Characterization of agglutinin-like sequence genes from non-albicans Candida and phylogenetic analysis of the ALS family

Not gently down the stream: flow induces amyloid bonding in environmental and pathological fungal biofilms

Surface-bound biofilms are the predominant microbial life form in the environment and host organisms. Many biofilms survive and thrive under physical stress from liquid flow in streams, fuel lines, blood, and airways. Strategies for biofilm persistence include shear-dependent adhesion (called catch bonding). In some cases, biofilms are physically strengthened by the formation of cross-β bonds between proteins: the same process that generates amyloids. Cross-β bonds have low dissociation rates. In biofilms, they bind cells to substrates, each other, and the biofilm matrix. Most fungal adhesins include amino acid sequences that can form amyloids. Shear flow activates these adhesins by unfolding pseudo-stable protein domains. The unfolding exposes sequence segments that can form cross-β bonds. These segments interact to form high-avidity adhesin patches on the cell surface. Thus, cross-β bonding is a consequence of flow-induced exposure of the cross-β core sequences. Liquid flow leads to both biofilm establishment through catch bonding and biofilm strengthening through amyloid-like bonds. This shear-dependent induction of biofilm establishment and persistence is a model for many microbial systems.IMPORTANCEThe microbes in biofilms persist in many environments, including industrial and pathological settings. These surface-associated communities show high resistance to antibiotics and microbicides. Biofilms also resist scouring by liquid flow. Amyloid-like cross-β bonds allow the establishment, strengthening, and persistence of many biofilms. This discovery opens a window on the novel use of anti-amyloid strategies to control microbes in biofilms.

Features of the rare pathogen Meyerozyma guilliermondii strain SO and comprehensive in silico analyses of its adherence-contributing virulence factor agglutinin-like sequences

Meyerozyma guilliermondii is a rare yeast pathogen contributing to the deadly invasive candidiasis. M. guilliermondii strain SO, as a promising protein expression host, showed 99% proteome similarity with the clinically isolated ATCC 6260 (type strain) in a recent comparative genomic analysis. However, their in vitro virulence features and in vivo pathogenicity were uncharacterized. This study aimed to characterize the in vitro and in vivo pathogenicity of M. guilliermondii strain SO and analyze its Als proteins (MgAls) via comprehensive bioinformatics approaches. M. guilliermondii strain SO showed lower and higher sensitivity towards β-mercaptoethanol and lithium, respectively than the avirulent S. cerevisiae but exhibited the same tolerance towards cell wall-perturbing Congo Red with C. albicans. With 7.5× higher biofilm mass, M. guilliermondii strain SO also demonstrated 75% higher mortality rate in the zebrafish embryos with a thicker biofilm layer on the chorion compared to the avirulent S. cerevisiae. Being one of the most important Candida adhesins, sequence and structural analyses of four statistically identified MgAls showed that MgAls1056 was predicted to exhibit the most conserved amyloid-forming regions, tandem repeat domain and peptide binding cavity (PBC) compared to C. albicans Als3. Favoured from the predicted largest ligand binding site and druggable pockets, it showed the highest affinity towards hepta-threonine. Non-PBC druggable pockets in the most potent virulence contributing MgAls1056 provide new insights into developing antifungal drugs targeting non-albicans Candida spp. Virtual screening of available synthetic or natural bioactive compounds and MgAls1056 deletion from the fungal genome should be further performed and validated experimentally.

Exploring the Biology, Virulence, and General Aspects of Candida dubliniensis

Fungal infections have become a growing public health concern, aggravated by the emergence of new pathogenic species and increasing resistance to antifungal drugs. The most common candidiasis is caused by Candida albicans; however, Candida dubliniensis has become an emerging opportunistic pathogen, and although less prevalent, it can cause superficial and systemic infections, especially in immunocompromised individuals. This yeast can colonize the oral cavity, skin, and other tissues, and has been associated with oral infections in patients with human immunodeficiency virus (HIV) and acquired immunodeficiency syndrome (AIDS), making it difficult to treat. The special interest in the study of this species lies in its ability to evade commonly used antifungal drugs, such as fluconazole, under different concentrations. In addition, it is difficult to identify because it can be confused with the species C. albicans, which could interfere with adequate treatment. Although the study of virulence factors in C. dubliniensis is limited, proteomic comparisons with C. albicans indicate that these virulence factors could be similar between the two species. However, differences could exist considering the evolutionary processes and lifestyle of each species. In this study, a detailed review of the current literature on C. dubliniensis was conducted, considering aspects such as biology, possible virulence factors, immune response, pathogen-host interaction, diagnosis, and treatment.

Similarities and Differences among Species Closely Related to Candida albicans: C. tropicalis, C. dubliniensis, and C. auris

Although Candida species are widespread commensals of the microflora of healthy individuals, they are also among the most important human fungal pathogens that under certain conditions can cause diseases (candidiases) of varying severity ranging from mild superficial infections of the mucous membranes to life-threatening systemic infections. So far, the vast majority of research aimed at understanding the molecular basis of pathogenesis has been focused on the most common species—Candida albicans. Meanwhile, other closely related species belonging to the CTG clade, namely, Candida tropicalis and Candida dubliniensis, are becoming more important in clinical practice, as well as a relatively newly identified species, Candida auris. Despite the close relationship of these microorganisms, it seems that in the course of evolution, they have developed distinct biochemical, metabolic, and physiological adaptations, which they use to fit to commensal niches and achieve full virulence. Therefore, in this review, we describe the current knowledge on C. tropicalis, C. dubliniensis, and C. auris virulence factors, the formation of a mixed species biofilm and mutual communication, the environmental stress response and related changes in fungal cell metabolism, and the effect of pathogens on host defense response and susceptibility to antifungal agents used, highlighting differences with respect to C. albicans. Special attention is paid to common diagnostic problems resulting from similarities between these species and the emergence of drug resistance mechanisms. Understanding the different strategies to achieve virulence, used by important opportunistic pathogens of the genus Candida, is essential for proper diagnosis and treatment.

MOLECULAR DETECTION OF THE TWO VIRULENCE GENES HWP1 AND ALS1 IN CANDIDA SPECIES ISOLATED FROM ONYCHOMYCOSIS

OBJECTIVE

The aim: This article was aimed to assess the prevalence of Candida species causing nail infections and to investigate the most important virulence genes that cause adhesion.

PATIENTS AND METHODS

Materials and methods: Samples were collected from General Hospital and the outpatient's clinics in Thi-Qar Province, southern Iraq, during the period from January 2021 to May 2021. Samples were inoculated on Sabouraud Dextrose Agar plates containing 0.5 mg chloramphenicol, then Petri dishes were incubated at 30°C under aerobic conditions and observed for Candida species growth for 24-72 hrs. All isolates were identified by morphologic and chromatic properties on CHROMagar and by Api Candida.

