Gastrointestinal colonization and systemic dissemination by Candida albicans and Candida tropicalis in intact and immunocompromised mice

Perspective on receptor-associated immune response to Candida albicans single and mixed infections: Implications for therapeutics in oropharyngeal candidiasis

Oropharyngeal candidiasis (OPC), commonly known as 'thrush', is an oral infection that usually dismantles oral mucosal integrity and malfunctions local innate and adaptive immunities in compromised individuals. The major pathogen responsible for the occurrence and progression of OPC is the dimorphic opportunistic commensal Candida albicans. However, the incidence induced by non-albicans Candida species including C. glabrata, C. tropicalis, C. dubliniensis, C. parapsilosis, and C. krusei are increasing in company with several oral bacteria, such as Streptococcus mutans, S. gordonii, S. epidermidis, and S. aureus. In this review, the microbiological and infection features of C. albicans and its co-contributors in the pathogenesis of OPC are outlined. Since the invasion and concomitant immune response lie firstly on the recognition of oral pathogens through diverse cellular surface receptors, we subsequently emphasize the roles of epidermal growth factor receptor, ephrin-type receptor 2, human epidermal growth factor receptor 2, and aryl hydrocarbon receptor located on oral epithelial cells to delineate the underlying mechanism by which host immune recognition to oral pathogens is mediated. Based on these observations, the therapeutic approaches to OPC comprising conventional and non-conventional antifungal agents, fungal vaccines, cytokine and antibody therapies, and antimicrobial peptide therapy are finally overviewed. In the face of newly emerging life-threatening microbes (C. auris and SARS-CoV-2), risks (biofilm formation and interconnected translocation among diverse organs), and complicated clinical settings (HIV and oropharyngeal cancer), the research on OPC is still a challenging task.

Biofilm-formation capability depends on environmental oxygen concentrations in Candida species

BACKGROUND

Although oxygen concentrations inside of the human body vary depending on organs or tissues, few reports describe the relationships between biofilm formation of Candida species and oxygen concentrations. In this study, we investigated the biofilm-forming capabilities of Candida species under various oxygen conditions.

METHODS

We evaluated the adhesion and biofilm formation of Candida albicans and C. tropicalis under aerobic, microaerobic (oxygen concentration 5%), or anaerobic conditions. We also examined how oxygen concentration affects adhesion/maturation by changing adhesion/maturation phase conditions. We used crystal violet assay to estimate the approximate biofilm size, performed microscopic observation of biofilm morphology, and evaluated adhesion-associated gene expression.

RESULTS

The adhered amount was relatively small except for a clinical strain of C. tropicalis. Our biofilm-formation analysis showed that C. albicans formed a higher-size biofilm under aerobic conditions, while C. tropicalis favored microaerobic conditions to form mature biofilms. Our microscopic observations were consistent with these biofilm-formation analysis results. In particular, C. tropicalis exhibited more hyphal formation under microaerobic conditions. By changing the adhesion/maturation phase conditions, we represented that C. albicans had favorable biofilm-formation capability under aerobic conditions, while C. tropicalis showed enhanced biofilm formation under microaerobic adhesion conditions. In good agreement with these results, the C. tropicalis adhesion-associated gene expression tended to be higher under microaerobic or anaerobic conditions.

CONCLUSIONS

C. albicans favored aerobic conditions to form biofilms, whereas C. tropicalis showed higher biofilm-formation ability and promoted hyphal growth under microaerobic conditions. These results indicate that favorable oxygen conditions significantly differ for each Candida species.

Comparative Analysis of the Fitness of Candida albicans Strains During Colonization of the Mice Gastrointestinal Tract

Candida albicans populations present in the mammalian gastrointestinal tract are a major source of candidemia and subsequent severe invasive candidiasis in those individuals with acquired or congenital immune defects. Understanding the mechanisms used by this fungus to colonize this niche is, therefore, of primary importance to develop new therapeutic options that could lead to control its proliferation in the host. The recent popularization of models of commensalism in mice combined with the already powerful tools in C. albicans genetics allows to analyze the role of specific genes during colonization. Fitness can be analyzed for a specific C. albicans strain (test strain) by comparing its growth in vivo with an otherwise isogenic control strain via the analysis of the luminal content of the mouse gastrointestinal tract using flow cytometry, qPCR, or viable fungal cell counting. While all these procedures have limitations, they can be used to estimate the degree of adaptation of the test strain to the mammalian tract by determining its relative abundance with an internal control strain. By using specific genetically engineered C. albicans and mouse strains, antibiotic regimes, or even germ-free mice, this methodology allows to determine the role of the host immunological status, the bacterial microbiota, or individual fungal features (e.g., dimorphism) in the process of colonization of C. albicans of the mammalian gut.

Characterization of the Effects of Candida Gastrointestinal Colonization on Clostridioides difficile Infection in a Murine Model

The role of fungal colonizers of the gastrointestinal tract during disease states is not well understood. Antibiotic treatment renders patients highly susceptible to infection by the bacterial pathogen C. difficile while also leading to blooms in fungal commensals, setting the stage for trans-kingdom interactions. Here, we describe a murine model of Candida gastrointestinal colonization coupled to a C. difficile infection (CDI) model, the measurement of CFU of both organisms, and collection of cecum and colon contents for the purpose of quantifying C. difficile toxin production. Additionally, we describe how to induce and purify C. difficile spores.

Candida albicans Isolates 529L and CHN1 Exhibit Stable Colonization of the Murine Gastrointestinal Tract

Candida albicans is a pathobiont that colonizes multiple niches in the body including the gastrointestinal (GI) tract but is also responsible for both mucosal and systemic infections. Despite its prevalence as a human commensal, the murine GI tract is generally refractory to colonization with the C. albicans reference isolate SC5314. Here, we identify two C. albicans isolates, 529L and CHN1, that stably colonize the murine GI tract in three different animal facilities under conditions where SC5314 is lost from this niche. Analysis of the bacterial microbiota did not show notable differences among mice colonized with the three C. albicans strains. We compared the genotypes and phenotypes of these three strains and identified thousands of single nucleotide polymorphisms (SNPs) and multiple phenotypic differences, including their ability to grow and filament in response to nutritional cues. Despite striking filamentation differences under laboratory conditions, however, analysis of cell morphology in the GI tract revealed that the three isolates exhibited similar filamentation properties in this in vivo niche. Notably, we found that SC5314 is more sensitive to the antimicrobial peptide CRAMP, and the use of CRAMP-deficient mice modestly increased the ability of SC5314 to colonize the GI tract relative to CHN1 and 529L. These studies provide new insights into how strain-specific differences impact C. albicans traits in the host and advance CHN1 and 529L as relevant strains to study C. albicans pathobiology in its natural host niche. IMPORTANCE Understanding how fungi colonize the GI tract is increasingly recognized as highly relevant to human health. The animal models used to study Candida albicans commensalism commonly rely on altering the host microbiome (via antibiotic treatment or defined diets) to establish successful GI colonization by the C. albicans reference isolate SC5314. Here, we characterize two C. albicans isolates that can colonize the murine GI tract without antibiotic treatment and can therefore be used as tools for studying fungal commensalism. Importantly, experiments were replicated in three different animal facilities and utilized three different mouse strains. Differential colonization between fungal isolates was not associated with alterations in the bacterial microbiome but rather with distinct responses to CRAMP, a host antimicrobial peptide. This work emphasizes the importance of C. albicans intraspecies variation as well as host antimicrobial defense mechanisms in defining the outcome of commensal interactions.

