Quantification of ALS1 gene expression in Candida albicans biofilms by RT-PCR using hybridisation probes on the LightCycler™

Antifungal Activity of Mefloquine Against Candida albicans Growth and Virulence Factors: Insights Into Mode of Action

The antimalarial drug Mefloquine has demonstrated antifungal activity against growth and virulence factors of Candida albicans. The current study focused on the identification of Mefloquine's mode of action in C. albicans by performing cell susceptibility assay, biofilm assay, live and dead assay, propidium iodide uptake assay, ergosterol quantification assay, cell cycle study, and gene expression studies by RT-PCR. Mefloquine inhibited the virulence factors in C. albicans, such as germ tube formation and biofilm formation at 0.125 and 1 mg/ml, respectively. Mefloquine-treated cells showed a decrease in the quantity of ergosterol content of cell membrane in a concentration-dependent manner. Mefloquine (0.25 mg/ml) arrested C. albicans cells at the G2/M phase and S phase of the cell cycle thereby preventing the progression of the normal yeast cell cycle. ROS level was measured to find out oxidative stress in C. albicans in the presence of mefloquine. The study revealed that, mefloquine was found to enhance the ROS level and subsequently oxidative stress. Gene expression studies revealed that mefloquine treatment upregulates the expressions of SOD1, SOD2, and CAT1 genes in C. albicans. In vivo, the antifungal efficacy of mefloquine was confirmed in mice for systemic candidiasis and it was found that there was a decrease in the pathogenesis of C. albicans after the treatment of mefloquine in mice. In conclusion, mefloquine can be used as a repurposed drug as an alternative drug against Candidiasis.

Osteoarticular Mycoses

Osteoarticular mycoses are chronic debilitating infections that require extended courses of antifungal therapy and may warrant expert surgical intervention. As there has been no comprehensive review of these diseases, the International Consortium for Osteoarticular Mycoses prepared a definitive treatise for this important class of infections. Among the etiologies of osteoarticular mycoses are Candida spp., Aspergillus spp., Mucorales, dematiaceous fungi, non-Aspergillus hyaline molds, and endemic mycoses, including those caused by Histoplasma capsulatum, Blastomyces dermatitidis, and Coccidioides species. This review analyzes the history, epidemiology, pathogenesis, clinical manifestations, diagnostic approaches, inflammatory biomarkers, diagnostic imaging modalities, treatments, and outcomes of osteomyelitis and septic arthritis caused by these organisms. Candida osteomyelitis and Candida arthritis are associated with greater events of hematogenous dissemination than those of most other osteoarticular mycoses. Traumatic inoculation is more commonly associated with osteoarticular mycoses caused by Aspergillus and non-Aspergillus molds. Synovial fluid cultures are highly sensitive in the detection of Candida and Aspergillus arthritis. Relapsed infection, particularly in Candida arthritis, may develop in relation to an inadequate duration of therapy. Overall mortality reflects survival from disseminated infection and underlying host factors.

Inhibitory effect of 405-nm blue LED light on the growth of Candida albicans and Streptococcus mutans dual-species biofilms on denture base resin

We investigated whether irradiation with 405-nm blue LED light could inhibit the growth of not only single- but dual-species biofilms formed by Candida albicans and Streptococcus mutans on denture base resin and cause the alteration in gene expression related to adhesion and biofilm formation. C. albicans and S. mutans single-/dual-species biofilms were formed on the denture base specimens. The biofilms were irradiated with 405-nm blue LED light (power density output: 280 mW/cm²) for 0 (control) and 40 min. Dual-species biofilms were analyzed using CFU assay and fluorescence microscopy, and single-/dual-species biofilms were analyzed using alamarBlue assays and gene expression analysis. To assess the inhibitory effect of irradiation on dual-species biofilms, specimens after irradiation were aerobically incubated for 12 h. After incubation, the inhibition of growth was assessed using CFU assays and fluorescence microscopy. Data were analyzed using the Mann-Whitney U or Student's t test (p < 0.05). Irradiation produced a significant inhibitory effect on biofilms. Fluorescence microscopy revealed that almost all C. albicans and S. mutans cells were killed by irradiation, and there was no notable difference in biofilm thickness immediately after irradiation and after irradiation and incubation for 12 h. alamarBlue assays indicated the growth of the biofilms was inhibited for 12-13 h. The expression of genes associated with adhesion and biofilm formation-als1 in C. albicans and ftf, gtfC, and gtfB in S. mutans-significantly reduced by irradiation. Irradiation with 405-nm blue LED light effectively inhibited the growth of C. albicans and S. mutans dual-species biofilms for 12 h.

