Nosocomial fungal infections: epidemiology, diagnosis, and treatment

Infektionen

Trotz Weiterentwicklung moderner Antibiotika in den letzten Jahren sind die Letalitätszahlen der bakteriellen (eitrigen) Meningitis weiterhin hoch; Überlebende haben häufig neurologische Residuen. Die ungünstigen klinischen Verläufe der bakteriellen Meningitis sind meist Folge intrakranieller Komplikationen, wie z. B. eines generalisierten Hirnödems, einer zerebrovaskulären arteriellen oder venösen Beteiligung oder eines Hydrozephalus.

Farnesol-induced apoptosis in Candida albicans is mediated by Cdr1-p extrusion and depletion of intracellular glutathione

Farnesol is a key derivative in the sterol biosynthesis pathway in eukaryotic cells previously identified as a quorum sensing molecule in the human fungal pathogen Candida albicans. Recently, we demonstrated that above threshold concentrations, farnesol is capable of triggering apoptosis in C. albicans. However, the exact mechanism of farnesol cytotoxicity is not fully elucidated. Lipophilic compounds such as farnesol are known to conjugate with glutathione, an antioxidant crucial for cellular detoxification against damaging compounds. Glutathione conjugates act as substrates for ATP-dependent ABC transporters and are extruded from the cell. To that end, this current study was undertaken to validate the hypothesis that farnesol conjugation with intracellular glutathione coupled with Cdr1p-mediated extrusion of glutathione conjugates, results in total glutathione depletion, oxidative stress and ultimately fungal cell death. The combined findings demonstrated a significant decrease in intracellular glutathione levels concomitant with up-regulation of CDR1 and decreased cell viability. However, addition of exogenous reduced glutathione maintained intracellular glutathione levels and enhanced viability. In contrast, farnesol toxicity was decreased in a mutant lacking CDR1, whereas it was increased in a CDR1-overexpressing strain. Further, gene expression studies demonstrated significant up-regulation of the SOD genes, primary enzymes responsible for defense against oxidative stress, with no changes in expression in CDR1. This is the first study describing the involvement of Cdr1p-mediated glutathione efflux as a mechanism preceding the farnesol-induced apoptotic process in C. albicans. Understanding of the mechanisms underlying farnesol-cytotoxicity in C. albicans may lead to the development of this redox-cycling agent as an alternative antifungal agent.

Candida albicans morphogenesis and host defence: discriminating invasion from colonization

Candida albicans is a common fungal pathogen of humans that colonizes the skin and mucosal surfaces of most healthy individuals. Until recently, little was known about the mechanisms by which mucosal antifungal defences tolerate colonizing C. albicans but react strongly when hyphae of the same microorganism attempt to invade tissue. In this Review, we describe the properties of yeast cells and hyphae that are relevant to their interaction with the host, and the immunological mechanisms that differentially recognize colonizing versus invading C. albicans.

Genetic variation in the dectin-1/CARD9 recognition pathway and susceptibility to candidemia

BACKGROUND

Candidemia is an important cause of morbidity and mortality in critically ill patients or patients undergoing invasive treatments. Dectin-1 is the main β-glucan receptor, and patients with a complete deficiency of either dectin-1 or its adaptor molecule CARD9 display persistent mucosal infections with Candida albicans. The role of genetic variation of DECTIN-1 and CARD9 genes on the susceptibility to candidemia is unknown.

METHODS

We assessed whether genetic variation in the genes encoding dectin-1 and CARD9 influence the susceptibility to candidemia and/or the clinical course of the infection in a large cohort of American and Dutch candidemia patients (n = 331) and noninfected matched controls (n = 351). Furthermore, functional studies have been performed to assess the effect of the DECTIN-1 and CARD9 genetic variants on cytokine production in vitro and in vivo in the infected patients.

RESULTS

No significant association between the single-nucleotide polymorphisms DECTIN-1 Y238X and CARD9 S12N and the prevalence of candidemia was found, despite the association of the DECTIN-1 238X allele with impaired in vitro and in vivo cytokine production.

CONCLUSIONS

Whereas the dectin-1/CARD9 signaling pathway is nonredundant in mucosal immunity to C. albicans, a partial deficiency of β-glucan recognition has a minor impact on susceptibility to candidemia.

