Adhesins and ligands involved in the interaction of Candida spp. with epithelial and endothelial surfaces

Acid proteinase, phospholipase and adherence properties of Candida parapsilosis strains isolated from clinical specimens of hospitalised patients

In this study, we investigated the presence of virulence factors in a total of 33 Candida parapsilosis strains, including adherence, acid proteinase and phospholipase production capabilities. Of the 33 strains, 19 were isolated from blood cultures of hospitalised fungaemic patients (study group 2). We also investigated the importance of other factors present in the development of fungaemia. The mean adherence values of 19 blood isolates and 14 non-blood isolates were found to be 52.63 and 57.96, respectively; these values did not differ significantly (P > 0.05). Nine non-blood strains (64.29%) of study group 2 and five blood strains (26.31%) of study group 1 were found to be positive for acid proteinase production; this difference was statistically significant (P < 0.05). Phospholipase production was found in five strains (26.31%) of the 19 blood isolates. None of the 14 non-blood strains exhibited phospholipase activity; this difference between the two groups was statistically significant (P < 0.05). In this study, correlations between adherence-phospholipase, and adherence-acid proteinase properties of strains were detected as well. In the present study, it has been observed that phospholipase production can be an important virulence factor in bloodstream infections caused by C. parapsilosis.

Interaction of pathogenic fungi with host cells: Molecular and cellular approaches

This review provides an overview of several molecular and cellular approaches that are likely to supply insights into the host-fungus interaction. Fungi present intra- and/or extracellular host-parasite interfaces, the parasitism phenomenon being dependent on complementary surface molecules. The entry of the pathogen into the host cell is initiated by the fungus adhering to the cell surface, which generates an uptake signal that may induce its cytoplasmatic internalization. Furthermore, microbial pathogens use a variety of their surface molecules to bind to host extracellular matrix (ECM) components to establish an effective infection. On the other hand, integrins mediate the tight adhesion of cells to the ECM at sites referred to as focal adhesions and also play a role in cell signaling. The phosphorylation process is an important mechanism of cell signaling and regulation; it has been implicated recently in defense strategies against a variety of pathogens that alter host-signaling pathways in order to facilitate their invasion and survival within host cells. The study of signal transduction pathways in virulent fungi is especially important in view of their putative role in the regulation of pathogenicity. This review discusses fungal adherence, changes in cytoskeletal organization and signal transduction in relation to host-fungus interaction.

Efficacy of the antiadhesin octyl O-(2-acetamido-2-deoxy-beta-D-galactopyranosyl)-(1-4)-2-O-propyl-beta-D-galactopyranoside (Fimbrigal-P) in a rat oral candidiasis model

Adherence of Candida albicans to buccal epithelial cells via its fimbrial subunit requires the minimal disaccharide sequence beta-GalNAc(1-4)-beta-galactosidase in host cell receptors asialo-GM1 or asialo-GM2. This and other disaccharides and some of its synthetic derivatives have been shown to inhibit purified fimbrial or pathogen binding in vitro. This study evaluates the in vivo efficacy of the propyl derivative of this disaccharide, octyl O-(2-acetamido-2-deoxy-beta-D-galactopyranosyl)-(1-4)-2-O-propyl-beta-D-galactopyranoside, or Fimbrigal-P, incorporated into a mucoadhesive polymer formulation in a rat oral candidiasis model. Colony counts of microcurette samples from the oral cavity and tongue homogenates were used to estimate the effectiveness of four treatment modalities to reduce oral fungal burden. All treatment modalities (preventative, premixing with the Candida inoculant, drinking water, and treatment) significantly reduced fungal burden compared to untreated control animals by day 9; however, the preventative and pre-mixing approaches provided a faster rate of fungal clearance. The low toxicity and immunogenicity of this synthetic carbohydrate and its stability in saliva, as demonstrated by high-performance liquid chromatography, make it a promising candidate for the prevention and treatment of microbial infections in which the pathogen relies on the beta-GalNAc(1-4)-beta-galactosidase disaccharide to establish adherence.

Frequency, species and molecular characterization of oral Candida in hosts of different age in China

INTRODUCTION

Research indicates that host age is a determining factor in yeast carriage. From the neonatal period, humans go through several dentition periods, and the emergence and substitution of teeth and changes in living habits greatly change the environment of the oral cavity, and therefore influence colonization by oral commensal organisms, certainly including Candida spp. No previous study of Candida carriage by different age groups divided by dentition has been reported. This study supplies data on the geographical specificity of C. albicans genotypic subgroup distribution.

METHODS

All test individuals came from a single geographical locale over a short period. Following mucosal swab sampling, CHROMagar Candida-yeast differential media were used to determine the frequency of carriage and species. All C. albicans strains were confirmed by PCR and PCR using primers reported to span a transposable intron region in the 25S rRNA gene was used to determine genotypic subgroups.

RESULTS

The results demonstrate that for the tested population, the frequency of Candida species and the distribution of C. albicans genotypic subgroups varied with age group. With increasing age, the frequency of C. albicans decreases, non-C. albicans yeasts increases; Genotypic subgroup A is the dominating strain in the oral cavities of healthy young individuals.

CONCLUSIONS

The influence of dentition substitution on oral yeast carriage was minor.

ABG1, a novel and essential Candida albicans gene encoding a vacuolar protein involved in cytokinesis and hyphal branching

Immunoscreening of a Candida albicans expression library resulted in the isolation of a novel gene encoding a 32.9-kDa polypeptide (288 amino acids), with 27.7% homology to the product of Saccharomyces cerevisiae YGR106c, a putative vacuolar protein. Heterozygous mutants in this gene displayed an altered budding growth pattern, characterized by the formation of chains of buds, decreasingly in size towards the apex, without separation of the daughter buds. Consequently, this gene was designated ABG1. A conditional mutant for ABG1 with the remaining allele under the control of the MET3 promoter did not grow in the presence of methionine and cysteine, demonstrating that ABG1 was essential for viability. Western analysis revealed the presence of a major 32.9-kDa band, mainly in a particulate fraction (P40) enriched in vacuoles, and tagging with green fluorescent protein confirmed that Abg1p localized to the vacuole. Vacuole inheritance has been linked to the regulation of branching frequency in C. albicans. Under repressing conditions, the conditional mutant had an increased frequency of branching under hyphal inducing conditions and an altered sensitivity to substances that interfered with cell wall assembly. Repression of ABG1 in the conditional mutant strain caused disturbance of normal size and number of vacuoles both in yeast and mycelial cells and also in the asymmetric vacuole inheritance associated with the characteristic pattern of germ tubes and branching in C. albicans. These observations indicate that ABG1 plays a key role in vacuole biogenesis, cytokinesis, and hyphal branching.

In vitro inhibitory effect of Streblus asper leaf-extract on adhesion of Candida albicans to human buccal epithelial cells

This in vitro study aimed at determining the effects of a sublethal concentration of Streblus asper Lour (Moraceae) leaf ethanolic extract on adherence of Candida albicans to human buccal epithelial cells (HBEC). The minimum concentration of Streblus asper leaf ethanolic extract (SAE) that significantly reduced adherence (P<0.05) after a 1-h exposure was 15.6 mg/ml. However, there was a significant reduction (P<0.05) of candidal adhesion to HBEC after 1-min exposure to 125 mg/ml of SAE. Pre-treatment of either Candida or HBEC, or both, with 125 mg/ml of SAE for 1h resulted in reduced adherence. SAE at concentrations of 125 and 250 mg/ml also showed 41 and 61% inhibition of germ tube formation, respectively, which might affect adherence. These findings indicate that the sublethal concentration of SAE may modulate candidal colonization of the oral mucosa thereby suppressing the invasive potential of the pathogen.