Interplay between Candida albicans and Lactic Acid Bacteria in the Gastrointestinal Tract: Impact on Colonization Resistance, Microbial Carriage, Opportunistic Infection, and Host Immunity

Emerging studies have highlighted the disproportionate role of Candida albicans in influencing both early community assembly of the bacterial microbiome and dysbiosis during allergic diseases and intestinal inflammation. Nonpathogenic colonization of the human gastrointestinal (GI) tract by C. albicans is common, and the role of this single fungal species in modulating bacterial community reassembly after broad-spectrum antibiotics can be readily recapitulated in mouse studies. One of the most notable features of C. albicans-associated dysbiotic states is a marked change in the levels of lactic acid bacteria (LAB). C. albicans and LAB share metabolic niches throughout the GI tract, and in vitro studies have identified various interactions between these microbes. The two predominant LAB affected are Lactobacillus species and Enterococcus species. Lactobacilli can antagonize enterococci and C. albicans, while Enterococcus faecalis and C. albicans have been reported to exhibit a mutualistic relationship. E. faecalis and C. albicans are also causative agents of a variety of life-threatening infections, are frequently isolated together from mixed-species infections, and share certain similarities in clinical presentation-most notably their emergence as opportunistic pathogens following disruption of the microbiota. In this review, we discuss and model the mechanisms used by Lactobacillus species, E. faecalis, and C. albicans to modulate each other's growth and virulence in the GI tract. With multidrug-resistant E. faecalis and C. albicans strains becoming increasingly common in hospital settings, examining the interplay between these three microbes may provide novel insights for enhancing the efficacy of existing antimicrobial therapies.

N-acetylglucosamine-mediated morphological transition in Candida albicans and Candida tropicalis

Morphological transitions in Candida species are key factors in facilitating invasion and adapting to environmental changes. N-acetylglucosamine (GlcNAc) is a monosaccharide signalling molecule that can regulate morphological transitions in Candida albicans and Candida tropicalis. Interestingly, although the uptake and metabolic pathways of GlcNAc and GlcNAc-mediated white-to-opaque cell switching are similar between the two Candida species, GlcNAc induces hyphal development in C. albicans, whereas it suppresses hyphal development in C. tropicalis. These findings indicate that the characteristics of C. albicans and C. tropicalis in response to GlcNAc are remarkably different. Here, we compare the conserved and divergent GlcNAc-mediated signalling pathways and catabolism between the two Candida species. Deletion of NGT1, a GlcNAc transportation gene, inhibited hyphal formation in C. albicans but promoted hyphal development in C. tropicalis. To further understand these opposite effects on filamentous growth in response to GlcNAc in the two Candida species, the cyclic adenosine monophosphate/protein kinase A (cAMP/PKA) signalling pathways in both C. albicans and C. tropicalis were compared. Interestingly, GlcNAc activated the cAMP/PKA signalling pathway of the two Candida species, suggesting that the hyphal development-regulated circuit is remarkably diverse between the two species. Indeed, the Ndt80-like gene REP1, which is critical for regulating GlcNAc catabolism, exhibits distinct roles in the hyphal development of C. albicans and C. tropicalis. These data suggest possible reasons for the divergent hyphal growth response in C. albicans and C. tropicalis upon GlcNAc induction.

Mycobiome in the Gut: A Multiperspective Review

Human gut is home to a diverse and complex microbial ecosystem encompassing bacteria, viruses, parasites, fungi, and other microorganisms that have an undisputable role in maintaining good health for the host. Studies on the interplay between microbiota in the gut and various human diseases remain the key focus among many researchers. Nevertheless, advances in sequencing technologies and computational biology have helped us to identify a diversity of fungal community that reside in the gut known as the mycobiome. Although studies on gut mycobiome are still in its infancy, numerous sources have reported its potential role in host homeostasis and disease development. Nonetheless, the actual mechanism of its involvement remains largely unknown and underexplored. Thus, in this review, we attempt to discuss the recent advances in gut mycobiome research from multiple perspectives. This includes understanding the composition of fungal communities in the gut and the involvement of gut mycobiome in host immunity and gut-brain axis. Further, we also discuss on multibiome interactions in the gut with emphasis on fungi-bacteria interaction and the influence of diet in shaping gut mycobiome composition. This review also highlights the relation between fungal metabolites and gut mycobiota in human homeostasis and the role of gut mycobiome in various human diseases. This multiperspective review on gut mycobiome could perhaps shed new light for future studies in the mycobiome research area.

Virulence assessment of six major pathogenic Candida species in the mouse model of invasive candidiasis caused by fungal translocation

Gastrointestinal colonization has been considered as the primary source of candidaemia; however, few established mouse models are available that mimic this infection route. We therefore developed a reproducible mouse model of invasive candidiasis initiated by fungal translocation and compared the virulence of six major pathogenic Candida species. The mice were fed a low-protein diet and then inoculated intragastrically with Candida cells. Oral antibiotics and cyclophosphamide were then administered to facilitate colonization and subsequent dissemination of Candida cells. Mice infected with Candida albicans and Candida tropicalis exhibited higher mortality than mice infected with the other four species. Among the less virulent species, stool titres of Candida glabrata and Candida parapsilosis were higher than those of Candida krusei and Candida guilliermondii. The fungal burdens of C. parapsilosis and C. krusei in the livers and kidneys were significantly greater than those of C. guilliermondii. Histopathologically, C. albicans demonstrated the highest pathogenicity to invade into gut mucosa and liver tissues causing marked necrosis. Overall, this model allowed analysis of the virulence traits of Candida strains in individual mice including colonization in the gut, penetration into intestinal mucosa, invasion into blood vessels, and the subsequent dissemination leading to lethal infections.

Review article: fungal alterations in inflammatory bowel diseases

BACKGROUND

Emerging data suggest that alterations in gut fungi may be associated with the pathogenesis of inflammatory bowel disease (IBD). In healthy individuals, gut commensal fungi act synergistically with other members of the microbiota to maintain homeostasis but their role in IBD is less clear.

AIM

To review the role of gut fungi and their trans-kingdom interactions with bacteria in IBD METHODS: A literature search was conducted on Ovid and Pubmed to select relevant animal and human studies that have reported fungi and IBD.

RESULTS

There is an increased total fungal load particularly of Candida and Malassezia species in the faeces and mucosa of Crohn's disease patients, and a lower fungal diversity in the faeces of ulcerative colitis patients. Caspase recruitment domain-containing protein (CARD)-9 polymorphism in Crohn's disease patients favours Malassezia colonisation that worsens gut inflammation. Diet high in carbohydrates increased the total abundance of Candida species, whereas protein-rich diet had the opposite effect. Anti-fungal therapies are mostly used to treat Candida albicans or Histoplasma capsulatum infections in IBD, whereas pilot studies of supplementing fungal probiotics Saccharomycopsis fibuligera, Saccharomyces boulardii and Saccharomyces cerevisiae CNCM I-3856 strain showed therapeutic effects in IBD.

CONCLUSIONS

Gut fungi are altered in patients with Crohn's disease and ulcerative colitis. Modulation of the fungal microbiota can be considered as a therapeutic approach for IBD. Future research should focus on understanding how the fungal microbiota interacts with other components of the gut microbiota in association with the pathogenesis and development of IBD.

HumanMycobiomeScan: a new bioinformatics tool for the characterization of the fungal fraction in metagenomic samples

Background

Modern metagenomic analysis of complex microbial communities produces large amounts of sequence data containing information on the microbiome in terms of bacterial, archaeal, viral and eukaryotic composition. The bioinformatics tools available are mainly devoted to profiling the bacterial and viral fractions and only a few software packages consider fungi. As the human fungal microbiome (human mycobiome) can play an important role in the onset and progression of diseases, a comprehensive description of host-microbiota interactions cannot ignore this component.