Cassettes for PCR-mediated gene tagging in Candida albicans utilizing nourseothricin resistance

In recent years a number of molecular tools have been reported for use in the human fungal pathogen Candida albicans, including PCR-mediated approaches for gene disruption, conditional expression and epitope tagging. Traditionally these methods have utilized auxotrophic markers; however, the availability of auxotrophic markers can be limiting and in some instances their use may also impact on the interpretation of results. As a result, the use of positive selection markers has now become more commonplace. Here we report the development and validation of a set of cassettes for PCR-mediated gene tagging and overexpression studies utilizing the nourseothricin resistance (CaNAT1) positive selection marker. In particular we have produced cassettes containing yeast-enhanced GFP, YFP, CFP, RFP and a combined V5-6xHis epitope tag. The cassettes are engineered for use in PCR-mediated gene tagging strategies where insertion is targeted to the 3' end of the gene of interest. In addition, to facilitate protein functional analysis and genetic suppression studies through the use of overexpression, we have also constructed a promoter replacement cassette containing the ENO1 promoter which is known to be expressed at a high level. These cassettes expand on the range of molecular tools available for working with C. albicans and may also be used in other Candida species that display sensitivity to nourseothricin.

Candida vaccines development from point view of US patent application

Candidiasis is the fourth most common bloodstream infection in hospitalized patients in the United States. Moreover, the mortality rate from Candida infections remains high, even after treatment with antifungal therapy. Vaccination would be a promising strategy for prevention of invasive fungal infections. In order to examine the main trends in anticandidal vaccine patenting activity, we conducted an analysis for anticandidal vaccine patents. We find 190 issued patent and 940 patent application documents containing the keywords Candida and vaccine within claims in the USA. Candida vaccines development, as evidenced by the numbers of issued patents, has decreased since the year 2002. Furthermore, the number of patent applications in Candida vaccines may indicate the strength of engaged resources were also in the status of stagnation during 2005-2007 and even a decline in 2008. Academic and nonprofit research institutions not only account for a large share of Candida vaccines patents but also apply for patents continually. Based on this analysis, the strength of Candida vaccines resources seems to remain stagnant in recent years due to patent prosecution or technical barrier in the filed of Candida vaccines. Therefore, we consider that Candida vaccines technology to still be under development and the researchers are still looking for scientific breakthrough in the filed.

The classical CD14⁺⁺ CD16⁻ monocytes, but not the patrolling CD14⁺ CD16⁺ monocytes, promote Th17 responses to Candida albicans

In the present study, we investigated the functional differences between cluster of differentiation (CD)14(++) CD16(-) and CD14(+) CD16(+) monocytes during anti-Candida host defense. CD14(++) CD16(-) are the "classical" monocytes and represent the majority of circulating monocytes in humans, while CD14(+) CD16(+) monocytes patrol the vasculature for maintenance of tissue integrity and repair. Both monocyte subsets inhibited the germination of live Candida albicans, and there was no difference in their capacity to phagocytose and kill Candida. Although production of IL-6 and IL-10 induced by C. albicans was found to be similar between monocyte subsets, IL-1β and prostaglandin E2 (PGE2) production was higher in CD14(++) CD16(-) compared with CD14(+) CD16(+) monocytes. In line with the increased production of IL-1β and PGE2, central mediators for inducing Th17 responses, CD14(++) CD16(-) monocytes induced greater Th17 responses upon stimulation with heat-killed C. albicans yeast. The percentage of cells that expressed mannose receptor (MR) was higher in the CD14(++) CD16(-) monocyte subset, and MR-specific stimulation induced higher Th17 responses only in co-cultures of CD14(++) CD16(-) monocytes and CD4 lymphocytes. In conclusion, both monocyte subsets have potent innate antifungal properties, but only CD14(++) CD16(-) monocytes are capable of inducing a potent Th17 response to C. albicans, an important component of antifungal host defense.

