phagocytosis of bio-particles coated with S. aureus or E. coli was blocked by ATP and the P2X7 receptor agonist BzATP, while yeast phagocytosis was not. A438079, an antagonist of P2X7 receptors, partially reverted the effects of ATP on bacterial phagocytosis. To determine if P2X7-mediated Ca²⁺ entry into macrophages was blocking the engulfment of bacteria, we measured phagocytic activity in the absence or presence of 2 mM extracellular Ca²⁺ with or without ATP. Ca²⁺, in the absence of ATP, was required for engulfment of E. coli and C. glabrata but not S. aureus. Adding ATP inhibited phagocytosis of S. aureus and E. coli regardless of Ca²⁺, suggesting that Ca²⁺ entry was not important for inhibiting phagocytosis. On the other hand, phagocytosis of normal or hyper-adherent C. glabrata mutants had an absolute requirement for extracellular Ca²⁺ due to yeast adhesion to macrophages mediated by Ca²⁺-dependent adhesion proteins. We conclude that unstimulated P2X7 from J774 cells act as scavenger receptor for the uptake of S. aureus and E. coli but not of yeast; Ca²⁺ entry via P2X7 receptors play no role in phagocytosis of S. aureus and E. coli; while the effect of Ca²⁺ on C. glabrata phagocytosis was mediated by the adhesins Epa1, Epa6 and Epa7.

Efficient Mating-Type Switching in Candida glabrata Induces Cell Death

Candida glabrata is an apparently asexual haploid yeast that is phylogenetically closer to Saccharomyces cerevisiae than to Candida albicans. Its genome contains three MAT-like cassettes, MAT, which encodes either MATa or MATalpha information in different strains, and the additional loci, HML and HMR. The genome also contains an HO gene homolog, but this yeast has never been shown to switch mating-types spontaneously, as S. cerevisiae does. We have recently sequenced the genomes of the five species that, together with C. glabrata, make up the Nakaseomyces clade. All contain MAT-like cassettes and an HO gene homolog. In this work, we express the HO gene of all Nakaseomyces and of S. cerevisiae in C. glabrata. All can induce mating-type switching, but, despite the larger phylogenetic distance, the most efficient endonuclease is the one from S. cerevisiae. Efficient mating-type switching in C. glabrata is accompanied by a high cell mortality, and sometimes results in conversion of the additional cassette HML. Mortality probably results from the cutting of the HO recognition sites that are present, in HML and possibly HMR, contrary to what happens naturally in S. cerevisiae. This has implications in the life-cycle of C. glabrata, as we show that efficient MAT switching is lethal for most cells, induces chromosomal rearrangements in survivors, and that the endogenous HO is probably rarely active indeed.

An effector Peptide family required for Drosophila toll-mediated immunity

In Drosophila melanogaster, recognition of an invading pathogen activates the Toll or Imd signaling pathway, triggering robust upregulation of innate immune effectors. Although the mechanisms of pathogen recognition and signaling are now well understood, the functions of the immune-induced transcriptome and proteome remain much less well characterized. Through bioinformatic analysis of effector gene sequences, we have defined a family of twelve genes – the Bomanins (Boms) – that are specifically induced by Toll and that encode small, secreted peptides of unknown biochemical activity. Using targeted genome engineering, we have deleted ten of the twelve Bom genes. Remarkably, inactivating these ten genes decreases survival upon microbial infection to the same extent, and with the same specificity, as does eliminating Toll pathway function. Toll signaling, however, appears unaffected. Assaying bacterial load post-infection in wild-type and mutant flies, we provide evidence that the Boms are required for resistance to, rather than tolerance of, infection. In addition, by generating and assaying a deletion of a smaller subset of the Bom genes, we find that there is overlap in Bom activity toward particular pathogens. Together, these studies deepen our understanding of Toll-mediated immunity and provide a new in vivo model for exploration of the innate immune effector repertoire.

Dedicated defense systems in the bodies of humans and other animals protect against dangerous microbes, such as bacteria and fungi. We study these processes in the fruit fly Drosophila, which can be readily grown and manipulated in the laboratory. In this animal, as in humans, protective activities are triggered when fragments of bacteria or fungi activate a system for defense gene regulation known as the Toll signaling pathway. The result is the large-scale production of defense molecules and, in many cases, clearance of the infection and survival of the animal. Although the systems for recognizing and initiating responses are well described, the role of many defense molecules is not understood. We have identified a group of closely related defense molecules in flies and used state-of-the-art genomic engineering to simultaneously eliminate most of the genes in the group. By comparing the effect of fungal or bacterial infection on the genetically altered flies and normal siblings, we find that this group of defense molecules is essential for disease resistance.

Force nanoscopy of hydrophobic interactions in the fungal pathogen Candida glabrata

Candida glabrata is an opportunistic human fungal pathogen which binds to surfaces mainly through the Epa family of cell adhesion proteins. While some Epa proteins mediate specific lectin-like interactions with human epithelial cells, others promote adhesion and biofilm formation on plastic surfaces via nonspecific interactions that are not yet elucidated. We report the measurement of hydrophobic forces engaged in Epa6-mediated cell adhesion by means of atomic force microscopy (AFM). Using single-cell force spectroscopy, we found that C. glabrata wild-type (WT) cells attach to hydrophobic surfaces via strongly adhesive macromolecular bonds, while mutant cells impaired in Epa6 expression are weakly adhesive. Nanoscale mapping of yeast cells using AFM tips functionalized with hydrophobic groups shows that Epa6 is massively exposed on WT cells and conveys strong hydrophobic properties to the cell surface. Our results demonstrate that Epa6 mediates strong hydrophobic interactions, thereby providing a molecular basis for the ability of this adhesin to drive biofilm formation on abiotic surfaces.

