Candida infections of medical devices

Ability of Candida albicans mutants to induce Staphylococcus aureus vancomycin resistance during polymicrobial biofilm formation

Candida albicans and Staphylococcus aureus form vigorous polymicrobial biofilms in serum, which may serve as the source of coinfection in patients. More importantly, S. aureus is highly resistant to vancomycin during polymicrobial biofilm formation, with no decreases in bacterial viability observed with up to 1,600 microg/ml drug. In these mixed-species biofilms, S. aureus preferentially associates with C. albicans hyphae, which express a variety of unique adhesins. We tested C. albicans mutants deficient in transcriptional regulators of morphogenesis (CPH1 and EFG1) and biofilm formation (BCR1) to investigate the role of hyphae in mediating polymicrobial biofilm formation. These mutants also have reduced expression of hypha-specific adhesins. The ability to form polymicrobial biofilms correlated with the ability to form hyphae in these mutants. However, only mutants that could adhere to the abiotic surface could induce S. aureus vancomycin resistance, regardless of the presence of hyphae. In examining factors that may mediate interspecies adhesion, we found that the C. albicans ALS family of adhesins (Als1 to Als7 and Als9) was not involved, and neither was the hypha-specific adhesin Hwp1. Therefore, polymicrobial biofilm formation and subsequent antibiotic resistance is a multifactorial process that may require a unique combination of fungal and/or bacterial adhesins.

The effect of Saccharomyces boulardii on Candida albicans-infected human intestinal cell lines Caco-2 and Intestin 407

Saccharomyces boulardii is a probiotic strain that confers many benefits to human enterocolopathies and is used against a number of enteric pathogens. Candida albicans is an opportunistic pathogen that causes intestinal infections in immunocompromised patients, and after translocation into the bloodstream, is responsible for serious systemic candidiasis. In this study, we investigated the influence of S. boulardii cells and its culture extract on C. albicans adhesion to Caco-2 and Intestin 407 cell lines. We also tested the proinflammatory IL-1beta, IL-6 and IL-8 cytokine expression by C. albicans-infected Caco-2 cells, using real-time RT-PCR. We found that both S. boulardii and its extract significantly inhibited C. albicans adhesion to epithelial cell lines. The IL-8 gene expression by C. albicans-infected Caco-2 cells was suppressed by the addition of S. boulardii extract. Our results indicate that S. boulardii affects C. albicans adhesion and reduces cytokine-mediated inflammatory host response.

Characterization of bacterial and fungal biofilms in chronic rhinosinusitis

BACKGROUND

Conclusive evidence exists that biofilms are present on the mucosa of chronic rhinosinusitis (CRS) patients. Less is known about the species constituting these biofilms. This study developed a fluorescence in situ hybridization (FISH) protocol for characterization of bacterial and fungal biofilms in CRS.

METHODS

Fifty CRS patients and 10 controls were recruited. Bacteria FISH probes for Staphylococcus aureus, Haemophilus influenzae, and Pseudomonas aeruginosa and a universal probe for fungi were applied to sinus mucosal specimens and then analyzed using confocal scanning laser microscopy.

RESULTS

Thirty-six of 50 CRS patients had biofilms present in contrast to 0/10 controls, suggesting a role for biofilms in the pathogenesis of this disease. S. aureus was the most common biofilm-forming organism. Eleven of 50 CRS patients had characteristic fungal biofilms present.

CONCLUSION

This is the largest study of biofilms in CRS. It has validated mucosal tissue cryopreservation for delayed biofilm analysis. Fungal biofilms have been identified and the importance of S. aureus biofilms in the polymicrobial etiology of CRS is highlighted.

Interactions between human phagocytes and Candida albicans biofilms alone and in combination with antifungal agents

BACKGROUND

Biofilm formation is an important component of vascular catheter infections caused by Candida albicans. Little is known about the interactions between human phagocytes, antifungal agents, and Candida biofilms.

METHODS

The interactions between C. albicans biofilms and human phagocytes alone and in combination with anidulafungin or voriconazole were investigated and compared with their corresponding planktonic counterparts by means of an in vitro biofilm model with clinical intravascular and green fluorescent protein (GFP)-expressing strains. Phagocyte-mediated and antifungal agent-mediated damages were determined by 2,3-bis[ 2- methoxy-4-nitro-5-sulfophenyl]2H-tetrazolium-5-carboxanilide assay, and structural effects were visualized by confocal microscopy. Oxidative burst was evaluated by flow cytometric measurement of dihydrorhodamine 123 oxidation, and cytokine release was measured by enzyme-linked immunosorbent assay.

RESULTS

Phagocytes alone and in combination with antifungal agents induced less damage against biofilms compared with planktonic cells. However, additive effects occurred between phagocytes and anidulafungin against Candida biofilms. Confocal microscopy demonstrated the absence of phagocytosis within biofilms but marked destruction caused by anidulafungin and phagocytes. Anidulafungin but not voriconazole elicited tumor necrosis factor alpha release from phagocytes compared with that from untreated biofilms.

CONCLUSIONS

C. albicans within biofilms are more resistant to phagocytic host defenses but are susceptible to additive effects between phagocytes and an echinocandin.

Pseudomonas aeruginosa secreted factors impair biofilm development in Candida albicans

Signal-mediated interactions between the human opportunistic pathogens Pseudomonas aeruginosa and Candida albicans affect virulence traits in both organisms. Phenotypic studies revealed that bacterial supernatant from four P. aeruginosa strains strongly reduced the ability of C. albicans to form biofilms on silicone. This was largely a consequence of inhibition of biofilm maturation, a phenomenon also observed with supernatant prepared from non-clinical bacterial species. The effects of supernatant on biofilm formation were not mediated via interference with the yeast–hyphal morphological switch and occurred regardless of the level of homoserine lactone (HSL) produced, indicating that the effect is HSL-independent. A transcriptome analysis to dissect the effects of the P. aeruginosa supernatants on gene expression in the early stages of C. albicans biofilm formation identified 238 genes that exhibited reproducible changes in expression in response to all four supernatants. In particular, there was a strong increase in the expression of genes related to drug or toxin efflux and a decrease in expression of genes associated with adhesion and biofilm formation. Furthermore, expression of YWP1, which encodes a protein known to inhibit biofilm formation, was significantly increased. Biofilm formation is a key aspect of C. albicans infections, therefore the capacity of P. aeruginosa to antagonize this has clear biomedical implications.

