Candidemia at a tertiary-care hospital: epidemiology, treatment, clinical outcome and risk factors for death

The demographic, clinical and microbiological data of patients with candidemia at the "Hopital Universitario La Fe", a tertiary-care hospital in Valencia, Spain, from 1995 to 1997 was analyzed retrospectively. Candida spp. were isolated in blood cultures from 145 patients, 32% of whom were children (25% of these were neonates). The most common species isolated was Candida albicans, followed by Candida parapsilosis, Candida krusei and Candida tropicalis. Risk factors for candidemia included underlying disease, therapy with broad-spectrum antibiotics and the presence of a central venous catheter. The majority of children were treated with amphotericin B, whereas 52% of adults received fluconazole. Overall mortality was 44% (30% in children and 50% in adults), and attributable mortality was 30% (24% in children and 33% in adults). Multivariate analysis indicated that neutropenia, corticosteroid therapy, lack of antifungal treatment, and failure to replace the central venous catheter were factors associated with candidemia-related death. Among the adult population, an APACHE II score greater than 15 predicted candidemia-related death.

Two cases of fungemia due to Candida lusitaniae and a literature review

Reported here are two cases of candidemia caused by Candida lusitaniae that occurred in two immunocompromised patients at Hospital Universitario "La Fe" in Valencia, Spain. Case 1 involved a low-birth-weight premature infant with congenital nephrotic syndrome who was successfully treated with amphotericin B, and case 2 involved a 50-year old woman with a high-grade malignancy lymphoma who succumbed to the infection. Antifungal susceptibility testing of the Candida lusitaniae isolates recovered from both patients revealed sensitivity to amphotericin, 5-flucytosine and fluconazole. Results are presented and discussed together with a comprehensive review of the literature, covering all previously reported cases of fungemia caused by this emerging pathogen.

[Correlation between in vitro susceptibility to antifungal drugs and the clinical evolution of patients with candidiasis and cryptococcosis]

The increase in the incidence of fungal infections and the emergence of resistance call for the development of techniques for measuring in vitro antifungal susceptibility that are useful for predicting clinical outcome in patients suffering from these infections. In the past, the lack of standardized testing techniques led to poor intra- and interlaboratory reproducibility. Recently, the National Committee for Clinical Laboratory Standards (NCCLS) has developed a reference method for antifungal susceptibility testing, document M27A. This document is a necessary and important step towards the standardization of antifungal susceptibility testing, which has important implications in the analysis of clinical and microbiological data. This article provides a comprehensive review of studies correlating in vitro antifungal susceptibility testing and clinical outcome. In general, it is possible to predict the therapeutic outcome, especially in HIV infected patients with oropharyngeal candidiasis treated with fluconazole. However, in other more heterogeneous groups of patients it is more difficult to correlate the in vitro and in vivo data.

Heterogeneous mechanisms of azole resistance in Candida albicans clinical isolates from an HIV-infected patient on continuous fluconazole therapy for oropharyngeal candidosis

Molecular mechanisms of azole resistance in Candida albicans include alterations in the target enzyme and increased efflux of drug, but the impact of specific treatment regimens on resistance has not been established. A patient with advanced AIDS was enrolled in a longitudinal study to receive continuous oral fluconazole (FLU) 200 mg/day for the treatment of oropharyngeal candidosis (OPC). Oral cultures were obtained at time of enrollment, during episodes of OPC and quarterly for surveillance. The patient had five symptomatic relapses on continuous FLU during 43 months. All OPC episodes were successfully treated with increasing doses of FLU although increased FLU MICs were detected for C. albicans isolates with progression of time. DNA-typing techniques demonstrated that resistance developed in a persistent strain of C. albicans. Both FLU-resistant and isogenic isolates with reduced susceptibility were detected in the same clinical samples through multiple episodes. Analysis of molecular mechanisms of resistance revealed overexpression of MDR and CDR genes encoding efflux pumps (but not ERG11) in isolates with decreased FLU susceptibility. In addition, the presence of the G464S amino acid substitution in their lanosterol demethylase, affecting its affinity for FLU, was also detected. However, other isogenic, but FLU-susceptible isolates recovered from the same samples did not harbour the mutation, indicating microevolution of yeast populations within the oral cavity. In this patient, the continuous antifungal pressure exerted by FLU resulted in development of resistance of multifactorial nature. Despite their clonal origin, different subpopulations of C. albicans demonstrated distinct resistance mechanisms, including concomitant presence and absence of functional point mutations in ERG11 genes.