[Anti-attachment effect of ethyl acetate extract of Huanglian Jiedu decoction on Candida glabrata]

OBJECTIVE

To investigate anti-attachment effect of ethyl acetate extract of Huanglian Jiedu decoction (EAHD) on Candida glabrata.

METHOD

Serial 2-fold dilution assay was used to determine the minimum inhibitory concentrations MICs of EAHD to C. glabrata. XTT assay was used to evaluate the effect of EAHD against adhesion of C. glabrata. Inverted microscope, scanning electron microscope (SEM) and fluorescein diacetate (FDA) staining were applied to observe the morphological changes of C. glabrata in adhesion. PCR was adopted to inspect the expression of attachment-related genes such as EPA1, EPA6 and EPA7.

RESULT

The MIC of EAHD and fluconazole to C. glabrata were 320 mg · L(-1) and 1 mg · L(-1) respectively. The total cells including budding cells decreased in a dose-dependent manner following EAHD treatment. The expressions of EPA1, EPA6 and EPA7 were downregulated dramatically after EAHD treatment.

CONCLUSION

EAHD could effectively inhibit adherence of C. glabrata.

Detection and quantification of fluconazole within Candida glabrata biofilms

Candida infections are often associated with biofilms and consequent high resistance to most common drugs (e.g. azoles). These resistance mechanisms are not only associated with the biofilm yeast physiology, but also with the presence of a diffusional barrier imposed by the biofilm matrix; however, the real biochemical role of the biofilm components remains very unclear. So, in order to further clarify this issue, we intend to determine, for the first time, fluconazole in biofilms within both supernatants and matrices. Candida biofilms were formed in the presence of fluconazole, and it was recovered from both supernatant and matrix cell-free fractions. Then, high-pressure liquid chromatography was used to identify and quantify the amount of drug that was present in the two fractions. Moreover, this study also showed that the presence of fluconazole in both fractions indicated that the drug administrated did not completely reach the cells, so this phenomena can easily be associated with lower biofilm susceptibility, since the drug administered did not completely reach the cells.

Lab-scale preparations of Candida albicans and dual Candida albicans-Candida glabrata biofilms on the surface of medical-grade polyvinyl chloride (PVC) perfusion tube using a modified gravity-supported free-flow biofilm incubator (GS-FFBI)

The assembly of a man-made gravity-supported free-flow biofilm incubator (GS-FFBI) was described, which was composed of a gas cushion injector and four incubators. The GS-FFBI had the characteristics of (i) a bottom-up flow direction, and (ii) lab-scale biofilm preparation without the use of a multichannel pump. Two opportunistic fungal strains, namely Candida albicans and Candida glabrata, were employed to incubate C. albicans and dual C. albicans-C. glabrata biofilms on the surface of medical-grade polyvinyl chloride perfusion tube. In terms of the results from {2, 3-bis (2-methoxy-4-nitro-5-sulfo-phenyl)-2H-tetrazolium-5-carboxanilide} (XTT) assay, dry weight measurement, colony-forming unit counting, susceptibility test, and scanning electron microscopy, it was demonstrated that GS-FFBI could form both stable single and dual Candida biofilms with no significant variations among the four incubators or the three daily incubations within 21h, and could operate for at least 96h smoothly with no contamination of stock medium. The results also indicated, for the first time, that C. albicans and C. glabrata might be co-existent competitively and symbiotically in the dual biofilms with flowing media. GS-FFBI would be a useful device to study in vitro morphological and physiological features of microbial biofilms in the medical settings.

β-Glucan induces reactive oxygen species production in human neutrophils to improve the killing of Candida albicans and Candida glabrata isolates from vulvovaginal candidiasis

Vulvovaginal candidiasis (VVC) is among the most prevalent vaginal diseases. Candida albicans is still the most prevalent species associated with this pathology, however, the prevalence of other Candida species, such as C. glabrata, is increasing. The pathogenesis of these infections has been intensely studied, nevertheless, no consensus has been reached on the pathogenicity of VVC. In addition, inappropriate treatment or the presence of resistant strains can lead to RVVC (vulvovaginal candidiasis recurrent). Immunomodulation therapy studies have become increasingly promising, including with the β-glucans. Thus, in the present study, we evaluated microbicidal activity, phagocytosis, intracellular oxidant species production, oxygen consumption, myeloperoxidase (MPO) activity, and the release of tumor necrosis factor α (TNF-α), interleukin-8 (IL-8), IL-1β, and IL-1Ra in neutrophils previously treated or not with β-glucan. In all of the assays, human neutrophils were challenged with C. albicans and C. glabrata isolated from vulvovaginal candidiasis. β-glucan significantly increased oxidant species production, suggesting that β-glucan may be an efficient immunomodulator that triggers an increase in the microbicidal response of neutrophils for both of the species isolated from vulvovaginal candidiasis. The effects of β-glucan appeared to be mainly related to the activation of reactive oxygen species and modulation of cytokine release.