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.

Medically important bacterial-fungal interactions

Whether it is in the setting of disease or in a healthy state, the human body contains a diverse range of microorganisms, including bacteria and fungi. The interactions between these taxonomically diverse microorganisms are highly dynamic and dependent on a multitude of microorganism and host factors. Human disease can develop from an imbalance between commensal bacteria and fungi or from invasion of particular host niches by opportunistic bacterial and fungal pathogens. This Review describes the clinical and molecular characteristics of bacterial-fungal interactions that are relevant to human disease.

Dispersion as an important step in the Candida albicans biofilm developmental cycle

Biofilms are dynamic microbial communities in which transitions between planktonic and sessile modes of growth occur interchangeably in response to different environmental cues. In the last decade, early events associated with C. albicans biofilm formation have received considerable attention. However, very little is known about C. albicans biofilm dispersion or the mechanisms and signals that trigger it. This is important because it is precisely C. albicans cells dispersed from biofilms that are the main culprits associated with candidemia and establishment of disseminated invasive disease, two of the gravest forms of candidiasis. Using a simple flow biofilm model recently developed by our group, we have performed initial investigations into the phenomenon of C. albicans biofilm dispersion, as well as the phenotypic characteristics associated with dispersed cells. Our results indicate that C. albicans biofilm dispersion is dependent on growing conditions, including carbon source and pH of the media used for biofilm development. C. albicans dispersed cells are mostly in the yeast form and display distinct phenotypic properties compared to their planktonic counterparts, including enhanced adherence, filamentation, biofilm formation and, perhaps most importantly, increased pathogenicity in a murine model of hematogenously disseminated candidiasis, thus indicating that dispersed cells are armed with a complete arsenal of “virulence factors” important for seeding and establishing new foci of infection. In addition, utilizing genetically engineered strains of C. albicans (tetO-UME6 and tetO-PES1) we demonstrate that C. albicans biofilm dispersion can be regulated by manipulating levels of expression of these key genes, further supporting the evidence for a strong link between biofilms and morphogenetic conversions at different stages of the C. albicans biofilm developmental cycle. Overall, our results offer novel and important insight into the phenomenon of C. albicans biofilm dispersion, a key part of the biofilm developmental cycle, and provide the basis for its more detailed analysis.

Candida albicans is the main causative agent of candidiasis, a difficult-to-treat infection that occurs mostly in severely immunosuppressed and other at-risk patients. Candidiasis is often associated with the formation of biofilms (attached microbial communities encapsulated within a protective matrix) on host surfaces and/or implantable medical devices, most notably intravascular catheters. In recent years, for C. albicans, the process of biofilm formation has received much attention. However, the same is not true for biofilm dispersion (the release of cells from the biofilm). This is important since these dispersed cells are responsible for the subsequent establishment of disseminated candidiasis at distal organs. Here we have taken advantage of a model of biofilm formation under conditions of flow recently described by our group to study and characterize the phenomenon of C. albicans biofilm dispersion. Rather than an end-stage process, our results indicate that dispersion occurs at all different stages of the biofilm developmental cycle and is influenced by nutritional and other physiochemical conditions. In addition, our findings provide initial insights into how this process is regulated at the molecular level. We also demonstrate that dispersed cells display distinct phenotypic properties that are associated with increased virulence, with important clinical repercussions.

Inhibition of electron transport chain assembly and function promotes photodynamic killing of Candida

Respiratory deficiency increases the sensitivity of the pathogenic fungi Candida albicans and Candida glabrata to oxidative stress induced by photodynamic therapy (PDT) sensitized by the cationic porphyrin meso-tetra (N-methyl-4-pyridyl) porphine tetra tosylate (TMP-1363). Since disruption of electron transport chain (ETC) function increases intracellular levels of reactive oxygen species in yeast, we determined whether interference with ETC assembly or function increased sensitivity to TMP-1363-PDT in C. albicans, C. glabrata and the non-pathogenic yeast Saccharomyces cerevisiae. Metabolic inhibitor antimycin A and defined genetic mutants were used to identify ETC components that contribute to the sensitivity to PDT. Inhibition of cytochrome bc(1) (Complex III) with antimycin A increases mitochondrial levels of reactive oxygen species. PDT performed following pre-treatment with antimycin A reduced colony forming units (CFU) of C. albicans and C. glabrata by approximately two orders of magnitude relative to PDT alone. A S. cerevisiae mitochondrial glutaredoxin grx5 mutant, defective in assembly of Fe-S clusters critical for Complex III function, displayed increased sensitivity to PDT. Furthermore, C. glabrata and S.cerevisiae mutants in cytochrome c oxidase (Complex IV) synthesis and assembly were also significantly more sensitive to PDT. These included suv3, encoding an ATP-dependent RNA helicase critical for maturation of cytochrome c oxidase subunit transcripts, and pet117, encoding an essential cytochrome c oxidase assembly factor. Following PDT, the reduction in CFU of these mutants was one to two orders of magnitude greater than in their respective parental strains. The data demonstrate that selective inhibition of ETC Complexes III and IV significantly increases the sensitivity of C. albicans, C. glabrata and S. cerevisiae to PDT sensitized with TMP-1363.