Characteristics of biofilm formation by Candida albicans

A variety of manifestations of Candida albicans infections are associated with the formation of biofilms on the surface of biomaterials. Cells in biofilms display phenotypic traits that are dramatically different from their free-floating planktonic counterparts, such as increased resistance to anti-microbial agents and protection form host defenses. Here, we describe the characteristics of C. albicans biofilm development using a 96 well microtitre plate model, microscopic observations and a colorimetric method based on the use of a modified tetrazolium salt (2,3-bis(2-methoxy-4-nitro-5-sulfo-phenyl)-2H-tetrazolium-5-carboxanilide, XTT) to monitor metabolic activities of cells within the biofilm. C. albicans biofilm formation was characterized by initial adherence of yeast cells (0-2 h), followed by germination and micro-colony formation (2-4 h), filamentation (4-6 h), monolayer development (6-8 h), proliferation (8-24 h) and maturation (24-48 h). The XTT-reduction assay showed a linear relationship between cellular density of the biofilm and metabolic activity. Serum and saliva pre-conditioning films increased the initial attachment of C. albicans, but had minimal effect on subsequent biofilm formation. Scanning electron microscopy and confocal scanning laser microscopy were used to visualize C. albicans biofilms. Mature C. albicans biofilms consisted of a dense network of yeasts cells and hyphal elements embedded within exopolymeric material. C. albicans biofilms displayed a complex three dimensional structure which demonstrated spatial heterogeneity and a typical architecture showing microcolonies with ramifying water channels. Antifungal susceptibility testing demonstrated the increased resistance of sessile C. albicans cells against clinically used fluconazole and amphotericin B as compared to their planktonic counterparts.

Prevalence of molecular mechanisms of resistance to azole antifungal agents in Candida albicans strains displaying high-level fluconazole resistance isolated from human immunodeficiency virus-infected patients

Molecular mechanisms of azole resistance in Candida albicans, including alterations in the target enzyme and increased efflux of drug, have been described, but the epidemiology of the resistance mechanisms has not been established. We have investigated the molecular mechanisms of resistance to azoles in C. albicans strains displaying high-level fluconazole resistance (MICs, > or =64 microg/ml) isolated from human immunodeficiency virus (HIV)-infected patients with oropharyngeal candidiasis. The levels of expression of genes encoding lanosterol 14alpha-demethylase (ERG11) and efflux transporters (MDR1 and CDR) implicated in azole resistance were monitored in matched sets of susceptible and resistant isolates. In addition, ERG11 genes were amplified by PCR, and their nucleotide sequences were determined in order to detect point mutations with a possible effect in the affinity for azoles. The analysis confirmed the multifactorial nature of azole resistance and the prevalence of these mechanisms of resistance in C. albicans clinical isolates exhibiting frank fluconazole resistance, with a predominance of overexpression of genes encoding efflux pumps, detected in 85% of all resistant isolates, being found. Alterations in the target enzyme, including functional amino acid substitutions and overexpression of the gene that encodes the enzyme, were detected in 65 and 35% of the isolates, respectively. Overall, multiple mechanisms of resistance were combined in 75% of the isolates displaying high-level fluconazole resistance. These results may help in the development of new strategies to overcome the problem of resistance as well as new treatments for this condition.

Standardized method for in vitro antifungal susceptibility testing of Candida albicans biofilms

Candida albicans is implicated in many biomaterial-related infections. Typically, these infections are associated with biofilm formation. Cells in biofilms display phenotypic traits that are dramatically different from those of their free-floating planktonic counterparts and are notoriously resistant to antimicrobial agents. Consequently, biofilm-related infections are inherently difficult to treat and to fully eradicate with normal treatment regimens. Here, we report a rapid and highly reproducible microtiter-based colorimetric assay for the susceptibility testing of fungal biofilms, based on the measurement of metabolic activities of the sessile cells by using a formazan salt reduction assay. The assay was used for in vitro antifungal susceptibility testing of several C. albicans strains grown as biofilms against amphotericin B and fluconazole and the increased resistance of C. albicans biofilms against these antifungal agents was demonstrated. Because of its simplicity, compatibility with a widely available 96-well microplate platform, high throughput, and automation potential, we believe this assay represents a promising tool for the standardization of in vitro antifungal susceptibility testing of fungal biofilms.

Biofilm formation by Candida dubliniensis

Candida dubliniensis is an opportunistic yeast closely related to Candida albicans that has been recently implicated in oropharyngeal candidiasis in human immunodeficiency virus-infected patients. Most manifestations of candidiasis are associated with biofilm formation, with cells in biofilms displaying properties dramatically different from free-living cells grown under normal laboratory conditions. Here, we report on the development of in vitro models of C. dubliniensis biofilms on the surfaces of biomaterials (polystyrene and acrylic) and on the characteristics associated with biofilm formation by this newly described species. Time course analysis using a formazan salt reduction assay to monitor metabolic activities of cells within the biofilm, together with microscopy studies, revealed that biofilm formation by C. dubliniensis occurred after initial focal adherence, followed by growth, proliferation, and maturation over 24 to 48 h. Serum and saliva preconditioning films enhanced the initial attachment of C. dubliniensis and subsequent biofilm formation. Scanning electron microscopy and confocal scanning laser microscopy were used to further characterize C. dubliniensis biofilms. Mature C. dubliniensis biofilms consisted of a dense network of yeasts cells and hyphal elements embedded within exopolymeric material. C. dubliniensis biofilms displayed spatial heterogeneity and an architecture showing microcolonies with ramifying water channels. Antifungal susceptibility testing demonstrated the increased resistance of sessile C. dubliniensis cells, including the type strain and eight different clinical isolates, against fluconazole and amphotericin B compared to their planktonic counterparts. C. dubliniensis biofilm formation may allow this species to maintain its ecological niche as a commensal and during infection with important clinical repercussions.