In vitro evaluation of adherence of Candida albicans, Candida glabrata, and Streptococcus mutans to an acrylic resin modified by experimental coatings

This study evaluated the effect of experimental coatings, containing zwitterion or hydrophilic monomers, on the adherence of Candida albicans, Candida glabrata, and Streptococcus mutans to an acrylic resin. Acrylic samples (smooth or rough surfaces) were left untreated (control) or coated with one of the following experimental coatings: 3-hydroxypropylmethacrylate (HP) or sulfobetaine methacrylate (S), at concentrations of 25, 30, or 35%. Half of the specimens were coated with saliva. The adhesion test was performed by incubating specimens in C. albicans, C. glabrata, and S. mutans suspensions at 37°C for 90 min. The number of adhered microorganisms was determined by metabolic activity (XTT) and by cell viability (CFU). All coated specimens exhibited lower absorbance and CFU values compared to control specimens. Saliva and roughness did not promote microorganism adherence. An XPS analysis confirmed the modification in the chemical composition of the coatings in the experimental samples. These experimental coatings significantly reduced the adherence of C. albicans, C. glabrata and S. mutans to acrylic resin.

Effects of fluconazole on Candida glabrata biofilms and its relationship with ABC transporter gene expression

Candida glabrata has emerged as the second most prevalent fungal pathogen and its ability to form biofilms has been considered one of the most important virulence factors, since biofilms present a high tolerance to antifungal agents used in fungal infection treatment. The mechanisms of biofilm tolerance to antifungal agents remain poorly understood. Thus, the aim of this study was to evaluate the effects of fluconazole (FLU) on the formation and control of C. glabrata biofilms and its relation with the expression of genes encoding for ABC transporters, CDR1, SNQ2, and PDR1. For that, minimal inhibitory concentration values for seven C. glabrata strains were determined and the effect of FLU against C. glabrata biofilms was evaluated by total biomass quantification and viable cell enumeration. Matrices from biofilms were analyzed in terms of protein, carbohydrate and DNA content. ABC transporter gene expression was analyzed for quantitative real-time PCR. In addition to the high amounts of proteins and carbohydrates detected in the extracellular matrices in the presence of FLU, this work showed that the overexpression of efflux pumps is a possible mechanism of biofilm tolerance to FLU and this phenomenon alters the structure of C. glabrata biofilms by creating cell clusters.

A mouse model for Candida glabrata hematogenous disseminated infection starting from the gut: evaluation of strains with different adhesion properties

Adhesion to digestive mucosa is considered a crucial first step in the pathogenicity of invasive Candida infections. Candida glabrata disseminated infections predominantly start from the gut. A mouse model of disseminated infection starting from the gut was set up. Hematogenous dissemination was obtained after a low-protein diet followed by a regimen of cyclophosphamide-methotrexate and an oral inoculation of the yeasts via the drinking water. The liver was the first organ infected (day 7 post-infection), and lethality was 100% at day 21 post-infection. This new mouse model was used to compare the mortality rate and fungal burden in deep organs induced by 5 strains exhibiting different levels of adhesion to enterocyte Caco-2 cells, as determined in a test on 36 C. glabrata strains. In this model, no statistical difference of lethality was demonstrated between the strains, and fungal burden varied in kidneys and lungs but without correlation with the level of adhesion to enterocytes. Further studies using the model developed here allow analysis of the crossing of the digestive mucosa by yeasts, and help relate this to yet-poorly understood adhesion phenotypes.

Histatin 5 resistance of Candida glabrata can be reversed by insertion of Candida albicans polyamine transporter-encoding genes DUR3 and DUR31

Candida albicans and Candida glabrata are predominant fungi associated with oral candidiasis. Histatin 5 (Hst 5) is a small cationic human salivary peptide with high fungicidal activity against C. albicans, however many strains of C. glabrata are resistant. Since Hst 5 requires fungal binding to cell wall components prior to intracellular translocation, reduced Hst 5 binding to C. glabrata may be the reason for its insensitivity. C. glabrata has higher surface levels of β-1,3-glucans as compared with C. albicans; however these differences did not account for reduced Hst 5 uptake and killing in C. glabrata. Similarly, the biofilm matrix of C. glabrata contained significantly higher levels of β-1,3-glucans compared with C. albicans, but it did not reduce the percentage of Hst 5 positive fungal cells in the biofilm. Hst 5 enters C. albicans cell through polyamine transporters Dur3p and Dur31p that are uncharacterized in C. glabrata. C. glabrata strains expressing CaDur3 and CaDur31 had two-fold higher killing and uptake of Hst 5. Thus, neither C. glabrata cell surface or biofilm matrix β-1,3-glucan levels affected Hst 5 toxicity; rather the crucial rate limiting step is reduced uptake that can be overcome by expression of C. albicans Dur proteins in C. glabrata.