CO2 enhances the formation, nutrient scavenging and drug resistance properties of C. albicans biofilms

C. albicans is the predominant human fungal pathogen and frequently colonises medical devices, such as voice prostheses, as a biofilm. It is a dimorphic yeast that can switch between yeast and hyphal forms in response to environmental cues, a property that is essential during biofilm establishment and maturation. One such cue is the elevation of CO₂ levels, as observed in exhaled breath for example. However, despite the clear medical relevance, the effect of CO₂ on C. albicans biofilm growth has not been investigated to date. Here we show that physiologically relevant CO₂ elevation enhances each stage of the C. albicans biofilm-forming process: from attachment through maturation to dispersion. The effects of CO₂ are mediated via the Ras/cAMP/PKA signalling pathway and the central biofilm regulators Efg1, Brg1, Bcr1 and Ndt80. Biofilms grown under elevated CO₂ conditions also exhibit increased azole resistance, increased Sef1-dependent iron scavenging and enhanced glucose uptake to support their rapid growth. These findings suggest that C. albicans has evolved to utilise the CO₂ signal to promote biofilm formation within the host. We investigate the possibility of targeting CO₂-activated processes and propose 2-deoxyglucose as a drug that may be repurposed to prevent C. albicans biofilm formation on medical airway management implants. We thus characterise the mechanisms by which CO₂ promotes C. albicans biofilm formation and suggest new approaches for future preventative strategies.

Heat Shock Protein 60, Insights to Its Importance in Histoplasma capsulatum: From Biofilm Formation to Host-Interaction

Heat shock proteins (Hsps) are among the most widely distributed and evolutionary conserved proteins, acting as essential regulators of diverse constitutive metabolic processes. The Hsp60 of the dimorphic fungal Histoplasma capsulatum is the major surface adhesin to mammalian macrophages and studies of antibody-mediated protection against H. capsulatum have provided insight into the complexity involving Hsp60. However, nothing is known about the role of Hsp60 regarding biofilms, a mechanism of virulence exhibited by H. capsulatum. Considering this, the present study aimed to investigate the influence of the Hsp60 on biofilm features of H. capsulatum. Also, the non-conventional model Galleria mellonella was used to verify the effect of this protein during in vivo interaction. The use of invertebrate models such as G. mellonella is highly proposed for the evaluation of pathogenesis, immune response, virulence mechanisms, and antimicrobial compounds. For that purpose, we used a monoclonal antibody (7B6) against Hsp60 and characterized the biofilm of two H. capsulatum strains by metabolic activity, biomass content, and images from scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM). We also evaluated the survival rate of G. mellonella infected with both strains under blockage of Hsp60. The results showed that mAb 7B6 was effective to reduce the metabolic activity and biomass of both H. capsulatum strains. Furthermore, the biofilms of cells treated with the antibody were thinner as well as presented a lower amount of cells and extracellular polymeric matrix compared to its non-treated controls. The blockage of Hsp60 before fungal infection of G. mellonella larvae also resulted in a significant increase of the larvae survival compared to controls. Our results highlight for the first time the importance of the Hsp60 protein to the establishment of the H. capsulatum biofilms and the G. mellonella larvae infection. Interestingly, the results with Hsp60 mAb 7B6 in this invertebrate model suggest a pattern of fungus-host interaction different from those previously found in a murine model, which can be due to the different features between insect and mammalian immune cells such as the absence of Fc receptors in hemocytes. However further studies are needed to support this hypothesis

Boesenbergia rotunda extract inhibits Candida albicans biofilm formation by pinostrobin and pinocembrin

ETHNOPHARMACOLOGICAL RELEVANCE

Boesenbergia rotunda (L.) Mansf. (Zingiberaceae) is an indigenous plant of Southeast Asia. Based on ethnopharmacological use, the rhizome is recommended in the treatment of stomachache, leukoplakia, abscesses, and leukorrhea in Thailand primary health care system. Candida albicans often causes leukorrhea, and infection of many mucosal sites. Its infection leads to serious illness.

AIM OF THE STUDY

This study aimed to investigate the effects of the ethanolic extract of the B. rotunda rhizome on C. albicans ATCC10231 in the stages of planktonic and biofilm formation and to explore the underlying mechanisms.

MATERIALS AND METHODS

The chemical composition of the extract was determined using ultra-performance liquid chromatography (UPLC). The planktonic growth of C. albicans was evaluated by the microdilution method, following EUCAST guidelines. For each stage of biofilm formation, the biofilm was assessed by the MTT assay. The biofilm structure was examined under a light microscope. The degree of cell surface hydrophobicity was measured. The mRNA levels of ALS1, ALS3, and ACT1 were determined by RT-qPCR.

RESULTS

The extract of B. rotunda consisted of 25% (w/w) pinostrobin and 12% (w/w) pinocembrin. All stages of C. albicans biofilm formation were significantly inhibited by the extract, whereas the planktonic growth did not change. Biofilm development greatly decreased due to the extract in a concentration-dependent manner, with an IC₅₀ value of 17.7 μg/mL. Pinostrobin and pinocembrin demonstrated inhibitory effects during this stage. These results were in accordance with the microscopic evaluation. The filamentous form decreased with pinocembrin rather than pinostrobin. Moreover, the cell surface hydrophobicity was significantly decreased by 6.25 and 12.5 μg/mL of the extract and 100 μM of pinocembrin. The ALS3 mRNA level was noticeably decreased by 12.5 μg/mL of the extract, 100 μM of pinostrobin, and 100 μM of pinocembrin. The ACT1 mRNA level decreased significantly with pinocembrin. However, the ALS1 mRNA level was not altered following all treatments.