Characterization of plant-derived saponin natural products against Candida albicans

Candida albicans is an opportunistic fungal pathogen capable of life-threatening disseminated infections particularly in immunocompromised patients. Resistance to many clinically used antifungal agents has created a need to identify and develop a new generation of compounds for therapeutic use. A compound screen to identify potential antifungal natural products was undertaken, identifying 12 saponins, some of which have not been previously described. In the Caenorhabditis elegans model, some saponins conferred nematode survival comparable to that of amphotericin B. Of the 12 antifungal saponins identified, two were selected for further analysis. C. albicans isolates were inhibited by these compounds at relatively low concentrations (16 and 32 microg mL(-1)) including isolates resistant to clinically used antifungal agents. C. albicans hyphae and biofilm formation were also disrupted in the presence of these natural products, and studies demonstrate that fungal cells in the presence of saponins are more susceptible to salt-induced osmotic stress. Although saponins are known for their hemolytic activity, no hemolysis of erythrocytes was observed at three times the minimal inhibitory concentration for C. albicans, suggesting the saponins may have a preference for binding to fungal ergosterol when compared to cholesterol. Importantly, when used in combination with photosensitizer compounds, the fungus displayed increased susceptibility to photodynamic inactivation due to the ability of the saponins to increase cell permeability, thereby facilitating penetration of the photosensitizers. The large proportion of compounds identified as antifungal agents containing saponin structural features suggests it may be a suitable chemical scaffold for a new generation of antifungal compounds.

Expression of CgCDR1, CgCDR2, and CgERG11 in Candida glabrata biofilms formed by bloodstream isolates

Many studies have shown that Candida biofilms are highly resistant to fluconazole. The mechanisms of acquired fluconazole resistance of Candida glabrata in non-biofilms have been elucidated, but the relevance of them relative to C. glabrata in biofilms are unknown. We examined by real-time PCR the expression of CgCDR1, CgCDR2, and CgERG11 of four bloodstream isolates of C. glabrata during the early (6 h), intermediate (15 h), and mature (48 h) phases of biofilm development. We found high levels of biofilm formation in vitro. At 6 and 15 h, the biofilms exhibited, in comparison to planktonic cells, approximately 1.5- and 3.3-fold upregulation of CgCDR1 and 0.5- and 3.1-fold upregulation of CgCDR2, respectively. However, at 48 h, neither gene was upregulated. In comparison, the expression of CgERG11 did not significantly increase during any of the three phases. Our results indicate a temporary increase in the expression of both CgCDR1 and CgCDR2 during the intermediate phase of C. glabrata biofilm development. In addition, the data collected at 48 h suggest that CgCDR1, CgCDR2, and CgERG11 may not play a role in the azole resistance of C. glabrata in mature biofilms.

Candida albicans biofilm formation in a new in vivo rat model

Device-associated microbial growth, including Candida biofilms, represents more than half of all human microbial infections and, despite a relatively small risk of implant-associated diseases, this type of infection usually leads to high morbidity, increased health-care costs and prolonged antimicrobial therapy. Animal models are needed to elucidate the complex host–pathogen interactions that occur during the development of attached and structured biofilm populations. We describe here a new in vivo model to study Candida biofilm, based on the avascular implantation of small catheters in rats. Polyurethane biomaterials challenged with Candida cells were placed underneath the skin of immunosuppressed animals following only minor surgery. The model allowed the study of up to ten biofilms at once, and the recovery of mature biofilms from 2 days after implantation. The adhering inoculum was adjusted to the standard threshold of positive diagnosis of fungal infection in materials recovered from patients. Wild-type biofilms were mainly formed of hyphal cells, and they were unevenly distributed across the catheter length as observed in infected materials in clinical cases. The hyphal multilayered structure of the biofilms of wild-type strains was observed by confocal microscopy and compared to the monolayer of yeast or hyphal cells of two well-known biofilm-deficient strains, efg1Δ/efg1Δ cph1Δ/cph1Δ and bcr1Δ/bcr1Δ, respectively. The subcutaneous Candida biofilm model relies on the use of implanted catheters with accessible, fast and minor surgery to the animals. This model can be used to characterize the ability of antimicrobial agents to eliminate biofilms, and to evaluate the prophylactic effect of antifungal drugs and biomaterial coatings.

Candidemia distribution, associated risk factors, and attributed mortality at a university-based medical center

Candida is the fourth most common cause of nosocomial bloodstream infections (BSI), being Candida albicans the most common species. This study evaluated the distribution of Candida spp isolates at a tertiary care medical center. The associated factors and outcome of patients with candidemia at the Puerto Rico Medical Center (PRMC) were evaluated. Laboratory data from May 2005 to April 2006 was reviewed. Blood cultures reported as positive for Candida spp were identified and records were reviewed. Two hundred and four blood cultures were reported with Candida spp, corresponding to 85 different episodes of candidemia in 82 patients: 3 patients presented more than one candidemia episode with two different Candida spp. In seventy-two percent (61/85) of candidemia episodes, the organism isolated was a non-albicans Candida, being C. parapsilosis the most common species isolated with 49% (42/85). Sixty five records were evaluated; of which 45 cases were reviewed (20 cases were excluded from the study due to incomplete information). The predominant factors identified were being on broad spectrum antibiotics 95.6% (43/45), central catheter placement 97.8% (44/45), mechanical ventilation 64.4% (29/45), and urinary catheter placement 73.3% (33/45). The mortality among the reviewed cases was 48.9% (22/45).

Interaction of Candida albicans biofilms with antifungals: transcriptional response and binding of antifungals to beta-glucans

Candida albicans can form biofilms that exhibit elevated intrinsic resistance to various antifungal agents, in particular azoles and polyenes. The molecular mechanisms involved in the antifungal resistance of biofilms remain poorly understood. We have used transcript profiling to explore the early transcriptional responses of mature C. albicans biofilms exposed to various antifungal agents. Mature C. albicans biofilms grown under continuous flow were exposed for as long as 2 h to concentrations of fluconazole (FLU), amphotericin B (AMB), and caspofungin (CAS) that, while lethal for planktonic cells, were not lethal for biofilms. Interestingly, FLU-exposed biofilms showed no significant changes in gene expression over the course of the experiment. In AMB-exposed biofilms, 2.7% of the genes showed altered expression, while in CAS-exposed biofilms, 13.0% of the genes had their expression modified. In particular, exposure to CAS resulted in the upregulation of hypha-specific genes known to play a role in biofilm formation, such as ALS3 and HWP1. There was little overlap between AMB- or CAS-responsive genes in biofilms and those that have been identified as AMB, FLU, or CAS responsive in C. albicans planktonic cultures. These results suggested that the resistance of C. albicans biofilms to azoles or polyenes was due not to the activation of specific mechanisms in response to exposure to these antifungals but rather to the intrinsic properties of the mature biofilms. In this regard, our study led us to observe that AMB physically bound C. albicans biofilms and beta-glucans, which have been proposed to be major constituents of the biofilm extracellular matrix and to prevent azoles from reaching biofilm cells. Thus, enhanced extracellular matrix or beta-glucan synthesis during biofilm growth might prevent antifungals, such as azoles and polyenes, from reaching biofilm cells, thus limiting their toxicity to these cells and the associated transcriptional responses.