Detailed comparison of Candida albicans and Candida glabrata biofilms under different conditions and their susceptibility to caspofungin and anidulafungin

Candida biofilm development can be influenced by diverse factors such as substrate, culture medium, carbohydrate source and pH. We have analysed biofilm formation of Candida albicans SC5314 and Candida glabrata ATCC 2001 wild-type strains in the presence of different media (RPMI 1640 versus YNB) and using different pH values (pH 5.6 or 7.0). We determined adhesion and biofilm formation on polystyrene, changes in the expression of adhesin genes during these processes and the susceptibility of mature biofilms to echinocandins. Biofilms formed on polystyrene by both Candida species proved to be influenced strongly by the composition of the medium rather than pH. C. albicans and C. glabrata formed thicker biofilms in RPMI 1640 medium, whereas in YNB medium, both species manifested adhesion rather than characteristic multilayer biofilm architecture. The stimulated biofilm formation in RPMI 1640 medium at pH 7.0 corroborated positively with increased expression of adhesin genes, essential to biofilm formation in vitro, including ALS3 and EAP1 in C. albicans and EPA6 in C. glabrata. The thicker biofilms grown in RPMI 1640 medium were more tolerant to caspofungin and anidulafungin than YNB-grown biofilms. We also observed that mature C. glabrata biofilms were less susceptible in RPMI 1640 medium to echinocandins than C. albicans biofilms. Environmental conditions, i.e. medium and pH, can significantly affect not only biofilm architecture, but also the expression profile of several genes involved during the different stages of biofilm development. In addition, growth conditions may also influence the antifungal-susceptibility profile of fungal populations within biofilm structures. Therefore, before designing any experimental biofilm set-up, it is important to consider the potential influence of external environmental factors on Candida biofilm development.

[Physiological characteristics of a low-pH tolerant strain Torulopsis glabrata RT-6]

OBJECTIVE

With the aim of elucidating the physiological characteristics of a low-pH tolerant strain Torulopsis glabrata RT-6.

METHODS

The intracellular pH, ATP level, the membrane bound H(+)-ATPase activity, the membrane fatty acid composition and the intracellular polyphosphate content of the parent strain CCTCC M202019 and the mutant strain RT-6 were determined and compared under different pH conditions.

RESULTS

Compared to that of the parent strain, the cell growth and pyruvate concentration of the mutant strain RT-6 were increased by 60.6% and 85.4% (56 h), respectively. Similarly, the strain RT-6 had higher intracellular pH compared to the control strain at external pH5.0, 4.5, and 4.0. The ATP content, the membrane bound H(+)-ATPase activity and the intracellular polyphosphate content of the mutant strain RT-6 were increased by 11.7%, 13.6%, and 3.5% at external pH 5.5, while at external pH 4.0, increased by 61%, 38.6%, and 30.8%, respectively. Furthermore, the mutant strain RT-6 exhibited higher content of the unsaturated fatty acids and higher membrane fluidity.

CONCLUSION

Discharging more intracellular H+ and inhibiting the intracellular H+ production contributed to the strain RT-6's higher intracellular pH, and therefore the acid tolerance.

Scanning and negative-staining electron microscopy of protoplast regeneration of a wild-type and two chitin synthase mutants in the pathogenic yeast Candida glabrata

Protoplast regeneration of a wild-type and two mutant strains of Candida glabrata defective in CHS3 homologues encoding class IV chitin synthase in Saccharomyces cerevisiae was examined by scanning and negative-staining electron microscopy. In the wild-type strain, small particles and short filaments appeared on the protoplast surface at 10 min, filamentous materials covered the entire surface of the protoplast at 1 h, granular materials started filling interspaces of filamentous materials at 2 h and regeneration was completed at 6 h. The filamentous materials consisted of microfibrils of various widths ranging from ≤5 to 40 nm, and composed of β-glucan. Protoplasts of the two chitin synthase mutant strains of Δchs3A and Δchs3B completed regeneration essentially by the same process as wild-type strain, although it took more time. These results suggest that CHS3A and CHS3B genes may have important roles in cell wall formation during protoplast regeneration, but can be compensated by other cell wall enzymes.

In vitro evaluation of antibiotic lock technique for the treatment of Candida albicans, C. glabrata, and C. tropicalis biofilms

Candidaemia associated with intravascular catheter-associated infections is of great concern due to the resulting high morbidity and mortality. The antibiotic lock technique (ALT) was previously introduced to treat catheter-associated bacterial infections without removal of catheter. So far, the efficacy of ALT against Candida infections has not been rigorously evaluated. We investigated in vitro activity of ALT against Candida biofilms formed by C. albicans, C. glabrata, and C. tropicalis using five antifungal agents (caspofungin, amphotericin B, itraconazole, fluconazole, and voriconazole). The effectiveness of antifungal treatment was assayed by monitoring viable cell counts after exposure to 1 mg/mL solutions of each antibiotic. Fluconazole, itraconazole, and voriconazole eliminated detectable viability in the biofilms of all Candida species within 7, 10, and 14 days, respectively, while caspofungin and amphotericin B did not completely kill fungi in C. albicans and C. glabrata biofilms within 14 days. For C. tropicalis biofilm, caspofungin lock achieved eradication more rapidly than amphotericin B and three azoles. Our study suggests that azoles may be useful ALT agents in the treatment of catheter-related candidemia.

[Opportunistic pathogen Candida glabrata and the mechanisms of its resistance to antifungal drugs]

Treatment of not only bacterial but also fungal infections is currently a growing concern. A major reason is the acquisition of multidrug resistance in both prokaryotic and human cells. The multidrug resistance phenotype is a cellular response to the presence of cytotoxic substances in the environment. The basic mechanism of multidrug resistance is overexpression of the membrane proteins involved in the extrusion of toxic substances outside the cell. The resistance mechanism based on the efflux of inhibitors as a result of the overproduction of transport proteins was also observed in some plant and animal pathogens and human tumour cells. The phenomenon of multidrug resistance associated with an excessive and long-term use of antifungals, in particular of azole derivatives, was also confirmed in the yeast Candida glabrata which is becoming a growing concern for health care professionals. Reduced susceptibility to azole derivatives in particular, a high potential for adapting to stressors, and multiple mechanisms of resistance to structurally and functionally unrelated antifungal drugs make the species C. glabrata a potential threat to hospital patients.