Results

HumanMycobiomeScan is a bioinformatics tool for the taxonomic profiling of the mycobiome directly from raw data of next-generation sequencing. The tool uses hierarchical databases of fungi in order to unambiguously assign reads to fungal species more accurately and > 10,000 times faster than other comparable approaches. HumanMycobiomeScan was validated using in silico generated synthetic communities and then applied to metagenomic data, to characterize the intestinal fungal components in subjects adhering to different subsistence strategies.

Conclusions

Although blind to unknown species, HumanMycobiomeScan allows the characterization of the fungal fraction of complex microbial ecosystems with good performance in terms of sample denoising from reads belonging to other microorganisms. HumanMycobiomeScan is most appropriate for well-studied microbiomes, for which most of the fungal species have been fully sequenced. This released version is functionally implemented to work with human-associated microbiota samples. In combination with other microbial profiling tools, HumanMycobiomeScan is a frugal and efficient tool for comprehensive characterization of microbial ecosystems through shotgun metagenomics sequencing.

Electronic supplementary material

The online version of this article (10.1186/s12864-019-5883-y) contains supplementary material, which is available to authorized users.

Microglia and amyloid precursor protein coordinate control of transient Candida cerebritis with memory deficits

Bloodborne infections with Candida albicans are an increasingly recognized complication of modern medicine. Here, we present a mouse model of low-grade candidemia to determine the effect of disseminated infection on cerebral function and relevant immune determinants. We show that intravenous injection of 25,000 C. albicans cells causes a highly localized cerebritis marked by the accumulation of activated microglial and astroglial cells around yeast aggregates, forming fungal-induced glial granulomas. Amyloid precursor protein accumulates within the periphery of these granulomas, while cleaved amyloid beta (Aβ) peptides accumulate around the yeast cells. CNS-localized C. albicans further activate the transcription factor NF-κB and induce production of interleukin-1β (IL-1β), IL-6, and tumor necrosis factor (TNF), and Aβ peptides enhance both phagocytic and antifungal activity from BV-2 cells. Mice infected with C. albicans display mild memory impairment that resolves with fungal clearance. Our results warrant additional studies to understand the effect of chronic cerebritis on cognitive and immune function.

The potential links between infections and neurodegenerative disorders are unclear. Here, Wu et al. present a mouse model of low-grade candidemia characterized by highly localized cerebritis, accumulation of amyloid precursor protein and beta peptides, and mild memory impairment that resolves with fungal clearance.

Forgotten fungi-the gut mycobiome in human health and disease

The human body is home to a complex and diverse microbial ecosystem that plays a central role in host health. This includes a diversity of fungal species that is collectively referred to as our 'mycobiome'. Although research into the mycobiome is still in its infancy, its potential role in human disease is increasingly recognised. Here we review the existing literature available on the human mycobiota with an emphasis on the gut mycobiome, including how fungi interact with the human host and other microbes. In doing so, we provide a comprehensive critique of the methodologies available to research the human mycobiota as well as highlighting the latest research findings from mycological surveys of different groups of interest including infants, obese and inflammatory bowel disease cohorts. This in turn provides new insights and directions for future studies in this burgeoning research area.

Role of mannose-binding lectin in intestinal homeostasis and fungal elimination

Mannose-binding lectin (MBL) is a soluble lectin of the innate immune system that is produced by the liver and secreted into the circulation where it activates the lectin complement pathway, enhances phagocytosis of microorganisms by leukocytes, and modulates inflammation. MBL can recognize patterns on the surface of different pathogens, including Candida albicans. Our aims were to investigate whether MBL is expressed in the gut epithelium and to examine its effect on the modulation of intestinal inflammation and C. albicans elimination. Using reverse transcriptase-PCR, MBL transcripts were highly expressed in different parts of the mouse gut. MBL expression was also detected by immunoblotting and immunolocalization in response to C. albicans colonization of the gut; the highest expression of MBL was detected in the stomach. Blocking MBL by administering mannans to mice increased C. albicans colonization. MBL-deficient mice had a higher level of colonization than wild-type mice. Dextran sodium sulfate-induced colitis promoted C. albicans dissemination to the kidneys and lungs of MBL-deficient mice. MBL-deficient mice exhibited elevated expression of interleukin (IL)-17, IL-23, dectin-1, and Toll-like receptor-4. This study shows that MBL expression is induced in the gut in response to C. albicans sensing and is required for intestinal homeostasis and host defense against C. albicans.

Adaptation of Candida albicans to commensalism in the gut

Candida albicans is a common resident of the oral cavity, GI tract and vagina in healthy humans where it establishes a commensal relationship with the host. Colonization of the gut, which is an important niche for the microbe, may lead to systemic dissemination and disease upon alteration of host defences. Understanding the mechanisms responsible for the adaptation of C. albicans to the gut is therefore important for the design of new ways of combating fungal diseases. In this review we discuss the available models to study commensalism of this yeast, the main mechanisms controlling the establishment of the fungus, such as microbiota, mucus layer and antimicrobial peptides, and the gene regulatory circuits that ensure its survival in this niche.

Morphology-Independent Virulence of Candida Species during Polymicrobial Intra-abdominal Infections with Staphylococcus aureus

Intra-abdominal polymicrobial infections cause significant morbidity and mortality. An experimental mouse model of Candida albicans-Staphylococcus aureus intra-abdominal infection (IAI) results in 100% mortality by 48 to 72 h postinoculation, while monomicrobial infections are avirulent. Mortality is associated with robust local and systemic inflammation without a requirement for C. albicans morphogenesis. However, the contribution of virulence factors coregulated during the yeast-to-hypha transition is unknown. This also raised the question of whether other Candida species that are unable to form hyphae are as virulent as C. albicans during polymicrobial IAI. Therefore, the purpose of this study was to evaluate the ability of non-albicans Candida (NAC) species with various morphologies and C. albicans transcription factor mutants (efg1/efg1 and cph1/cph1) to induce synergistic mortality and the accompanying inflammation. Results showed that S. aureus coinoculated with C. krusei or C. tropicalis was highly lethal, similar to C. albicans, while S. aureus-C. dubliniensis, S. aureus-C. parapsilosis, and S. aureus-C. glabrata coinoculations resulted in little to no mortality. Local and systemic interleukin-6 (IL-6) and prostaglandin E2 (PGE2) levels were significantly elevated during symptomatic and/or lethal coinfections, and hypothermia strongly correlated with mortality. Coinoculation with C. albicans strains deficient in the transcription factor Efg1 but not Cph1 reversed the lethal outcome. These results support previous findings and demonstrate that select Candida species, without reference to any morphological requirement, induce synergistic mortality, with IL-6 and PGE2 acting as key inflammatory factors. Mechanistically, signaling pathways controlled by Efg1 are critical for the ability of C. albicans to induce mortality from an intra-abdominal polymicrobial infection.

Distinct stages during colonization of the mouse gastrointestinal tract by Candida albicans

Candida albicans is a member of the human microbiota, colonizing both the vaginal and gastrointestinal tracts. This yeast is devoid of a life style outside the human body and the mechanisms underlying the adaptation to the commensal status remain to be determined. Using a model of mouse gastrointestinal colonization, we show here that C. albicans stably colonizes the mouse gut in about 3 days starting from a dose as low as 100 cells, reaching steady levels of around 10⁷ cells/g of stools. Using fluorescently labeled strains, we have assessed the competition between isogenic populations from different sources in cohoused animals. We show that long term (15 days) colonizing cells have increased fitness in the gut niche over those grown in vitro or residing in the gut for 1–3 days. Therefore, two distinct states, proliferation and adaptation, seem to exist in the adaptation of this fungus to the mouse gut, a result with potential significance in the prophylaxis and treatment of Candida infections.