Comparison of DNA-based typing methods to assess genetic diversity and relatedness among Candida albicans clinical isolates

Three serial isolates of Candida albicans were obtained from each of five HIV infected patients with recurrent oropharyngeal candidiasis from the same geographical area. Isolates from one patient remained susceptible to fluconazole whereas serial isolates from the other four patients showed decreasing susceptibilities to the drug. Strain identity was investigated by pulse-field gel electrophoretic (PFGE) separation of chromosomes, restriction fragment length polymorphism (RFLP) of chromosomal DNA, Southern blot analysis with the moderately repetitive probe Ca3 of the materials present in the RFLP gels after transfer to nylon membranes, and random amplification of polymorphic DNA (RAPD). All techniques were able to group isolates obtained from the same patient. Techniques resulting in more complex banding profiles exhibited increased discriminatory power allowing detection of strain variants. Methods resulting in less complex banding patterns, especially Southern hybridization of SfiI digested chromosomal DNA with the moderately repetitive probe Ca3, were more helpful to determine isogenicity among isolates obtained from the same patient. The combination of results from methods with high discriminatory power (to maximize detection of strain variants) and methods resulting in less complex banding patterns (to allow determination of isogenic isolates) should facilitate the delineation of the epidemiology of C. albicans infection.

Interactions between Candida albicans and the human extracellular matrix component tenascin-C

Tenascins are large multimeric proteins that contain repeated structural motifs that include epidermal growth factor (EGF)-like repeats, fibronectin type III repeats and a globular fibrinogen-like domain, and are involved in tissue and organ morphogenesis, as well as in adhesion and migration of cells. C. albicans germ-tubes, but not blastospores, were able to bind to soluble human tenascin-C as revealed by an indirect immunofluorescence assay. However, materials present in cell wall extracts from both morphologies attached to tenascin-C immobilized in wells of a microtiter plate. The binding specificity was demonstrated by the inhibitory effect of antibodies against C. albicans cell wall components and an anti-tenascin antibody, but not anti-laminin antibody. Fibronectin, but not fibrinogen, inhibited binding, thus indicating a role of the fibronectin type III repeats in the interaction between the fungus and tenascin-C. Binding of C. albicans cell wall materials to tenascin was RGD- and divalent cation-independent.

Evidence for the presence of complex carbohydrates in Candida albicans cell wall glycoproteins

In order to test the hypothesis that cell wall glycoproteins of Candida albicans contained non-mannan oligosaccharides, the sugar composition of cell wall extracts and fractions of cell wall extracts was examined by means of fluorophore-assisted carbohydrate electrophoresis (FACE). In addition to the expected mannose, glucose, and N-acetyl-glucosamine, this analysis showed the presence of galactose, N-acetyl-galactosamine, fucose, and sialic acid and two unknown sugars. These sugars are also associated with complex oligosaccharides of mammalian glycoproteins. Presence of fucosylated cell wall components was further demonstrated by lectin-blotting analysis of cell wall extracts. Besides their structural role, complex carbohydrate structures on the surface of C. albicans may represent additional motifs through which interactions of this fungus with host cells and tissues could be established.

Candida albicans fibrinogen binding mannoprotein: expression in clinical strains and immunogenicity in patients with candidiasis

A 58 kDa cell wall-associated fibrinogen binding mannoprotein (mp58), previously characterized by our group in a Candida albicans laboratory strain (ATCC 26555), was found to be also present in the cell wall of clinical isolates of this fungus. Most strains examined appear to have functional mp58 species, as detected by their ability to bind fibrinogen. Western immunoblot analysis, with a monovalent polyclonal antibody generated against the mp58 species from strain ATCC 26555, revealed differences in recognition patterns depending on the strain tested and the culture conditions used. Serum samples from normal and Candida infected individuals were examined for the presence of antibodies against mp58 by Western immunoblotting. None of the sera from control individuals and patients suffering from superficial candidiasis contained antibodies against mp58. However, positive reactivity with this antigen and other cell wall constituents was detected for all sera from patients with confirmed systemic candidiasis. Together, these results suggest that mp58 could play an active role during infection and may be useful as a specific antigenic marker for candidiasis.