Roles of calcineurin and Crz1 in antifungal susceptibility and virulence of Candida glabrata

A Candida glabrata calcineurin mutant exhibited increased susceptibility to both azole antifungal and cell wall-damaging agents and was also attenuated in virulence. Although a mutant lacking the downstream transcription factor Crz1 displayed a cell wall-associated phenotype intermediate to that of the calcineurin mutant and was modestly attenuated in virulence, it did not show increased azole susceptibility. These results suggest that calcineurin regulates both Crz1-dependent and -independent pathways depending on the type of stress.

The asexual yeast Candida glabrata maintains distinct a and alpha haploid mating types

The genome of the type strain of Candida glabrata (CBS138, ATCC 2001) contains homologs of most of the genes involved in mating in Saccharomyces cerevisiae, starting with the mating pheromone and receptor genes. Only haploid cells are ever isolated, but C. glabrata strains of both mating types are commonly found, the type strain being MAT alpha and most other strains, such as BG2, being MATa. No sexual cycle has been documented for this species. In order to understand which steps of the mating pathway are defective, we have analyzed the expression of homologs of some of the key genes involved as well as the production of mating pheromones and the organism's sensitivity to artificial pheromones. We show that cells of opposite mating types express both pheromone receptor genes and are insensitive to pheromones. Nonetheless, cells maintain specificity through regulation of the alpha1 and alpha2 genes and, more surprisingly, through differential splicing of the a1 transcript.

Attachment and entry of Candida famata in monocytes and epithelial cells

Candida albicans is considered the main pathogenic yeast responsible for a multitude of infective disorders. However, other yeasts, such as Candida famata, are being recognized as potential emerging pathogens that cause several types of infections in humans and animals. Consequently, we have investigated the adhesion and internalization of Candida famata into monocytes and epithelial cells. The interaction of the yeast with the cells is very rapid and takes place during the first 15 min of injection. However, the affinity of the yeast for the cells varies, THP-1 (human monocytes) being the highest and followed in decreasing order by HeLa (human carcinoma), HaCaT, and Pam-212 (human and mouse keratinocytes, respectively). Heat inactivation or treatment with nystatin, significantly decreases yeast adhesion to cells. Immunofluorescence, as well as scanning and transmission electron microscopy, reveals that cell lines are able to internalize C. famata. At 48 h after infection, most of the yeasts located inside cells appear degraded, but some yeasts recovered from lysed cells, were still viable. Adhesion and internalization of C. famata into HeLa cells were found to be lower than those of C. albicans and C. glabrata, but higher than those of S. cerevisiae. In addition, infection with C. famata results in actin microfilaments rearrangement. This article presents novel data in the interaction of this pathogenic yeast with mammalian cells.

In vitro biofilm formation of Candida albicans and non-albicans Candida species under dynamic and anaerobic conditions

An understanding of biofilm behavior of Candida species under different environmental conditions is key to the development of effective preventive measures for candidal infections. Hence in this study we assessed the impact of the environmental milieu on Candida biofilm formation using polystyrene, flat-bottomed 96-well microtiter plates. A total of 20, comprising 10 clinical isolates each of Candida albicans and, non-albicans species of Candida were compared for their biofilm forming ability both under aerobic and anaerobic conditions, and static and dynamic conditions. XTT reduction assay was used to quantify the sessile growth. Biofilm formation of all 10 C. albicans isolates differed significantly between dynamic and static states under both atmospheric conditions (P<0.05). For non-albicans Candida species, a significant difference in biofilm growth between dynamic and static states was noted only when incubated aerobically (P<0.05), and no significant difference in biofilm formation was noted between aerobic and anaerobic conditions. Scanning electron microscopy revealed that C. albicans produced a compact multilayered biofilm embedded in noticeably higher quantity of extracellular polymeric matrix in aerobic/dynamic conditions compared with anaerobic/static conditions. Our data indicate that biofilm formation of C. albicans and non-albicans Candida species is modulated by hydrodynamic conditions and ambient oxygen gradients. However, further work is required to fully elucidate how Candida biofilms persist within the oral milieu under such challenging ecological pressures.

Oral epithelium?Candida glabrata interactions in vitro

BACKGROUND

Oropharyngeal candidiasis is a common opportunistic infection and Candida glabrata is the second or third most frequently isolated species from oropharyngeal candidiasis lesions, after Candida albicans. The aim of this study was to study the cytokine-inducing and cell-damaging potential of C. glabrata in oral epithelial cells and compare this to C. albicans.

METHODS

Oral epithelial cell lines and primary gingival epithelial cells were cocultured with C. glabrata strains GDH2269 and 94-11 or C. albicans strains SC5314 and ATCC28366. Supernatants were analysed for the presence of interleukin-1alpha (IL-1alpha), IL-8 and granulocyte-macrophage colony-stimulating factor (GM-CSF) by enzyme-linked immunosorbent assay. The cytotoxity of different strains was determined using the CytoTox-96 assay.