A viability assay for Candida albicans based on the electron transfer mediator 2,6-dichlorophenolindophenol

Candida albicans is an opportunistic fungal pathogen with comparably high respiratory activity. Thus, we established a viability test based on 2,6-dichlorophenolindophenol (DCIP), a membrane-permeable electron transfer agent. NADH dehydrogenases catalyze the reduction of DCIP by NADH, and the enzymatic activity can be determined either electrochemically via oxidation reactions of DCIP or photometrically. Among the specific respiratory chain inhibitors, only the complex I inhibitor rotenone decreased the DCIP signal from C. albicans, leaving residual activity of approximately 30%. Thus, the DCIP-reducing activity of C. albicans was largely dependent on complex I activity. C. albicans is closely related to the complex I-negative yeast Saccharomyces cerevisiae, which had previously been used in DCIP viability assays. Via comparative studies, in which we included the pathogenic complex I-negative yeast Candida glabrata, we could define assay conditions that allow a distinction of complex I-negative and -positive organisms. Basal levels of DCIP turnover by S.cerevisiae and C. glabrata were only 30% of those obtained from C. albicans but could be increased to the C. albicans level by adding glucose. No significant increases were observed with galactose. DCIP reduction rates from C. albicans were not further increased by any carbon source.

Vaccines for invasive fungal infections

Morbidity and mortality from invasive fungal infections remain unacceptably high despite availability of new antifungal agents, underscoring the need for more effective preventative strategies. Due to our enhanced understanding of the host defense and pathogenetic mechanisms that lead to invasive fungal infections, it should be feasible to develop vaccines targeting these infections. A common immunological theme across many vaccine candidates for invasive fungal infections has been the need to activate a cell-based, pro-inflammatory, Th1 or Th17 immune response to improve phagocytic killing of the fungi. Since neutralization of virulence factor functions has not been required for many active vaccines to function, the antigenic repertoire available for testing should not be limited to virulence factors. With expansion of our fundamental understanding of the immunology of fungal infections, the biggest barrier to development of fungal vaccines is the lack of available capital to translate discoveries made at the bench into biological agents used at the bedside. Continued education on the importance and feasibility of vaccination for such infections, combined with continued development of vaccine antigens and adjuvants, is necessary.

[Update: invasive fungal infections: Diagnosis and treatment in surgical intensive care medicine]

Fungal infections are of great relevance in surgical intensive care and Candida species represent the predominant part of fungal pathogens. Invasive aspergillosis is also relevant especially in patients with chronic pulmonary diseases. It is crucial for therapy success to begin adequate antifungal treatment at an early stage of the disease. Risk stratification of individual patient symptoms is essential for therapy timing. In case of suspected or proven candida infection, fluconazole is the agent of choice when the patient is clinically stable and no azoles have been administrated in advance and the local epidemiology makes azol resistance unlikely. For clinically instable patients with organ dysfunction the echinocandins serve as primary therapy because of their broad spectrum and reasonable safety profile. Due to a relevant proportion of azole resistant Candida species, susceptibility testing should be done routinely. Depending on the species detected de-escalating to an azole is feasible if organ dysfunctions have resolved. An invasive aspergillosis is primarily treated with voriconazole.

Host-pathogen interactions and virulence-associated genes during Candida albicans oral infections

Oral infections with Candida albicans are very common diseases in even only mildly immunocompromised patients. By using genome-wide microarrays, in vitro infection models and samples from patients with pseudomembranous candidiasis, several genes have been identified which encode known and unknown fungal factors associated with oral infection. The expression of selected genes has been investigated via qRT-PCR in both in vitro models and in vivo samples from patients. Several lines of evidence suggest that fungal morphology plays a key role in adhesion to and invasion into oral epithelial cells and mutants lacking regulators of hyphal formation are attenuated in their ability to invade and damage epithelial cells. Adhesion is mediated by hyphal-associated factors such as Hwp1 and the Als adhesin family. Hyphal formation facilitates epithelial invasion via two routes: active penetration and induced endocytosis. While induced endocytosis is predominantly mediated by the adhesin and invasin Als3, active penetration seems to be supported by hydrolase activity and mechanical pressure. Expression profiles reflect the morphological switch and an adaptive response to neutral pH, non-glucose carbon sources, and nitrosative stress.