Candida albicans proteinases and host/pathogen interactions

Candida infections are common, debilitating and often recurring fungal diseases and a problem of significant clinical importance. Candida albicans, the most virulent of the Candida spp., can cause severe mucosal and life-threatening systemic infections in immunocompromised hosts. Attributes that contribute to C. albicans virulence include adhesion, hyphal formation, phenotypic switching and extracellular hydrolytic enzyme production. The extracellular hydrolytic enzymes, especially the secreted aspartyl proteinases (Saps), are one of few gene products that have been shown to directly contribute to C. albicans pathogenicity. Because C. albicans is able to colonize and infect almost every tissue in the human host, it may be crucial for the fungus to possess a number of similar but independently regulated and functionally distinct secreted proteinases to provide sufficient flexibility in order to survive and promote infection at different niche sites. The aim of this review is to explore the functional roles of the C. albicans proteinases and how they may contribute to the host/pathogen interaction in vivo.

Posttranslational modifications required for cell surface localization and function of the fungal adhesin Aga1p

Adherence of fungal cells to host substrates and each other affects their access to nutrients, sexual conjugation, and survival in hosts. Adhesins are cell surface proteins that mediate these different cell adhesion interactions. In this study, we examine the in vivo functional requirements for specific posttranslational modifications to these proteins, including glycophosphatidylinositol (GPI) anchor addition and O-linked glycosylation. The processing of some fungal GPI anchors, creating links to cell wall beta-1,6 glucans, is postulated to facilitate postsecretory traffic of proteins to cell wall domains conducive to their functions. By studying the yeast sexual adhesin subunit Aga1p, we found that deletion of its signal sequence for GPI addition eliminated its activity, while deletions of different internal domains had various effects on function. Substitution of the Aga1p GPI signal domain with those of other GPI-anchored proteins, a single transmembrane domain, or a cysteine capable of forming a disulfide all produced functional adhesins. A portion of the cellular pool of Aga1p was determined to be cell wall resident. Aga1p and the alpha-agglutinin Agalpha1p were shown to be under glycosylated in cells lacking the protein mannosyltransferase genes PMT1 and PMT2, with phenotypes manifested only in MATalpha cells for single mutants but in both cell types when both genes are absent. We conclude that posttranslational modifications to Aga1p are necessary for its biogenesis and activity. Our studies also suggest that in addition to GPI-glucan linkages, other cell surface anchorage mechanisms, such as transmembrane domains or disulfides, may be employed by fungal species to localize adhesins.

Clinical microbiology of bacterial and fungal sepsis in very-low-birth-weight infants

Twenty percent of very-low-birth-weight (<1500 g) preterm infants experience a serious systemic infection, and despite advances in neonatal intensive care and antimicrobials, mortality is as much as threefold higher for these infants who develop sepsis than their counterparts without sepsis during their hospitalization. Outcomes may be improved by preventative strategies, earlier and accurate diagnosis, and adjunct therapies to combat infection and protect the vulnerable preterm infant during an infection. Earlier diagnosis on the basis of factors such as abnormal heart rate characteristics may offer the ability to initiate treatment prior to the onset of clinical symptoms. Molecular and adjunctive diagnostics may also aid in diagnosing invasive infection when clinical symptoms indicate infection but no organisms are isolated in culture. Due to the high morbidity and mortality, preventative and adjunctive therapies are needed. Prophylaxis has been effective in preventing early-onset group B streptococcal sepsis and late-onset Candida sepsis. Future research in prophylaxis using active and passive immunization strategies offers prevention without the risk of resistance to antimicrobials. Identification of the differences in neonatal intensive care units with low and high infection rates and implementation of infection control measures remain paramount in each neonatal intensive care unit caring for preterm infants.

Candida albicans-induced inflammatory response in human keratinocytes. Candida albicans-induzierte Entzundungsantwort humaner Keratinozyten

Candida albicans strains 3153a, ATCC 48867, CBS 2730, DSM 70014, and Vir 13 were cultivated and sterile C. albicans filtrates were produced. The interaction of soluble Candida factors of these infiltrates with human HaCaT keratinocytes was assayed in vitro. The following parameters were analyzed: cell proliferation, protein synthesis, nuclear matrix protein (NMP) 41 release, cytokine release (IL-1beta, soluble IL-2 receptor, IL-6, and IL-8), and reactive oxygen species (ROS). Cell counts at 1, 12, and 24 h were significantly lower for C. albicans strains CBS 2730 and VIR 13 (P < 0.05). There was no significant change for the remaining strains. Neither the protein synthesis nor the NMP-41 release was significantly affected. IL-6 and IL-8 were stimulated by C. albicans filtrates to different amounts with higher levels in strains of low virulence. There was no effect on the other cytokines. The production of ROS by HaCaT keratinocytes was suppressed. The induction of an inflammatory keratinocyte response by soluble C. albicans factors may play a role among the host-yeast interactions.

Surface glycans of Candida albicans and other pathogenic fungi: physiological roles, clinical uses, and experimental challenges

Although fungi have always been with us as commensals and pathogens, fungal infections have been increasing in frequency over the past few decades. There is a growing body of literature describing the involvement of carbohydrate groups in various aspects of fungal disease. Carbohydrates comprising the cell wall or capsule, or as a component of glycoproteins, are the fungal cell surface entities most likely to be exposed to the surrounding environment. Thus, the fungus-host interaction is likely to involve carbohydrates before DNA, RNA, or even protein. The interaction between fungal and host cells is also complex, and early studies using whole cells or crude cell fractions often produced seemingly conflicting results. What was needed, and what has been developing, is the ability to identify specific glycan structures and determine how they interact with immune system components. Carbohydrate analysis is complicated by the complexity of glycan structures and by the challenges of separating and detecting carbohydrates experimentally. Advances in carbohydrate chemistry have enabled us to move from the foundation of composition analysis to more rapid characterization of specific structures. This, in turn, will lead to a greater understanding of how fungi coexist with their hosts as commensals or exist in conflict as pathogens.

The influence of surface carbohydrates during in vitro infection of mammalian cells by the dermatophyte Trichophyton rubrum

In order to better understand the role played by surface glycoconjugates during host cell adhesion and endocytosis of Trichophyton rubrum, we looked for the presence of carbohydrate-binding adhesins on the microconidia surface and their role on cellular interaction with epithelial and macrophages cells. The interaction of T. rubrum with chinese hamster ovary epithelial cells and their glycosylation-deficient mutants demonstrated a higher adhesion index in Lec1 and Lec2 mutants, that express mannose and galactose, respectively. Endocytosed fungi were shown preferentially in Lec2 cells. Addition of the carbohydrates to the interaction medium, pretreatment with lectins and with sodium periodate decreased the adhesion and endocytic index for all mutants. The ability of the fungus to penetrate into mammalian cells was confirmed in experiments using macrophages treated with cytochalasin D. Flow cytometric analysis showed that this fungus recognizes mannose and galactose. The binding was inhibited by the addition of methyl alpha-D-mannopyranoside and methyl alpha-D-galactopyranoside, and showed higher fluorescence intensity at 37 than at 28 degrees C. Trypsin treatment and heating of the cells reduced the binding, suggesting a (glyco) protein nature for the microconidia adhesins. The presence of lectin-like molecules in fungus cell could be observed by scanning electron microscopy of the fungus incubated with colloidal-gold labeled neoglycoproteins. Our results suggest that T. rubrum has the ability to invade mammalian cells and expresses carbohydrate-specific adhesins on microconidia surface that recognize mannose and galactose. These adhesins may play an important role on the adhesion and invasion of the fungus during the infectious process of dermatophytosis.