RESULTS

Results: Twenty five isolates were obtained from hundred samples, which belong to five species of the genus Candida, distributed in percentage 9(36%), 4(16%), 4(16%), 4(16%) and 3(12%) of C. glabrata, C. krusei, C. albicans, C. famata and C. tropicalis consecutively and one isolate was not identified. Monoplex PCR technique was used to detect virulence genes (hwp1 and als1) of Candida species. Four Candida albicans isolates (16%) were carried of both hwp1 and als1 genes.

CONCLUSION

Conclusions: The virulence gene (hwp1) can be relied upon in molecular detection as a special diagnostic tool of Candida albicans species except other types causing Candidal onychomycosis.

Opportunistic yeast pathogen Candida spp.: Secreted and membrane-bound virulence factors

Candidiasis is a fungal infection caused by Candida spp. especially Candida albicans, C. glabrata, C. parapsilosis and C. tropicalis. Although the medicinal therapeutic strategies have rapidly improved, the mortality rate due to candidiasis has continuously increased. The secreted and membrane-bound virulence factors (VFs) are responsible for fungal invasion, damage and translocation through the host enterocytes besides the evasion from host immune system. VFs such as agglutinin-like sequences (Als), heat shock protein 70, phospholipases, secreted aspartyl proteinases (Sap), lipases, enolases and phytases are mostly hydrolases which degrade the enterocyte membrane components except for candidalysin, the VF acts as a peptide toxin to induce necrotic cell lysis. To date, structural studies of the VFs remain underexplored, hindering their functional analyses. Among the VFs, only secreted aspartyl proteinases and agglutinin-like sequences have their structures deposited in Protein Data Bank (PDB). Therefore, this review scrutinizes the mechanisms of these VFs by discussing the VF-deficient studies of several Candida spp. and their abilities to produce these VFs. Nonetheless, their latest reported sequential and structural analyses are discussed to impart a wider perception of the host-pathogen interactions and potential vaccine or antifungal drug targets. This review signifies that more VFs structural investigations and mining in the emerging Candida spp. are required to decipher their pathogenicity and virulence mechanisms compared to the prominent C. albicans.

LAY ABSTRACT

Candida virulence factors (VFs) including mainly enzymes and proteins play vital roles in breaching the human intestinal barrier and causing deadly candidiasis. Limited VFs' structural studies hinder deeper comprehension of their mechanisms and thus the design of vaccines and antifungal drugs against fungal infections.

Susceptibility to Oral Antiseptics and Virulence Factors Ex Vivo Associated with Candida spp. Isolated from Dental Prostheses

PURPOSE

To isolate Candida spp. from dental prosthesis users' saliva and to evaluate the isolates for the presence of several virulence factors. This research also aimed to investigate the antifungal activity of 3 commercial mouthwashes/oral antiseptic formulations containing 0.12% chlorhexidine, 0.07% cetylpyridinium, or 0.075% cetylpyridinium against planktonic and sessile (biofilm mode) yeast cells.

MATERIALS AND METHODS

Forty-three Candida yeasts were isolated from 32 of 70 selected patients, and the virulence factors of C. albicans, C. krusei, C. glabrata, C. tropicalis, and C. parapsilosis species were investigated by polymerase chain reaction (PCR) and proteinase in plates. Minimum inhibitory concentration (MIC), and in vitro biofilm assay evaluated the antifungal activity of antiseptics.

RESULTS

C. albicans, C. krusei, C. glabrata, C. tropicalis, and C. parapsilosis were detected in mono and mixed cultures. Only C. albicans displayed genes related to adhesion and proteinases (ALS2, ALS3, SAP1, and SAP3). The aspartate proteinase activity was found in 60.46% of isolates. The tested antiseptic formulations exhibited a MIC less than 1.25% toward yeasts in the planktonic mode. According to XTT ((2,3-bis(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide) assay results, most Candida isolates and all mixed cultures formed biofilms within 24 hours. The evaluated antiseptic formulations were also active against biofilms.

CONCLUSION

Most virulence factors investigated here (ALS2, ALS3, SAP1, and SAP3) occurred in the majority of the Candida spp. isolates, especially in C. albicans. The tested mouthwash formulations were effective against all the yeast isolates in both the planktonic and sessile growth modes. Developing alternative therapies that can avoid or control biofilm formation is necessary to prevent oral candidiasis and other Candida spp. infections.

Candida parapsilosis: from Genes to the Bedside

Patients with suppressed immunity are at the highest risk for hospital-acquired infections. Among these, invasive candidiasis is the most prevalent systemic fungal nosocomial infection. Over recent decades, the combined prevalence of non-albicans Candida species outranked Candida albicans infections in several geographical regions worldwide, highlighting the need to understand their pathobiology in order to develop effective treatment and to prevent future outbreaks. Candida parapsilosis is the second or third most frequently isolated Candida species from patients. Besides being highly prevalent, its biology differs markedly from that of C. albicans, which may be associated with C. parapsilosis' increased incidence. Differences in virulence, regulatory and antifungal drug resistance mechanisms, and the patient groups at risk indicate that conclusions drawn from C. albicans pathobiology cannot be simply extrapolated to C. parapsilosis Such species-specific characteristics may also influence their recognition and elimination by the host and the efficacy of antifungal drugs. Due to the availability of high-throughput, state-of-the-art experimental tools and molecular genetic methods adapted to C. parapsilosis, genome and transcriptome studies are now available that greatly contribute to our understanding of what makes this species a threat. In this review, we summarize 10 years of findings on C. parapsilosis pathogenesis, including the species' genetic properties, transcriptome studies, host responses, and molecular mechanisms of virulence. Antifungal susceptibility studies and clinician perspectives are discussed. We also present regional incidence reports in order to provide an updated worldwide epidemiology summary.

Differential Behavior of Non-albicans Candida Species in the Central Nervous System of Immunocompetent and Immunosuppressed Mice

The genus Candida includes commensal fungi that can cause local and systemic infections, frequently involving vital organs as the central nervous system (CNS). Candida spp. occupy the fourth place among infections that affect the CNS. Although the incidence of Candida albicans is decreasing among patients under immunosuppressive therapies, the incidence of non-albicans Candida is increasing. In this context, the objective of this work was to evaluate the ability of non-albicans Candida species to spread to the CNS of immunocompetent and immunosuppressed mice. Adult female C57BL/6 mice were treated with prednisolone, intravenously infected with Candida glabrata, Candida krusei and Candida parapsilosis yeasts and then evaluated at the 3rd and 14th days after infection. All Candida species disseminated to the brain from immunocompetent animals and induced local inflammation at the third day post-infection. The immunosuppression resulted in body weight loss, leukopenia and reduced IL-2 production by spleen cell cultures. Higher fungal loads were recovered from the CNS of immunosuppressed mice. Inflammatory infiltration associated to a Th1 subset profile was higher in brain samples from C. krusei immunosuppressed mice compared with immunocompetent ones. Additionally, C. krusei was able to transform into pseudohypha inside microglia in vitro infected cells and also to induce elevated nitric oxide production. Altogether, these results indicate that C. glabrata, C. krusei and C. parapsilosis are able to disseminate to the CNS and promote local inflammation in both immunocompetent and immunosuppressed mice. C. krusei displayed a distinct behavior at the CNS triggering a local Th1 profile. The possible contribution of these non-albicans Candida species to other CNS pathologies as multiple sclerosis, Parkinson’s and Alzheimer’s diseases deserves further attention.