CONCLUSION

The ethanolic extract of B. rotunda could inhibit biofilm formation of C. albicans, especially during the biofilm development stage, by means of reducing the cell surface hydrophobicity and suppressing the ALS3 mRNA expression. Pinocembrin had a stronger effect on ALS3 mRNA expression than pinostrobin. Only pinocembrin significantly decreased the ACT1 mRNA level.

Phenotypic and genotypic evaluation of adherence and biofilm development in Candida albicans respiratory tract isolates from hospitalized patients

In recent years, a significant number of epidemiological variations have been observed for fungal infections. In immunocompromised patients, Candida albicans is crucially involved in invasive infections, mostly originating in respiratory tract colonization. The global rise in candidiasis has led researchers to investigate possible correlations between fungal strains virulence profiles and their pathogenic potential, among the most investigated genes being those involved in adherence and biofilm development. In this study, we established the adherence gene profiles of C. albicans strains isolated from respiratory tract secretions in patients hospitalized for cardiovascular diseases and correlated them with the ability of the respective strains to colonize the epithelial cells and form biofilms on the inert substratum. The strains isolated from the lower respiratory tract exhibited the highest adherence capacity and were intensive biofilm producers. The SAP9, ALS3, ALS5, and ALS6 genes were the most frequently detected. There was a significant association between the presence of ALS 3 gene and the cellular substrate colonizing potential of the harboring strains. We also found that the strains expressing SAP9 were more virulent in the phenotypic assays. Detecting the presence of adherence genes from different clinical isolates is a cost-effective tool that would allow researchers to predict the virulence of a certain strain and estimate its potential to adhere to host cells and develop biofilms.

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.

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.

In vitro Paracoccidioides brasiliensis biofilm and gene expression of adhesins and hydrolytic enzymes

Paracoccidioides species are dimorphic fungi that initially infect the lungs but can also spread throughout the body. The spreading infection is most likely due to the formation of a biofilm that makes it difficult for the host to eliminate the infection. Biofilm formation is crucial for the development of infections and confines the pathogen to an extracellular matrix. Its presence is associated with antimicrobial resistance and avoidance of host defenses. This current study provides the first description of biofilm formation by Paracoccidioides brasiliensis (Pb18) and an analysis of gene expression, using real-time PCR, associated with 3 adhesins and 2 hydrolytic enzymes that could be associated with the virulence profile. Biofilm formation was analyzed using fluorescence microscopy, scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM). Metabolic activity was determined using the XTT reduction assay. P. brasiliensis was able to form mature biofilm in 144 h with a thickness of 100 μm. The presence of a biofilm was found to be associated with an increase in the expression of adhesins and enzymes. GP43, enolase, GAPDH and aspartyl proteinase genes were over-expressed, whereas phospholipase was down-regulated in biofilm. The characterization of biofilm formed by P. brasiliensis may contribute to a better understanding of the pathogenesis of paracoccidioidomycosis as well as the search for new therapeutic alternatives; while improving the effectiveness of treatment.

Inhibition of Candida albicans biofilm development by unencapsulated Enterococcus faecalis cps2

Background/purpose

In the oral environment, Candida albicans interacts with many bacteria, including Enterococcus faecalis. We investigated the susceptibility of C. albicans biofilm development to the presence of unencapsulated E. faecalis cps2 in comparison with reference strains (E. faecalis ATCC 29212) or their respective spent medium (collected at 6 hours).

Material and methods

Crystal violet stain was used to measure the total biofilm mass, whereas quantitative real-time polymerase chain reaction was used to analyze the change in expression of the mRNA of hypha morphology (ALS1 and ALS3) and biofilm maturation (EFB1).

Results

At the intermediate stage, C. albicans resisted the presence of each E. faecalis strain tested and their spent medium. However, at the maturation stage, the unencapsulated strain was stronger in reducing C. albicans biofilms than the reference strain (P < 0.05). At this maturation stage, the transcription levels of each gene tested decreased in the presence of either E. faecalis strains or their respective spent medium. The unencapsulated strain was more pronounced in reducing ALS1/ALS3 expression, whereas the respective spent medium had a similar capability to restrict the expression of EFB1.

Conclusion

This study showed, the unencapsulated strain is more effective in inhibiting C. albicans biofilm development compared with the reference strains. In contrast, the secreted molecules produced by each strain tested are necessary in controlling the growths of C. albicans biofilm.