Characterization of Virulence-Related Phenotypes in Candida Species of the CUG Clade

Candida species cause a variety of mucosal and invasive infections and are, collectively, the most important human fungal pathogens in the developed world. The majority of these infections result from a few related species within the "CUG clade," so named because they use a nonstandard translation for that codon. Some members of the CUG clade, such as Candida albicans, present significant clinical problems, whereas others, such as Candida (Meyerozyma) guilliermondii, are uncommon in patients. The differences in incidence rates are imperfectly correlated with virulence in animal models of infection, but comparative analyses that might provide an explanation for why some species are effective pathogens and others are not have been rare or incomplete. To better understand the phenotypic basis for these differences, we characterized eight CUG clade species--C. albicans, C. dubliniensis, C. tropicalis, C. parapsilosis, Clavispora lusitaniae, M. guilliermondii, Debaryomyces hansenii, and Lodderomyces elongisporus--for host-relevant phenotypes, including nutrient utilization, stress tolerance, morphogenesis, interactions with phagocytes, and biofilm formation. Two species deviated from expectations based on animal studies and human incidence. C. dubliniensis was quite robust, grouping in nearly all assays with the most virulent species, C. albicans and C. tropicalis, whereas C. parapsilosis was substantially less fit than might be expected from its clinical importance. These findings confirm the utility of in vitro measures of virulence and provide insight into the evolution of virulence in the CUG clade.

Calcineurin controls hyphal growth, virulence, and drug tolerance of Candida tropicalis

Candida tropicalis, a species closely related to Candida albicans, is an emerging fungal pathogen associated with high mortality rates of 40 to 70%. Like C. albicans and Candida dubliniensis, C. tropicalis is able to form germ tubes, pseudohyphae, and hyphae, but the genes involved in hyphal growth machinery and virulence remain unclear in C. tropicalis. Recently, echinocandin- and azole-resistant C. tropicalis isolates have frequently been isolated from various patients around the world, making treatment difficult. However, studies of the C. tropicalis genes involved in drug tolerance are limited. Here, we investigated the roles of calcineurin and its potential target, Crz1, for core stress responses and pathogenesis in C. tropicalis. We demonstrate that calcineurin and Crz1 are required for hyphal growth, micafungin tolerance, and virulence in a murine systemic infection model, while calcineurin but not Crz1 is essential for tolerance of azoles, caspofungin, anidulafungin, and cell wall-perturbing agents, suggesting that calcineurin has both Crz1-dependent and -independent functions in C. tropicalis. In addition, we found that calcineurin and Crz1 have opposite roles in controlling calcium tolerance. Calcineurin serves as a negative regulator, while Crz1 plays a positive role for calcium tolerance in C. tropicalis.

Murine models of Candida gastrointestinal colonization and dissemination

Ninety-five percent of infectious agents enter through exposed mucosal surfaces, such as the respiratory and gastrointestinal (GI) tracts. The human GI tract is colonized with trillions of commensal microbes, including numerous Candida spp. Some commensal microbes in the GI tract can cause serious human infections under specific circumstances, typically involving changes in the gut environment and/or host immune conditions. Therefore, utilizing animal models of fungal GI colonization and dissemination can lead to significant insights into the complex pathophysiology of transformation from a commensal organism to a pathogen and host-pathogen interactions. This paper will review the methodologic approaches used for modeling GI colonization versus dissemination, the insights learned from these models, and finally, possible future directions using these animal modeling systems.

The emerging world of the fungal microbiome

The study of the fungal microbiota ('mycobiome') is a new and rapidly emerging field that lags behind our understanding of the bacterial microbiome. Every human has fungi as part of their microbiota, but the total number of fungal cells is orders of magnitude smaller than that of the bacterial microbiota. However, the impact of the mycobiome on human health is significant, especially as a reservoir for blooms of pathogenic microbes when the host is compromised and as a potential cofactor in inflammatory diseases and metabolic disorders.

Hosting infection: experimental models to assay Candida virulence

Although normally commensals in humans, Candida albicans, Candida tropicalis, Candida parapsilosis, Candida glabrata, and Candida krusei are capable of causing opportunistic infections in individuals with altered physiological and/or immunological responses. These fungal species are linked with a variety of infections, including oral, vaginal, gastrointestinal, and systemic infections, with C. albicans the major cause of infection. To assess the ability of different Candida species and strains to cause infection and disease requires the use of experimental infection models. This paper discusses the mucosal and systemic models of infection available to assay Candida virulence and gives examples of some of the knowledge that has been gained to date from these models.

The contribution of mouse models to our understanding of systemic candidiasis

Some Candida species are common commensals, which can become opportunistic pathogens in susceptible hosts. In severely ill patients, Candida species, particularly Candida albicans, can cause life-threatening systemic infections. These infections are difficult to diagnose, as symptoms are similar to those of systemic bacterial infections. These difficulties can lead to delays in initiation in antifungal therapy, which contributes to the high mortality rates (> 40%) associated with these infections. In order to investigate systemic Candida infection, mouse models have been developed that mimic human disease, the most common being the intravenous infection model and the gastrointestinal colonization and dissemination model. This review discusses the two models and the contributions that they have made to our understanding of fungal virulence, host response to infection and the development of novel antifungal therapies and diagnostics.

Candida tropicalis in human disease

Candida tropicalis is one of the more common Candida causing human disease in tropical countries; the frequency of invasive disease varies by geography causing 3--66% of candidaemia. C. tropicalis is taxonomically close to C. albicans and shares many pathogenic traits. C. tropicalis is particularly virulent in neutropenic hosts commonly with hematogenous seeding to peripheral organs. For candidaemia and invasive candidiasis amphotericin B or an echinocandin are recommended as first-line treatment, with extended-spectrum triazoles acceptable alternatives. Primary fluconazole resistance is uncommon but may be induced on exposure. Physicians in regions where C. tropicalis is common need to be mindful of this lesser-described pathogen.

Candida albicans heme oxygenase and its product CO contribute to pathogenesis of candidemia and alter systemic chemokine and cytokine expression

Mammalian heme oxygenases play important roles in immune regulation by producing immunosuppressive CO. The pathogenic yeast Candida albicans encodes a heme oxygenase, Hmx1, that is specifically induced by the host protein hemoglobin, suggesting a role in the pathogenesis of disseminated bloodstream infections. We show that exposing mice to therapeutic levels of CO increases C. albicans virulence, whereas an HMX1 null strain has decreased virulence in murine disseminated candidiasis. Levels of several regulatory cytokines and chemokines are decreased in mice infected with the null strain, and initial lesions in the kidney are more rapidly cleared after polymorphonuclear leukocyte infiltration. Reconstitution of one or both alleles restores virulence to the level of wild type. Growth in vitro and initial organ burdens in infected mice are not decreased and host iron overload does not restore virulence for the null strain, suggesting that early growth in the host is not limited by Hmx1-mediated iron scavenging. In contrast, inhaled CO partially reverses the virulence defect of the null strain and restores several host cytokine responses to wild-type levels. Collectively, these results show that C. albicans Hmx1 expression and CO production limit the host immune response and contribute to the pathogenesis of candidemia.