Antifungal drug resistance of oral fungi

Fungi comprise a minor component of the oral microbiota but give rise to oral disease in a significant proportion of the population. The most common form of oral fungal disease is oral candidiasis, which has a number of presentations. The mainstay for the treatment of oral candidiasis is the use of polyenes, such as nystatin and amphotericin B, and azoles including miconazole, fluconazole, and itraconazole. Resistance of fungi to polyenes is rare, but some Candida species, such as Candida glabrata and C. krusei, are innately less susceptible to azoles, and C. albicans can acquire azole resistance. The main mechanism of high-level fungal azole resistance, measured in vitro, is energy-dependent drug efflux. Most fungi in the oral cavity, however, are present in multispecies biofilms that typically demonstrate an antifungal resistance phenotype. This resistance is the result of multiple factors including the expression of efflux pumps in the fungal cell membrane, biofilm matrix permeability, and a stress response in the fungal cell. Removal of dental biofilms, or treatments to prevent biofilm development in combination with antifungal drugs, may enable better treatment and prevention of oral fungal disease.

Biofilms of non-Candida albicans Candida species: quantification, structure and matrix composition

Most cases of candidiasis have been attributed to C. albicans, but recently, non- Candida albicans Candida (NCAC) species have been identified as common pathogens. The ability of Candida species to form biofilms has important clinical repercussions due to their increased resistance to antifungal therapy and the ability of yeast cells within the biofilms to withstand host immune defenses. Given this clinical importance of the biofilm growth form, the aim of this study was to characterize biofilms produced by three NCAC species, namely C. parapsilosis, C. tropicalis and C. glabrata. The biofilm forming ability of clinical isolates of C. parapsilosis, C. tropicalis and C. glabrata recovered from different sources, was evaluated by crystal violet staining. The structure and morphological characteristics of the biofilms were also assessed by scanning electron microscopy and the biofilm matrix composition analyzed for protein and carbohydrate content. All NCAC species were able to form biofilms although these were less extensive for C. glabrata compared with C. parapsilosis and C. tropicalis. It was evident that C. parapsilosis biofilm production was highly strain dependent, a feature not evident with C. glabrata and C. tropicalis. Scanning electron microscopy revealed structural differences for biofilms with respect to cell morphology and spatial arrangement. Candida parapsilosis biofilm matrices had large amounts of carbohydrate with less protein. Conversely, matrices extracted from C. tropicalis biofilms had low amounts of carbohydrate and protein. Interestingly, C. glabrata biofilm matrix was high in both protein and carbohydrate content. The present work demonstrates that biofilm forming ability, structure and matrix composition are highly species dependent with additional strain variability occurring with C. parapsilosis.

Antimicrobial Activity and Biocompatibility of Polyurethane—Iodine Complexes

Polyurethane (PU), one of the most versatile biomedical materials, strongly binds iodine, one of the most effective antiseptics, through the formation of a charge-transfer complex. The PU—Iodine complexes were characterized with UV/Vis study and X-ray photoelectron spectroscopy (XPS) analysis. The new materials evoked potent antimicrobial activity against Gram-negative and Gram-positive bacteria (including methicillin-resistant Staphylococcus aureus, vancomycin-resistant Enterococcus faecium, and bacterial spores), fungi, and viruses, as well as inhibited surface bacterial colonization and biofilm-formation. Based on the Kirby-Bauer test, the antimicrobial effects occurred through the slow release of iodine. The iodine release rate can be controlled by the preparation conditions of the PU—Iodine complex. Trypan blue exclusion analysis indicated that PU—Iodine has excellent mammalian cell viability. The PU—Iodine complexes have the potential for a wide range of medical, dental, and other related applications.

Our current understanding of fungal biofilms

Fungal biofilms are an escalating clinical problem associated with significant rates of mortality. Candida albicans is the most notorious of all fungal biofilm formers. However, non-Candida species, yeasts such as Cryptococcus neoformans, and filamentous moulds such as Aspergillus fumigatus, have been shown to be implicated in biofilm-associated infections. Fungal biofilms have distinct developmental phases, including adhesion, colonisation, maturation and dispersal, which are governed by complex molecular events. Recalcitrance to antifungal therapy remains the greatest threat to patients with fungal biofilms. This review discusses our current understanding of the basic biology and clinical implications associated with fungal biofilms.

Exopolysaccharide analysis of biofilm-forming Candida albicans

AIM

The major objective of the study was to analyse exopolysaccharide produced by a biofilm forming-clinical strain of Candida albicans.

METHODS AND RESULTS

The biofilm-forming ability of C. albicans recovered from infected intrauterine devices (IUDs) was evaluated using XTT (2,3-bis[2-methoxy-4-nitro-5-sulfophenyl]-2H-tetrazolium-5-carboxanilide) reduction assay. The morphological characteristics of the biofilm were assessed using scanning electron microscopy (SEM), atomic force microscopy (AFM) and confocal laser scanning microscopy (CLSM). Biochemical characterization of the exopolysaccharide was carried out by gel permeation chromatography, gas chromatography (GC), Fourier transform infrared (FTIR) spectroscopy and nuclear magnetic resonance (NMR) spectroscopy. Microscopic studies of C. albicans biofilm revealed complex, heterogeneous three-dimensional structure, in which yeast cells and hyphal elements were entrenched within exopolysaccharides matrix. Chromatographic analysis data indicated C. albicans exopolysaccharide (c. 300 kDa) to be made up of four major sugar units. The FTIR spectrum revealed specific absorbance of O-H, C-H, O=C=O, C=O, C-N and C-C ring stretching. (1) H and (13) C NMR data showed the presence of β (1→6) and β (1→3) linkages in the exopolysaccharide chain that were assigned to α-D-glucose and β-D-glucose, α-D-mannose, α-L-rhamnose and N-acetyl glucosamine (β-D-GlcNAc), respectively.