Interaction of the mucosal barrier with accessory immune cells during fungal infection

The mucosal epithelium is of central importance in host defence and immune surveillance, as it is the primary cell layer that initially encounters environmental microorganisms. Induction of antifungal innate immune responses depends on recognition of fungal components by host pattern recognition receptors. Members of the Toll-like receptor family have emerged as key sensors that recognize fungal pathogens and trigger defence responses. During oral infection with the fungal pathogen Candida albicans, a large number of cytokines is secreted by oral epithelial cells, which in turn activate myeloid cells in the submucosal layers to clear the invading pathogen. Recent data provide novel insights into the complex molecular mechanisms of innate immune responses initiated by cooperation between epithelial cells and neutrophils. In this review, we discuss the role of epithelial TLRs and how the immunological crosstalk between C. albicans-infected oral epithelium and neutrophils protects the mucosal surface from fungal invasion and cell injury.

The dectin-1/inflammasome pathway is responsible for the induction of protective T-helper 17 responses that discriminate between yeasts and hyphae of Candida albicans

In the mucosa, the immune pathways discriminating between colonizing and invasive Candida, thus inducing tolerance or inflammation, are poorly understood. Th17 responses induced by Candida albicans hyphae are central for the activation of mucosal antifungal immunity. An essential step for the discrimination between yeasts and hyphae and induction of Th17 responses is the activation of the inflammasome by C. albicans hyphae and the subsequent release of active IL-1β in macrophages. Inflammasome activation in macrophages results from differences in cell-wall architecture between yeasts and hyphae and is partly mediated by the dectin-1/Syk pathway. These results define the dectin-1/inflammasome pathway as the mechanism that enables the host immune system to mount a protective Th17 response and distinguish between colonization and tissue invasion by C. albicans.

Analysis of the Aspergillus fumigatus proteome reveals metabolic changes and the activation of the pseurotin A biosynthesis gene cluster in response to hypoxia

The mold Aspergillus fumigatus is the most important airborne fungal pathogen. Adaptation to hypoxia represents an important virulence attribute for A. fumigatus. Therefore, we aimed at obtaining a comprehensive overview about this process on the proteome level. To ensure highly reproducible growth conditions, an oxygen-controlled, glucose-limited chemostat cultivation was established. Two-dimensional gel electrophoresis analysis of mycelial and mitochondrial proteins as well as two-dimensional Blue Native/SDS-gel separation of mitochondrial membrane proteins led to the identification of 117 proteins with an altered abundance under hypoxic in comparison to normoxic conditions. Hypoxia induced an increased activity of glycolysis, the TCA-cycle, respiration, and amino acid metabolism. Consistently, the cellular contents in heme, iron, copper, and zinc increased. Furthermore, hypoxia induced biosynthesis of the secondary metabolite pseurotin A as demonstrated at proteomic, transcriptional, and metabolite levels. The observed and so far not reported stimulation of the biosynthesis of a secondary metabolite by oxygen depletion may also affect the survival of A. fumigatus in hypoxic niches of the human host. Among the proteins so far not implicated in hypoxia adaptation, an NO-detoxifying flavohemoprotein was one of the most highly up-regulated proteins which indicates a link between hypoxia and the generation of nitrosative stress in A. fumigatus.

Aspergillus fumigatus is a ubiquitously distributed filamentous fungus and an important human pathogen. To colonize the human lung, A. fumigatus has to adapt to low oxygen concentrations. We analyzed the cytosolic and mitochondrial proteome of A. fumigatus under normoxic in comparison to hypoxic conditions using an oxygen-controlled chemostat. Hypoxia led to an increased respiratory capacity, induction of the biosynthesis of the secondary metabolite pseurotin A and presumably nitrosative stress.