A novel immunocompetent murine model for Candida albicans-promoted oral epithelial dysplasia

Candida albicans is a common opportunistic pathogen found in the oral mucosa. Clinical observations indicate a significant positive association between oral Candida carriage or infection and oral epithelial dysplasia/neoplasia. The aim of this study was to test whether C. albicans is able to promote epithelial dysplasia or carcinoma in a mouse model of infection where a carcinogen (4 Nitroquinoline 1-oxide [4NQO]) was used as initiator of neoplasia. Mice were divided into four groups: group 1 received 4NQO alone; group 2 received 4NQO followed by C. albicans (ATCC 90234); group 3 received vehicle dimethyl sulfoxide (DMSO) followed by C. albicans and group 4 was untreated. Although 4NQO treated mice did not develop oral lesions, mice exposed to both 4NQO and C. albicans developed oral dysplastic lesions 19 weeks after exposure to 4NQO. Mice challenged with C. albicans only developed hyperplastic lesions. The expression of Ki-67 and p16, two cell-cycle associated proteins that are frequently deregulated in oral dysplasia/neoplasia, was also tested in these lesions. Ki-67 and p16 expression increased from normal to hyperplastic to dysplastic mucosa and was highest in the group exposed to both 4NQO and C. albicans. In conclusion, we showed that C. albicans plays a role in the promotion of oral dysplasia in a mouse model of infection when 4NQO was used as initiator of oral neoplasia.

Saccharomyces boulardii decreases inflammation and intestinal colonization by Candida albicans in a mouse model of chemically-induced colitis

The present study was designed to investigate the effects of Saccharomyces boulardii on inflammation and intestinal colonization by Candida albicans in a BALB/c mouse model of colitis that had been induced by dextran-sulfate-sodium (DSS). Colonization with C. albicans was established by oral gavage with a 200 microL suspension of 10(7) yeast cells. A 1.5% solution of DSS was administered in drinking water 1 h after C. albicans oral challenge, while 10(7) cells of S. boulardii was inoculated daily by oral gavage for 1 week. Faeces were collected daily for 2 weeks. Seven groups of mice consisting of those that were administered either C. albicans or S. boulardii or both were sacrificed after 14 days and samples of the colon were taken for histological scoring and real-time PCR (RT-PCR) analysis of inflammatory cytokines and toll-like receptors (TLRs). Compared to control animals that did not receive DSS, the number of C. albicans colonies recovered from faeces was significantly greater in mice receiving DSS. In contrast, the colony forming units (CFUs) of C. albicans were greatly reduced in mice receiving S. boulardii. The administration of this yeast decreased the severity of DSS-induced clinical scores and histological inflammation. At the mRNA expression level, an increase in TLR2 and TLR4 resulting from the presence of S. boulardii was associated with a reduction in the inflammatory cytokines TNFalpha and INFgamma. In mice receiving DSS and C. albicans, TLR4 was over-expressed by stimulation with both yeasts, but TLR2 and TNFalpha, which were increased by the administration of C. albicans alone, were decreased in the presence of S. boulardii. These results indicate that S. boulardii decreased inflammation and C. albicans colonization in this BALB/c mouse model of colitis.

Mucosal damage and neutropenia are required for Candida albicans dissemination

Candida albicans fungemia in cancer patients is thought to develop from initial gastrointestinal (GI) colonization with subsequent translocation into the bloodstream after administration of chemotherapy. It is unclear what components of the innate immune system are necessary for preventing C. albicans dissemination from the GI tract, but we have hypothesized that both neutropenia and GI mucosal damage are critical for allowing widespread invasive C. albicans disease. We investigated these parameters in a mouse model of C. albicans GI colonization that led to systemic spread after administration of immunosuppression and mucosal damage. After depleting resident GI intestinal flora with antibiotic treatment and achieving stable GI colonization levels of C. albicans, it was determined that systemic chemotherapy with cyclophosphamide led to 100% mortality, whereas selective neutrophil depletion, macrophage depletion, lymphopenia or GI mucosal disruption alone resulted in no mortality. Selective neutrophil depletion combined with GI mucosal disruption led to disseminated fungal infection and 100% mortality ensued. GI translocation and dissemination by C. albicans was also dependent on the organism's ability to transform from the yeast to the hyphal form. This mouse model of GI colonization and fungemia is useful for studying factors of innate host immunity needed to prevent invasive C. albicans disease as well as identifying virulence factors that are necessary for fungal GI colonization and dissemination. The model may also prove valuable for evaluating therapies to control C. albicans infections.

Cleavage of E-cadherin: a mechanism for disruption of the intestinal epithelial barrier by Candida albicans

To investigate how intestinal epithelial cells respond to contact with Candida albicans, an organism able to invade the bloodstream via the gastrointestinal tract, we focused on the junction proteins occludin, E-cadherin, and desmoglein-2. The levels of these 3 junction proteins were reduced in lysates of human intestinal epithelial monolayers (Caco-2) after a 24-h inoculation with C. albicans, compared with lysates from Saccharomyces cerevisiae-inoculated monolayers. Treatment with pepstatin A did not change the effect of C. albicans on full-length occludin, desmoglein-2, and E-cadherin; however, pepstatin A enhanced the accumulation of a 35-kDa fragment derived from the intracellular portion of E-cadherin. This 35-kDa fragment also accumulated in the presence of gamma-secretase inhibitors. These observations suggest that enhancement of E-cadherin cleavage by C. albicans generates an intracellular E-cadherin fragment that can serve as a substrate for gamma-secretase. An 89-kDa extracellular fragment of E-cadherin was detected in supernatants of C. albicans-inoculated monolayers; this cleavage event was insensitive to both pepstatin A and gamma-secretase inhibitors. Transepithelial electrical resistance, a measure of monolayer integrity, decreased significantly and synchronously with increased generation of the 89-kDa extracellular E-cadherin fragment. Cleavage of E-cadherin may destabilize the homotypic interactions between adjacent epithelial cells and could contribute to loss of monolayer integrity. These experiments identify 2 E-cadherin cleavage events that are enhanced by contact with C. albicans: an intracellular cleavage event that generates a substrate for gamma-secretase and an extracellular cleavage event that is temporally associated with an increase in monolayer permeability.

Epidemiology of invasive candidiasis: a persistent public health problem

Invasive candidiasis (IC) is a leading cause of mycosis-associated mortality in the United States. We examined data from the National Center for Health Statistics and reviewed recent literature in order to update the epidemiology of IC. IC-associated mortality has remained stable, at approximately 0.4 deaths per 100,000 population, since 1997, while mortality associated with invasive aspergillosis has continued to decline. Candida albicans remains the predominant cause of IC, accounting for over half of all cases, but Candida glabrata has emerged as the second most common cause of IC in the United States, and several less common Candida species may be emerging, some of which can exhibit resistance to triazoles and/or amphotericin B. Crude and attributable rates of mortality due to IC remain unacceptably high and unchanged for the past 2 decades. Nonpharmacologic preventive strategies should be emphasized, including hand hygiene; appropriate use, placement, and care of central venous catheters; and prudent use of antimicrobial therapy. Given that delays in appropriate antifungal therapy are associated with increased mortality, improved use of early empirical, preemptive, and prophylactic therapies should also help reduce IC-associated mortality. Several studies have now identified important variables that can be used to predict risk of IC and to help guide preventive strategies such as antifungal prophylaxis and early empirical therapy. However, improved non-culture-based diagnostics are needed to expand the potential for preemptive (or early directed) therapy. Further research to improve diagnostic, preventive, and therapeutic strategies is necessary to reduce the considerable morbidity and mortality associated with IC.

Dengue hemorrhagic shock and disseminated candidiasis

Dengue fever, one of the common endemic viral fevers, often presents with fever, rash, and mild liver dysfunction. However, plasma leakage induced by dengue virus infection can lead to dengue hemorrhagic fever and dengue shock syndrome, and it can cause severe complications including liver failure and encephalopathy. Infection of dengue virus with other pathogens is an unusual but serious complication. We report a case of dengue shock syndrome with liver failure and impaired consciousness. The patient developed a disseminated Candida tropicalis infection, which may have been due to translocation of the fungus from the intestine damaged by the dengue virus.