The role of Mss11 in Candida albicans biofilm formation

Candida albicans is an opportunistic human pathogen that can form a biofilm on biotic or inert surfaces such as epithelia and clinical devices. In this study, we examine the formation of C. albicans biofilm by establishing a key gene-centered network based on protein-protein interaction (PPI) and gene expression datasets. Starting from C. albicans Cph1 and Efg1, transcription factors associated with morphogenesis of biofilm formation, a network elucidates the complex cellular process and predicts potential unknown components related to biofilm formation. Subsequently, we analyzed the functions of Mss11 among these identified proteins to test the efficiency of the proposed computational approach. MSS11-deleted mutants were compared with a wild-type strain, indicating that the mutant is defective in forming a mature biofilm and partially attenuates the virulence of C. albicans in an infected mouse model. Finally, a DNA microarray analysis was conducted to identify the potential target genes of C. albicans Mss11. The findings of this study clarify complex gene or protein interaction during the biofilm formation process of C. albicans, supporting the application of a systems biology approach to study fungal pathogenesis.

Diagnostics method for the rapid quantitative detection and identification of low-level contamination of high-purity water with pathogenic bacteria

High-purity water (HPW) can be contaminated with pathogenic microorganisms, which may result in human infection. Current culture-based techniques for the detection of microorganisms from HPW can be slow and laborious. The aim of this study was to develop a rapid method for the quantitative detection and identification of pathogenic bacteria causing low-level contamination of HPW. A novel internally controlled multiplex real-time PCR diagnostics assay was designed and optimized to specifically detect and identify Pseudomonas aeruginosa and the Burkholderia genus. Sterile HPW, spiked with a bacterial load ranging from 10 to 10(3) cfu/100 ml, was filtered and the bacterial cells were removed from the filters by sonication. Total genomic DNA was then purified from these bacteria and subjected to testing with the developed novel multiplex real-time PCR diagnostics assay. The specific P. aeruginosa and Burkholderia genus assays have an analytical sensitivity of 3.5 genome equivalents (GE) and 3.7 GE, respectively. This analysis demonstrated that it was possible to detect a spiked bacterial load of 1.06 × 10(2) cfu/100 ml for P. aeruginosa and 2.66 × 10(2) cfu/100 ml for B. cepacia from a 200-ml filtered HPW sample. The rapid diagnostics method described can reliably detect, identify, and quantify low-level contamination of HPW with P. aeruginosa and the Burkholderia genus in <4 h. We propose that this rapid diagnostics method could be applied to the pharmaceutical and clinical sectors to assure the safety and quality of HPW, medical devices, and patient-care equipment.

Human serum promotes Candida albicans biofilm growth and virulence gene expression on silicone biomaterial

Objectives

Systemic candidal infections are a common problem in hospitalized patients due to central venous catheters fabricated using silicone biomaterial (SB). We therefore evaluated the effect of human serum on C. albicans biofilm morphology, growth, and the expression of virulence-related genes on SB in vitro.

Methods

We cultivated C. albicans SC5314 (wild-type strain, WT) and its derivative HLC54 (hyphal mutant, HM) for 48 h in various conditions, including the presence or absence of SB discs, and human serum. The growth of planktonic and biofilm cells of both strains was monitored at three time points by a tetrazolium salt reduction assay and by scanning electron microscopy. We also analyzed by RT-PCR its expression of the virulence-related genes ALS3, HWP1, EAP1, ECE1, SAP1 - SAP10, PLB1, PLB2, PLC and PLD.

Results

At each time point, planktonic cells of WT strain cultured in yeast nitrogen base displayed a much higher expression of EAP1 and HWP1, and a moderately higher ALS3 expression, than HM cells. In planktonic cells, expression of the ten SAP genes was higher in the WT strain initially, but were highly expressed in the HM strain by 48 h. Biofilm growth of both strains on SB was promoted in the presence of human serum than in its absence. Significant upregulation of ALS3, HWP1, EAP1, ECE1, SAP1, SAP4, SAP6 - SAP10, PLB1, PLB2 and PLC was observed for WT biofilms grown on serum-treated SB discs for at least one time point, compared with biofilms on serum-free SB discs.

Conclusions

Human serum stimulates C. albicans biofilm growth on SB discs and upregulates the expression of virulence genes, particularly adhesion genes ALS3 and HWP1, and hydrolase-encoding genes SAP, PLB1 and PLB2. This response is likely to promote the colonization of this versatile pathogen within the human host.