Zygomycosis in Immunocompromised non-Haematological Patients

Zygomycoses caused by fungi of the mucorales order (mucormycoses) are emerging fungal diseases with a high fatality rate. The most important risk factors include neutropenia or functional neutropenia, diabetic ketoacidosis, iron overload, major trauma, prolonged use of corticosteroids, illicit intravenous drug (ID) use, neonatal prematurity, malnourishment, and maybe a previous exposure to antifungal agents with no activity against zygomycetes, such as voriconazole and echinocandins.A high index of suspicion is crucial for the diagnosis, as prompt and appropriate management can considerably reduce morbidity and mortality. Suspicion index can be increased through recognition of the differential patterns of clinical presentation. In the non- haematological immunocompromised patients, mucormycosis can manifest in various clinical forms, depending on the underlying condition: mostly as rhino-orbital or rhino-cerebral in diabetes patients, pulmonary infection in patients with malignancy or solid organ transplantation, disseminated infection in iron overloaded or deferoxamine treated patients, cerebral - with no sinus involvement - in ID users, gastrointestinal in premature infants or malnourishment, and cutaneous after direct inoculation in immunocompetent individuals with trauma or burns.Treating a patient's underlying medical condition and reducing immunosuppression are essential to therapy. Rapid correction of metabolic abnormalities is mandatory in cases such as uncontrolled diabetes, and corticosteroids or other immunosuppressive drugs should be discontinued where feasible. AmphotericinB or its newer and less toxic lipid formulations are the drugs of choice regarding antifungal chemotherapy, while extensive surgical debridement is essential to reduce infected and necrotic tissue. A high number of cases could be prevented through measures including diabetes control programmes and proper pre- and post-surgical hygiene.

Cell signals, cell contacts, and the organization of yeast communities

Even relatively simple species have evolved mechanisms to organize individual organisms into communities, such that the fitness of the group is greater than the fitness of isolated individuals. Within the fungal kingdom, the ability of many yeast species to organize into communities is crucial for their growth and survival, and this property has important impacts both on the economy and on human health. Over the last few years, studies of Saccharomyces cerevisiae have revealed several fundamental properties of yeast communities. First, strain-to-strain variation in the structures of these groups is attributable in part to variability in the expression and functions of adhesin proteins. Second, the extracellular matrix surrounding these communities can protect them from environmental stress and may also be important in cell signaling. Finally, diffusible signals between cells contribute to community organization so that different regions of a community express different genes and adopt different cell fates. These findings provide an arena in which to view fundamental mechanisms by which contacts and signals between individual organisms allow them to assemble into functional communities.

Study on fungal flora of tap water as a potential reservoir of fungi in hospitals in Sari city, Iran

OBJECTIVE

The aim of the present investigation was to evaluate the fungal flora of tap water from university hospitals of Sari city, Iran.

MATERIALS AND METHODS

During a 1-year period, 240 water samples were collected from four university hospitals. All water samples were collected in sterile polystyrene bottles. A volume of 100ml of the samples passed through sterile 0.45-micrometer filters. The filters were placed directly on malt extract agar and incubated at 27°C for 3 to 7 days. Routine mycological techniques were applied to identification of grown fungi.

RESULTS

Out of 240 plates, 77.5% were positive for fungal growth. Twelve different genera were identified. Aspergillus (29.7%), Cladosporium (26.7%) and Penicillium (23.9%) were the most common isolated. Among Aspergillus species, A. flavus had the highest frequency. Highest colony counts were found in autumn. Aspergillus predominated in autumn, Cladosporium in winter and spring and Penicillium in summer.

CONCLUSION

The results of our study showed that hospital water should be considered as a potential reservoir of fungi particularly Aspergillus.

Lack of trehalose accelerates H2O2-induced Candida albicans apoptosis through regulating Ca2+ signaling pathway and caspase activity

Trehalose is a non-reducing disaccharide and can be accumulated in response to heat or oxidative stresses in Candida albicans. Here we showed that a C. albicans tps1Δ mutant, which is deficient in trehalose synthesis, exhibited increased apoptosis rate upon H(2)O(2) treatment together with an increase of intracellular Ca(2+) level and caspase activity. When the intracellular Ca(2+) level was stimulated by adding CaCl(2) or A23187, both the apoptosis rate and caspase activity were increased. In contrast, the presence of two calcium chelators, EGTA and BAPTA, could attenuate these effects. Moreover, we investigated the role of Ca(2+) pathway in C. albicans apoptosis and found that both calcineurin and the calcineurin-dependent transcription factor, Crz1p, mutants showed decreased apoptosis and caspase activity upon H(2)O(2) treatment compared to the wild-type cells. Expression of CaMCA1, the only gene found encoding a C. albicans metacaspase, in calcineurin-deleted or Crz1p-deleted cells restored the cell sensitivity to H(2)O(2). Our results suggest that Ca(2+) and its downstream calcineurin/Crz1p/CaMCA1 pathway are involved in H(2)O(2)-induced C. albicans apoptosis. Inhibition of this pathway might be the mechanism for the protective role of trehalose in C. albicans.