Gastrointestinal Candida colonisation promotes sensitisation against food antigens by affecting the mucosal barrier in mice

BACKGROUNDS AND AIMS

Controversy still exists as to whether gastrointestinal colonisation by Candida albicans contributes to aggravation of atopic dermatitis. We hypothesised that Candida colonisation promotes food allergy, which is known to contribute to a pathogenic response in atopic dermatitis. We tested this using a recently established murine Candida colonisation model.

METHODS

Candida colonisation in the gastrointestinal tract was established by intragastric inoculation with C albicans in mice fed a synthetic diet. To investigate sensitisation against food antigen, mice were intragastrically administered with ovalbumin every other day for nine weeks, and antiovalbumin antibody titres were measured weekly. To examine gastrointestinal permeation of food antigen, plasma concentrations of ovalbumin were measured following intragastric administration of ovalbumin.

RESULTS

Ovalbumin specific IgG and IgE titres were higher in BALB/c mice with Candida colonisation than in normal mice. Gastrointestinal permeation of ovalbumin was enhanced by colonisation in BALB/c mice. Histological examination showed that colonisation promoted infiltration and degranulation of mast cells. Candida colonisation did not enhance ovalbumin permeation in mast cell deficient W/Wv mice but did in congenic littermate control +/+ mice. Reconstitution of mast cells in W/Wv mice by transplantation of bone marrow derived mast cells restored the ability to increase ovalbumin permeation in response to Candida colonisation.

CONCLUSIONS

These results suggest that gastrointestinal Candida colonisation promotes sensitisation against food antigens, at least partly due to mast cell mediated hyperpermeability in the gastrointestinal mucosa of mice.

The proinflammatory response induced by wild-type Yersinia pseudotuberculosis infection inhibits survival of yop mutants in the gastrointestinal tract and Peyer's patches

Single-strain infections and coinfections are frequently used to assess roles of virulence factors in infected tissues. After oral inoculation of mice, Yersinia pseudotuberculosis yopE and yopH mutants colonize the intestines and Peyer's patches in single-strain infections but fail to persist in competition with wild-type Y. pseudotuberculosis, indicating that these two infection models provide different insights into the roles of Yops. To determine how wild-type Y. pseudotuberculosis hinders yop mutant survival, yop mutant colonization and host responses were investigated in several different infection models that isolated specific features of wild-type Y. pseudotuberculosis infection. Infection with wild-type Y. pseudotuberculosis caused significantly more inflammation than yop mutants. Results from coinfections of gamma interferon (IFN-gamma)-/- mice revealed that IFN-gamma-regulated defenses target these mutants, suggesting that YopE and YopH protect Y. pseudotuberculosis from these defenses in BALB/c mice. We developed an oral-intraperitoneal infection model to evaluate the effects of spleen and liver colonization by Y. pseudotuberculosis on yop mutants in the intestines. Spleen and liver infection increased inflammation and decreased yop mutant survival in the intestines, indicating that infection of these organs has consequences in intestinal tissues. Finally, competition infections with Y. pseudotuberculosis mutants with various abilities to induce inflammation demonstrated that survival of the yopE, but not the yopH, mutant was consistently decreased in inflamed tissues. In summary, infection with Y. pseudotuberculosis in intestinal and systemic sites induces intestinal inflammation, which decreases yop mutant survival. Thus, competition studies with wild-type yersiniae reveal critical roles of Yops in combating host responses to a normal virulent infection.

Is the remarkable contradiction between histology and 14C urea breath test in the detection of Helicobacter pylori due to false-negative histology or false-positive 14C urea breath test?

We assessed the diagnostic value of the 14C urea breath test (UBT) in the detection of Helicobacter pylori compared with histology and the rapid urease test (RUT). The study included 68 patients (22 men and 46 women) with dyspeptic symptoms. H. pylori status was evaluated by 14C UBT, RUT and histology. Sensitivity, specificity, positive and negative predictive values, and diagnostic accuracy were determined for 14C UBT and for RUT. Histology revealed dense yeast-like micro-organisms in the biopsy specimens in all patients with false-positive results by 14C UBT (n = 8), a significantly higher proportion than in patients with negative 14C UBT (five of 31). The low specificity of the H. pylori 14C UBT should not be neglected by accepting histology results as false-negative. Gastric mucosal colonization by yeast-like micro-organisms with urease activity can account for the high frequency of false-positive results for 14C UBT.

Gastric colonization of Candida albicans differs in mice fed commercial and purified diets

It has been difficult to produce persistent colonization by Candida albicans in the gastrointestinal tract of adult mice without the use of antibiotics and immunosuppressants. We hypothesized that diet influences the colonization of C. albicans and tested the hypothesis. BALB/c mice fed either a commercial rodent diet or a nutritionally adequate mixture of purified ingredients were inoculated i.g. with C. albicans (5 x 10(7) cells). Gastrointestinal colonization was examined by fecal culture, tissue culture, and histology. Mice fed the purified diet had a high fecal recovery of C. albicans [5-6log(10) colony forming units (cfu)/g feces] throughout the experimental period (6 wk), and the major site of colonization was the stomach. C. albicans was undetectable in the feces of mice fed the commercial diet 2 wk after inoculation. Immunosuppressants induced systemic dissemination of C. albicans in mice fed the purified diet. The number of lactobacilli and the concentration of organic acids in the stomach were significantly lower in mice fed the purified diet than in those fed the commercial diet. In vitro culture experiments revealed that acetic and lactic acids suppressed the growth of C. albicans. These results suggest that a reduction in lactobacilli in the stomach of mice fed the purified diet contributed to sustained gastric candidiasis. We therefore propose a novel model of sustained gastric candidiasis by a single i.g. inoculation of C. albicans in healthy adult mice fed a purified diet.

Animal models in the analysis of Candida host-pathogen interactions

An increasingly diverse array of clinically relevant animal models of candidiasis have been established that mimic both the immune perturbations of the host and tissue-specific features of candidiasis in humans. Cause-and-effect analysis of Candida host-pathogen interactions using these animal models has made a quantum leap forward in the genomic era, with the concurrent construction of C. albicans mutants with targeted mutations of putative virulence factors, the application of microarrays and other emerging technologies to comprehensively assess C. albicans gene expression in vivo, and construction of transgenic and knockout mice to simulate specific host immunodeficiencies. The opportunity to combine these powerful tools will yield an unprecedented wealth of new information on the molecular and cellular pathogenesis of candidiasis.

Pharmacokinetics/pharmacodynamics of echinocandins

The novel class of echinocandins represents a milestone in antifungal drug research that has further expanded our therapeutic options. The favorable pharmacokinetic profile of the echinocandins has been elucidated in animal and human studies. The echinocandins are targeted for once-daily dosing and are not metabolized through the cytochrome P450 enzyme system, and they are generally well tolerated due to lack of mechanism-based toxicity. Little is known, however, about the disposition of these compounds in tissues and body fluids and the relationships between dosage, concentrations in the body, and antifungal efficacy in vivo. Many unanswered questions remain, including the importance of the high protein binding and the concentrations of free antifungal agents at target sites. Although recent attempts have been made to ensure the reproducibility of in vitro tests, the clinical usefulness of these tests is still unreliable and their relevance remains controversial. In vitro activity must be correlated with achievable concentrations at the site of infection. As little is known about the relationship between the pharmacokinetics and the pharmacodynamics of the echinocandins, increased incorporation of these principles in experimental and clinical studies is an important objective that will benefit the treatment and prophylaxis of life-threatening invasive fungal infections in immunocompromised patients.

Determinants of Candidemia and Candidemia-Related Death in Cardiothoracic ICU Patients

STUDY OBJECTIVES

To develop and prospectively validate models of independent predictors of candidemia and candidemia-related death in cardiothoracic ICU (CICU) patients.