In vitro cariogenic potential of Candida albicans

The adherence and dissociation of Candida albicans, C. tropicalis, Streptococcus mutans and S. sanguis to six substrates including hydroxylapatite (HAP) which exhibit various hydrophobicity, was examined by the use of a bioluminescent adenosine triphosphate (ATP) assay. Dissolution of HAP by C. albicans or S. mutans was determined spectrophotometrically by the use of o-cresolphthalein complexone. In the adherence of C. tropicalis, S. mutans and S. sanguis, the amount of adherent cells correlated with the hydrophobicity of the substrates. In contrast, the adherence of C. albicans to HAP was extraordinary high, although the adherence of the fungi also correlated with the hydrophobicity of the substrates, except for HAP. The yeasts attached to HAP was effectively removed by high concentration of either phosphate or calcium ions. The amount of calcium-release from HAP caused by C. albicans and S. mutans was 113 microg ml(-1) (final pH = 3.45), and 5.4 microg ml(-1) (final pH 4.81), respectively and the maximum growth of C. albicans and S. mutans was 10(7) cfu ml(-1) and 7.4 x 10(12) cfu ml(-1), respectively. The results, taken together, suggest that C. albicans adhere to HAP specifically through electrostatic interaction, and that, in a much smaller number (1.0/7.4 x 10(5)), C. albicans possesses the ability to dissolve HAP to a greater extent (approximately 20-fold) when compared with S. mutans.

Current perspectives on ophthalmic mycoses

Fungi may infect the cornea, orbit and other ocular structures. Species of Fusarium, Aspergillus, Candida, dematiaceous fungi, and Scedosporium predominate. Diagnosis is aided by recognition of typical clinical features and by direct microscopic detection of fungi in scrapes, biopsy specimens, and other samples. Culture confirms the diagnosis. Histopathological, immunohistochemical, or DNA-based tests may also be needed. Pathogenesis involves agent (invasiveness, toxigenicity) and host factors. Specific antifungal therapy is instituted as soon as the diagnosis is made. Amphotericin B by various routes is the mainstay of treatment for life-threatening and severe ophthalmic mycoses. Topical natamycin is usually the first choice for filamentous fungal keratitis, and topical amphotericin B is the first choice for yeast keratitis. Increasingly, the triazoles itraconazole and fluconazole are being evaluated as therapeutic options in ophthalmic mycoses. Medical therapy alone does not usually suffice for invasive fungal orbital infections, scleritis, and keratitis due to Fusarium spp., Lasiodiplodia theobromae, and Pythium insidiosum. Surgical debridement is essential in orbital infections, while various surgical procedures may be required for other infections not responding to medical therapy. Corticosteroids are contraindicated in most ophthalmic mycoses; therefore, other methods are being sought to control inflammatory tissue damage. Fungal infections following ophthalmic surgical procedures, in patients with AIDS, and due to use of various ocular biomaterials are unique subsets of ophthalmic mycoses. Future research needs to focus on the development of rapid, species-specific diagnostic aids, broad-spectrum fungicidal compounds that are active by various routes, and therapeutic modalities which curtail the harmful effects of fungus- and host tissue-derived factors.

Candida albicans secreted aspartyl proteinases in virulence and pathogenesis

Candida albicans is the most common fungal pathogen of humans and has developed an extensive repertoire of putative virulence mechanisms that allows successful colonization and infection of the host under suitable predisposing conditions. Extracellular proteolytic activity plays a central role in Candida pathogenicity and is produced by a family of 10 secreted aspartyl proteinases (Sap proteins). Although the consequences of proteinase secretion during human infections is not precisely known, in vitro, animal, and human studies have implicated the proteinases in C. albicans virulence in one of the following seven ways: (i) correlation between Sap production in vitro and Candida virulence, (ii) degradation of human proteins and structural analysis in determining Sap substrate specificity, (iii) association of Sap production with other virulence processes of C. albicans, (iv) Sap protein production and Sap immune responses in animal and human infections, (v) SAP gene expression during Candida infections, (vi) modulation of C. albicans virulence by aspartyl proteinase inhibitors, and (vii) the use of SAP-disrupted mutants to analyze C. albicans virulence. Sap proteins fulfill a number of specialized functions during the infective process, which include the simple role of digesting molecules for nutrient acquisition, digesting or distorting host cell membranes to facilitate adhesion and tissue invasion, and digesting cells and molecules of the host immune system to avoid or resist antimicrobial attack by the host. We have critically discussed the data relevant to each of these seven criteria, with specific emphasis on how this proteinase family could contribute to Candida virulence and pathogenesis.

A TEM/SEM study of the microbial plaque overlying the necrotic gingival papillae of HIV-seropositive, necrotizing ulcerative periodontitis

The purpose of this study was to examine by transmission (TEM) and scanning electron microscopy (SEM) the supragingival microbial plaque overlying the ulcerated gingival papillae of necrotizing ulcerative periodontitis (NUP) lesions in HIV-seropositive patients. The microbiota of NUP and HIV-seropositive patients with periodontitis has been reported to be similar to that of conventional periodontitis in non-infected subjects, although several investigators have also reported high recovery rates of microbes not generally associated with the indigenous oral microbial flora. Light and electron microscopic observations and microbial culture studies indicate a similar high prevalence of spirochetes in both necrotizing ulcerative gingivitis (NUG) and NUP. In addition, several studies have reported more frequent isolation of Candida albicans from diseased periodontal sites in HIV-seropositive patients than from non-diseased sites. Ten male and six female patients, each HIV-seropositive and exhibiting NUP, constituted the study population. Two biopsies of involved gingival papillae from between posterior teeth were obtained from each patient and processed for examination by both TEM and SEM. Microscopic examination revealed a surface biofilm comprised of a mixed microbial flora of various morphotypes in 81.3% of biopsy specimens. The subsurface flora featured dense aggregations of spirochetes in 87.5% of specimens. Zones of aggregated polymorphonuclear leukocytes and necrotic cells were also noted. Yeasts were observed in 65.6% of specimens and herpes-like viruses in 56.5% of the specimens. Collectively, except for the presence of yeast and viruses, the results suggest that the microbial flora and possibly the soft tissue lesions of NUP and necrotizing ulcerative gingivitis are very similar.

The role of surface carbohydrates on the interaction of microconidia of Trichophyton mentagrophytes with epithelial cells

The presence of carbohydrate-binding adhesins on the microconidia of Trichophyton mentagrophytes surface and their role on cellular interactions were investigated. Flow cytometry showed that this fungus recognizes the sugars mannose and galactose. The binding was inhibited by the addition of methyl alpha-D-mannopyranoside and methyl alpha-D-galactopyranoside, and showed higher fluorescence intensity at 37 degrees C than 28 degrees C. Trypsin treatment and heating of the cells reduced the binding, suggesting a (glyco) protein nature of the microconidia adhesin. The interaction of the fungus to Chinese hamster ovary epithelial cells and its glycosylation-deficient mutants demonstrated a higher adhesion index in Lec1 and Lec2 mutants, which express mannose and galactose, respectively, as the terminal carbohydrate on the cell surface. Endocytosed fungi were shown preferentially in Lec2 cells. Addition of the carbohydrates methyl alpha-D-mannopyranoside and methyl alpha-D-galactopyranoside to the interaction medium, pretreatment of Lec1 and Lec2 cells with lectins Concanavalina A and Arachis hypogaea and pretreatment with sodium periodate decreased the adhesion and the endocytic index. Examination of thin section by transmission electron microscopy showed that after fungal ingestion by Lec2 cells the fungi are enclosed in a 'loose'-type vacuole while the other cells are found within a 'tight'-type membrane-bound cytoplasmic vacuole. Our results suggest the occurrence of carbohydrate-specific adhesins on microconidia surface that recognize mannose and galactose. This may have a role in the adhesion process during the infectious process of dermatophytosis.