CONCLUSIONS

Study suggested the production of a water soluble c. 300 kDa exopolysaccharide by C. albicans made up of glucose, mannose, rhamnose and N-acetyl glucosamine subunits.

SIGNIFICANCE AND IMPACT OF THE STUDY

The study could assist in the development of novel therapeutics aimed at disrupting C. albicans biofilms that will translate into improved clearance of Candida-related infections.

Apoptosis in Candida biofilms exposed to amphotericin B

Candida biofilms are resistant to a range of antifungal agents in current clinical use. The basis of this drug resistance is not clear, but in some cases it could be due to the presence of a small number of drug-tolerant or persister cells. In this study, specific staining methods were used to investigate the existence of persisters and apoptosis in Candida biofilms subjected to different concentrations of amphotericin B. Fluorescein diacetate staining revealed the presence of persisters in biofilms of one of two strains of Candida albicans tested, and in biofilms of Candida krusei and Candida parapsilosis. Caspase activity, indicative of apoptosis, was detected with SR-FLICA and (aspartyl)(2)-rhodamine 110 fluorochrome-based staining reagents in all of these biofilms. The general inhibitor of mammalian caspases, Z-VAD-FMK, when used at a low concentration (2.5 microM), increased the viability of drug-treated biofilms up to 11.5-fold (P <0.001 %). Seven specific caspase inhibitors had different effects on C. albicans biofilm viability, but inhibitors of caspases-1, -9, -5, -3 and -2 all significantly increased cell survival (40-fold, 8-fold, 3.5-fold, 1.9-fold and 1.7-fold, respectively). However, histone deacetylase (HDA) inhibitors enhanced the activity of amphotericin B for biofilms of all three Candida species. Sodium butyrate and sodium valproate, for example, when added concurrently with amphotericin B, completely eliminated biofilm populations of C. albicans. Overall, our results demonstrate an apoptotic process in amphotericin-treated biofilms of three Candida species. They also indicate that HDA inhibitors can enhance the action of the drug and in some cases even eradicate persister subpopulations, suggesting that histone acetylation might activate apoptosis in these cells.

Human fungal pathogen Candida albicans in the postgenomic era: an overview

Candida albicans is an opportunistic human fungal pathogen and is responsible for candidiasis. Owing to the improvement in healthcare, the number of immunocompromised patients in hospitals has increased worldwide and these individuals are susceptible to infections caused by many pathogenic microbes, among which C. albicans is one of the major players. Currently, the complete genome sequence of this pathogen is available and the size of this was estimated to be of 16 Mb. Annotation of C. albicans genome revealed that there are 6114 open reading frames (ORFs), of which 774 are specific to C. albicans. This poses a challenge as well as an opportunity to the Candida community to understand the functions of the unknown genes, especially those specific to C. albicans. Efforts have been made by the Candida community to systematically delete the ORFs and assign the functions. This will, in turn, help in understanding the biology of C. albicans and its interactions with animals as well as humans, and better drugs can be developed to treat Candida infections. In this article, we review updates on the Candida biology in the context of the availability of the genome sequence, its functional analysis and anti-Candida therapy. Finally, in the light of present trends in Candida research and current challenges, various opportunities are identified and suggestions are made.

Characteristics of Candida albicans biofilms grown in a synthetic urine medium

Urinary tract infections (UTIs) are the most common type of nosocomial infection, and Candida albicans is the most frequent organism causing fungal UTIs. Presence of an indwelling urinary catheter represents a significant risk factor for UTIs. Furthermore, these infections are frequently associated with the formation of biofilms on the surface of these catheters. Here, we describe the characterization of C. albicans biofilms formed in vitro using synthetic urine (SU) medium and the frequently used RPMI medium and compare the results. Biofilms of C. albicans strain SC5314 were formed in 96-well microtiter plates and on silicon elastomer pieces using both SU and RPMI media. Biofilm formation was monitored by microscopy and a colorimetric XTT [2,3-bis(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide] reduction assay. As in biofilms grown in RPMI medium, time course studies revealed that biofilm formation using SU medium occurred after an initial adherence phase, followed by growth, proliferation, and maturation. However, microscopy techniques revealed that the architectural complexity of biofilms formed in SU medium was lower than that observed for those formed using RPMI medium. In particular, the level of filamentation of cells within the biofilms formed in SU medium was diminished compared to those in the biofilms grown in RPMI medium. This observation was also corroborated by expression profiling of five filamentation-associated genes using quantitative real-time reverse transcriptase PCR. Sessile C. albicans cells were resistant to fluconazole and amphotericin B, irrespective of the medium used to form the biofilms. However, caspofungin exhibited potent in vitro activity at therapeutic levels against C. albicans biofilms grown in both SU and RPMI media.

A comparison of Pseudomonas aeruginosa biofilm development on ZnSe and TiO2 using attenuated total reflection Fourier transform infrared spectroscopy

The growth of Pseudomonas aeruginosa PAO1 biofilms on ZnSe internal reflection elements (IREs) was compared with their growth on TiO(2)-coated ZnSe over several days using attenuated total reflection Fourier transform infrared (ATR-FT-IR) spectroscopy. The effect of the TiO(2) coating on the IR spectra of reference compounds and cell suspensions was determined to aid in the interpretation of the data. The presence of TiO(2) on the surface of a ZnSe IRE tripled the size of the amide II peak and facilitated the detection of pyoverdin production due to its increased adsorption on the coated surface. A 50% increase in the length of the lag phase was observed for PAO1 growth on TiO(2)-coated surfaces as compared to growth on ZnSe. Biofilms on both surfaces exhibited a growth maximum for all components, followed by restructuring at the surface characterized by a decrease in the signal. The composition of biofilms grown on TiO(2) was relatively constant after the restructuring phase, while the extracellular polymeric substance (EPS) component of the biofilms grown on ZnSe gradually increased. The peak due to the carbohydrate component of EPS was much larger in the spectra of biofilms than in those of planktonic cells. The increase of the pyoverdin signal over time in the spectra of the biofilms on TiO(2) closely followed the overall increase in biomass. However, no signal from pyoverdin was detected in the presence of ferric ions.