DESIGN

(1) An initial, prospective, one-center, case-control, independent predictor-model determining study; and (2) a prospective, two-center, model-validation study.

SETTING

The initial study was performed at the 14-bed CICU of the Onassis Cardiac Surgery Center, Athens, Greece; the model-validation study was performed at the Onassis Cardiac Surgery Center CICU and the 12-bed CICU of Henry Dunant General Hospital, Athens, Greece.

PATIENTS

In the initial study, 4,312 patients admitted to the Onassis Center CICU between March 1997 and October 1999 were considered for enrollment; 30 candidemic and 120 control patients (case/control ratio, 1/4) matched according to potential confounders were ultimately enrolled. In the model-validation study, 2,087 patients admitted to the Onassis and Henry Dunant CICUs between November 1999 and May 2002 were prospectively enrolled.

MEASUREMENTS AND RESULTS

Models of predictors of candidemia and associated death were constructed with stepwise logistic regression and subsequently validated. Independent candidemia predictors were ongoing invasive mechanical ventilation (IMV) > OR =10 days, hospital-acquired bacterial infection and/or bacteremia, cardiopulmonary bypass duration > 120 min, and diabetes mellitus. Model performance was as follows: sensitivity, 53.3%/57.9%; specificity, 100%/100%; positive predictive value (PPV), 100%/100%; negative predictive value (NPV), 88.9%/99.6%; and accuracy, 90.1%/99.6% (initial/model-validation study values, respectively). IMV > or =10 days and hospital-acquired bacterial infection/bacteremia were the two strongest candidemia predictors. APACHE (acute physiology and chronic health evaluation) II score > or =30 at candidemia onset independently predicted candidemia-related death with 80.0%/85.7% sensitivity, 80%/75% specificity, 66.7%/66.7% PPV, 88.9%/88.9% NPV, and 80.0%/78.9% accuracy (initial/model-validation study values, respectively).

CONCLUSIONS

We provided a set of easily determinable independent predictors of the occurrence of candidemia in CICU patients. Our results provide a rationale for implementing preventive measures in the form of independent predictor control, and initiating antifungal prophylaxis in high-risk CICU patients.

Candidemia in women with breast carcinoma treated with high-dose chemotherapy and autologous bone marrow transplantation

BACKGROUND

Invasive fungal infections, including candidemia, pose a major threat to patients with impaired immune defenses, including bone marrow transplantation (BMT) recipients. During 1992-1997, 845 women with multiple lymph node positive or metastatic breast carcinoma underwent high-dose chemotherapy (HDC) and subsequent autologous BMT at Duke University Medical Center. No systemic antifungal prophylaxis was administered. The purpose of the current study was to evaluate the risk and long-term outcome of candidemia in this patient population.

METHODS

Clinical data were collected on patients with candidemia, and a group of age-matched control patients were identified who underwent HDC and BMT for breast carcinoma in the same time period. The difference in crude mortality between these two groups was used to calculate the attributable mortality of candidemia. The genetic relatedness of the fungal blood stream isolates was investigated by DNA fingerprinting. Antifungal susceptibility testing was performed using serial microdilution.

RESULTS

Twenty-nine of 845 women developed candidemia (3.4%). The crude mortality of women with candidemia was 35% at 90 days after transplantation but 11% among women in the matched control group who were without infection (P = 0.01), for an attributable mortality rate of 24%. The most common pathogen was Candida tropicalis (50%), followed by Candida albicans (23%). The mortality was highest for women who were infected with C. albicans, followed by C. tropicalis, and other Candida species (P = 0.037). DNA fingerprinting of the yeasts revealed genetic heterogeneity in all species. However, 9 of 15 C. tropicalis isolates had identical DNA fingerprint profiles, suggesting spread of this genotype from a common source. All yeast isolates were susceptible to amphotericin B, and 20 of 30 isolates were susceptible to <or= 8 microg/mL of fluconazole.

CONCLUSIONS

Candidemia was relatively infrequent after HDC and autologous BMT in women with for multiple lymph node positive or metastatic breast carcinoma. This was true even in the absence of systemic antifungal prophylaxis. The mortality attributable to candidemia in this patient population was 24% and was higher among patients who were infected by C. albicans compared with patients who were infected by other Candida, non-albicans species.

Is Candida albicans a trigger in the onset of coeliac disease?

Coeliac disease is a T-cell-mediated autoimmune disease of the small intestine that is induced by ingestion of gluten proteins from wheat, barley, or rye. We postulate that Candida albicans is a trigger in the onset of coeliac disease. The virulence factor of C albicans-hyphal wall protein 1 (HWP1)-contains aminoacid sequences that are identical or highly homologous to known coeliac disease-related alpha-gliadin and gamma-gliadin T-cell epitopes. HWP1 is a transglutaminase substrate, and is used by C albicans to adhere to the intestinal epithelium. Furthermore, tissue transglutaminase and endomysium components could become covalently linked to the yeast. Subsequently, C albicans might function as an adjuvant that stimulates antibody formation against HWP1 and gluten, and formation of autoreactive antibodies against tissue transglutaminase and endomysium.

Hepatosplenic fungal infection in patients with acute leukemia in Taiwan: incidence, treatment, and prognosis

Nosocomial fungal infection increases gradually and has become the leading pathogen at National Taiwan University Hospital since 1993. From January 1995 through May 2002, hepatosplenic fungal infection (HSF) was diagnosed in 37 (7.4%) of the 500 adult patients with acute leukemia who received chemotherapy at this hospital. There was no significant difference in the incidence of HSF between the patients with acute myeloid leukemia and those with acute lymphoblastic leukemia, or between the patients treated with high-dose chemotherapy and those with conventional or low-dose chemotherapy. Candida tropicalis was the leading pathogen, followed by Candida albicans. The computed tomography scan showed multiple hypodense lesions in the liver (89%), spleen (70%), and kidney (27%). Eighteen patients were initially treated with fluconazole and 19 with amphotericin B. Nineteen patients received the planned chemotherapy after the diagnosis of HSF. Among them, eight patients underwent hematopoietic stem cell transplantation and seven patients survived more than 100 days post-transplantation; none of these patients had relapse of prior HSF. Twenty-three patients (62%) died during a median follow up of 10 months, but only seven died due to HSF. In conclusion, a substantial percentage of patients with acute leukemia acquired HSF after chemotherapy and carried high mortality. However, HSF itself is not a contraindication for subsequent chemotherapy and hematopoietic stem cell transplantation.

Revisiting the source of candidemia: skin or gut?

The source of candidemia has been the subject of considerable debate, with some suggesting a origin in the gastrointestinal tract and others suggesting a skin origin. To evaluate the potential sources of candidemia, we performed a computerized search of the MEDLINE database for studies published from January 1966 through September 2000 and we identified relevant abstracts presented at national meetings. We reviewed the literature with special emphasis on studies that used appropriate definitions, evaluated both gut and skin as sources, and conducted molecular-relatedness studies. Among 203 candidemia studies published, we identified 21 that evaluated a specific source for candidemia and only 5 that performed molecular typing. Those studies and additional experimental, epidemiologic, and molecular-relatedness studies strongly suggested that the gut is an important source of candidemia, and studies that supported the skin as a source for this infection were surprisingly incomplete.

Risk Factors for Candida tropicalis fungemia in patients with cancer

The risk factors for and presentation of Candida tropicalis fungemia, in comparison with those of Candida albicans, have been incompletely characterized. We compared 43 cases of C. tropicalis fungemia with 148 cases of C. albicans fungemia. In univariate analysis, patients with C. tropicalis fungemia were more likely to have leukemia (P=.0006), prolonged neutropenia (P=.03), and a positive blood culture for more days (P=.02). The 2 groups did not differ with regard to baseline Acute Physiology and Chronic Health Evaluation (APACHE) II score, frequency of catheter-associated fungemia, or response to antifungals. In multivariate analysis, patients with C. tropicalis fungemia were more likely to have leukemia (P=.02), previous neutropenia (P=.002), and a longer stay in the intensive care unit during the infectious episode (P=.01). Also, the response of the breakthrough C. tropicalis fungemia was lower (P=.05). In conclusion, the host determinants associated with susceptibility to C. tropicalis are leukemia and prolonged neutropenia.