Cell wall proteinaceous components in isolates of Candida albicans and non-albicans species from HIV-infected patients with oropharyngeal candidiasis

Oropharyngeal candidiasis (OPC) remains a common opportunistic infection in HIV-infected patients. Candida albicans is the most frequent causative agent of OPC. However, non-albicans spp. are being increasingly isolated. Candidal cell wall proteins and mannoproteins play important roles in the biology and patogenesis of candidiasis. In the present study, we have analyzed the proteinaceous components associated with cell wall extracts from C. albicans, Candida tropicalis, Candida pseudotropicalis, Candida krusei, Candida glabrata, Candida parapsilosis, Candida guilliermondii and Candida rugosa obtained from HIV-infected patients with recurrent OPC. Cell wall proteinaceous components were extracted with beta-mercaptoethanol and analyzed using electrophoresis, immunoblotting (with antisera generated against C. albicans cell wall components, and with serum samples and oral saline rinses from patients with OPC), and lectin-blotting (concanavalin A) techniques. Numerous molecular species were solubilized from the various isolates. Major qualitative and quantitative differences in the polypeptidic and antigenic profiles associated with the cell wall extracts from the different Candida spp. were discernible. Some of the antibody preparations generated against C. albicans cell wall components were able to recognize homologous materials present in the extracts from non-albicans spp. Information on cell wall antigens of Candida species may be important in the therapy and prevention of HIV-related OPC.

Cell wall and secreted proteins of Candida albicans: identification, function, and expression

The cell wall is essential to nearly every aspect of the biology and pathogenicity of Candida albicans. Although it was initially considered an almost inert cellular structure that protected the protoplast against osmotic offense, more recent studies have demonstrated that it is a dynamic organelle. The major components of the cell wall are glucan and chitin, which are associated with structural rigidity, and mannoproteins. The protein component, including both mannoprotein and nonmannoproteins, comprises some 40 or more moieties. Wall proteins may differ in their expression, secretion, or topological location within the wall structure. Proteins may be modified by glycosylation (primarily addition of mannose residues), phosphorylation, and ubiquitination. Among the secreted enzymes are those that are postulated to have substrates within the cell wall and those that find substrates in the extracellular environment. Cell wall proteins have been implicated in adhesion to host tissues and ligands. Fibrinogen, complement fragments, and several extracellular matrix components are among the host proteins bound by cell wall proteins. Proteins related to the hsp70 and hsp90 families of conserved stress proteins and some glycolytic enzyme proteins are also found in the cell wall, apparently as bona fide components. In addition, the expression of some proteins is associated with the morphological growth form of the fungus and may play a role in morphogenesis. Finally, surface mannoproteins are strong immunogens that trigger and modulate the host immune response during candidiasis.

Serologic response to cell wall mannoproteins and proteins of Candida albicans

The cell wall of Candida albicans not only is the structure in which many biological functions essential for the fungal cells reside but also is a significant source of candidal antigens. The major cell wall components that elicit a response from the host immune system are proteins and glycoproteins, the latter being predominantly mannoproteins. Both the carbohydrate and protein moieties are able to trigger immune responses. Although cell-mediated immunity is often considered to be the most important line of defense against candidiasis, cell wall protein and glycoprotein components also elicit a potent humoral response from the host that may include some protective antibodies. Proteins and glycoproteins exposed at the most external layers of the wall structure are involved in several types of interactions of fungal cells with the exocellular environment. Thus, coating of fungal cells with host antibodies has the potential to influence profoundly the host-parasite interaction by affecting antibody-mediated functions such as opsonin-enhanced phagocytosis and blocking the binding activity of fungal adhesins for host ligands. In this review, the various members of the protein and glycoprotein fraction of the C. albicans cell wall that elicit an antibody response in vivo are examined. Although a number of proteins have been shown to stimulate an antibody response, for some of these species the response is not universal. On the other hand, some of the studies demonstrate that certain cell wall antigens and anti-cell wall antibodies may be the basis for developing specific and sensitive serologic tests for the diagnosis of candidasis, particularly the disseminated form. In addition, recent studies have focused on the potential for antibodies to cell wall protein determinants to protect the host against infection. Hence, a better understanding of the humoral response to cell wall antigens of C. albicans may provide the basis for the development of (i) effective procedures for the serodiagnosis of disseminated candidiasis and (ii) novel prophylactic (vaccination) and therapeutic strategies for the management of this type of infection.

Cloning of a cDNA fragment encoding part of the protein moiety of the 58-kDa fibrinogen-binding mannoprotein of Candida albicans

Immunoscreening of a Candida albicans expression library with antibodies against the 58 kDa fibrinogen-binding mannoprotein (mp58) of the fungus resulted in the isolation of clones encoding the protein moiety of this molecule. Sequence of the 0.9 kb cDNA of one of the clones selected for further analysis, revealed an open reading frame coding for 292 amino acids, which displays sequence similarity to proteins belonging to a family of immunodominant antigens of Aspergillus spp. The gene corresponding to this cDNA was named FBP1 (fibrinogen-binding protein). These results represent the first report on the identification of C. albicans genes encoding surface receptors for host proteins.