Hospital epidemiology and infection control in acute-care settings

Health care-associated infections (HAIs) have become more common as medical care has grown more complex and patients have become more complicated. HAIs are associated with significant morbidity, mortality, and cost. Growing rates of HAIs alongside evidence suggesting that active surveillance and infection control practices can prevent HAIs led to the development of hospital epidemiology and infection control programs. The role for infection control programs has grown and continues to grow as rates of antimicrobial resistance rise and HAIs lead to increasing risks to patients and expanding health care costs. In this review, we summarize the history of the development of hospital epidemiology and infection control, common HAIs and the pathogens causing them, and the structure and role of a hospital epidemiology and infection control program.

Genomewide expression profile analysis of the Candida glabrata Pdr1 regulon

The ABC transporters Candida glabrata Cdr1 (CgCdr1), CgPdh1, and CgSnq2 are known to mediate azole resistance in the pathogenic fungus C. glabrata. Activating mutations in CgPDR1, a zinc cluster transcription factor, result in constitutive upregulation of these ABC transporter genes but to various degrees. We examined the genomewide gene expression profiles of two matched azole-susceptible and -resistant C. glabrata clinical isolate pairs. Of the differentially expressed genes identified in the gene expression profiles for these two matched pairs, there were 28 genes commonly upregulated with CgCDR1 in both isolate sets including YOR1, LCB5, RTA1, POG1, HFD1, and several members of the FLO gene family of flocculation genes. We then sequenced CgPDR1 from each susceptible and resistant isolate and found two novel activating mutations that conferred increased resistance when they were expressed in a common background strain in which CgPDR1 had been disrupted. Microarray analysis comparing these reengineered strains to their respective parent strains identified a set of commonly differentially expressed genes, including CgCDR1, YOR1, and YIM1, as well as genes uniquely regulated by specific mutations. Our results demonstrate that while CgPdr1 activates a broad repertoire of genes, specific activating mutations result in the activation of discrete subsets of this repertoire.

Epithelial sensing of fungal invasion

The mechanisms discriminating mucosal colonization from invasion by Candida albicans are unclear. In this issue, Moyes et al. show that epithelial cells discriminate between colonizing yeasts and invading hyphae by mechanisms involving c-Fos and MKP1 phosphatase, opening up new avenues for understanding the pathophysiology of mucosal fungal infections.

Proteolytic cleavage of covalently linked cell wall proteins by Candida albicans Sap9 and Sap10

The cell wall of the human-pathogenic fungus Candida albicans is a robust but also dynamic structure which mediates adaptation to changing environmental conditions during infection. Sap9 and Sap10 are cell surface-associated proteases which function in C. albicans cell wall integrity and interaction with human epithelial cells and neutrophils. In this study, we have analyzed the enzymatic properties of Sap9 and Sap10 and investigated whether these proteases cleave proteins on the fungal cell surface. We show that Sap9 and Sap10, in contrast to other aspartic proteases, exhibit a near-neutral pH optimum of proteolytic activity and prefer the processing of peptides containing basic or dibasic residues. However, both proteases also cleaved at nonbasic sites, and not all tested peptides with dibasic residues were processed. By digesting isolated cell walls with Sap9 or Sap10, we identified the covalently linked cell wall proteins (CWPs) Cht2, Ywp1, Als2, Rhd3, Rbt5, Ecm33, and Pga4 as in vitro protease substrates. Proteolytic cleavage of the chitinase Cht2 and the glucan-cross-linking protein Pir1 by Sap9 was verified using hemagglutinin (HA) epitope-tagged versions of both proteins. Deletion of the SAP9 and SAP10 genes resulted in a reduction of cell-associated chitinase activity similar to that upon deletion of CHT2, suggesting a direct influence of Sap9 and Sap10 on Cht2 function. In contrast, cell surface changes elicited by SAP9 and SAP10 deletion had no major impact on the phagocytosis and killing of C. albicans by human macrophages. We propose that Sap9 and Sap10 influence distinct cell wall functions by proteolytic cleavage of covalently linked cell wall proteins.