Candida in the ICU

Invasive Candida infections are becoming increasingly recognized in critically ill patients. These infections result in serious morbidity, can be life threatening, and are expensive to manage. Early suspicion of Candida infection and the use of timely and proper antifungal treatment can improve outcome. Although treatment of documented, deep-seated Candida infections in nonneutropenic patients has been studied extensively, guidelines for the management of suspected but undocumented cases of invasive Candida infections in critically ill patients have not been clearly established. Future work should focus on better delineation of the sector of critically ill patients who have suspected invasive Candida infection and who could benefit from the use of empiric antifungal therapy, and on the investigation of novel approaches for the potential salvage of devices infected with Candida species.

Proteomic analysis of cytoplasmic and surface proteins from yeast cells, hyphae, and biofilms of Candida albicans

Candida albicans is a human commensal and opportunistic pathogen that participates in biofilm formation on host surfaces and on medical devices. We used DIGE analysis to assess the cytoplasmic and non-covalently attached cell-surface proteins in biofilm formed on polymethylmethacrylate and planktonic yeast cells and hyphae. Of the 1490 proteins spots from cytoplasmic and 580 protein spots from the surface extracts analyzed, 265 and 108 were differentially abundant respectively (>or=1.5-fold, p <0.05). Differences of both greater and lesser abundance were found between biofilms and both planktonic conditions as well as between yeast cells and hyphae. The identity of 114 cytoplasmic and 80 surface protein spots determined represented 73 and 25 unique proteins, respectively. Analyses showed that yeast cells differed most in cytoplasmic profiling while biofilms differed most in surface profiling. Several processes and functions were significantly affected by the differentially abundant cytoplasmic proteins. Particularly noted were many of the enzymes of respiratory and fermentative pentose and glucose metabolism, folate interconversions and proteins associated with oxidative and stress response functions, host response, and multi-organism interaction. The differential abundance of cytoplasmic and surface proteins demonstrated that sessile and planktonic organisms have a unique profile.

Time course global gene expression analysis of an in vivo Candida biofilm

Candida infection of devices is common and invariably associated with biofilm growth. Exploratory microarray studies were undertaken to identify target genes associated with biofilm formation from an in vivo catheter model over time. We compared messenger RNA levels from Candida albicans grown in an in vivo central venous catheter biofilm model at 12 h (intermediate growth) and 24 h (mature) to in vitro planktonic cells without a biofilm substrate, using C. albicans oligo arrays. A total of 124 transcripts were similarly up-regulated at the 12- and 24-h time points. Ontology categories most highly represented included energy/metabolism (12%), carbohydrate (10%), and protein (13%) synthesis and modification, and transport (6%). Numerous genes were previously identified from in vitro biofilm studies. These genes included those associated with hyphal growth, amino acid metabolism, adherence, drug resistance, ergosterol biosynthesis, and beta-glucan synthesis. In the current data set, adherence genes were unique to those from the earlier time point. Differences between the current in vivo biofilm expression data and that previously reported from in vitro models, including alterations in metabolism and carbohydrate processing, may be due to the continuous availability of nutrients from host serum and the incorporation of the host-pathogen interaction.

Inhibitors of cellular signalling are cytotoxic or block the budded-to-hyphal transition in the pathogenic yeast Candida albicans

The pathogenic yeast Candida albicans can grow in multiple morphological states including budded, pseudohyphal and true hyphal forms. The ability to interconvert between budded and hyphal forms, herein termed the budded-to-hyphal transition (BHT), is important for C. albicans virulence, and is regulated by multiple environmental and cellular signals. To identify small-molecule inhibitors of known cellular processes that can also block the BHT, a microplate-based morphological assay was used to screen the BIOMOL-Institute of Chemistry and Cell Biology (ICCB) Known Bioactives collection from the ICCB-Longwood Screening Facility (Harvard Medical School, Boston, MA, USA). Of 480 molecules tested, 53 were cytotoxic to C. albicans and 16 were able to block the BHT without inhibiting budded growth. These 16 BHT inhibitors affected protein kinases, protein phosphatases, Ras signalling pathways, G protein-coupled receptors, calcium homeostasis, nitric oxide and guanylate cyclase signalling, and apoptosis in mammalian cells. Several of these molecules were also able to inhibit filamentous growth in other Candida species, as well as the pathogenic filamentous fungus Aspergillus fumigatus, suggesting a broad fungal host range for these inhibitory molecules. Results from secondary assays, including hyphal-specific transcription and septin localization analysis, were consistent with the inhibitors affecting known BHT signalling pathways in C. albicans. Therefore, these molecules will not only be invaluable in deciphering the signalling pathways regulating the BHT, but also may serve as starting points for potential new antifungal therapeutics.

Candida albicans and Staphylococcus aureus form polymicrobial biofilms: effects on antimicrobial resistance

Candida albicans readily forms biofilms on the surface on indwelling medical devices, and these biofilms serve as a source of local and systemic infections. It is estimated that 27% of nosocomial C. albicans bloodstream infections are polymicrobial, with Staphylococcus aureus as the third most common organism isolated in conjunction with C. albicans. We tested whether S. aureus and C. albicans are able to form a polymicrobial biofilm. Although S. aureus formed poor monoculture biofilms in serum, it formed a substantial polymicrobial biofilm in the presence of C. albicans. In terms of architecture, S. aureus formed microcolonies on the surface of the biofilm, with C. albicans serving as the underlying scaffolding. In addition, S. aureus matrix staining revealed a different phenotype in polymicrobial versus monomicrobial biofilms, suggesting that S. aureus may become coated in the matrix secreted by C. albicans. S. aureus resistance to vancomycin was enhanced within the polymicrobial biofilm, required viable C. albicans, and was in part mediated by C. albicans matrix. However, the growth or sensitivity to amphotericin B of C. albicans is not altered in the polymicrobial biofilm.