Expression of the fibrinogen binding mannoprotein and the laminin receptor of Candida albicans in vitro and in infected tissues

We have previously reported a 37 kDa laminin-binding protein (p37) and a 58 kDa fibrinogen-binding mannoprotein (mp58) on the surface of Candida albicans. A few yeast cells expressed both functional receptors at the surface while germ tubes expressed a functional mp58 fibrinogen but not a functional p37 laminin receptor. These receptors were heterogeneously dispersed at the surface as shown by binding of rabbit antiserum to mp58 (PAb anti-mp58) and antiserum to the human high affinity laminin receptor. In this report we have used a dual fluorescence technique to determine if the two receptors colocalize, perhaps as part of a receptor complex. Fibrinogen was used as a probe for mp58 and polyclonal antiserum generated to the p37 (PAb anti-p37) was used as a probe for the 37 kDa laminin-binding protein. Both receptors were heterogeneously distributed, but the receptors were not colocalized as the areas of concentration of each receptor were different. Immunohistochemical analysis of tissue sections from patients with disseminated and superficial candidiasis with PAb anti-p37 and PAb anti-mp58 revealed that both receptors were also expressed in infected tissues. The patterns of morphological expression were similar to the in vitro patterns detected by immunofluorescence.

Members of the Hsp70 family of proteins in the cell wall of Saccharomyces cerevisiae

Western blot (immunoblot) analysis of cell wall and cytosolic extracts obtained from parental and ssa1 and ssa2 single- and double-mutant strains of Saccharomyces cerevisiae showed that the heat shock protein 70 (Hsp70) products of these genes, previously thought to be restricted to the cell interior, are also present in the cell wall. A cell wall location was further confirmed by indirect immunofluorescence with intact cells and biotinylation of extracellular Hsp70. Hsp70s have been implicated in translocation across the membrane and as molecular chaperones, and changes in the profile of cell wall proteins suggested that these proteins may have a similar role in the cell wall.

Evidence for presence in the cell wall of Candida albicans of a protein related to the hsp70 family

We have previously reported the isolation of several clones from a cDNA expression library from Candida albicans, one of which was associated with a constitutively expressed 70-kDa protein. The moiety was present in the beta-mercaptoethanol extracts of cell walls from both blastoconidia and germ tubes. The surface expression of this moiety was revealed by an indirect immunofluorescence assay using affinity-purified antibody to the fusion protein produced by the clone. The 0.68-kb cDNA insert was sequenced. A database search revealed extensive homology with the 70-kDa family of stress or heat shock proteins (hsps). The 77% homology with another C. albicans HSP70 sequence suggested that this fragment represented a second member of the HSP70 family in this organism. Homology ranging from 65 to 76% was observed with members of four subfamilies (SSA, SSB, SSC, and SSD) of the Saccharomyces cerevisiae HSP70 gene family. The nucleic acid sequence and the deduced amino acid sequence of the open reading frame showed greatest homology with SSA1 and SSA2 sequences, and the gene corresponding to the cDNA clone was designated C. albicans SSA2. The relationship with the SSA family was supported by reactivity of the 70-kDa component with antibody recognizing the Ssa proteins of S. cerevisiae. The presence of an hsp70 in the cell wall was confirmed by two additional methods. Cell wall proteins were biotinylated with a non-membrane-permeable derivative to distinguish extracellular from cytosolic proteins. Biotinylated hsp70 was detected by Western blotting (immunoblotting) among the biotinylated components affinity purified by chromatography on streptavidin, thereby establishing its presence in the cell wall. Immunoelectron microscopy showed that the 70-kDa component was present at the cell surface as well as the outer surface of the plasma membrane and extended through the cell wall, occasionally appearing to reach the cell surface through channels. Northern (RNA) blot analysis showed that the gene was expressed in yeast cells growing in yeast extract-peptone medium at both 25 and 37 degrees C and in Lee medium at 25 degrees C and during formation of germ tubes in Lee medium 37 degrees C. No obvious increase in the expression level was detected after the temperature shift. Members of the hsp70 family have been reported to be immunoreactive. The fusion protein produced by the cDNA clone was recognized by serum from healthy individuals and patients with candidiasis. Since members of the hsp70 family of eucaryotic proteins are associated with chaperone and translocation functions, in addition to being immunogenic, this protein may play a role in the assembly and function of other cell wall proteins.

Common and form-specific cell wall antigens of Candida albicans as released by chemical and enzymatic treatments

In order to investigate the antigenic properties of the proteins and mannoproteins present in the cell surface of Candida albicans, and to identify individual antigenic moieties and their distribution, a number of polyclonal antisera were obtained by immunizing rabbits with chemical and enzymatic cell wall extracts obtained from intact cells from both growth forms (yeast and mycelium) of the fungus. Prior to injection, wall moieties present in the extracts were subjected to different treatments and/or purification procedures such as adsorption onto polystyrenelatex microbeads or electrophoretic separation. When used as probes in indirect immunofluorescence assays, the different antisera gave rise to different fluorescence patterns varying in intensity and topological localization of the reactivity in C. albicans cells. When the different antisera were used as probes in Western blots of wall proteinaceous materials solubilized from both blastospores and germ tubes, differences in reactivity and specificity were readily discernible, allowing to identify a number of common and form-specific cell wall components. Of special interest was the fact that one of the antisera raised, after adsorption onto heat-killed blastospores, specifically recognized medium to low molecular weight moieties present only in the cell wall extracts from germ tubes. When this antiserum was used as probe in immunofluorescence assays, reactivity was confined to the hyphal extensions. Together, these observations seem to indicate that the different antibody preparations described in this report could represent important tools in the study of different aspects of the cell wall biology in C. albicans, including the identification and study of the distribution of common and form-specific cell wall-bound antigens.