Role for the fibrinogen-binding proteins coagulase and Efb in the Staphylococcus aureus-Candida interaction

Staphylococcus aureus and Candida species are increasingly coisolated from implant-associated polymicrobial infections creating an incremental health care problem. Synergistic effects between both genera seem to facilitate the formation of mixed S. aureus-Candida biofilms, which is thought to play a critical role in coinfections with these microorganisms. To identify and characterize S. aureus factors involved in the interaction with Candida species, we affinity-panned an S. aureus phage display library against Candida biofilms in the presence or absence of fibrinogen. Repeatedly isolated clones contained DNA fragments encoding portions of the S. aureus fibrinogen-binding proteins coagulase or Efb. The coagulase binds to prothrombin in a 1:1 ratio thereby inducing a conformational change and non-proteolytic activation of prothrombin, which in turn cleaves fibrinogen to fibrin. Efb has been known to inhibit opsonization. To study the role of coagulase and Efb in the S. aureus-Candida cross-kingdom interaction, we performed flow-cytometric phagocytosis assays. Preincubation with coagulase reduced the phagocytosis of Candida yeasts by granulocytes significantly and dose-dependently. By using confocal laser scanning microscopy, we demonstrated that the coagulase mediated the formation of fibrin surrounding the candidal cells. Furthermore, the addition of Efb significantly protected the yeasts against phagocytosis by granulocytes in a dose-dependent and saturable fashion. In conclusion, the inhibition of phagocytosis of Candida cells by coagulase and Efb via two distinct mechanisms suggests that S. aureus might be beneficial for Candida to persist as it helps Candida to circumvent the host immune system.

Carbon source-induced reprogramming of the cell wall proteome and secretome modulates the adherence and drug resistance of the fungal pathogen Candida albicans

The major fungal pathogen Candida albicans can occupy diverse microenvironments in its human host. During colonization of the gastrointestinal or urogenital tracts, mucosal surfaces, bloodstream, and internal organs, C. albicans thrives in niches that differ with respect to available nutrients and local environmental stresses. Although most studies are performed on glucose-grown cells, changes in carbon source dramatically affect cell wall architecture, stress responses, and drug resistance. We show that growth on the physiologically relevant carboxylic acid, lactate, has a significant impact on the C. albicans cell wall proteome and secretome. The regulation of cell wall structural proteins (e.g. Cht1, Phr1, Phr2, Pir1) correlated with extensive cell wall remodeling in lactate-grown cells and with their increased resistance to stresses and antifungal drugs, compared with glucose-grown cells. Moreover, changes in other proteins (e.g. Als2, Gca1, Phr1, Sap9) correlated with the increased adherence and biofilm formation of lactate-grown cells. We identified mating and pheromone-regulated proteins that were exclusive to lactate-grown cells (e.g. Op4, Pga31, Pry1, Scw4, Yps7) as well as mucosa-specific and other niche-specific factors such as Lip4, Pga4, Plb5, and Sap7. The analysis of the corresponding null mutants confirmed that many of these proteins contribute to C. albicans adherence, stress, and antifungal drug resistance. Therefore, the cell wall proteome and secretome display considerable plasticity in response to carbon source. This plasticity influences important fitness and virulence attributes known to modulate the behavior of C. albicans in different host microenvironments during infection.

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.

Identification and differential gene expression of adhesin-like wall proteins in Candida glabrata biofilms

An important initial step in biofilm development and subsequent establishment of fungal infections by the human pathogen Candida glabrata is adherence to a surface. Adherence is mediated through a large number of differentially regulated cell wall-bound adhesins. The fungus can modify the incorporation of adhesins in the cell wall allowing crucial adaptations to new environments. In this study, expression and cell wall incorporation of C. glabrata adhesins were evaluated in biofilms cultured in two different media: YPD and a semi-defined medium SdmYg. Tandem mass spectrometry of isolated C. glabrata cell walls identified 22 proteins including six adhesins: the novel adhesins Awp5 and Awp6, Epa3 and the previously identified adhesins Epa6, Awp2 and Awp4. Regulation of expression of these and other relevant adhesin genes was investigated using real-time qPCR analysis. For most adhesin genes, significant up-regulation was observed in biofilms in at least one of the culturing media. However, this was not the case for EPA6 and AWP2, which is consistent with their gene products already being abundantly present in planktonic cultures grown in YPD medium. Furthermore, most of the adhesin genes tested also show medium-dependent differential regulation. These results underline the idea that many adhesins in C. glabrata are involved in biofilm formation and that their expression is tightly regulated and dependent on environmental conditions and growth phase. This may contribute to its potential to form resilient biofilms and cause infection in various host tissues.

Recent advances in the development of nucleic acid diagnostics

Since the early 1970s, the use of nucleic acid sequences for specific diagnostic applications has followed a somewhat linear pattern of development. Early methods for restriction enzyme digestion, as well as reverse transcription, were followed in the late 1970s by Southern, northern and dot blotting, as well as DNA sequencing. In 1985, the description of PCR and the routine laboratory manipulation of sufficient quantities of DNA for diagnostics, resulted in the exponential growth of molecular biology. Subsequently, alternative DNA and RNA amplification protocols followed. The last 10 years have seen the second explosion in molecular biology with the development of real-time quantitative PCR and oligonucleotide microarrays. This advancement continues with the development of methods for 'direct' nucleic acid target detection from samples without in vitro amplification, and enhanced transduction elements for improved sensitivity of nucleic acid detection. In this article, we will describe the current state of the art in nucleic acid diagnostics, the use of nucleic acid-based diagnostics in clinical practice and the emerging technologies in the field. Finally, we will describe future trends and expected advances in the field.