Candida tropicalis biofilm formation and expression levels of the CTRG ALS-like genes in sessile cells

Candida tropicalis is an emergent pathogen with a high rate of mortality associated with it; however, less is known about its pathogenic capacity. Biofilm formation (BF) has important clinical repercussions, and it begins with adherence to a substrate. The adherence capacity depends principally on the cell surface hydrophobicity (CSH) and, at a later stage, on specific adherence due to adhesins. The ALS family in C. tropicalis, implicated in adhesion and BF, is represented in several CTRG genes. In this study, we determined the biofilm-forming ability, the primary adherence, and the CSH of C. tropicalis, including six isolates from blood and seven from urine cultures. We also compared the expression of four CTRG ALS-like genes (CTRG_01028, CTRG_02293, CTRG_03786, and CTRG_03797) in sessile versus planktonic cells, selected for their possible contribution to BF. All the C. tropicalis strains were biofilm producers, related to its filamentation capacity; all the strains displayed a high adherence ability correlated to the CSH, and all the strains expressed the CTRG genes in both types of growth. Urine isolates present, although not significantly, higher CSH, adherence, and biofilm formation than blood isolates. This study reveals that three CTRG ALS-like genes-except CTRG_03797-were more upregulated in biofilm cells, although with a considerable variation in expression across the strains studied and between the CTRG genes. C. tropicalis present a high biofilm capacity, and the overexpression of several CTRG ALS-like genes in the sessile cells suggests a role by the course of the biofilm formation.

Caenorhabditis elegans as a Model Host to Monitor the Candida Infection Processes

C. elegans has several advantages as an experimental host for the study of infectious diseases. Worms are easily maintained and propagated on bacterial lawns. The worms can be frozen for long term storage and still maintain viability years later. Their short generation time and large brood size of thousands of worms grown on a single petri dish, makes it relatively easy to maintain at a low cost. The typical wild type adult worm grows to approximately 1.5 mm in length and are transparent, allowing for the identification of several internal organs using an affordable dissecting microscope. A large collection of loss of function mutant strains are readily available from the C. elegans genetic stock center, making targeted genetic studies in the nematode possible. Here we describe ways in which this facile model host has been used to study Candida albicans, an opportunistic fungal pathogen that poses a serious public health threat.

Biological Roles of Protein-Coding Tandem Repeats in the Yeast Candida Albicans

Tandem repeat (TR) DNA mutates faster than other DNA by insertion and deletion of repeats. Large parts of eukaryotic proteomes are encoded by ORFs containing protein-coding TRs (TR-ORFs, pcTRs) with largely unknown biological consequences. We explored these in the yeast Candida albicans, an opportunistic human pathogen. We found that almost half of C. albicans’ proteins are encoded by TR-ORFs. pcTR frequency differed only moderately between different gene (GO) categories. Bioinformatic predictions of genome-wide mutation rates and clade-specific differences in pcTR allele frequencies indicated that pcTRs (i) significantly increase the genome-wide mutation rate; (ii) significantly impact on fitness and (iii) allow the evolution of selectively advantageous clade-specific protein variants. Synonymous mutations reduced the repetitiveness of many amino acid repeat-encoding pcTRs. A survey, in 58 strains, revealed that in some pcTR regions in which repetitiveness was not significantly diminished by synonymous mutations the habitat predicted which alleles were present, suggesting roles of pcTR mutation in short-term adaptation and pathogenesis. In C. albicans pcTR mutation apparently is an important mechanism for mutational advance and possibly also rapid adaptation, with synonymous mutations providing a mechanism for adjusting mutation rates of individual pcTRs. Analyses of Arabidopsis and human pcTRs showed that the latter also occurs in other eukaryotes.

Candida-Epithelial Interactions

A plethora of intricate and dynamic molecular interactions occur between microbes and the epithelial cells that form the mucosal surfaces of the human body. Fungi, particularly species of Candida, are commensal members of our microbiota, continuously interacting with epithelial cells. Transient and localised perturbations to the mucosal environment can facilitate the overgrowth of fungi, causing infection. This minireview will examine the direct and indirect mechanisms by which Candida species and epithelial cells interact with each other, and explore the factors involved in the central processes of adhesion, invasion, and destruction of host mucosal surfaces.

Ceratocystis cacaofunesta genome analysis reveals a large expansion of extracellular phosphatidylinositol-specific phospholipase-C genes (PI-PLC)

BACKGROUND

The Ceratocystis genus harbors a large number of phytopathogenic fungi that cause xylem parenchyma degradation and vascular destruction on a broad range of economically important plants. Ceratocystis cacaofunesta is a necrotrophic fungus responsible for lethal wilt disease in cacao. The aim of this work is to analyze the genome of C. cacaofunesta through a comparative approach with genomes of other Sordariomycetes in order to better understand the molecular basis of pathogenicity in the Ceratocystis genus.

RESULTS

We present an analysis of the C. cacaofunesta genome focusing on secreted proteins that might constitute pathogenicity factors. Comparative genome analyses among five Ceratocystidaceae species and 23 other Sordariomycetes fungi showed a strong reduction in gene content of the Ceratocystis genus. However, some gene families displayed a remarkable expansion, in particular, the Phosphatidylinositol specific phospholipases-C (PI-PLC) family. Also, evolutionary rate calculations suggest that the evolution process of this family was guided by positive selection. Interestingly, among the 82 PI-PLCs genes identified in the C. cacaofunesta genome, 70 genes encoding extracellular PI-PLCs are grouped in eight small scaffolds surrounded by transposon fragments and scars that could be involved in the rapid evolution of the PI-PLC family. Experimental secretome using LC-MS/MS validated 24% (86 proteins) of the total predicted secretome (342 proteins), including four PI-PLCs and other important pathogenicity factors.

CONCLUSION

Analysis of the Ceratocystis cacaofunesta genome provides evidence that PI-PLCs may play a role in pathogenicity. Subsequent functional studies will be aimed at evaluating this hypothesis. The observed genetic arsenals, together with the analysis of the PI-PLC family shown in this work, reveal significant differences in the Ceratocystis genome compared to the classical vascular fungi, Verticillium and Fusarium. Altogether, our analyses provide new insights into the evolution and the molecular basis of plant pathogenicity.