Dynamic expression of cell wall proteins of Candida albicans revealed by probes from cDNA clones

Five cDNA clones were selected from the positive clones detected by screening a germ tube expression library constructed in lambda gt11 with rabbit antisera raised against cell wall extracts of Candida albicans. The selected clones were amplified and used to obtain affinity purified antibodies by eluting from the expressed proteins that had been previously transferred onto nitrocellulose discs. The antibodies obtained were used as probes in immunoblots of the cell wall extracts separated by denaturing polyacrylamide electrophoresis. A single protein band was detected for each clone. Detection of products of the cloned sequences varied according to the extraction procedure and/or cell morphology. These products included bands exhibiting apparent molecular weights of 40, 58, 68 and 70 kDa present in beta-mercaptoethanol (beta ME) extracts from both yeast and germ tubes, and a 30 kDa beta ME extracted protein specific for germ tubes. The expression of these products at the cell surface was confirmed by indirect immunofluorescence. Expression of the mRNAs of the different cDNA clones varied according to growth- and morphology-related factors and showed no direct correlation between expression and presence in the cell wall. These observations suggest that complex mechanisms are involved in the regulation and expression of cell surface components of C. albicans.

Preliminary characterization of the material released to the culture medium by Candida albicans yeast and mycelial cells

Culture filtrate concentrates were obtained from Candida albicans yeast and mycelial cells grown in the presence of 14C-protein hydrolysate for radioactive labeling of cellular polypeptides. Both growth forms released to the medium minor but significant amounts of proteinaceous materials. The analysis of culture filtrate concentrates by means of SDS-polyacrylamide gel electrophoresis and fluorography revealed a similar and complex electrophoretic pattern, though some qualitative and quantitative differences between samples obtained from yeast and mycelial cells were observed. Materials released, mostly composed of mannoproteins as shown by their affinity towards concanavalin A, presented (i) cross-reactivity (by Western immunoblotting and ELISA) against polyclonal antisera to genuine cell wall components (among them the 58-kilodalton fibrinogen-binding mannoprotein) and (ii) high affinity for polystyrene-latex microbeads. Results presented suggest a possible common identity for the molecules shed to the medium and the cell wall protein and mannoprotein constituents.

Adhesion of Candida albicans to brain tissue of Macaca mulata in an ex vivo assay

An ex vivo adhesion assay was used to examine adhesion of Candida albicans yeast cells to brain tissue of the primate Macaca mulata. Tissues from frontal lobes and striatum (caudate, putamen, and portions of the globus pallidus) were used in the assay. Yeast cells adhered to gray matter at about six times the level of adhesion to white matter. The fungus was able to bind to different cell types within the cortex, basal ganglia, and white matter. Binding to neurons, small neurons or glia, endothelial cells, and neuropil was observed.

Evidence for the presence of collagenous domains in Candida albicans cell surface proteins

Rabbit polyclonal antibodies (PAbs) directed towards the amino-terminal cysteine-rich 7S domain (PAb anti-7S), the major internal collagenous domain (PAb anti-type IV), and the C-terminal noncollagenous region (PAb anti-NC1) of the type IV collagen molecule were probed by indirect immunofluorescence against Candida albicans blastoconidia and germinated blastoconidia. Most nongerminating cells and mother blastoconidia from which germ tubes originated showed strong fluorescence when PAb anti-7S was used, whereas with PAb anti-type IV, fluorescence was found almost exclusively on the surface of filamentous forms. A patched fluorescent pattern rather than a homogenous confluent fluorescence was observed in all cases. No fluorescent cells were observed with PAb anti-NC1. By Western immunoblotting, PAb anti-type IV cross-reacted primarily with a polypeptide of 37 kDa present in wall extracts obtained from intact cells of both growth forms by treatment with beta-mercaptoethanol, whereas PAb anti-7S recognized a major 58-kDa antigen also present in both extracts, along with some other high-molecular-mass (> 106-kDa) polydisperse species present only in the material released from blastoconidia with beta-mercaptoethanol. No reactive bands were observed when PAb anti-NC1 was used as a probe in Western immunoblotting experiments. The sensitivities or resistances to collagenase digestion of the different polypeptides that cross-reacted with PAbs anti-type IV and anti-7S suggest the existence of cell wall components in C. albicans that contain epitopes that mimic the collagenous domains of the type IV collagen molecule.