Overexpression of CDR1 and CDR2 genes plays an important role in fluconazole resistance in Candida albicans with G487T and T916C mutations

This study was designed to investigate potential resistance mechanisms by studying the expression of resistant genes in 14 fluconazole-resistant Candida albicans isolates, with G487T and T916C mutations in the 14alpha-demethylase (ERG11) gene, collected from human immunodeficiency virus uninfected patients and a fluconazole-susceptible control strain. The in vitro susceptibilities of the C. albicans isolates to fluconazole were determined using the broth microdilution method and a disc diffusion assay. Expression of Candida drug resistance (CDR)1, CDR2, ERG11, fluconazole resistance (FLU)1 and multidrug resistance (MDR)1 genes was measured using real-time reverse transcription-polymerase chain reaction and evaluated relative to the expression of the control gene 18SrRNA. The CDR1 and CDR2 genes were upregulated in all the fluconazole-resistant C. albicans isolates, whereas only a few isolates showed high expression of MDR1, FLU1 and ERG11 genes compared with the control strain. In conclusion, overexpression of the CDR1 and CDR2 genes may play an important role in fluconazole-resistant C. albicans with G487T and T916C mutations.

Real-time PCR expression profiling of genes encoding potential virulence factors in Candida albicans biofilms: identification of model-dependent and -independent gene expression

Background

Candida albicans infections are often associated with biofilm formation. Previous work demonstrated that the expression of HWP1 (hyphal wall protein) and of genes belonging to the ALS (agglutinin-like sequence), SAP (secreted aspartyl protease), PLB (phospholipase B) and LIP (lipase) gene families is associated with biofilm growth on mucosal surfaces. We investigated using real-time PCR whether genes encoding potential virulence factors are also highly expressed in biofilms associated with abiotic surfaces. For this, C. albicans biofilms were grown on silicone in microtiter plates (MTP) or in the Centres for Disease Control (CDC) reactor, on polyurethane in an in vivo subcutaneous catheter rat (SCR) model, and on mucosal surfaces in the reconstituted human epithelium (RHE) model.

Results

HWP1 and genes belonging to the ALS, SAP, PLB and LIP gene families were constitutively expressed in C. albicans biofilms. ALS1-5 were upregulated in all model systems, while ALS9 was mostly downregulated. ALS6 and HWP1 were overexpressed in all models except in the RHE and MTP, respectively. The expression levels of SAP1 were more pronounced in both in vitro models, while those of SAP2, SAP4 and SAP6 were higher in the in vivo model. Furthermore, SAP5 was highly upregulated in the in vivo and RHE models. For SAP9 and SAP10 similar gene expression levels were observed in all model systems. PLB genes were not considerably upregulated in biofilms, while LIP1-3, LIP5-7 and LIP9-10 were highly overexpressed in both in vitro models. Furthermore, an elevated lipase activity was detected in supernatans of biofilms grown in the MTP and RHE model.

Conclusions

Our findings show that HWP1 and most of the genes belonging to the ALS, SAP and LIP gene families are upregulated in C. albicans biofilms. Comparison of the fold expression between the various model systems revealed similar expression levels for some genes, while for others model-dependent expression levels were observed. This suggests that data obtained in one biofilm model cannot be extrapolated to other model systems. Therefore, the need to use multiple model systems when studying the expression of genes encoding potential virulence factors in C. albicans biofilms is highlighted.

An extensive circuitry for cell wall regulation in Candida albicans

Protein kinases play key roles in signaling and response to changes in the external environment. The ability of Candida albicans to quickly sense and respond to changes in its environment is key to its survival in the human host. Our guiding hypothesis was that creating and screening a set of protein kinase mutant strains would reveal signaling pathways that mediate stress response in C. albicans. A library of protein kinase mutant strains was created and screened for sensitivity to a variety of stresses. For the majority of stresses tested, stress response was largely conserved between C. albicans, Saccharomyces cerevisiae, and Schizosaccharomyces pombe. However, we identified eight protein kinases whose roles in cell wall regulation (CWR) were not expected from functions of their orthologs in the model fungi Saccharomyces cerevisiae and Schizosaccharomyces pombe. Analysis of the conserved roles of these protein kinases indicates that establishment of cell polarity is critical for CWR. In addition, we found that septins, crucial to budding, are both important for surviving and are mislocalized by cell wall stress. Our study shows an expanded role for protein kinase signaling in C. albicans cell wall integrity. Our studies suggest that in some cases, this expansion represents a greater importance for certain pathways in cell wall biogenesis. In other cases, it appears that signaling pathways have been rewired for a cell wall integrity response.