Amyloid-Like β-Aggregates as Force-Sensitive Switches in Fungal Biofilms and Infections

Cellular aggregation is an essential step in the formation of biofilms, which promote fungal survival and persistence in hosts. In many of the known yeast cell adhesion proteins, there are amino acid sequences predicted to form amyloid-like β-aggregates. These sequences mediate amyloid formation in vitro. In vivo, these sequences mediate a phase transition from a disordered state to a partially ordered state to create patches of adhesins on the cell surface. These β-aggregated protein patches are called adhesin nanodomains, and their presence greatly increases and strengthens cell-cell interactions in fungal cell aggregation. Nanodomain formation is slow (with molecular response in minutes and the consequences being evident for hours), and strong interactions lead to enhanced biofilm formation. Unique among functional amyloids, fungal adhesin β-aggregation can be triggered by the application of physical shear force, leading to cellular responses to flow-induced stress and the formation of robust biofilms that persist under flow. Bioinformatics analysis suggests that this phenomenon may be widespread. Analysis of fungal abscesses shows the presence of surface amyloids in situ, a finding which supports the idea that phase changes to an amyloid-like state occur in vivo. The amyloid-coated fungi bind the damage-associated molecular pattern receptor serum amyloid P component, and there may be a consequential modulation of innate immune responses to the fungi. Structural data now suggest mechanisms for the force-mediated induction of the phase change. We summarize and discuss evidence that the sequences function as triggers for protein aggregation and subsequent cellular aggregation, both in vitro and in vivo.

An Update on Candida tropicalis Based on Basic and Clinical Approaches

Candida tropicalis has emerged as one of the most important Candida species. It has been widely considered the second most virulent Candida species, only preceded by C. albicans. Besides, this species has been recognized as a very strong biofilm producer, surpassing C. albicans in most of the studies. In addition, it produces a wide range of other virulence factors, including: adhesion to buccal epithelial and endothelial cells; the secretion of lytic enzymes, such as proteinases, phospholipases, and hemolysins, bud-to-hyphae transition (also called morphogenesis) and the phenomenon called phenotypic switching. This is a species very closely related to C. albicans and has been easily identified with both phenotypic and molecular methods. In addition, no cryptic sibling species were yet described in the literature, what is contradictory to some other medically important Candida species. C. tropicalis is a clinically relevant species and may be the second or third etiological agent of candidemia, specifically in Latin American countries and Asia. Antifungal resistance to the azoles, polyenes, and echinocandins has already been described. Apart from all these characteristics, C. tropicalis has been considered an osmotolerant microorganism and this ability to survive to high salt concentration may be important for fungal persistence in saline environments. This physiological characteristic makes this species suitable for use in biotechnology processes. Here we describe an update of C. tropicalis, focusing on all these previously mentioned subjects.

Identification of proteins involved in the adhesionof Candida species to different medical devices

Adhesion is the first step for Candida species to form biofilms on medical devices implanted in the human host. Both the physicochemical nature of the biomaterial and cell wall proteins (CWP) of the pathogen play a determinant role in the process. While it is true that some CWP have been identified in vitro, little is known about the CWP of pathogenic species of Candida involved in adhesion. On this background, we considered it important to investigate the potential role of CWP of C. albicans, C. glabrata, C. krusei and C. parapsilosis in adhesion to different medical devices. Our results indicate that the four species strongly adher to polyvinyl chloride (PVC) devices, followed by polyurethane and finally by silicone. It was interesting to identify fructose-bisphosphate aldolase (Fba1) and enolase 1 (Eno1) as the CWP involved in adhesion of C. albicans, C. glabrata and C. krusei to PVC devices whereas phosphoglycerate kinase (Pgk) and Eno1 allow C. parapsilosis to adher to silicone-made implants. Results presented here suggest that these CWP participate in the initial event of adhesion and are probably followed by other proteins that covalently bind to the biomaterial thus providing conditions for biofilm formation and eventually the onset of infection.

Distinct Expression Levels of ALS, LIP, and SAP Genes in Candida tropicalis with Diverse Virulent Activities

Candia tropicalis is an increasingly important human pathogen, causing nosocomial fungemia among patients with neutropenia or malignancy. However, limited research has been published concerning its pathogenicity. Based on the phenotypes of C. tropicalis in our previous study, we selected nine representative strains with different activities of virulence factors (adhesion, biofilm formation, secreted aspartic proteinases, and hemolysins), and one reference strain, ATCC750. The present study aimed to investigate the filamentation ability, the expression of virulence genes (ALST1-3, LIP1, LIP4, and SAPT1-4) and the cell damage of C. tropicalis strains with diverse virulences. C. tropicalis exhibited strain-dependent filamentation ability, which was positively correlated with biofilm formation. Reverse transcriptase PCR analysis showed that the ALST3 and SAPT3 genes had the highest expression in their corresponding genes for most C. tropicalis. The expressions of virulence genes, except ALST3 on polystyrene, were upregulated compared with growth in the planktonic and on human urinary bladder epithelial cell line (TCC-SUP) surface. Clustering analysis of virulence genes showed that isolates had a high biofilm forming ability on polystyrene formed a group. Lactate dehydrogenase assays showed that the cell damage induced by C. tropicalis markedly increased with longer infection time (24 and 48 h). Strain FXCT01, isolated from blood, caused the most serious cell damage; while ZRCT52, which had no filamentation ability, caused the least cell damage. Correlation analysis demonstrated significant correlation existed between adhesion on epithelial cells or the expression of ALST2-3 and cell damage. Overall, our results supported the view that adhesion and filamentation may play significant roles in the cell damage caused by C. tropicalis.

Candida albicans Agglutinin-Like Sequence (Als) Family Vignettes: A Review of Als Protein Structure and Function

Approximately two decades have passed since the description of the first gene in the Candida albicans ALS (agglutinin-like sequence) family. Since that time, much has been learned about the composition of the family and the function of its encoded cell-surface glycoproteins. Solution of the structure of the Als adhesive domain provides the opportunity to evaluate the molecular basis for protein function. This review article is formatted as a series of fundamental questions and explores the diversity of the Als proteins, as well as their role in ligand binding, aggregative effects, and attachment to abiotic surfaces. Interaction of Als proteins with each other, their functional equivalence, and the effects of protein abundance on phenotypic conclusions are also examined. Structural features of Als proteins that may facilitate invasive function are considered. Conclusions that are firmly supported by the literature are presented while highlighting areas that require additional investigation to reveal basic features of the Als proteins, their relatedness to each other, and their roles in C. albicans biology.