Maintenance of mating cell integrity requires the adhesin Fig2p

Fungal adhesins represent a large family of serine/threonine-rich secreted glycoproteins. Adhesins have been shown to play roles in heterotypic and homotypic cell-cell adhesion processes, morphogenetic pathways and invasive/pseudohyphal growth, frequently in response to differentiation cues. Here we address the role of the Saccharomyces cerevisiae mating-specific adhesin Fig2p. Cells lacking FIG2 possess a variety of mating defects that relate to processes involving the cell wall, including morphogenetic defects, cell fusion defects, and alterations in agglutination activities. We found that mating-specific morphogenetic defects caused by the absence of FIG2 are suppressible by increased external osmolarity and that, during mating, fig2delta cells display reduced viability relative to wild-type cells. These defects result from alterations in signaling activated by the mating and cell integrity pathways. Finally, we show that fig2delta zygotes also have defects in zygotic spindle positioning that are osmoremedial, whereas the requirements for FIG2 in normal cell-cell agglutination and cell fusion during mating are insensitive to changes in the extracellular osmotic environment. We conclude that FIG2 performs distinct functions in the mating cell wall that are separable with respect to their ability to be suppressed by changes in external osmolarity and that a fundamental role of FIG2 in mating cells is the maintenance of cell integrity.

Pathogenesis, microbiological and clinical aspects of oral candidiasis (candidosis)

The clinical significance of the oral candidiasis (either as independent disorder, or as a part of another disease) is increasing with time. The diagnosis and local treatment of the oral candidiasis may not be satisfactory, this disorder cannot be eliminated without the correct diagnosis and management of the underlying disease. At the same time, some disorders, such as Candida induced leukoplakia, may significantly enhance tumor development. Fungal infection of the mouth is often the initial sign of several immunodeficiency diseases. It is, therefore, very important to clarify the background of a fungal infection, since this may be critical regarding the prognosis.

Candida albicans expresses a focal adhesion kinase-like protein that undergoes increased tyrosine phosphorylation upon yeast cell adhesion to vitronectin and the EA.hy 926 human endothelial cell line

The signaling pathways triggered by adherence of Candida albicans to the host cells or extracellular matrix are poorly understood. We provide here evidence in C. albicans yeasts of a p105 focal adhesion kinase (Fak)-like protein (that we termed CaFak), antigenically related to the vertebrate p125Fak, and its involvement in integrin-like-mediated fungus adhesion to vitronectin (VN) and EA.hy 926 human endothelial cell line. Biochemical analysis with different anti-chicken Fak antibodies identified CaFak as a 105-kDa protein and immunofluorescence and cytofluorimetric analysis on permeabilized cells specifically stain C. albicans yeasts; moreover, confocal microscopy evidences CaFak as a cytosolic protein that colocalizes on the membrane with the integrin-like VN receptors upon yeast adhesion to VN. The protein tyrosine kinase (PTK) inhibitors genistein and herbimycin A strongly inhibited C. albicans yeast adhesion to VN and EA.hy 926 endothelial cells. Moreover, engagement of alpha v beta 3 and alpha v beta 5 integrin-like on C. albicans either by specific monoclonal antibodies or upon adhesion to VN or EA.hy 926 endothelial cells stimulates CaFak tyrosine phosphorylation that is blocked by PTK inhibitor. A role for CaFak in C. albicans yeast adhesion was also supported by the failure of VN to stimulate its tyrosine phosphorylation in a C. albicans mutant showing normal levels of CaFak and VNR-like integrins but displaying reduced adhesiveness to VN and EA.hy 926 endothelial cells. Our results suggest that C. albicans Fak-like protein is involved in the control of yeast cell adhesion to VN and endothelial cells.

Influence of sub-inhibitory concentrations of conventional antifungals on metabolism of Candida albicans and on its adherence to polystyrene and extracellular matrix proteins

Five antifungal agents with different mechanisms of action were compared for their ability to affect mitochondrial dehydrogenase activity and adherence capacity of Candida albicans to polystyrene and extracellular matrix proteins. Only amphotericin B inhibited mitochondrial dehydrogenase activity when the culture medium was supplemented with galactose. 5-Fluorocytosine and terbinafine did not affect this activity, whereas itraconazole and fluconazole improved it. Furthermore, in these experimental conditions, the effect of sub-inhibitory concentrations of antifungals on adherence was dependent on the tested antifungal and the adherence surface: amphotericin B inhibited adherence to polystyrene and fibrinogen, but improved adherence to extracellular matrix. For all surfaces tested, when culture medium was supplemented with galactose, fluorocytosine did not affect adherence, and itraconazole, fluconazole and terbinafine inhibited adherence. Our results also confirmed the influence of the carbohydrates: sub-minimum inhibitory concentrations (MIC) of itraconazole increased or did not modify the mitochondrial metabolism of yeasts when the culture medium was supplemented with galactose, but this antifungal always decreased mitochondrial metabolism when the culture medium was supplemented with glucose. These data indicate that antifungals used below their MIC values can have various effects. It is important to distinguish the effects of antifungals on the metabolism of C. albicans from effects on its adherence capacity. The former effects are linked to the viability of the yeast and the latter depends on the colonization of cellular as opposed to inert surfaces.

Saliva promotes Candida albicans adherence to human epithelial cells

Adhesion of Candida cells to oral surfaces is an initial event in pathogenesis. Since specific immobilized salivary components mediate the binding of Candida albicans to hydroxyapatite, we hypothesized that saliva may also promote adherence to oral epithelia via a similar mechanism. In an in vitro model, C. albicans ATCC 10261 yeast cells adhered in a saturable manner to monolayers of three cultured human epithelial cell lines (A549, HEp-2, and HET-1A). The addition of whole saliva to the assay promoted the binding of C. albicans to all cell lines in a dose-dependent manner, but pre-incubation of the epithelial cells with pooled whole saliva had no effect on subsequent adherence. Pre-incubation of the yeast cells with pooled whole saliva, however, significantly enhanced (by up to 120%, P < 0.05) binding to epithelial cell monolayers, and pooled saliva that had been pre-incubated with C. albicans yeast cells was defective in promoting yeast adherence. There was a negative correlation (r = 0.68, P < 0.005) between specific IgA titers against whole cells of C. albicans and adherence-promoting activities for individual saliva samples. The adhesion-inhibitory effect of specific anti-C. albicans IgA was reversed by depletion of IgA from saliva by affinity chromatography. Factors in whole saliva, therefore, bound to the yeast cells, counter the C. albicans-specific salivary IgA inhibitory effect on adhesion and promote the adherence of C. albicans yeast cells to cultured epithelial cells.

Human immunodeficiency virus type 1 Tat binds to Candida albicans, inducing hyphae but augmenting phagocytosis in vitro

Tat, the human immunodeficiency virus type 1 (HIV-1) transactivating protein, binds through its RGD-motif to human integrin receptors. Candida albicans, the commonest cause of mucosal candidiasis in subjects infected with HIV-1, also possesses RGD-binding capacity. The present study reveals that Tat binds to C. albicans but not to C. tropicalis. Tat binding was markedly reduced by laminin and to a lesser extent by a complement C3 peptide containing the RGD motif, but not by a control peptide. The outgrowth of C. albicans was accelerated following binding of Tat, but phagocytosis of opsonized C. albicans was also increased after Tat binding. Thus, Tat binding promotes fungal virulence by inducing hyphae but may also reduce it by augmenting phagocytosis. The net effect of Tat in vivo is difficult to judge but in view of the many disease-promoting effects of Tat we propose that accelerating the formation of hyphae dominates over the augmentation of phagocytosis.

Involvement of alpha(v)beta3 integrin-like receptor and glycosaminoglycans in Candida albicans germ tube adhesion to vitronectin and to a human endothelial cell line

The present study was undertaken to investigate the expression of alpha(v)beta3 and alpha(v)beta5 integrin-like vitronectin receptors (VNRs) on Candida albicans germ tube and their involvement in its adhesion to vitronectin (VN) and human endothelial cells. By immunofluorescence and FACS analysis, several monoclonal antibodies directed against human alpha(v) or beta3 integrin subunit or alpha(v)beta3 and alpha(v)beta5 heterodimers, positively stained C. albicans germ tubes. C. albicans germ tubes specifically adhered (45-50%) to VN and this adhesion was markedly inhibited by RGD-, but not RGE-containing peptides. Adhesion of C. albicans germ tubes to VN was strongly inhibited by anti-alphav, anti-beta3 or anti-alpha(v)beta3, but not by alpha(v)beta5 monoclonal antibody. C. albicans germ tube adhesion to VN was also inhibited by glycosaminoglycans (GAGs) such as heparin or chondroitin sulphate. Finally, we show that C. albicans germ tubes adhere to the human EA.hy 926 endothelial cell line. This adhesion is markedly blocked by anti-beta3 monoclonal antibody, GRGDSP peptide or heparin, and is completely abolished by their combination. Overall these results indicate that C. albicans germ tube adherence to VN and to a human endothelial cell line is mediated by alpha(v)beta3, but not by alpha(v)beta5-like integrin, and depends on GAGs which may act by regulating alpha(v)beta3 integrin-like/VN adhesive interaction.