Biofilm formation and effect of caspofungin on biofilm structure of Candida species bloodstream isolates

Candida biofilms are microbial communities, embedded in a polymeric matrix, growing attached to a surface, and are highly recalcitrant to antimicrobial therapy. These biofilms exhibit enhanced resistance against most antifungal agents except echinocandins and lipid formulations of amphotericin B. In this study, biofilm formation by different Candida species, particularly Candida albicans, C. tropicalis, and C. parapsilosis, was evaluated, and the effect of caspofungin (CAS) was assessed using a clinically relevant in vitro model system. CAS displayed in vitro activity against C. albicans and C. tropicalis cells within biofilms. Biofilm formation was evaluated after 48 h of antifungal drug exposure, and the effects of CAS on preformed Candida species biofilms were visualized using scanning electron microscopy (SEM). Several species-specific differences in the cellular morphologies associated with biofilms were observed. Our results confirmed the presence of paradoxical growth (PG) in C. albicans and C. tropicalis biofilms in the presence of high CAS concentrations. These findings were also confirmed by SEM analysis and were associated with the metabolic activity obtained by biofilm susceptibility testing. Importantly, these results suggest that the presence of atypical, enlarged, conical cells could be associated with PG and with tolerant cells in Candida species biofilm populations. The clinical implications of these findings are still unknown.

Prevalence, distribution, and antifungal susceptibility profiles of Candida parapsilosis, C. orthopsilosis, and C. metapsilosis in a tertiary care hospital

Candida parapsilosis, an emergent agent of nosocomial infections, was previously made up of a complex of three genetically distinct groups (groups I, II, and III). Recently, the C. parapsilosis groups have been renamed as distinct species: C. parapsilosis sensu stricto, C. orthopsilosis, and C. metapsilosis. In Portugal, no data pertaining to the distribution and antifungal susceptibility of these Candida species are yet available. In the present report, we describe the incidence and distribution of C. parapsilosis sensu stricto, C. orthopsilosis, and C. metapsilosis among 175 clinical and environmental isolates previously identified by conventional methods as C. parapsilosis. We also evaluated the in vitro susceptibilities of the isolates to fluconazole, voriconazole, posaconazole, amphotericin B, and two echinocandins, caspofungin and anidulafungin. Of the 175 isolates tested, 160 (91.4%) were identified as C. parapsilosis sensu stricto, 4 (2.3%) were identified as C. orthopsilosis, and 5 (2.9%) were identified as C. metapsilosis. Six isolates corresponded to species other than the C. parapsilosis group. Interestingly, all isolates from blood cultures corresponded to C. parapsilosis sensu stricto. Evaluation of the antifungal susceptibility profile showed that only nine (5.6%) C. parapsilosis sensu stricto strains were susceptible-dose dependent or resistant to fluconazole, and a single strain displayed a multiazole-resistant phenotype; two (1.3%) C. parapsilosis sensu stricto strains were amphotericin B resistant. All C. orthopsilosis and C. metapsilosis isolates were susceptible to azoles and amphotericin B. A high number of strains were nonsusceptible to the echinocandins (caspofungin and anidulafungin).

Identification of yeast in chronic wounds using new pathogen-detection technologies

OBJECTIVE

To evaluate the ability of two new diagnostic methods to detect and accurately identify yeast associated with chronic wound infections.

METHOD

Fungal tag-encoded FLX amplicon pyrosequencing (fTEFAP), a universal fungal identification method, bacterial tag-encoded FLX amplicon pyrosequencing (bTEFAP), a universal bacterial identification method, and a new quantitative polymerase chain reaction (qPCR) wound pathogen panel were used to evaluate three chronic wounds suspected to contain yeast.

RESULTS

Forty wound samples were analysed in addition to the three samples suspected of containing yeast. The qPCR panel, which targets Candida albicans, detected this yeast in two of the three wound samples. In contrast, fTEFAP detected yeast in each of the three samples: two showed Candida albicans and the third Candida parapsilosis. fTEFAP also identified a lower level of Candida tropicalis in one of the wounds that was positive for Candida albicans. The qPCR wound panel results were returned within two hours, while the fTEFAP results were returned within 24 hours.

CONCLUSION

Two new molecular methods have been developed to aid wound pathogen diagnostics. The quantitative PCR wound panel is rapid but is limited to major wound-associated bacteria and yeasts. The universal fTEFAP and bTEFAP methods take 24 hours to return results but are able to detect the relative contribution of any bacteria of yeast in a chronic wound diagnostic sample.

DECLARATION OF INTEREST

Southwest Regional Wound Care Center is a clinical wound-care provider seeking to improve the ability of wound care practitioners to help patients. The Research and Testing Laboratory develops molecular methods including fTEFAP, bTEFAP and the quantitative PCR wound panel.

Effect of filamentation and mode of growth on antifungal susceptibility of Candida albicans

Biofilm formation involving profuse hyphal growth is a major characteristic of Candida spp. and confers higher antifungal resistance than its planktonic mode of growth. We investigated the antifungal susceptibility of Candida albicans and its hyphal mutants (Delta efg1/efg1, Delta cph1/cph1 and DeltaDelta cph1/cph1 efg1/efg1) to commonly used antifungals during planktonic, adhesion and biofilm modes of growth. The minimum inhibitory concentration (MIC) of each antifungal agent was determined for a lower inoculum (1x10(3) cells/mL) and higher inoculum (1x10(7) cells/mL) of planktonic Candida. Furthermore, MICs of C. albicans biofilms and adhesion modes of growth were determined with a standard XTT assay. Candida albicans in adhesion and biofilm modes of growth, but not in planktonic mode, were resistant to all five antifungal agents tested. Although Delta efg1/efg1 and DeltaDelta cph1/cph1 efg1/efg1 mutants formed less biofilm than wild-type C. albicans SC5314, they were similarly resistant to caspofungin. However, these mutants were more sensitive to amphotericin B and nystatin than the wild-type. Adhesion per se confers increased resistance to antifungal agents, which is further pronounced in the biofilm mode of Candida. Filamentation does not appear to be a major determinant of the antifungal resistance in Candida biofilms.