RESULTS

Compared to C. albicans, C. glabrata induced different proinflammatory cytokine responses in oral epithelial cells; a high level of GM-CSF induction was only detected in C. glabrata-infected cells and not in C. albicans-infected cells, regardless of the origin of these cells (cell lines or primary cells) or the strain used. Like C. albicans, C. glabrata induced an IL-1alpha response by oral epithelial cells, but this response was both strain-dependent and epithelial cell origin-dependent. Unlike C. albicans, C. glabrata failed to induce a strong IL-8 response in any of the cell systems studied. Finally, in these studies C. glabrata showed lower cytotoxicity than C. albicans.

CONCLUSIONS

C. glabrata is less cytotoxic than C. albicans and induces different proinflammatory cytokine responses in oral epithelial cells.

Biology of the pathogenic yeast Candida glabrata

The yeasts, being favorite eukaryotic microorganisms used in food industry and biotechnologies for production of biomass and various substances, are also used as model organisms in genetic manipulation, molecular and biological research. In this respect, Saccharomyces cerevisiae is the best-known species but current situation in medicine and industry requires the use of other species. Here we summarize the basic taxonomic, morphological, physiological, genetic, etc. information about the pathogenic yeast Candida glabrata that is evolutionarily very closely related to baker's yeast.

The bZip transcription factor Cgap1p is involved in multidrug resistance and required for activation of multidrug transporter gene CgFLR1 in Candida glabrata

Transcriptional regulation in response to environmental challenges is crucial for survival of many organisms. In this study, we characterized structural and functional properties of CgAP1, a Saccharomyces cerevisiae YAP1 ortholog, which encodes a transcription factor involved in various stress responses. Deletion of CgAP1 led to decreased resistance to hydrogen peroxide, 4-nitroquinoline-N-oxide (4-NQO), benomyl, and cadmium chloride, which could be fully recovered by reintroduction of an intact CgAP1. CgAP1 was shown to function in S. cerevisiae as it restored the drug resistance of the yap1 mutant. Moreover, overexpression of CgAP1 in a S. cerevisiae wild-type strain increased its resistance to cycloheximide, 1,10-phenanthroline, 4-NQO, and fluconazole. Overexpression of CgAP1 also phenotypically suppressed the drug sensitivity of two Yap1p-regulated transporter mutants, Deltaatr1 and Deltaflr1, to diamide, 4-NQO, and cadmium. Northern blot analysis indicated that Cgap1p regulates the benomyl-induced expression of CgFLR1, a homolog of S. cerevisiae FLR1, which encodes a transporter of the major facilitator superfamily. In contrast to the S. cerevisiae flr1 mutant, deletion of CgFLR1 in C. glabrata only resulted in increased sensitivity to benomyl, diamide, and menadione, but not 4-NQO, cycloheximide, or fluconazole. Taken together, this report demonstrated that CgAP1 plays a critical role in response to various stresses in C. glabrata and reduces the stress through transcriptional activation of its target genes including CgFLR1.

Pdr1 regulates multidrug resistance in Candida glabrata: gene disruption and genome-wide expression studies

Candida glabrata emerged in the last decade as a common cause of mucosal and invasive fungal infection, in large part due to its intrinsic or acquired resistance to azole antifungals such as fluconazole. In C. glabrata clinical isolates, the predominant mechanism behind azole resistance is upregulated expression of multidrug transporter genes CDR1 and PDH1. We previously reported that azole-resistant mutants (MIC >or= 64 microg ml(-1)) of strain 66032 (MIC = 16 microg ml(-1)) similarly show coordinate CDR1-PDH1 upregulation, and in one of these (F15) a putative gain-of-function mutation was identified in the single homologue of Saccharomyces cerevisiae transcription factors Pdr1-Pdr3. Here we show that disruption of C. glabrata PDR1 conferred equivalent fluconazole hypersensitivity (MIC = 2 microg ml(-1)) to both F15 and 66032 and eliminated both constitutive and fluconazole-induced CDR1-PDH1 expression. Reintroduction of wild-type or F15 PDR1 fully reversed these effects; together these results demonstrate a role for this gene in both acquired and intrinsic azole resistance. CDR1 disruption had a partial effect, reducing fluconazole trailing in both strains while restoring wild-type susceptibility (MIC = 16 microg ml(-1)) to F15. In an azole-resistant clinical isolate, PDR1 disruption reduced azole MICs eight- to 64-fold with no effect on sensitivity to other antifungals. To extend this analysis, C. glabrata microarrays were generated and used to analyse genome-wide expression in F15 relative to its parent. Homologues of 10 S. cerevisiae genes previously shown to be Pdr1-Pdr3 targets were upregulated (YOR1, RTA1, RSB1, RPN4, YLR346c and YMR102c along with CDR1, PDH1 and PDR1 itself) or downregulated (PDR12); roles for these genes include small molecule transport and transcriptional regulation. However, expression of 99 additional genes was specifically altered in C. glabrata F15; their roles include transport (e.g. QDR2, YBT1), lipid metabolism (ATF2, ARE1), cell stress (HSP12, CTA1), DNA repair (YIM1, MEC3) and cell wall function (MKC7, MNT3). These azole resistance-associated changes could affect C. glabrata tissue-specific virulence; in support of this, we detected differences in F15 oxidant, alcohol and weak acid sensitivities. C. glabrata provides a promising model for studying the genetic basis of multidrug resistance and its impact on virulence.