[Role of Lactobacillus as protector against vaginal candidiasis]

BACKGROUND

To evaluate the possible protector role of Lactobacillus against vaginal candidiasis.

PATIENTS AND METHOD

In vitro studies performed to assess the capacity of 15 Lactobacillus strains to block the adhesion of two Candida albicans and one C. glabrata strain to vaginal epithelial cells and to inhibit the growth of these yeasts. Moreover, the presence of Lactobacillus was analyzed in 115 vaginal exudates from women with vaginal candidiasis.

RESULTS

Only 8 of the 15 lactobacilli studied significantly blocked the adhesion of C. albicans Y18 to vaginal cells. Lactobacilli from group III showed the greatest blocking capacity (62.9%), followed by group II (50.6%) and group I (26.1%). In solid assays, none of the 15 Lactobacillus strains studied was able to inhibit growth of the 3 yeasts. However, in liquid assays some lactobacilli evidenced a certain degree of inhibitory power against C. albicans Y17 (35.7%, 41.7% and 38.1% of light transmittance for Lactobacillus groups I, II and III, respectively). Lactobacillus was detected in 89.6% of women with vaginal candidiasis (by microscopy in 87.8% and by culture in 72.2%).

CONCLUSIONS

These results lead us to suggest that probably Lactobacillus provides protection against vaginal candidiasis.

Virulence factors of Candida albicans

Candidiasis is a common infection of the skin, oral cavity and esophagus, gastrointestinal tract, vagina and vascular system of humans. Although most infections occur in patients who are immunocompromised or debilitated in some other way, the organism most often responsible for disease, Candida albicans, expresses several virulence factors that contribute to pathogenesis. These factors include host recognition biomolecules (adhesins), morphogenesis (the reversible transition between unicellular yeast cells and filamentous, growth forms), secreted aspartyl proteases and phospholipases. Additionally, 'phenotypic switching' is accompanied by changes in antigen expression, colony morphology and tissue affinities in C. albicans and several other Candida spp. Switching might provide cells with a flexibility that results in the adaptation of the organism to the hostile conditions imposed not only by the host but also by the physician treating the infection.

The ALS gene family of Candida albicans

The ALS gene family of Candida albicans encodes large cell-surface glycoproteins that are implicated in the process of adhesion to host surfaces. ALS genes are also found in other Candida species that are isolated from cases of clinical disease. Genes in the ALS family are differentially regulated by physiologically relevant mechanisms. ALS genes exhibit several levels of variability including strain- and allele-specific size differences for the same gene, strain-specific differences in gene regulation, the absence of particular ALS genes in certain isolates, and additional ALS coding regions in others. The differential regulation and genetic variability of the ALS genes results in a diverse cell-surface Als protein profile that is also affected by growth conditions. The ALS genes are one example of a gene family associated with pathogenicity mechanisms in C. albicans and other Candida species.

Structural requirements for hemoglobin to induce fibronectin receptor expression in Candida albicans

Hemoglobin (Hb) is a host factor that induces expression of a promiscuous receptor on Candida albicans for fibronectin (FN) and several other extracellular matrix proteins. FN receptor expression was induced by ferric (Hb(+)Met and Hb(+)CN), ferrous (HbCO and HbO(2)), and cobalt-protoporphyrin derivatives of Hb, whereas globin was inactive. The Hb derivatives all exhibited saturable, dose-dependent kinetics of FN receptor induction, suggesting that Hb may be acting as a receptor ligand. Soluble Hb bound saturably to a low-affinity binding site [K(d) = (1.1+/-0.2) x 10(-6) M] on C. albicans blastospores. However, uptake of (55)FeHb revealed that heme or iron transport into the cell is not required for induction, since internalization of (55)Fe from Hb did not occur until after induction of FN binding. The serum Hb-binding protein, haptoglobin, specifically abrogated this response, indicating that protein structure rather than the heme ligand or iron is necessary for induction of this signaling pathway. C. albicans also adhered to immobilized Hb, which was sufficient to induce FN receptor expression, and to Hb polymers that formed in defined Hb liquid media in the presence of cells. Formation of Hb polymers in solution required metabolic energy, since the aggregation process was halted with azide addition. Collectively, these data demonstrate that C. albicans recognizes polymerized Hb through multivalent low-affinity interactions, and this may be a host environmental cue that triggers extracellular matrix receptor expression at a septic site.

A Saccharomyces gene family involved in invasive growth, cell-cell adhesion, and mating

The cell wall of bakers' yeast contains a family of glycosyl-phosphatidylinositol (GPI)-linked glycoproteins of domain structure similar to the adhesins of pathogenic fungi. In wild-type cells each of these proteins has a unique function in different developmental processes (mating, invasive growth, cell-cell adhesion, or filamentation). What unifies these developmental events is adhesion, either to an inert substrate or to a cell. Although they differ in their specificities, many of these proteins can substitute for each other when overexpressed. For example, Flo11p is required during vegetative growth for haploid invasion and diploid filamentation, whereas Fig2p is required for mating. When overexpressed, Flo11p and Fig2p can function in mating, invasion, filamentation, and flocculation. The ability of Flo11p to supply Fig2p function in mating depends on its intracellular localization to the mating projection, where Fig2p normally functions in the adhesion of mating cells. Our data show that even distant family members retain the ability to carry out disparate functions if localized and expressed appropriately.

Cellular actin is affected by interaction with Candida albicans

Attachment of Candida albicans, an important opportunistic pathogen, to host tissues is an initial step in the development of the infection. The events occurring in the fungal and in the host cells after interaction are poorly understood. In this study we concentrated on the events occurring in the mammalian cells after the interaction with Candida, with emphasis on the cytoskeleton actin. Human cell line cells (HEp2) were exposed to C. albicans or C. albicans-secreted material (culture filtrate) (actin-rearranging Candida-secreted factor, arcsf). The HEp2 cells were examined for cellular changes using confocal laser microscopy (CLSM), transmission and scanning electron microscopy (TEM and SEM). The CLSM studies, using fluorescein isothiocyanate-labeled C. albicans and rhodamine phalloidin actin staining, revealed yeasts adhering to the HEp2 cells or internalized into the cells, with actin surrounding the fungi. Furthermore, actin rearrangement from filamentous network to actin aggregates was noticed. Interaction between the HEp2 cells and C. albicans could be demonstrated also by SEM and TEM after a 2-4-h exposure of the cells to the fungus. Yeasts and hyphae were found attaching to the surface and within the cells. CLSM studies revealed that exposure of HEp2 cells to arcsf was also followed by cellular actin rearrangement, reduced membrane ruffling and decreased cellular motility. The effect was dose- and time-dependent. All these data indicate that the interaction of Candida with HEp2 cells involves signaling events and affects the cellular actin.