Vulvovaginal candidiasis: Epidemiology, microbiology and risk factors

Vulvovaginal candidiasis (VVC) is an infection caused by Candida species that affects millions of women every year. Although Candida albicans is the main cause of VVC, the identification of non-Candida albicans Candida (NCAC) species, especially Candida glabrata, as the cause of this infection, appears to be increasing. The development of VVC is usually attributed to the disturbance of the balance between Candida vaginal colonization and host environment by physiological or nonphysiological changes. Several host-related and behavioral risk factors have been proposed as predisposing factors for VVC. Host-related factors include pregnancy, hormone replacement, uncontrolled diabetes, immunosuppression, antibiotics, glucocorticoids use and genetic predispositions. Behavioral risk factors include use of oral contraceptives, intrauterine device, spermicides and condoms and some habits of hygiene, clothing and sexual practices. Despite a growing list of recognized risk factors, much remains to be elucidated as the role of host versus microorganisms, in inducing VVC and its recurrence. Thus, this review provides information about the current state of knowledge on the risk factors that predispose to VVC, also including a revision of the epidemiology and microbiology of VVC, as well as of Candida virulence factors associated with vaginal pathogenicity.

The Candida albicans agglutinin-like sequence family of adhesins: functional insights gained from structural analysis

Candida albicans colonizes many host sites suggesting its interaction with diverse ligands. Candida albicans adhesion is mediated by a number of proteins including those in the Als (agglutinin-like sequence) family, which have been studied intensively. The recent solution of the Als binding domain structure ended years of speculation regarding the molecular mechanism for Als adhesive function. Als adhesins bind flexible C termini from a broad collection of proteins, providing the basis for adhesion to various cell types and perhaps for C. albicans broad tissue tropism. Understanding adhesive functions at the molecular level will reveal the sequence of events in C. albicans pathogenesis, from host recognition to complex interactions such as development of polymicrobial biofilms or disseminated disease.

Phenotypic switching in Candida tropicalis: association with modification of putative virulence attributes and antifungal drug sensitivity

Although Candida tropicalis has become an increasingly important human pathogen, little is known regarding its potential to cause disease. In this study we evaluated the phenotypic switching ability of C. tropicalis and analyzed the effect of switching on biological properties related to virulence factors. We demonstrated that C. tropicalis switched spontaneously, reversibly and at high frequency (10(-1) to 10(-3)) when grown on yeast extract-peptone-D-glucose (YPD) agar medium. Phenotypic switching in five clinical isolates of C. tropicalis resulted in colonies exhibiting the following morphologies: crepe, rough, crater, irregular center, mycelial and diffuse. The majority of the variant colonies were associated with higher percentages of filamentous growth relative to their parental unswitched isolates. Significant differences (P < 0.05) in the production of hemolytic factor were found between most of the switched variants and their respective parental counterparts. Variant colonies exhibiting the crepe (derived from isolates 49.07 and 100.10) and rough phenotype (derived from isolate 49.07) had higher biofilm formation than their parental counterparts exhibiting a smooth dome surface (P < 0.05). Our data revealed that switching was correlated with changes in the in vitro minimum inhibitory concentrations (MICs) of a subset of the switched variants phenotypes to itraconazole. While the MIC to itraconazole was higher for crepe variant compared with its parental isolate 49.07, the rough variant of 100.10 had a lower MIC to this antifungal agent. The presented data support the role of phenotypic switching in promoting changes in phenotypic expression of putative virulence traits and itraconazole susceptibility of clinical isolates of C. tropicalis.

Unexpected genomic variability in clinical and environmental strains of the pathogenic yeast Candida parapsilosis

Invasive candidiasis is the most commonly reported invasive fungal infection worldwide. Although Candida albicans remains the main cause, the incidence of emerging Candida species, such as C. parapsilosis is increasing. It has been postulated that C. parapsilosis clinical isolates result from a recent global expansion of a virulent clone. However, the availability of a single genome for this species has so far prevented testing this hypothesis at genomic scales. We present here the sequence of three additional strains from clinical and environmental samples. Our analyses reveal unexpected patterns of genomic variation, shared among distant strains, that argue against the clonal expansion hypothesis. All strains carry independent expansions involving an arsenite transporter homolog, pointing to the existence of directional selection in the environment, and independent origins of the two clinical isolates. Furthermore, we report the first evidence for the existence of recombination in this species. Altogether, our results shed new light onto the dynamics of genome evolution in C. parapsilosis.

Cell aggregations in yeasts and their applications

Yeasts can display four types of cellular aggregation: sexual, flocculation, biofilm formation, and filamentous growth. These cell aggregations arise, in some yeast strains, as a response to environmental or physiological changes. Sexual aggregation is part of the yeast mating process, representing the first step of meiotic recombination. The flocculation phenomenon is a calcium-dependent asexual reversible cellular aggregation that allows the yeast to withstand adverse conditions. Biofilm formation consists of multicellular aggregates that adhere to solid surfaces and are embedded in a protein matrix; this gives the yeast strain either the ability to colonize new environments or to survive harsh environmental conditions. Finally, the filamentous growth is the ability of some yeast strains to grow in filament forms. Filamentous growth can be attained by two different means, with the formation of either hyphae or pseudohyphae. Both hyphae and pseudohyphae arise when the yeast strain is under nutrient starvation conditions and they represent a means for the microbial strain to spread over a wide area to survey for food sources, without increasing its biomass. Additionally, this filamentous growth is also responsible for the invasive growth of some yeast.

Candida species: new insights into biofilm formation

Biofilms of Candida albicans, Candida parapsilosis, Candida glabrata and Candida tropicalis are associated with high indices of hospital morbidity and mortality. Major factors involved in the formation and growth of Candida biofilms are the chemical composition of the medical implant and the cell wall adhesins responsible for mediating Candida-Candida, Candida-human host cell and Candida-medical device adhesion. Strategies for elucidating the mechanisms that regulate the formation of Candida biofilms combine tools from biology, chemistry, nanoscience, material science and physics. This review proposes the use of new technologies, such as synchrotron radiation, to study the mechanisms of biofilm formation. In the future, this information is expected to facilitate the design of new materials and antifungal compounds that can eradicate nosocomial Candida infections due to biofilm formation on medical implants. This will reduce dissemination of candidiasis and hopefully improve the quality of life of patients.

Insights into Candida tropicalis nosocomial infections and virulence factors

Candida tropicalis is considered the first or the second non-Candida albicans Candida (NCAC) species most frequently isolated from candidosis, mainly in patients admitted in intensive care units (ICUs), especially with cancer, requiring prolonged catheterization, or receiving broad-spectrum antibiotics. The proportion of candiduria and candidemia caused by C. tropicalis varies widely with geographical area and patient group. Actually, in certain countries, C. tropicalis is more prevalent, even compared with C. albicans or other NCAC species. Although prophylactic treatments with fluconazole cause a decrease in the frequency of candidosis caused by C. tropicalis, it is increasingly showing a moderate level of fluconazole resistance. The propensity of C. tropicalis for dissemination and the high mortality associated with its infections might be strongly related to the potential of virulence factors exhibited by this species, such as adhesion to different host surfaces, biofilm formation, infection and dissemination, and enzymes secretion. Therefore, the aim of this review is to outline the present knowledge on all the above-mentioned C. tropicalis virulence traits.