Candida albicans is the major fungal commensal and pathogen of humans. Like most microorganisms, C. albicans is surrounded and protected by a cell wall. This cell wall has two purposes: to act as a rigid “exoskeleton” to prevent cells from bursting, and to provide a surface where a cell can interact with the outside environment while protecting the cell itself from this environment. Maintenance of this structure has been well studied in the model fungus, Saccharomyces cerevisiae, but previous evidence suggested that C. albicans might have additional inputs to this process. By creating and testing a library of mutant strains for sensitivity to cell wall stress, we were able to identify a number of conserved genes with roles in this process not shared by their S. cerevisiae counterparts. Although some of these genes had previously been linked to cell wall integrity, it appears that they have increased impact on this process in C. albicans. For other genes, their role in cell wall integrity may represent a novel connection. Our findings provide insight into novel aspects of cell wall integrity in this pathogen and lay a foundation for its more detailed analysis.

Correlation between biofilm formation and the hypoxic response in Candida parapsilosis

The ability of Candida parapsilosis to form biofilms on indwelling medical devices is correlated with virulence. To identify genes that are important for biofilm formation, we used arrays representing approximately 4,000 open reading frames (ORFs) to compare the transcriptional profile of biofilm cells growing in a microfermentor under continuous flow conditions with that of cells in planktonic culture. The expression of genes involved in fatty acid and ergosterol metabolism and in glycolysis, is upregulated in biofilms. The transcriptional profile of C. parapsilosis biofilm cells resembles that of Candida albicans cells grown under hypoxic conditions. We therefore subsequently used whole-genome arrays (representing 5,900 ORFs) to determine the hypoxic response of C. parapsilosis and showed that the levels of expression of genes involved in the ergosterol and glycolytic pathways, together with several cell wall genes, are increased. Our results indicate that there is substantial overlap between the hypoxic responses of C. parapsilosis and C. albicans and that this may be important for biofilm development. Knocking out an ortholog of the cell wall gene RBT1, whose expression is induced both in biofilms and under conditions of hypoxia in C. parapsilosis, reduces biofilm development.

Candida albicans cell wall proteins

The Candida albicans cell wall maintains the structural integrity of the organism in addition to providing a physical contact interface with the environment. The major components of the cell wall are fibrillar polysaccharides and proteins. The proteins of the cell wall are the focus of this review. Three classes of proteins are present in the candidal cell wall. One group of proteins attach to the cell wall via a glycophosphatidylinositol remnant or by an alkali-labile linkage. A second group of proteins with N-terminal signal sequences but no covalent attachment sequences are secreted by the classical secretory pathway. These proteins may end up in the cell wall or in the extracellular space. The third group of proteins lack a secretory signal, and the pathway(s) by which they become associated with the surface is unknown. Potential constituents of the first two classes have been predicted from analysis of genome sequences. Experimental analyses have identified members of all three classes. Some members of each class selected for consideration of confirmed or proposed function, phenotypic analysis of a mutant, and regulation by growth conditions and transcription factors are discussed in more detail.

Candida biofilms: is adhesion sexy?

The development of Candida albicans biofilms requires two types of adhesion molecule - the Als proteins and Hwp1. Mutational analyses have recently revealed that these molecules play complementary roles, and their characteristics suggest that they may have evolved from primitive mating agglutinins.

Complementary adhesin function in C. albicans biofilm formation

BACKGROUND

Biofilms are surface-associated microbial communities with significant environmental and medical impact. Here, we focus on an adherence mechanism that permits biofilm formation by Candida albicans, the major invasive fungal pathogen of humans.

RESULTS

The Als surface-protein family has been implicated in biofilm formation, and we show that Als1 and Als3 have critical but redundant roles. Overexpression of several other Als proteins permits biofilm formation in a biofilm-defective als1/als1 als3/als3 strain, thus arguing that the function of Als proteins in this process is governed by their respective expression levels. The surface protein Hwp1 is also required for biofilm formation, and we find that a mixture of biofilm-defective hwp1/hwp1 and als1/als1 als3/als3 strains can form a hybrid biofilm both in vitro and in vivo in a catheter infection model. Complementary function of Hwp1 and Als1 and 3 seems to reflect their interaction because expression of Hwp1 in the heterologous host S. cerevisiae permits adherence to wild-type C. albicans, but not to an als1/als1 als3/als3 strain.

CONCLUSIONS

The complementary roles of Hwp1 and Als1 and Als3 in biofilm formation are analogous to the roles of sexual agglutinins in mating reactions. This analogy suggests that biofilm-adhesin complementarity may promote formation of monospecies biofilms.

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.