Association of Mycobacterium leprae with human endothelial cells in vitro

Endothelial cell infection by Mycobacterium leprae has long been described histologically in all types of leprosy and in some of the acute reactions occurring in this disease. Recent evidence from experimental lepromatous neuritis indicates that M. leprae colonizes endothelial cells of epineural blood vessels even in sites of minimal infection, suggesting that interaction between these cells and M. leprae may play an important role in the selective localization of this organism to peripheral nerve. To begin to study the mechanisms involved, we have examined the interaction between M. leprae and human umbilical vein endothelial cells (HUVEC) in vitro using light microscopy, scanning and transmission electron microscopy, and confocal laser scanning microscopy. When M. leprae were added to confluent monolayers of HUVEC, uptake increased slowly to a maximum at 24 hours. Maximal percentages of infected cells were similar at ratios of organisms:cell over a range of 25:1 to 100:1. The bacilli appeared to lie within membrane-bound vacuoles at all time points. The kinetics of association of M. leprae with HUVEC are much slower than has previously been observed with macrophages, possibly due to differences in the binding of M. leprae. Compared with other pathogens that infect endothelial cells, M. leprae also appear to be ingested more slowly, and to a more limited degree. The receptors involved in M. leprae binding to endothelial cells and the impact of intracellular infection by M. leprae on these cells remain to be determined.

Oral colonization by Candida albicans

Candida albicans is a commensal yeast normally present in small numbers in the oral flora of a large proportion of humans. Colonization of the oral cavity by C. albicans involves the acquisition and maintenance of a stable yeast population. Micro-organisms are continually being removed from the oral cavity by host clearance mechanisms, and so, in order to survive and inhabit this eco-system, C. albicans cells have to adhere and replicate. The oral cavity presents many niches for C. albicans colonization, and the yeast is able to adhere to a plethora of ligands. These include epithelial and bacterial cell-surface molecules, extracellular matrix proteins, and dental acrylic. In addition, saliva molecules, including basic proline-rich proteins, adsorbed to many oral surfaces promote C. albicans adherence. Several adhesins present in the C. albicans cell wall have now been partially characterized. Adherence involves lectin, protein-protein, and hydrophobic interactions. As C. albicans cells evade host defenses and colonize new environments by penetrating tissues, they are exposed to new adherence receptors and respond by expressing alternative adhesins. The relatively small number of commensal Candida cells in the oral flora raises the possibility that strategies can be devised to prevent oral colonization and infection. However, the variety of oral niches and the complex adherence mechanisms of the yeast mean that such a goal will remain elusive until more is known about the contribution of each mechanism to colonization.

Adhesion of Candida albicans, but not Candida krusei, to salivary statherin and mimicking host molecules

The aim of the present study was to identify salivary molecules affecting adhesion of Candida albicans and Candida krusei to salivary pellicles and epithelial cells. Strains of C. albicans (GDH18, GDH3339, CA1957, ATCC 28366 and ATCC 10321), but not C. krusei (strains ATCC 14243 and Ck9), bound to saliva-coated hydroxyapatite and buccal epithelial cells. Parotid saliva fractions containing statherin, glycosylated proline-rich proteins (PRP) and as yet unidentified components mediated adhesion of strain GDH18; Fuc alpha 1-2Gal beta 1-4Glc partly inhibited the adhesion to those fractions not containing statherin. Pure statherin, but not PRP-1, mediated dose-dependent adhesion of C. albicans strain GDH18 to hydroxyapatite beads. Candida isolates (GDH18, GDH3339 and CA1957) bound somewhat more avidly to statherin/saliva relative to ATCC strains 28366 and 10321, while the opposite was true for adhesion to buccal epithelial cells. Adhesion of C. albicans strain GDH18 to saliva-coated hydroxyapatite and buccal epithelial cells was completely (93%) and partly (43%) blocked by statherin-specific immunoglobulin G (IgG) antibodies, respectively. Control IgG antibodies did not block Candida adhesion. Blockage of Candida adhesion to epithelial cells also occurred with Fuc alpha 1-2Gal beta 1-4Glc (49%) and N-acetylglucosamine (38%), while statherin specific IgG antibodies in combination with Fuc alpha 1-2Gal beta 1-4Glc almost completely eliminated Candida adhesion (79%). In addition, statherin in solution blocked the adhesion of strain GDH18 to epithelial cells by inducing aggregation of Candida cells.

Mechanisms of the proinflammatory response of endothelial cells to Candida albicans infection

Endothelial cells can influence significantly the host inflammatory response against blood-borne microbial pathogens. Previously, we found that endothelial cells respond to in vitro infection with Candida albicans by secreting interleukin 8 (IL-8) and expressing E-selectin, intercellular adhesion molecule 1 (ICAM-1), and vascular cell adhesion molecule 1 (VCAM-1). We have now examined the mechanisms mediating this endothelial cell response. We determined that C. albicans stimulated endothelial cells to synthesize tumor necrosis factor alpha (TNF-alpha), which in turn induced these infected cells to secrete IL-8 and express E-selectin by an autocrine mechanism. Expression of VCAM-1 was mediated not only by TNF-alpha but also by IL-1alpha and IL-1beta, all of which were synthesized by endothelial cells in response to C. albicans. These three cytokines remained primarily cell associated rather than being secreted. Candidal induction of ICAM-1 expression was independent of TNF-alpha, IL-1alpha, and IL-1beta. These observations demonstrate that different proinflammatory endothelial cell responses to C. albicans are induced by distinct mechanisms. A clear understanding of these mechanisms is important for therapeutically modulating the endothelial cell response to C. albicans and perhaps other opportunistic pathogens that disseminate hematogenously.

Candida albicans clinical isolates inactivated by formalin with different adherence to buccal epithelial cells induce proinflammatory and regulatory cytokines in human peripheral blood mononuclear cells

Besides the activation of phagocytes, the release of cytokines is the most important immunological defence mechanism of an organism against infection with Candida albicans. On the other hand cytokines induced in the organism by the yeast itself are able to modulate the immune responses of the host. We investigated whether eight clinically isolated strains of C. albicans inactivated by formalin as well as a laboratory strain were able to induce proinflammatory and regulatory cytokines in peripheral blood mononuclear cells (PBMC) of four different donors. Under our assay conditions the yeast strains induced the cytokines interleukin-1 beta (IL-1 beta), interferon-gamma (IFN-gamma) and interleukin-10 (IL-10) in PBMC to varying extents, but not the cytokine interleukin-4 (IL-4). We observed a difference in the reaction of the individual donors to the stimulus C. albicans but on the other hand the extent of the cytokine signal seemed to be dependent on the yeast strain as well. No correlation was found between the ability of the individual C. albicans strains to induce cytokines in PBMC and their ability to adhere to buccal epithelial cells. Determination of the cytokine induction potential of C. albicans strains possibly may contribute to the detection of new virulence factors of this yeast.

[Adherence and invasion-two pathogenicity factors in bacterial and fungal pathogens]

Pathogenicity factors such as adhesins, toxins, capsules, and other microbial gene products are involved as causative agents for infectious diseases. Therefore, the pathogenicity of organisms is increasingly studied on a molecular level. In bacteriology, unspecific adherence mechanisms and receptor-specific adhesins have to be distinguished. An adhesin-mediated invasion of pathogenic organisms in eukaryotic host cells could be relevant for pathogenesis. In mycology, various specific adhesins are involved in colonization of the host. Aspartyl proteases and phospholipases are relevant for adherence and invasion of host structures by pathogenic yeasts. Resistance factors have a central function in the distribution of infectious organisms. Gene-transfer, point mutations and efflux mechanisms are involved in the development of antibiotic drug resistance. Antifungal drug resistance does occur predominantly in Candida albicans against azole drugs. As underlying mechanisms point mutations in the ERG11 gene, encoding for the target enzyme of azoles, as well as energy-dependent efflux mechanisms were identified. Whether these mycotic factors are specific virulence factors or "fitness-factors" for a better survival of these organisms in the host, and if a possible alternating effect exists between resistance and virulence mechanisms is currently under investigation.

Effect of INT1 gene on Candida albicans murine intestinal colonization

BACKGROUND

Increased intestinal colonization with Candida albicans is believed to be a major factor predisposing immunocompromised and postsurgical patients to systemic candidiasis, although the mechanisms facilitating C. albicans colonization remain unclear. Because previous studies have linked the C. albicans INT1 gene to filament formation, epithelial adherence, and mouse virulence, experiments were designed to evaluate the effect of INT1 on intestinal colonization.