Adherence and biofilm formation of non-Candida albicans Candida species

Most cases of candidosis have been attributed to Candida albicans, but recently non-C. albicans Candida species have been identified as frequent human pathogens. Candida pathogenicity has been attributed to several factors, including adhesion to medical devices and/or host cells, biofilm formation, and secretion of hydrolytic enzymes (proteases, phospholipases and haemolysins). Although 'new'Candida species are emerging, there is still a lack of information about their pathogenicity. This review discusses recent advances in our knowledge of Candida glabrata, Candida parapsilosis and Candida tropicalis virulence factors, specifically those of adhesion and biofilm formation, which are key components in Candida pathogenicity.

Candida tropicalis in human disease

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

Comparative genomics and the evolution of pathogenicity in human pathogenic fungi

Because most fungi have evolved to be free-living in the environment and because the infections they cause are usually opportunistic in nature, it is often difficult to identify specific traits that contribute to fungal pathogenesis. In recent years, there has been a surge in the number of sequenced genomes of human fungal pathogens, and comparison of these sequences has proved to be an excellent resource for exploring commonalities and differences in how these species interact with their hosts. In order to survive in the human body, fungi must be able to adapt to new nutrient sources and environmental stresses. Therefore, genes involved in carbohydrate and amino acid metabolism and transport and genes encoding secondary metabolites tend to be overrepresented in pathogenic species (e.g., Aspergillus fumigatus). However, it is clear that human commensal yeast species such as Candida albicans have also evolved a range of specific factors that facilitate direct interaction with host tissues. The evolution of virulence across the human pathogenic fungi has occurred largely through very similar mechanisms. One of the most important mechanisms is gene duplication and the expansion of gene families, particularly in subtelomeric regions. Unlike the case for prokaryotic pathogens, horizontal transfer of genes between species and other genera does not seem to have played a significant role in the evolution of fungal virulence. New sequencing technologies promise the prospect of even greater numbers of genome sequences, facilitating the sequencing of multiple genomes and transcriptomes within individual species, and will undoubtedly contribute to a deeper insight into fungal pathogenesis.

Protection by anti-beta-glucan antibodies is associated with restricted beta-1,3 glucan binding specificity and inhibition of fungal growth and adherence

Anti-β-glucan antibodies elicited by a laminarin-conjugate vaccine confer cross-protection to mice challenged with major fungal pathogens such as Candida albicans, Aspergillus fumigatus and Cryptococcus neoformans. To gain insights into protective β-glucan epitope(s) and protection mechanisms, we studied two anti-β-glucan monoclonal antibodies (mAb) with identical complementarity-determining regions but different isotypes (mAb 2G8, IgG2b and mAb 1E12, IgM). C. albicans, the most relevant fungal pathogen for humans, was used as a model.

Both mAbs bound to fungal cell surface and to the β1,3-β1,6 glucan of the fungal cell wall skeleton, as shown by immunofluorescence, electron-microscopy and ELISA. They were also equally unable to opsonize fungal cells in a J774 macrophage phagocytosis and killing assay. However, only the IgG2b conferred substantial protection against mucosal and systemic candidiasis in passive vaccination experiments in rodents. Competition ELISA and microarray analyses using sequence-defined glucan oligosaccharides showed that the protective IgG2b selectively bound to β1,3-linked (laminarin-like) glucose sequences whereas the non-protective IgM bound to β1,6- and β1,4-linked glucose sequences in addition to β1,3-linked ones. Only the protective IgG2b recognized heterogeneous, polydisperse high molecular weight cell wall and secretory components of the fungus, two of which were identified as the GPI-anchored cell wall proteins Als3 and Hyr1. In addition, only the IgG2b inhibited in vitro two critical virulence attributes of the fungus, hyphal growth and adherence to human epithelial cells.

Our study demonstrates that the isotype of anti-β-glucan antibodies may affect details of the β-glucan epitopes recognized, and this may be associated with a differing ability to inhibit virulence attributes of the fungus and confer protection in vivo. Our data also suggest that the anti-virulence properties of the IgG2b mAb may be linked to its capacity to recognize β-glucan epitope(s) on some cell wall components that exert critical functions in fungal cell wall structure and adherence to host cells.

Recognition of Candida albicans Als3 by the germ tube-specific monoclonal antibody 3D9.3

Monoclonal antibody 3D9.3 (MAb 3D9.3) reacts with the surface of Candida albicans germ tubes and recognizes a protein epitope. We used a two-step chromatography procedure to purify and identify the antigen (3D9) from C. albicans strain 66396 germ tubes. MAb 3D9.3 recognized two intense protein bands at 140 and 180 kDa. A comparative analysis between theoretical and experimental mass spectrum peaks showed that both bands corresponded to Als3. This conclusion was supported by lack of reactivity between MAb 3D9.3 and an als3Delta/als3Delta mutant strain, and the fact that an immunoglobulin preparation enriched for Als3 specificity recognized the purified 3D9 antigen. PCR demonstrated that C. albicans strain 66396 has two different-sized ALS3 alleles that correspond to the two purified protein bands. Strain- and species-specificity of the 3D9 epitope were studied with various C. albicans strains and Candida species, such as closely related Candida dubliniensis. The 3D9 epitope was detected only in C. albicans, demonstrating the utility of MAb 3D9.3 for differentiation between C. albicans and C. dubliniensis. Adhesion assays demonstrated that MAb 3D9.3 blocks adhesion of C. albicans germ tubes to human buccal epithelial cells and vascular endothelial cells.

Molecular and Cellular Mechanisms That Lead to Candida Biofilm Formation

Fungal infections in the oral cavity are mainly caused by C. albicans, but other Candida species are also frequently identified. They are increasing in prevalence, especially in denture-wearers and aging people, and may lead to invasive infections, which have a high mortality rate. Attachment to mucosal tissues and to abiotic surfaces and the formation of biofilms are crucial steps for Candida survival and proliferation in the oral cavity. Candida species possess a wide arsenal of glycoproteins located at the exterior side of the cell wall, many of which play a determining role in these steps. In addition, C. albicans secretes signaling molecules that inhibit the yeast-to-hypha transition and biofilm formation. In vivo, Candida species are members of mixed biofilms, and subject to various antagonistic and synergistic interactions, which are beginning to be explored. We believe that these new insights will allow for more efficacious treatments of fungal oral infections. For example, the use of signaling molecules that inhibit biofilm formation should be considered. In addition, cell-wall biosynthetic enzymes, wall cross-linking enzymes, and wall proteins, which include adhesins, proteins involved in biofilm formation, fungal-bacterial interactions, and competition for surface colonization sites, offer a wide range of potential targets for therapeutic intervention.