Kre29p is a novel nuclear protein involved in DNA repair and mitotic fidelity in Candida glabrata

Candida glabrata KRE29 is an ortholog of Saccharomyces cerevisiae KRE29. S. cerevisiae Kre29p has been identified by affinity purification as a subunit of the Smc5-Smc6 complex, which is required for DNA repair and chromosome segregation. However, mutant phenotypes of S. cerevisiae KRE29 have not been well characterized and none of its orthologs' functions has been reported. Here we report phenotypic characteristics of a C. glabrata kre29 deletant. The absence of C. glabrata Kre29p resulted in decreased viability, exhibiting cell cycle arrest between late S-phase and metaphase even under normal growth conditions, and also caused an increase of plasmid loss rate, implying that Kre29p is required for mitotic chromosome transmission fidelity. The deletant showed increased sensitivity to high temperature as well as to DNA damaging agents including UV, gamma ray, 4-nitroquinoline-1-oxide and methyl methanesulfonate, and the phenotypes were restored in the KRE29 reintegrant. Consistent with the Deltakre29 phenotypes, a Kre29p-GFP fusion protein was located in the nucleus. Furthermore, Kre29p-GFP became concentrated and formed distinct foci after exposure to 4-nitroquinoline-1-oxide. These results suggest the involvement of C. glabrata Kre29p in DNA repair. To our knowledge, this is the first report addressing a cellular protein involved in DNA repair in C. glabrata.

Candida glabrata Ste11 is involved in adaptation to hypertonic stress, maintenance of wild-type levels of filamentation and plays a role in virulence

The conserved family of fungal Ste11 mitogen activated protein kinase/kinases play important roles in several signalling cascades. We have cloned the STE11 homologue from the fungal pathogen Candida glabrata. The C. glabrata gene is present in a single copy in the genome, contains a well-conserved catalytic domain typical of the serine-threonine protein kinases and a sterile alpha motif widespread in signalling and nuclear proteins. Hypothetical translation of C. glabrata STE11 suggests that the protein has 64% identity and 77% similarity at the amino acid level to Saccharomyces cerevisiae Ste11. We have shown that C. glabrata STE11 can complement the mating defect and partially rescue the reduced nitrogen starvation induced filamentation of S. cerevisiae ste11 mutants. Functional analysis of a C. glabrata ste11 null mutant demonstrates that Ste11 is required for adaptation to hypertonic stress but is largely dispensable for maintenance of cell wall integrity. It also plays a role in C. glabrata nitrogen starvation induced filamentation. Survival analysis revealed that C. glabrata ste11 mutants, while still able to cause disease, are attenuated for virulence compared to reconstituted, STE11 cells. These data suggest that C. glabrata Ste11, in a similar fashion to the S. cerevisiae protein, functions in a number of different signalling modules.

Candida glabrata Fungemia in Transplant Patients Receiving Voriconazole after Fluconazole

The clinical impact of voriconazole resistance in Candida glabrata is not well described. Five hematopoietic stem cell transplant recipients that developed breakthrough Candida glabrata bloodstream infections while receiving voriconazole are described and the clinical management and susceptibility profiles of their isolates are reported. All patients were markedly immunosuppressed, and in all cases, voriconazole use was preceded by prolonged fluconazole exposure (median 60 days); median voriconazole exposure prior to candidemia was 48 days. Isolates from 4 patients were shown to be resistant to fluconazole and itraconazole when tested in vitro; these same isolates had MICs to voriconazole and posaconazole > or = 2 microg/ml. Clinical failure to voriconazole may result from deficits in host defense, retained infected foci, and adaptation of the organism to environmental pressures, the specific sequence and mechanisms of which warrant further study. Clinicians must maintain a high index of suspicion for these infections in highly susceptible hosts despite voriconazole therapy, particularly when voriconazole use is preceded by prolonged fluconazole exposure.

Phenotypic switching in Candida glabrata accompanied by changes in expression of genes with deduced functions in copper detoxification and stress

Most strains of Candida glabrata switch spontaneously between a number of phenotypes distinguishable by graded brown coloration on agar containing 1 mM CuSO4, a phenomenon referred to as "core switching." C. glabrata also switches spontaneously and reversibly from core phenotypes to an irregular wrinkle (IWr) phenotype, a phenomenon referred to as "irregular wrinkle switching." To identify genes differentially expressed in the core phenotypes white (Wh) and dark brown (DB), a cDNA subtraction strategy was employed. Twenty-three genes were identified as up-regulated in DB, four in Wh, and six in IWr. Up-regulation was verified in two unrelated strains, one a and one alpha strain. The functions of these genes were deduced from the functions of their Saccharomyces cerevisiae orthologs. The majority of genes up-regulated in DB (78%) played deduced roles in copper assimilation, sulfur assimilation, and stress responses. These genes were differentially up-regulated in DB even though the conditions of growth for Wh and DB, including CuSO4 concentration, were identical. Hence, the regulation of these genes, normally regulated by environmental cues, has been usurped by switching, presumably as an adaptation to the challenging host environment. These results are consistent with the suggestion that switching provides colonizing populations with a minority of cells expressing a phenotype that allows them to enrich in response to an environmental challenge, a form of rapid adaptation. However, DB is the most commonly expressed phenotype at sites of host colonization, in the apparent absence of elevated copper levels. Hence, up-regulation of these genes by switching suggests that in some cases they may play roles in colonization and virulence not immediately obvious from the roles played by their orthologs in S. cerevisiae.