MATERIALS AND METHODS

Mice were orally inoculated with either the parent strain (CAF2, INT/INT1), an int1 heterozygote (CAG1, INT1/int1), an int1 homozygote (CAG3, int1/int1), or a reintegrant (CAG5, int1/int1 + INT1), and sacrificed 3 and 7 days later for quantitative analysis of cecal C. albicans.

RESULTS

Following oral inoculation with 10(3) C. albicans, only small numbers of each strain were recovered from the cecal flora of normal mice. However, in mice pretreated with oral antibiotics, cecal colonization of each strain was increased (P < 0.01). In addition, cecal colonization was reduced for all int1 mutant strains compared with the parent strain (P < 0.05). By light microscopy, all four C. albicans strains were easily observed in the ileal lumen as both budding yeast and filamentous forms, although only occasional yeast forms appeared adherent to the intestinal epithelium.

CONCLUSIONS

C. albicans readily colonized and replicated in the ceca of antibiotic-treated mice. The presence of two functional copies of INT1 appeared to facilitate C. albicans cecal colonization, suggesting that intestinal colonization may be another virulence factor associated with INT1 and that the gene product may be an attractive target to control C. albicans intestinal colonization.

Systemic infection following intravenous inoculation of mice with Candida albicans int1 mutant strains

The Candida albicans gene INT1 is associated with epithelial adhesion, hyphal formation, and virulence. C. albicans strains carrying two, one, or no functional INT1 alleles were used to assess the association between mortality and C. albicans persistence in the liver and kidney of intravenously inoculated mice. Mice were injected with 10(5) C. albicans CAF2 (parent strain, INT1/INT1), C. albicans CAG3 (homozygous disruptant, Int1/int1), or C. albicans CAG5 (heterozygous reintegrant, int1/int1 + INT1). Mortality was monitored and mice were sacrificed on Days 1, 7, 14, and 21 for quantitative analysis of kidney and liver microbes, with histologic analysis of these tissues as well. Mortality was highest for mice injected with the wild-type strain CAF2 (INT1/INT1) and lowest for mice injected with the homozygous disruptant CAG3 (int/int1). Yeast were readily cleared from the liver of all mice injected with any of the three C. albicans strains. Although the mutant strains CAG3 and CAG5 are defective for hyphal formation in vitro, there was histological evidence of abundant hyphal formation in the renal pelvis of mice injected with these strains. Compared to the wild-type strain, mutant strains were associated with reduced mortality but increased C. albicans persistence in the kidney. Thus, the absolute ability to form hyphae in the kidney did not appear to modulate either C. albicans-induced mortality or the course of progressive infection in the kidney. In addition, reduced virulence was paradoxically associated with increased, not decreased, persistence of C. albicans in the kidney.

Detection of Als proteins on the cell wall of Candida albicans in murine tissues

A murine model of disseminated candidiasis was utilized to determine whether Candida albicans Als proteins are produced in vivo. The kidneys, spleen, heart, liver, and lungs were collected from mice inoculated with one of three C. albicans strains (SC5314, B311, or WO-1). Immunohistochemical analysis of murine tissues by using a rabbit polyclonal anti-Als serum indicated that Als proteins were produced by each C. albicans cell in the tissues examined. Patterns of staining with the anti-Als serum were similar among the C. albicans strains tested. These data indicated that Als protein production was widespread in disseminated candidiasis and that, despite strain differences in ALS gene expression previously noted in vitro, Als protein production in vivo was similar among C. albicans strains. The extensive production of Als proteins in vivo and their presence on the C. albicans cell wall position these proteins well for a role in host-pathogen interaction.

An adhesin of the yeast pathogen Candida glabrata mediating adherence to human epithelial cells

Candida glabrata is an important fungal pathogen of humans that is responsible for about 15 percent of mucosal and systemic candidiasis. Candida glabrata adhered avidly to human epithelial cells in culture. By means of a genetic approach and a strategy allowing parallel screening of mutants, it was possible to clone a lectin from a Candida species. Deletion of this adhesin reduced adherence of C. glabrata to human epithelial cells by 95 percent. The adhesin, encoded by the EPA1 gene, is likely a glucan-cross-linked cell-wall protein and binds to host-cell carbohydrate, specifically recognizing asialo-lactosyl-containing carbohydrates.

Salivary histatin 5 induces non-lytic release of ATP from Candida albicans leading to cell death

Salivary histatins are potent in vitro antifungal proteins and have promise as therapeutic agents against oral candidiasis. We performed pharmacological studies directed at understanding the biochemical basis of Hst 5 candidacidal activity. Three inhibitors of mitochondrial metabolism: carbonyl cyanide p-chlorophenylhydrazone, dinitrophenol, and azide inhibited Hst 5 killing of Candida albicans, while not inhibiting cellular ATP production. In contrast, Hst 5 caused a drastic reduction of C. albicans intracellular ATP content, which was a result of an efflux of ATP. Carbonyl cyanide p-chlorophenylhydrazone, dinitrophenol, and azide inhibited Hst 5-induced ATP efflux, thus establishing a correlation between ATP release and cell killing. Furthermore, C. albicans cells were respiring and had polarized membranes at least 80 min after ATP release, thus implying a non-lytic exit of cellular ATP in response to Hst 5. Based on evidence that transmembrane ATP efflux can occur in the absence of cytolysis through a channel-like pathway and that released ATP can act as a cytotoxic mediator by binding to membrane purinergic receptors, we evaluated whether extracellular ATP released by Hst 5 may have further functional role in cell killing. Consistent with this hypothesis, purinergic agonists BzATP and adenosine 5'O-(thiotriphosphate) induced loss of C. albicans cell viability and purinergic antagonists prevented Hst 5 killing.

Effect of antifungal agents on the binding of Candida albicans to immobilized amino acids and bovine serum albumin

In this study the effects of different antifungal agents on the binding of Candida albicans yeast cells to different supports were examined. Pre-treatment with amphotericin B or dithiothreitol (DTT) severely reduced the ability of C. albicans yeasts to bind to plastic, while the effects of pre-treatment with fluconazole, ketoconazole or flucytosine were less marked. Both DTT and amphotericin B reduced the binding of yeasts to bovine serum albumin (BSA) and amino acids at low concentrations, while the other antifungal agents were effective at concentrations several-fold higher than their MICs. These data suggest that DTT and amphotericin B affect the yeast cell wall components, and alter both hydrophobic interactions with plastic, and the more specific interactions with BSA and amino acids. By contrast, the effect of the azoles and flucytosine appears to be largely restricted to hydrophobic interactions.

Candida glabrata: review of epidemiology, pathogenesis, and clinical disease with comparison to C. albicans

Until recently, Candida glabrata was considered a relatively nonpathogenic commensal fungal organism of human mucosal tissues. However, with the increased use of immunosuppressive agents, mucosal and systemic infections caused by C. glabrata have increased significantly, especially in the human immunodeficiency virus-infected population. A major obstacle in C. glabrata infections is their innate resistance to azole antimycotic therapy, which is very effective in treating infections caused by other Candida species. Candida glabrata, formerly known as Torulopsis glabrata, contrasts with other Candida species in its nondimorphic blastoconidial morphology and haploid genome. C. glabrata currently ranks second or third as the causative agent of superficial (oral, esophageal, vaginal, or urinary) or systemic candidal infections, which are often nosocomial. Currently, however, there are few recognized virulence factors of C. glabrata and little is known about the host defense mechanisms that protect against infection. Two established animal models (systemic and vaginal) have been established to study treatment, pathogenesis, and immunity. Treatment of C. glabrata infections can include azoles but often requires amphotericin B or flucytosine. This review summarizes all known clinical and experimental information about C. glabrata infections with comparisons to C. albicans as a means of contrasting the two species commonly observed and emphasizing the many recognized differences.