Temporal analysis of Candida albicans gene expression during biofilm development

Microarrays were used to identify changes in gene expression associated with Candida albicans biofilm development. Two biofilm substrates (denture and catheter), and two C. albicans strains for each substrate, were tested to remove model- and strain-dependent variability from the overall dataset. Three biofilm developmental phases were examined: early (6 h), intermediate (12 h), and mature (48 h). Planktonic specimens were collected at the same time points. Data analysis focused primarily on gene expression changes over the time-course of biofilm development. Glycolytic and non-glycolytic carbohydrate assimilation, amino acid metabolism, and intracellular transport mechanisms were important during the early phase of biofilm formation. These early events increase intracellular pools of pyruvate, pentoses and amino acids, which prepare the biofilm for the large biomass increase that begins around 12 h of development. This developmental stage demands energy and utilizes specific transporters for amino acids, sugars, ions, oligopeptides and lactate/pyruvate. At mature phase (48 h), few genes were differentially expressed compared with the 12 h time point, suggesting a relative lack of initiation of new metabolic activity. Data analysis to assess biofilm model-specific gene expression showed more dynamic changes in the denture model than in the catheter model. Data analysis to identify gene expression changes that are associated with each strain/substrate combination identified the same types of genes that were identified in the analysis of the entire dataset. Collectively, these data suggest that genes belonging to different, but interconnected, functional categories regulate the morphology and phenotype of C. albicans biofilm.

Development and evaluation of different normalization strategies for gene expression studies in Candida albicans biofilms by real-time PCR

BACKGROUND

Candida albicans biofilms are commonly found on indwelling medical devices. However, the molecular basis of biofilm formation and development is not completely understood. Expression analysis of genes potentially involved in these processes, such as the ALS (Agglutinine Like Sequence) gene family can be performed using quantitative PCR (qPCR). In the present study, we investigated the expression stability of eight housekeeping genes potentially useful as reference genes to study gene expression in Candida albicans (C. albicans) biofilms, using the geNorm Visual Basic Application (VBA) for Microsoft Excel. To validate our normalization strategies we determined differences in ALS1 and ALS3 expression levels between C. albicans biofilm cells and their planktonic counterparts.

RESULTS

The eight genes tested in this study are ranked according to their expression stability (from most stable to least stable) as follows: ACT1 (beta-actin)/PMA1 (adenosine triphosphatase), RIP (ubiquinol cytochrome-c reductase complex component), RPP2B (cytosolic ribosomal acidic protein P2B), LSC2 (succinyl-CoA synthetase beta-subunit fragment), IMH3 (inosine-5'-monophosphate dehydrogenase fragment), CPA1 (carbamoyl-phosphate synthethase small subunit) and GAPDH (glyceraldehyde-3-phosphate dehydrogenase). Our data indicate that five genes are necessary for accurate and reliable normalization of gene expression data in C. albicans biofilms. Using different normalization strategies, we found a significant upregulation of the ALS1 gene and downregulation of the ALS3 gene in C. albicans biofilms grown on silicone disks in a continous flow system, the CDC reactor (Centre for Disease Control), for 24 hours.

CONCLUSION

In conclusion, we recommend the use of the geometric mean of the relative expression values from the five housekeeping genes (ACT1, PMA1, RIP, RPP2B and LSC2) for normalization, when analysing differences in gene expression levels between C. albicans biofilm cells and planktonic cells. Validation of the normalization strategies described above showed that the ALS1 gene is overexpressed and the ALS3 gene is underexpressed in C. albicans biofilms grown on silicone in the CDC reactor for 24 hours.

Genetics and genomics of Candida albicans biofilm formation

Biofilm formation by the opportunistic fungal pathogen Candida albicans is a complex process with significant consequences for human health: it contributes to implanted medical device-associated infections. Recent advances in gene expression profiling and genetic analysis have begun to clarify the mechanisms that govern C. albicans biofilm development and acquisition of unique biofilm phenotypes. Such studies have identified candidate adhesin genes, and have revealed that biofilm drug resistance is multifactorial. Newly defined cell-cell communication pathways also have profound effects on biofilm formation. Future challenges include the elucidation of the structure and function of the extracellular exopolymeric substance that surrounds biofilm cells, and the extension of in vitro biofilm observations to newly developed in vivo biofilm models.

Regulation of cell-surface genes and biofilm formation by the C. albicans transcription factor Bcr1p

The impact of many microorganisms on their environment depends upon their ability to form surface bound communities called biofilms [1]. Biofilm formation on implanted medical devices has severe consequences for human health by providing both a portal of entry and a sanctuary for invasive bacterial and fungal pathogens [1 and 2]. Biofilm regulators and adherence molecules are extensively defined for many bacterial pathogens [3, 4, and 5], but not for fungal pathogens such as Candida albicans. Elongated filaments called hyphae are a prominent feature of C. albicans biofilms, and known genes that promote biofilm formation are required for hyphal development [2, 6, 7 and 8]. From a new library of transcription-factor mutants, we identify Bcr1p, a zinc finger protein required for formation of biofilms but not hyphae. Expression analysis shows that Bcr1p activates cell-surface protein and adhesin genes, including several induced during hyphal development. BCR1 expression depends upon the hyphal regulator Tec1p. Thus, BCR1 is a downstream component of the hyphal regulatory network that couples expression of cell-surface genes to hyphal differentiation. Our results indicate that hyphal cells are specialized to present adherence molecules that support biofilm integrity.