The Yak1p kinase controls expression of adhesins and biofilm formation in Candida glabrata in a Sir4p-dependent pathway

Biofilm is the predominant type of microbial development in natural environments, and potentially represents a major form of resistance or source of recurrence during host infection. Although a large number of studies have focussed on the genetics of bacterial biofilm formation, very little is known about the genes involved in this type of growth in fungi. A genetic screen for Candida glabrata Biofilm mutants was performed using a 96-well plate model of biofilm formation. Study of the isolated mutant strains allowed the identification of four genes involved in biofilm formation (RIF1, SIR4, EPA6 and YAK1). Epa6p is a newly identified adhesin required for biofilm formation in this pathogenic yeast. EPA6 and its close paralogue EPA7 are located in subtelomeric regions and their transcription is regulated by Sir4p and Rif1p, two proteins involved in subtelomeric silencing. Biofilm growth conditions induce the transcription of EPA6 and EPA7: this is dependent on the presence of an intact subtelomeric silencing machinery and is independent of the Mpk1p signalling pathway. Finally, the kinase Yak1p is required for expression of both adhesin genes and acts through a subtelomeric silencing machinery-dependent pathway.

Nicotinic acid limitation regulates silencing of Candida adhesins during UTI

The adherence of Candida glabrata to host cells is mediated, at least in part, by the EPA genes, a family of adhesins encoded at subtelomeric loci, where they are subject to transcriptional silencing. We show that normally silent EPA genes are expressed during murine urinary tract infection (UTI) and that the inducing signal is the limitation of nicotinic acid (NA), a precursor of nicotinamide adenine dinucleotide (NAD+). C. glabrata is an NA auxotroph, and NA-induced EPA expression is likely the result of a reduction in NAD+ availability for the NAD+-dependent histone deacetylase Sir2p. The adaptation of C. glabrata to the host, therefore, involves a loss of metabolic capacity and exploitation of the resulting auxotrophy to signal a particular host environment.

Breakthrough Fungal Infections in Stem Cell Transplant Recipients Receiving Voriconazole

Infection with voriconazole-resistant fungi may become problematic, because organisms with decreased susceptibility have been noted. Breakthrough fungal infections occurred in 13 of 139 patients who received voriconazole at our center during the period of September 1998 through September 2003. Zygomycetes were found in 6 patients, and Candida glabrata bloodstream infection occurred in 4 patients. Minimal inhibitory concentrations were > or =1 microg/mL for all available isolates. Yeasts and molds with decreased susceptibility to voriconazole may cause invasive infection in patients treated successfully for aspergillosis.

Interactions of Candida albicans with other Candida spp. and bacteria in the biofilms

AIMS

To study the interactions between Candida albicans and 12 other species of Candida and bacteria in biofilms.

METHODS AND RESULTS

The number of cells within growing biofilms in a polystyrene tube model was measured after adding C. albicans to preformed biofilms of other micro-organisms and vice versa. It was also measured after simultaneous biofilm formation of C. albicans and other micro-organisms. The number of cells of C. albicans within the growing biofilms decreased significantly (P < 0.05) when the fungus was added to preformed biofilms of Candida spp. and bacteria except, with C. parapsilosis, Torulopsis glabrata and the glycocalyx producer Pseudomonas aeruginosa. When C. parapsilosis, Staphylococcus epidermidis (nonglycocalyx producer) or Serratia marcescens was added to preformed biofilms of C. albicans, the number of cells of these micro-organisms increased in the growing biofilms.

CONCLUSIONS

Biofilms of C. albicans are capable of holding other micro-organisms and more likely to be heterogeneous with other bacteria and fungi in the environment and on medical devices.

SIGNIFICANCE AND IMPACT OF THE STUDY

Recognition of the heterogeneity of biofilm-associated organisms can influence treatment decisions, particularly in patients who do not respond to initial appropriate therapy.

Candida glabrata Ste20 is involved in maintaining cell wall integrity and adaptation to hypertonic stress, and is required for wild-type levels of virulence

The conserved family of fungal Ste20 p21-activated serine-threonine protein kinases regulate several signalling cascades. In Saccharomyces cerevisiae Ste20 is involved in pheromone signalling, invasive growth, the hypertonic stress response, cell wall integrity and binds Cdc42, a Rho-like small GTP-binding protein required for polarized morphogenesis. We have cloned the STE20 homologue from the fungal pathogen Candida glabrata and have shown that it is present in a single copy in the genome. Translation of the nucleotide sequence predicts that C. glabrata Ste20 contains a highly conserved p21-activated serine-threonine protein kinase domain, a binding site for G-protein beta subunits and a regulatory Rho-binding domain that enables the kinase to interact with Cdc42 and/or Rho-like small GTPases. C. glabrata Ste20 has 53% identity and 58% predicted amino acid similarity to S. cerevisiae Ste20 and can complement both the nitrogen starvation-induced filamentation and mating defects of S. cerevisiae ste20 mutants. Analysis of ste20 null and disrupted strains suggest that in C. glabrata Ste20 is required for a fully functional hypertonic stress response and intact cell wall integrity pathway. C. glabrata Ste20 is not required for nitrogen starvation-induced filamentation. Survival analysis revealed that C. glabrata ste20 mutants, while still able to cause disease, are mildly attenuated for virulence compared to reconstituted STE20 cells.