Use of recombinant antigens for the diagnosis of invasive candidiasis

Invasive candidiasis is a frequent and often fatal complication in immunocompromised and critically ill patients. Unfortunately, the diagnosis of invasive candidiasis remains difficult due to the lack of specific clinical symptoms and a definitive diagnostic method. The detection of antibodies against different Candida antigens may help in the diagnosis. However, the methods traditionally used for the detection of antibodies have been based on crude antigenic fungal extracts, which usually show low-reproducibility and cross-reactivity problems. The development of molecular biology techniques has allowed the production of recombinant antigens which may help to solve these problems. In this review we will discuss the usefulness of recombinant antigens in the diagnosis of invasive candidiasis.

Production of monoclonal antibodies for detection of a secreted aspartyl proteinase from Candida spp. in biologic specimens

Secreted acid proteinases (SAP) constitute an important group of virulence factors in Candida albicans. In the present work, an acid proteinase from C. albicans was sequentially purified from the supernatant of a yeast culture by precipitation with ammonium sulfate, ion exchange chromatography, and molecular exclusion chromatography, yielding a specific enzymatic activity of 204.1 IU/mg on bovine serum albumin (BSA). The molecular mass of the purified proteinase was estimated at 43 kd after exclusion chromatography and at 41 kd by nondenaturating sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The purified proteinase was able to degrade BSA at pH 2.5, but was not active on collagen, and it was significantly inhibited by pepstatin A. The immunization of BALB/c mice with the purified proteinase and later fusion of their spleen cells with myeloma cells resulted in 19 monoclonal antibody secreting hybridomas (MAbs) capable of detecting SAP in enzyme-linked immunosorbent assay (ELISA) assays. All MAbs obtained are isotype IgG1 kappa (kappa) immunoglobulins and develop a 41 kd protein band by Western blot (WB) in samples of SAP obtained from C. albicans (12-A) and C. dubliniensis (strain 778) crude extracts. The anti-SAP MAbs were used in capture ELISA and two combinations of these antibodies proved suitable for SAP detection, that is, MAP1 (1B1B3) or MAP2 (2D2C10) as coat antibodies, and biotinylated MAP3 (2A6E8) as detect antibody. Capture ELISA using these sets of MAbs detected over 32 ng/mL protein in purified SAP samples as well as in crude C. albicans and C. dubliniensis extracts. The results herein obtained allow for the prediction of how this set of antibodies can be useful for SAP detection in biologic specimens.

Discovering the secrets of the Candida albicans agglutinin-like sequence (ALS) gene family--a sticky pursuit

The agglutinin-like sequence (ALS) family of Candida albicans includes eight genes that encode large cell-surface glycoproteins. The high degree of sequence relatedness between the ALS genes and the tremendous allelic variability often present in the same C. albicans strain complicated definition and characterization of the gene family. The main hypothesis driving ALS family research is that the genes encode adhesins, primarily involved in host-pathogen interactions. Although adhesive function has been demonstrated for several Als proteins, the challenge of studying putative adhesins in a highly adhesive organism like C. albicans has led to varying ideas about how best to pursue such investigations, and results that are sometimes contradictory. Recent analysis of alsdelta/alsdelta strains suggested roles for Als proteins outside of adhesion to host surfaces, and a broader scope of Als protein function than commonly believed. The availability and use of experimental methodologies to study C. albicans at the genomic level, and the ALS family en masse, have advanced knowledge of these genes and emphasized their importance in C. albicans biology and pathogenesis.

A biochemical guide to yeast adhesins: glycoproteins for social and antisocial occasions

Fungi are nonmotile eukaryotes that rely on their adhesins for selective interaction with the environment and with other fungal cells. Glycosylphosphatidylinositol (GPI)-cross-linked adhesins have essential roles in mating, colony morphology, host-pathogen interactions, and biofilm formation. We review the structure and binding properties of cell wall-bound adhesins of ascomycetous yeasts and relate them to their effects on cellular interactions, with particular emphasis on the agglutinins and flocculins of Saccharomyces and the Als proteins of Candida. These glycoproteins share common structural motifs tailored to surface activity and biological function. After being secreted to the outer face of the plasma membrane, they are covalently anchored in the wall through modified GPI anchors, with their binding domains elevated beyond the wall surface on highly glycosylated extended stalks. N-terminal globular domains bind peptide or sugar ligands, with between millimolar and nanomolar affinities. These affinities and the high density of adhesins and ligands at the cell surface determine microscopic and macroscopic characteristics of cell-cell associations. Central domains often include Thr-rich tandemly repeated sequences that are highly glycosylated. These domains potentiate cell-to-cell binding, but the molecular mechanism of such an association is not yet clear. These repeats also mediate recombination between repeats and between genes. The high levels of recombination and epigenetic regulation are sources of variation which enable the population to continually exploit new niches and resources.

Candida species adhesion to oral epithelium: factors involved and experimental methodology used

Due to the increasing prevalence and emergence of Non-Candida albicans Candida (NCAC) species, especially in immunosupressed patients, it is becoming urgent to deepen the current knowledge about virulence factors of these species. Adhesion of cells to epithelium is considered one of the major virulence factors of Candida species. However, relatively little is known concerning the adhesion mechanisms of NCAC species to epithelium, as well as about the factors affecting the adhesion process. This review focuses both the mechanisms that regulate the adhesion interactions and the factors involved and the description of the experimental methodology that has been used to perform the adhesion assays.

The CRH family coding for cell wall glycosylphosphatidylinositol proteins with a predicted transglycosidase domain affects cell wall organization and virulence of Candida albicans

In Candida albicans UTR2 (CSF4), CRH11, and CRH12 are members of a gene family (the CRH family) that encode glycosylphosphatidylinositol-dependent cell wall proteins with putative transglycosidase activity. Deletion of genes of this family resulted in additive sensitivity to compounds interfering with normal cell wall formation (Congo red, calcofluor white, SDS, and high Ca(2+) concentrations), suggesting that these genes contribute to cell wall organization. A triple mutant lacking UTR2, CRH11, and CRH12 produced a defective cell wall, as inferred from increased sensitivity to cell wall-degrading enzymes, decreased ability of protoplasts to regenerate a new wall, constitutive activation of Mkc1p, the mitogen-activated protein kinase of the cell wall integrity pathway, and an increased chitin content of the cell wall. Importantly, this was accompanied by a decrease in alkali-insoluble 1,3-beta-glucan but not total glucan content, suggesting that formation of the linkage between 1,3-beta-glucan and chitin might be affected. In support of this idea, localization of a Utr2p-GFP fusion protein largely coincided with areas of chitin incorporation in C. albicans. As UTR2 and CRH11 expression is regulated by calcineurin, a serine/threonine protein phosphatase involved in tolerance to antifungal drugs, cell wall morphogenesis, and virulence, this points to a possible relationship between calcineurin and the CRH family. Deletion of UTR2, CRH11, and CRH12 resulted in only a partial overlap with calcineurin-dependent phenotypes, suggesting that calcineurin has additional targets. Interestingly, cells deleted for UTR2, CRH11, and CRH12 were, like a calcineurin mutant, avirulent in a mouse model of systemic infection but retained the capacity to colonize target organs (kidneys) as the wild type. In conclusion, this work establishes the role of UTR2, CRH11, and CRH12 in cell wall organization and integrity.