Quorum sensing in the dimorphic fungus Candida albicans is mediated by farnesol

The inoculum size effect in the dimorphic fungus Candida albicans results from production of an extracellular quorum-sensing molecule (QSM). This molecule prevents mycelial development in both a growth morphology assay and a differentiation assay using three chemically distinct triggers for germ tube formation (GTF): L-proline, N-acetylglucosamine, and serum (either pig or fetal bovine). In all cases, the presence of QSM prevents the yeast-to-mycelium conversion, resulting in actively budding yeasts without influencing cellular growth rates. QSM exhibits general cross-reactivity within C. albicans in that supernatants from strain A72 are active on five other strains of C. albicans and vice versa. The QSM excreted by C. albicans is farnesol (C(15)H(26)O; molecular weight, 222.37). QSM is extracellular, and is produced continuously during growth and over a temperature range from 23 to 43 degrees C, in amounts roughly proportional to the CFU/milliliter. Production is not dependent on the type of carbon source nor nitrogen source or on the chemical nature of the growth medium. Both commercial mixed isomer and (E,E)-farnesol exhibited QSM activity (the ability to prevent GTF) at a level sufficient to account for all the QSM activity present in C. albicans supernatants, i.e., 50% GTF at ca. 30 to 35 microM. Nerolidol was ca. two times less active than farnesol. Neither geraniol (C(10)), geranylgeraniol (C(20)), nor farnesyl pyrophosphate had any QSM activity.

Sustained gastrointestinal colonization and systemic dissemination by Candida albicans, Candida tropicalis and Candida parapsilosis in adult mice

The ability of nine clinical isolates of Candida species (three C. albicans, three C. tropicalis and three C. parapsilosis) to colonize and invade the gastrointestinal (GI) tract of adult male CD-1 (ICR) mice was determined. The effect of dietary tetracycline plus glucose supplementation on colonization was evaluated. Strains were intragastrically inoculated. Tetracycline and glucose altered substantially aerobic flora, especially streptococci (average fall 1.1 +/-0.3 log(10) CFU/g, p<0.01 by the Student's t test). At two weeks after oral challenge, sustained and high colonization of GI tract by Candida (mean 5,28 +/- 0.18 log(10) CFU/g, p<0.01) was achieved in all mice receiving glucose-tetracycline supplementation, excepting in animals inoculated with one of C. tropicalis isolates. Histologic sections of the stomachs revealed multiple intraepithelial micro-abscesses associated with hyphae in the region of the cardial-atrium fold. Under immunosuppression, systemic spread of C. albicans and C. tropicalis was observed in 62% and 24% of animals receiving dietary supplementation respectively. Dissemination was not noted for C. parapsilosis isolates. We have developed a simple and inexpensive murine model of sustained colonization of GI tract. This model could be useful for analyzing prophylaxis, treatment and diagnosis of systemic Candida infections and for evaluating virulence of strains.

Characterization of binding of Candida albicans to small intestinal mucin and its role in adherence to mucosal epithelial cells

In order to approximate and adhere to mucosal epithelial cells, Candida must traverse the overlying mucus layer. Interactions of Candida species with mucin and human buccal epithelial cells (BECs) were thus investigated in vitro. Binding of the Candida species to purified small intestinal mucin showed a close correlation with their hierarchy of virulence. Significant differences (P < 0.05) were found among three categories of Candida species adhering highly (C. dubliniensis, C. tropicalis, and C. albicans), moderately (C. parapsilosis and C. lusitaniae) or weakly (C. krusei and C. glabrata) to mucin. Adherence of C. albicans to BECs was quantitatively inhibited by graded concentrations of mucin. However, inhibition of adherence was reversed by pretreatment of mucin with pronase or C. albicans secretory aspartyl proteinase Sap2p but not with sodium periodate. Saturable concentration- and time-dependent binding of mucin to C. albicans was abrogated by pronase or Sap2p treatment of mucin but was unaffected by beta-mercaptoethanol, sodium periodate, neuraminidase, lectins, or potentially inhibitory sugars. Probing of membrane blots of the mucin with C. albicans revealed binding of the yeast to the 66-kDa cleavage product of the 118-kDa C-terminal glycopeptide of mucin. Although no evidence was found for the participation of C. albicans cell surface mannoproteins in specific receptor-ligand binding to mucin, inhibition of binding by p-nitrophenol (1 mM) and tetramethylurea (0.36 M) revealed that hydrophobic interactions are involved in adherence of C. albicans to mucin. These results suggest that C. albicans may both adhere to and enzymatically degrade mucins by the action of Saps, and that both properties may act to modulate Candida populations in the oral cavity and gastrointestinal tract.

Identification and cloning of GCA1, a gene that encodes a cell surface glucoamylase from Candida albicans

Adherence of yeast cells of Candida albicans to human oesophageal cells is greater when cells are grown in 500 mM D-galactose in comparison to D-glucose at the same concentration. Moreover, a 190 kDa mannoprotein (MP190) from a yeast cell wall preparation is highly expressed when cells are grown in the presence of galactose but less so in glucose. We now report on the identification of the MP190 and the isolation of its encoding gene. MP190 was purified, and three internal peptides were isolated and sequenced. Each of the three peptides showed significant homology (65-85%) with a glucoamylase (GAM1) from the yeast, Schwanniomyces occidentalis. In order to isolate the C. albicans homologue of GAM1 (GCA1), we probed a genomic library with a 0.9-kb internal fragment of the S. occidentalis GAM1 and isolated a 2.3-kb clone that corresponded to the 5' region of the gene. Polymerase chain reaction (PCR) amplification was used to isolate the remainder of the open reading frame. GCA1 encodes a 946 amino acid protein containing three putative hydrophobic, membrane-spanning domains and 15 potential N-glycosylation sites. Both Gca1p and GAM1 are novel to the family of glycosyl hydrolases. Northern analysis indicated that GCA1 is transcribed to a greater extent in galactose than in sucrose or glucose. Also, using reverse transcriptase (RT)-PCR, we observed expression of GCA1 in a rat model of oral candidiasis, indicating that Gca1p is expressed during disease development.

Fungal colonization of the stomach and its clinical relevance

The aim of this study was to estimate the frequency of fungal colonization of the stomach of patients suffering from gastric ulcer (GU) and chronic gastritis (CG) and the influence of fungal colonization of the stomach on the process of ulcer healing. We investigated 293 patients aged 20-80 years. Before and after 4 weeks of sucralfate treatment they underwent endoscopy of the stomach, histological examination of biopsies taken from the ulcer margin or inflamed gastric mucosa and mycological examinations of the gastric juice, surface brushing and biopsies. The studies revealed a high concentration of fungi in 54.2% patients with GU and 10.3% with CG. Candida albicans was the most frequently isolated organism. Fungal colonization of the stomach impairs the process of gastric ulcer healing. Control examination after 4 weeks of sucralfate therapy showed the ratio of GU healing in 62% of patients with a high concentration of fungi in comparison with 78% of patients not colonized with fungi (P < 0.05). A significantly longer duration of ulcer symptoms in the group of patients with a high concentration of fungi in the stomach was also observed. There was no correlation between the level of fungal antibodies, of Candida antigen in the serum and the concentration of fungi in the stomach.