Candida bloodstream infection: data from a teaching hospital in Mato Grosso do Sul, Brazil

The incidence of Candida bloodstream infection has increased over the past years. In the Center-West region of Brazil, data on candidemia are scarce. This paper reports a retrospective analysis of 96 cases of Candida bloodstream infection at a Brazilian tertiary-care teaching hospital in the state of Mato Grosso do Sul, from January 1998 to December 2006. Demographic, clinical and laboratory data were collected from medical records and from the hospital's laboratory database. Patients' ages ranged from three days to 92 years, with 53 (55.2%) adults and 43 (44.8%) children. Of the latter, 25 (58.1%) were newborns. The risk conditions most often found were: long period of hospitalization, utilization of venous central catheter, and previous use of antibiotics. Fifty-eight (60.4%) patients died during the hospitalization period and eight (13.7%) of them died 30 days after the diagnosis of candidemia. Candida albicans (45.8%) was the most prevalent species, followed by C. parapsilosis (34.4%), C. tropicalis (14.6%) and C. glabrata (5.2%). This is the first report of Candida bloodstream infection in the state of Mato Grosso do Sul and it highlights the importance of considering the possibility of invasive Candida infection in patients exposed to risk factors, particularly among neonates and the elderly.

Disruption of the GPI protein-encoding gene IFF4 of Candida albicans results in decreased adherence and virulence

Candida albicans is the most important cause of systemic fungal infection in immunocompromised humans. Candidiasis is often initiated by the adherence and the colonization of inert surfaces such as peripheral venous catheters, central catheters, prosthetic cardiac valves, and other prostheses. We have studied the early stage of adherence and have shown that the disruption of C. albicans IFF4 gene encoding a GPI-anchor protein, led to a decrease of adherence of the germ tubes to plastic. Here, we demonstrated the role of the IFF4 gene in adherence to silicone catheter, as well as in virulence using a murine model of disseminated candidiasis. The iff4 Delta null mutant showed both a decrease of adherence to silicone catheter and a reduction of virulence. This work presents evidence for the importance of the IFF4 gene in host-fungal interaction.

Hypoxic adaptation by Efg1 regulates biofilm formation by Candida albicans

Hypoxia is encountered frequently by Candida albicans during systemic infection of the human host. We tested if hypoxia allows biofilm formation by C. albicans, which is a major cause of perseverance and antifungal resistance in C. albicans infections. Using an in vitro biofilm system, we unexpectedly discovered that several positive regulators of biofilm formation during normoxia, including Tec1, Ace2, Czf1, Och1, and Als3, had little or no influence on biofilm development during hypoxia, irrespective of the carbon dioxide level, indicating that C. albicans biofilm pathways differ depending on the oxygen level. In contrast, the Efg1 and Flo8 regulators were required for both normoxic and hypoxic biofilm formation. To explore the role of Efg1 during hypoxic and/or biofilm growth, we determined transcriptome kinetics following release of EFG1 expression by a system under transcriptional control of a doxycycline-inducible promoter. During hypoxia, Efg1 rapidly induced expression of all major classes of genes known to be associated with normoxic biofilm formation, including genes involved in glycolysis, sulfur metabolism, and antioxidative and peroxisome activities, as well as genes for iron uptake. The results suggest that hypoxic adaptation mediated by the Efg1 and Flo8 regulators is required even during normoxic biofilm development, while hypoxic biofilm formation in deep tissues or in organs may generate foci of C. albicans infections.

Interaction of Candida albicans with an intestinal pathogen, Salmonella enterica serovar Typhimurium

Candida albicans is an opportunistic human fungal pathogen that normally resides in the gastrointestinal tract and on the skin as a commensal but can cause life-threatening invasive disease. Salmonella enterica serovar Typhimurium is a gram-negative bacterial pathogen that causes a significant amount of gastrointestinal infection in humans. Both of these organisms are also pathogenic to the nematode Caenorhabditis elegans, causing a persistent gut infection leading to worm death. In the present study, we used a previously developed C. elegans polymicrobial infection model to assess the interactions between S. Typhimurium and C. albicans. We observed that when C. elegans is infected with C. albicans and serovar Typhimurium, C. albicans filamentation is inhibited. The inhibition of C. albicans filamentation by S. Typhimurium in C. elegans appeared to be mediated by a secretary molecule, since filter-sterilized bacterial supernatant was able to inhibit C. albicans filamentation. In vitro coculture assays under planktonic conditions showed that S. Typhimurium reduces the viability of C. albicans, with greater effects seen at 37 degrees C than at 30 degrees C. Interestingly, S. Typhimurium reduces the viability of both yeast and filamentous forms of C. albicans, but the killing appeared more rapid for the filamentous cells. The antagonistic interaction was also observed in a C. albicans biofilm environment. This study describes the interaction between two diverse human pathogens that reside within the gastrointestinal tract and shows that the prokaryote, S. Typhimurium, reduces the viability of the eukaryote, C. albicans. Identifying the molecular mechanisms of this interaction may provide important insights into microbial pathogenesis.

Penetration of antifungal agents through Candida biofilms

A filter disk assay is described, which measures the penetration of antifungal agents through Candida biofilms. The technique involves forming a colony biofilm on a polycarbonate membrane filter, and capping it with a second, smaller membrane filter followed by a wetted paper disk of the type used in zone-of-inhibition assays. The entire assembly is transferred to agar medium containing the antifungal agent of interest. During subsequent incubation, the drug diffuses out of the agar and through the biofilm 'sandwich' to the moistened paper disk. The drug concentration in the disk can be determined by measuring the zone of growth inhibition that it produces on medium seeded with an indicator strain of Candida albicans in standard bioassays. Additional procedures are outlined for determining the viabilities of drug-treated biofilms and for examining biofilm morphology by scanning electron microscopy.