Fibronectin and laminin binding of urogenital and oral prevotella species

88 strains of five Prevotella species--P. bivia, P. buccae, P. disiens, P. oralis, and P. oris--were examined for their fibronectin and laminin binding properties with the aid of latex particle agglutination assays. Beside single protein binding activities, all species showed strains that adhered to both fibronectin and laminin. The oral species, P. buccae, P. oralis, and P. oris were found to interact with laminin to a pronouncedly higher extent than with fibronectin. The urogenital species, P. bivia and P. disiens showed comparable activities of binding to fibronectin and laminin, with P. bivia exhibiting higher matrix protein binding rates than P. disiens. Within the oral species group, P. oralis showed a higher percentage of fibronectin and laminin reactive strains than did P. buccae and P. oris. The finding of species-related different binding properties may throw some light on the known differences in clinical relevance and pathogenicity of the urogenital species, P. bivia and P. disiens, but does so only in part concerning the oral species, P. buccae, P. oralis, and P. oris. Moreover, the observed differences in matrix protein binding of Prevotella species may have implications in chemotaxis and opsonization on the one hand and maintenance of colonization activities under antibiotic therapy on the other.

Reduced pathogenicity of a Candida albicans MAP kinase phosphatase (CPP1) mutant in the murine mastitis model

Candida albicans strains with a deletion of the mitogen-activated protein kinase tyrosine phosphatase gene (CPP1) are derepressed in the yeast-to-hyphal transition on solid surfaces in vitro at ambient temperatures and this gene is therefore required for repression of the yeast-to-hyphal switch. The pathology caused by a CPP1 null mutant strain was compared with that of the null mutant into which the wild-type CPP1 gene was introduced by homologous recombination and with the wild-type parent strain in a murine mycotic mastitis model. The mammary glands of lactating mice (at day 5 postpartum) were infected for 2, 4 and 6 days with 1 x 10(5), 1 x 10(6) and 1 x 10(7) cell-forming units before euthanasia. Infected and non-infected control glands were evaluated histopathologically. The null mutant strains showed less severe pathology than the two control strains. The Cpplp tyrosine phosphatase may thus be considered a virulence determinant during localized infection in C. albicans.

Identification of Candida albicans ALS2 and ALS4 and localization of als proteins to the fungal cell surface

Additional genes in the growing ALS family of Candida albicans were isolated by PCR screening of a genomic fosmid library with primers designed from the consensus tandem-repeat sequence of ALS1. This procedure yielded fosmids encoding ALS2 and ALS4. ALS2 and ALS4 conformed to the three-domain structure of ALS genes, which consists of a central domain of tandemly repeated copies of a 108-bp motif, an upstream domain of highly conserved sequences, and a domain of divergent sequences 3' of the tandem repeats. Alignment of five predicted Als protein sequences indicated conservation of N- and C-terminal hydrophobic regions which have the hallmarks of secretory signal sequences and glycosylphosphatidylinositol addition sites, respectively. Heterologous expression of an N-terminal fragment of Als1p in Saccharomyces cerevisiae demonstrated function of the putative signal sequence with cleavage following Ala17. This signal sequence cleavage site was conserved in the four other Als proteins analyzed, suggesting identical processing of each protein. Primary-structure features of the five Als proteins suggested a cell-surface localization, which was confirmed by indirect immunofluorescence with an anti-Als antiserum. Staining was observed on mother yeasts and germ tubes, although the intensity of staining on the mother yeast decreased with elongation of the germ tube. Similar to other ALS genes, ALS2 and ALS4 were differentially regulated. ALS4 expression was correlated with the growth phase of the culture; ALS2 expression was not observed under many different in vitro growth conditions. The data presented here demonstrate that ALS genes encode cell-surface proteins and support the conclusion that the size and number of Als proteins on the C. albicans cell surface vary with strain and growth conditions.

Molecular cloning and characterization of a Candida albicans gene coding for cytochrome c haem lyase and a cell wall-related protein

Immunoscreening of a Candida albicans cDNA library with a monoclonal antibody (mAb 4C12) recognizing an epitope present in high-molecular-weight mannoprotein (HMWM) components specific for the mycelial cell walls (a 180 kDa component and a poly-dispersed 260 kDa species) resulted in the isolation of the gene CaCYC3 encoding for cytochrome c haem lyase (CCHL). The CaCYC3 gene was transcribed preferentially in mycelial cells in which two mRNA transcripts of 0.8 and 1 kb were found. The nucleotide and the deduced amino acid sequences of this gene displayed 45% homology and 46% identity, respectively, to the Saccharomyces cerevisiae CYC3 gene and shared common features with other reported genes encoding for CCHL. The CaCYC3 gene restored the respiratory activity when transformed in a S. cerevisiae cyc3- mutant strain. A C. albicans CYC3 null mutant was constructed after sequential disruption using the hisG::URA3::hisG ('ura-blaster') cassette. Null mutant cells were unable to use lactate as a sole carbon source and had a reduced ability to form germ tubes. Western immunoblotting analysis of subcellular fractions from wild-type and null mutant strains demonstrated the presence of two gene products, a 33kDa mitochondrial protein and a 40 kDa cell wall-associated moiety reacting with antibodies against CCHL, in both yeast cells and germ tubes. mAb 4C12 still reacted with the CaCYC3 null mutant (by immunofluorescence and immunoblotting) but showed an altered pattern of immunoreactivity against cell wall HMWM species, indicating a relationship between these moieties and the CaCYC3 gene products. The results suggest that the CaCYC3 gene encodes two proteins, one targeted to the mitochondria and the other to the cell wall.

Candidacidal activity of salivary histatins. Identification of a histatin 5-binding protein on Candida albicans

Candida albicans is the predominant species of yeast isolated from patients with oral candidiasis, which is frequently a symptom of human immunodeficiency virus infection and is a criterion for staging and progression of AIDS. Salivary histatins (Hsts) are potent in vitro antifungal agents and have great promise as therapeutic agents in humans with oral candidiasis. The molecular mechanisms by which Hsts kill yeast cells are not known. We report here, that unlike other antimicrobial proteins, Hsts do not display lytic activities to lipid membranes, measured by release and dequenching of the fluorescent dye calcein. Analysis of the magnitude and time course of Hst-induced calcein release from C. albicans cells further showed that loss of cell integrity was a secondary effect following cell death, rather than the result of primary disruption of the yeast cell membrane. 125I-Hst 5 binding studies indicated that C. albicans expressed a class of saturable binding sites (KD = 1 microM), numbering 8.6 x 10(5) sites/cell. Both Hst 3 and Hst 4 competed for these binding sites with similar affinities, which is consistent with the micromolar concentration of Hsts required for candidacidal activity. Specific 125I-Hst 5 binding was not detected to C. albicans spheroplasts, which were 14-fold less susceptible to Hst 5 killing, compared with intact cells in candidacidal assays. In overlay experiments, 125I-Hst 5 bound to a 67-kDa protein detected in C. albicans whole cell lysates and crude membrane fractions, but not in the yeast cell wall fraction. Consistent with the overlay data, cross-linking of 125I-Hst 5 to C. albicans resulted in the appearance of a specific 73-kDa 125I-Hst 5-containing complex that was not detected in the cell wall. 125I-Hst 5-binding protein of similar size was also observed in susceptible S. cerevisiae strain TI#20. This is the first description of Hst 5 binding sites on C. albicans which mediate cell killing and identification of a 67-kDa yeast Hst 5-binding protein. The binding characteristics of Hst 5 are in agreement with the observed potency of its biological effect and provide crucial information to the use of Hst 5 as a therapeutic agent. The presence of a specific C. albicans Hst 5-binding protein provides further insight into the potential mechanism of yeast killing and suggests a basis for differential activity between yeast killing and the nontoxic nature of Hsts to humans.