Comparative study of the C3d receptor and 58-kilodalton fibrinogen-binding mannoproteins of Candida albicans

Using polyclonal antibodies (PAbs) raised against the Candida albicans C3d receptor (CR2; PAb anti-CR2) and the 58-kDa fibrinogen-binding mannoprotein (mp58; PAb anti-mp58) as well as ligand interactions, we have studied the relationship between these two receptors. In an indirect immunofluorescence assay with germ tubes, greater intensity was observed on the mother blastoconidium when PAb anti-CR2 was used, whereas greater intensity was localized to the hyphal extension when PAb anti-mp58 or binding of soluble fibrinogen was used. No competition or change in the fluorescence pattern was observed in dual-labeling experiments with PAb anti-CR2 and either fibrinogen or PAb anti-mp58. Binding competition also was not observed in an enzyme-linked immunosorbent assay using the components present in a beta-mercaptoethanol extract from the cell wall of germ tubes. In immunoblots, PAb anti-CR2 recognized three different discrete bands with apparent molecular masses of 21, 40, and 66 kDa in the beta-mercaptoethanol extracts from the cell wall, whereas a different, single, broader band with an apparent molecular mass of 58 kDa was detected with PAb anti-mp58. However, when nondenaturing conditions were used to separate the materials present in the cell wall extracts, no reactivity could be detected on Western blots (immunoblots) with PAb anti-mp58. When PAb anti-CR2 was used for analysis, a single band migrating in the area corresponding to approximately 40 kDa was detected. These observations suggest a higher molecular weight for mp58 and one or more of the components detected with PAb anti-CR2 in their native state.

Adherence of germ tubes of Candida albicans to tissues from immunocompromised mice

The influence of immune status of the host on binding of germ tubes of Candida albicans to murine tissue sections in an ex vivo assay was examined. Generally, germ tubes appeared randomly adhered to the tissues examined and binding was unaffected by immunodeficiency induced by treatment with cyclophosphamide and cortisone acetate. Adherence was somewhat reduced in spleen and kidney sections or increased in liver sections and unchanged in lymph node sections from treated mice compared to sections from control animals. Scanning electron micrographs showed organisms appeared to be loosely or tightly bound to the surface or partially embedded in spleen sections from both control and treated mice. These observations suggested that qualitative and quantitative difference in adhesion of germ tubes to various tissues may contribute little to the susceptibility of the immunodeficient animal to candidal infection.

Murine tissues exposed to cytotoxic drugs display altered patterns of Candida albicans adhesion

An ex vivo adhesion assay was used to examine the binding of Candida albicans yeast cells to tissues from mice treated with cytotoxic drugs such as lipopolysaccharide and the clinically used anticancer drugs doxorubicin, cisplatin, and vincristine. No major differences were observed in binding of the fungal cells to liver and kidney tissues from treated or untreated animals. All drug-treated spleens displayed altered patterns of C. albicans adhesion compared with the control group, with yeast cells bound not only to the marginal zone but also to the white and red pulp. Immunostaining for macrophages, which are proposed as the site of normal adhesion, showed no apparent differences between the control and the experimental spleens that could account for the change in adhesion patterns. Scanning electron microscopy images suggested that yeast binding to the white pulp of treated tissue is mediated through fibers, perhaps extracellular matrix components exposed as result of the cytotoxic treatment. Exposure of new attachment sites for C. albicans in treated tissues may facilitate initiation of infection.

Binding of the extracellular matrix component entactin to Candida albicans

We have investigated the interaction between Candida albicans and entactin, a recently characterized glycoprotein present in the extracellular matrix, especially in the basement membrane. Organisms of both the yeast and the hyphal morphologies of the fungus had the ability to bind recombinant entactin, as detected by an indirect immunofluorescence assay. Material present in the 2-mercaptoethanol cell wall extracts from both C. albicans growth forms was capable of binding to immobilized recombinant entactin in a dose-dependent manner. Binding to entactin was approximately twice that observed for laminin. Binding of an extract component(s) to entactin was partially inhibited by an Arg-Gly-Asp-Ser peptide. A polyclonal antientactin antiserum, as well as a pooled antiserum preparation raised against components present in different C. albicans cell wall extracts, completely or almost completely abolished binding. The existence of morphology-specific receptor-like molecules which bind to different domains of the entactin molecule was ruled out in a competition binding assay. The entactin-binding material(s) in the cell wall also displayed some ability to bind laminin and fibronectin, since preadsorption in the presence of these extracellular matrix components resulted in reduction of binding to entactin. Moieties with a molecular mass of approximately 25, 44, and 65 kDa present in the 2-mercaptoethanol cell wall extracts from both blastoconidia and germ tubes were detected in a ligand affinity blotting experiment as having the ability to bind entactin. Interactions between C. albicans and entactin could be important in mediating adhesion of the fungus to the host tissues and may play a role in the establishment of the disseminated form of the disease.