Gene transcription studies of Candida albicans following infection of HEp2 epithelial cells

Previously we observed that infection of HEp2 epithelial cells with Candida albicans results in HEp2 cell actin rearrangement as well as reduced membrane ruffling and motility and that supernatants of a C. albicans culture (Candida metabolite) caused the same changes. In this study, we used microarray analysis to determine changes in gene transcription of C. albicans following infection of HEp2 cells compared to control cultures grown in the absence of HEp2 cells. We observed 201 genes whose regulation was increased at least 2-fold following a 3 h incubation with HEp2 cells as well as 87 genes that are down-regulated. Among the up-regulated genes were ALS2 and ALS5 both of which encode proteins that provide an adherence function for C. albicans. To confirm the changes in ALS transcription, we measured by RT-PCR ALS1-9 at 1 h intervals for a total of 4 h. After 1 h of infection, several of the ALS genes were up-regulated compared to C. albicans grown alone. At 2-4 h, an increase in most of the ALS genes was observed in both infected and control cultures. ALS7 transcription was observed only at 3-4 h, but transcription was similar in both infected and control cultures. By RT-PCR, ALS2 and 5, similar to the microarray data, were significantly increased in infected cells at 3 h. Our results show that gene transcription following the adherence of C. albicans to HEp2 cells includes the up-regulation of genes encoding members of a family of known host recognition adhesins that may be critical to successful colonization and invasion of the organism.

In vitro evaluation of virulence attributes of Candida spp. isolated from patients affected by diabetes mellitus

BACKGROUND

Diabetes mellitus is a common disease found worldwide and it has been previously suggested that oral candidal infections may be more frequent or severe in patients with this disease. Systemic and local factors may influence the balance between the host and yeasts, and favour the transformation of Candida isolates from commensal to pathogenic microorganisms. Candida species have developed specific virulence mechanisms that confer the ability to colonise host surfaces, to invade deeper host tissue, or to evade host defences. Few studies have investigated the expression of the virulence attributes of oral Candida isolates in patients with diabetes mellitus.

MATERIAL AND METHODS

The in vitro extracellular proteinase production and the in vitro ability to adhere to fibronectin of 229 Candida isolates of two geographic different groups of patients with diabetes mellitus and of healthy subjects were assessed.

RESULTS

Candida isolates of patients with diabetes mellitus expressed a higher ability to adhere than those of healthy subjects. Higher levels of adhesion were also recorded in patients with a lower oral Candida colonisation. No differences were observed in the in vitro expression of extracellular proteinase of Candida isolates of patients with diabetes mellitus and those of non-diabetic subjects. Isolates of patients with type 2 diabetes mellitus expressed greater levels of proteinase than isolates of type 1 diabetes mellitus.

CONCLUSIONS

Diabetes mellitus could be considered as an additional variable that may influence not only oral Candida carriage but also the ability of isolates to enhance the expression of virulence attributes.

Flocculation, adhesion and biofilm formation in yeasts

Yeast cells possess a remarkable capacity to adhere to abiotic surfaces, cells and tissues. These adhesion properties are of medical and industrial relevance. Pathogenic yeasts such as Candida albicans and Candida glabrata adhere to medical devices and form drug-resistant biofilms. In contrast, cell-cell adhesion (flocculation) is a desirable property of industrial Saccharomyces cerevisiae strains that allows the easy separation of cells from the fermentation product. Adhesion is conferred by a class of special cell wall proteins, called adhesins. Cells carry several different adhesins, each allowing adhesion to specific substrates. Several signalling cascades including the Ras/cAMP/PKA and MAP kinase (MAPK)-dependent filamentous growth pathways tightly control synthesis of the different adhesins. Together, these pathways trigger adhesion in response to stress, nutrient limitation or small molecules produced by the host, such as auxin in plants or NAD in mammals. In addition, adhesins are subject to subtelomeric epigenetic switching, resulting in stochastic expression patterns. Internal tandem repeats within adhesin genes trigger recombination events and the formation of novel adhesins, thereby offering fungi an endless reservoir of adhesion properties. These aspects of fungal adhesion exemplify the impressive phenotypic plasticity of yeasts, allowing them to adapt quickly to stressful environments and exploit new opportunities.

The anti-Candida vaccine based on the recombinant N-terminal domain of Als1p is broadly active against disseminated candidiasis

We have previously shown that vaccination with a vaccine based on the recombinant N-terminal domain of Als1p (rAls1p-N) protected BALB/c mice against disseminated infection caused by a single strain of Candida albicans (A. S. Ibrahim, B. J. Spellberg, V. Avenissian, Y. Fu, S. G. Filler, and J. E. Edwards, Jr., Infect. Immun. 73:999-1005, 2005, and B. J. Spellberg, A. S. Ibrahim, V. Avenissian, S. G. Filler, C. Myers, Y. Fu, and J. E. Edwards, Jr., Infect. Immun. 73:6191-6193, 2005). Here we show that the rAls1p-N vaccine also improves survival of outbred mice from disseminated candidiasis and that it is active against multiple virulent strains of C. albicans and non-C. albicans spp.

Candida dubliniensis: ten years on

Candida dubliniensis was first described as a novel species in 1995. This organism is very closely related to the important human yeast pathogen, Candida albicans. However, despite the very close phylogenetic relationship between C. albicans and C. dubliniensis and the fact that they share a large number of phenotypic traits, epidemiological and virulence model data indicate that the former is a far more successful pathogen. In order to investigate the molecular basis of the lower virulence of C. dubliniensis recent comparative genomic hybridisation studies have revealed the absence and divergence of specific genes implicated in candidal virulence. Data from the C. dubliniensis genome sequencing project will allow a complete comparison between the genomes of the two species to be performed and thus enhance our understanding of candidal virulence and how virulence has evolved in Candida species.

Features and functions of covalently linked proteins in fungal cell walls

The cell walls of many ascomycetous yeasts consist of an internal network of stress-bearing polysaccharides, which serve as a scaffold for a dense external layer of glycoproteins. GPI-modified proteins are the most abundant cell wall proteins and often display a common organization. Their C-terminus can link them covalently to the polysaccharide network, they possess an internal serine- and threonine-rich spacer domain, and the N-terminal region contains a functional domain. Other proteins bind to the polysaccharide network through a mild-alkali-sensitive linkage. Many cell wall proteins are carbohydrate/glycan-modifying enzymes; adhesion proteins are prominent; proteins involved in iron uptake are present, and also specialized proteins that probably help the fungus to survive in its natural environment. The protein composition of the cell wall depends on environmental conditions and developmental stage. We present evidence that the cell wall of mycelial species of the Ascomycotina is similarly organized and contains glycoproteins with comparable functions.