A comparative study on cell wall antigens and cell surface hydrophobicity in clinical isolates of Candida albicans

Characterization of common cell surface-bound antigens in Candida albicans strains, particularly those expressed in the walls of mycelial cells might be useful in the diagnosis of systemic candidiasis. Hence, antigenic similarities among wall proteins and mannoproteins from C. albicans clinical serotype A and B isolates, were studied using polyclonal (mPAbs) and monoclonal (MAb 4C12) antibodies raised against wall antigens from the mycelial form of a common C. albicans serotype A laboratory strain (ATCC 26555). Zymolyase digestion of walls isolated from cells of the different strains studied grown at 37 degrees C (germination conditions), released, in all cases, numerous protein and mannoprotein components larger than 100 kDa, along with a 33-34 kDa species. The pattern of major antigens exhibiting reactivity towards the mPAbs preparation was basically similar for all the serotype A and B isolates, though minor strain-specific bands were also observed. The immunodeterminant recognized by MAb 4C12 was found to be absent or present in very low amounts in C. albicans isolates other than the ATCC 26555 strain, yet high molecular weight species similar in size (e.g., 260 kDa) to the wall antigen against which MAb 4C12 was raised, were observed, particularly in wall digests from serotype A strains. Cell surface hydrophobicity, an apparently important virulence factor in C. albicans, of the cell population of each serotype B strain was lower than that of the corresponding serotype A counterparts, which is possibly due to the fact that the former strains exhibited a reduced ability to form mycelial filaments under the experimental conditions used.

Heterogeneous surface distribution of the fibrinogen-binding protein on Candida albicans

As detected by indirect immunofluorescence and confocal microscopy, fibrinogen binding was heterogeneously distributed on the surface of Candida albicans. A low level of binding was generally observed homogeneously distributed on some yeast and most hyphal extensions of germ tubes. However, on most hyphal extensions, there were randomly distributed areas of increased expression, as revealed by patches of greater fluorescence intensity.

Evidence for the presence of a high-affinity laminin receptor-like molecule on the surface of Candida albicans yeast cells

Two polypeptides of 37 and 67 kDa that bind laminin were detected in cell wall extracts of Candida albicans blastoconidia. The 37-kDa species, found only in yeast cell wall extracts, cross-reacted with a rabbit polyclonal antibody (PAb 4160) directed towards the carboxyl-terminal laminin-binding domain present in the human 67-kDa high-affinity laminin receptor (67LR) and its 37-kDa precursor (37LRP), whereas another antibody (PAb 4056), directed against internal domains of 67LR and 37LRP, recognized a 37-kDa species in wall extracts from both blastoconidia and germinated blastoconidia. Indirect immunofluorescence with PAb 4160 showed a patchy binding pattern only on yeast cells that represented about 10% of the entire blastoconidia population.

Adherence of Candida albicans germ tubes to murine tissues in an ex vivo assay

Adhesion of Candida albicans germ tubes to murine tissues was examined. An ex vivo assay previously employed to examine adhesion of yeast cells of C. albicans was adapted for use with germ tubes. Binding of germ tubes to kidney, liver, spleen, and lymph node tissues was found to occur throughout the tissue section, with little morphologic specificity. In general, more organisms adhered to spleen and lymph node tissues than to kidney and liver tissues. Observation of adhesion with scanning organisms adhered to spleen and lymph node tissues than to kidney and liver tissues. Observation of adhesion with scanning electron microscopy showed three germ tube-tissue interactions described as loose, tight, or embedded.

Diagnosis of systemic candidiasis by enzyme immunoassay detection of specific antibodies to mycelial phase cell wall and cytoplasmic candidal antigens

Diagnosis of systemic Candida infections was attempted by the use of an enzyme-linked immunosorbent assay (EIA) to detect IgG antibodies towards cell wall-bound and cytoplasmic candidal antigens. Cell wall antigens were sequentially solubilized by treatment of germinated blastoconidia of Candida albicans (ATCC 26555 strain) with beta-mercaptoethanol (beta ME extract) and digestion with Zymolyase 20T, a beta-glucanase preparation (Zymolyase extract). Protoplasts obtained after treatment with Zymolyase were osmotically lysed (cytoplasmic antigens). Sera were obtained from patients with systemic (n = 28) and superficial (n = 46) candidiasis. Control sera were obtained from normal healthy individuals (n = 31) and from hospitalized patients at low (n = 36) and at high (n = 13) risk of developing systemic candidiasis yet showing no symptoms of candidal infection. Detection of antibodies in crude sera samples by EIA using all of these antigenic extracts was highly specific (98-100%), but sensitivity of the method was low (3.5-17.8%). However, adsorption of sera with latex microspheres coated with purified Candida mannan in order to selectively remove anti-mannan antibodies prior to EIA improved the diagnostic efficiency of this test. Improvement was particularly noticeable when the beta ME extract was used as antigenic preparation, yielding a sensitivity of 89.2% and a specificity of 98.6%.