Comparative genomics and the evolution of pathogenicity in human pathogenic fungi

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

Proteome profiling and functional classification of intracellular proteins from conidia of the human-pathogenic mold Aspergillus fumigatus

Aspergillus fumigatus is a ubiquitously distributed filamentous fungus that has emerged as one of the most serious life-threatening pathogens in immunocompromised patients. The mechanisms for its pathogenicity are poorly understood. Here, we analyzed the proteome of dormant A. fumigatus conidia as the fungal entity having the initial contact with the host. Applying two-dimensional polyacrylamide gel electrophoresis (2-D PAGE), we established a 2-D reference map of conidial proteins. By MALDI-TOF mass spectrometry, we identified a total number of 449 different proteins. We show that 57 proteins of our map are over-represented in resting conidia compared to mycelium. Enzymes involved in reactive oxygen intermediates (ROI) detoxification, pigment biosynthesis, and conidial rodlet layer formation were highly abundant in A. fumigatus spores and most probably account for their enormous stress resistance. Interestingly, pyruvate decarboxylase and alcohol dehydrogenase were detectable in dormant conidia, suggesting that alcoholic fermentation plays a role during dormancy or early germination. Moreover, we show that enzymes for rapid reactivation of protein biosynthesis and metabolic processes are preserved in resting conidia, which therefore feature the potential to immediately respond to an environmental stimulus by germination. The generated data lay the foundations for further proteomic analyses and a better understanding of fungal pathogenesis.

From Saccharomyces cerevisiae to Candida glabratain a few easy steps: important adaptations for an opportunistic pathogen

The opportunistic human fungal pathogen Candida glabrata is closely related to Saccharomyces cerevisiae, yet it has evolved to survive within mammalian hosts. Which traits help C. glabrata to adapt to this different environment? Which specific responses are crucial for its survival in the host? The main differences seem to include an extended repertoire of adhesin genes, high drug resistance, an enhanced ability to sustain prolonged starvation and adaptations of the transcriptional wiring of key stress response genes. Here, we discuss the properties of C. glabrata with a focus on the differences to related fungi.

Heterologous expression of Candida albicans cell wall-associated adhesins in Saccharomyces cerevisiae Reveals differential specificities in adherence and biofilm formation and in binding oral Streptococcus gordonii

Colonization and infection of the human host by opportunistic pathogen Candida albicans derive from an ability of this fungus to colonize mucosal tissues and prosthetic devices within the polymicrobial communities present. To determine the functions of C. albicans cell wall proteins in interactions with host or bacterial molecules, Saccharomyces cerevisiae was utilized as a surrogate host to express C. albicans cell wall proteins Als3p, Eap1p, Hwp1p, and Rbt1p. Salivary pellicle and fibrinogen were identified as novel substrata for Als3p and Hwp1p, while only Als3p mediated adherence of S. cerevisiae to basement membrane collagen type IV. Parental S. cerevisiae cells failed to form biofilms on salivary pellicle, polystyrene, or silicone, but cells expressing Als3p or Hwp1p exhibited significant attachment to each surface. Virulence factor Rbt1p also conferred lower-level binding to salivary pellicle and polystyrene. S. cerevisiae cells expressing Eap1p formed robust biofilms upon polystyrene surfaces but not salivary pellicle. Proteins Als3p and Eap1p, and to a lesser degree Hwp1p, conferred upon S. cerevisiae the ability to bind cells of the oral primary colonizing bacterium Streptococcus gordonii. These interactions, which occurred independently of amyloid aggregate formation, provide the first examples of specific C. albicans surface proteins serving as receptors for bacterial adhesins. Streptococcus gordonii did not bind parental S. cerevisiae or cells expressing Rbt1p. Taken collectively, these data suggest that a network of cell wall proteins comprising Als3p, Hwp1p, and Eap1p, with complementary adhesive functions, promotes interactions of C. albicans with host and bacterial molecules, thus leading to effective colonization within polymicrobial communities.

Protection of the oral mucosa by salivary histatin-5 against Candida albicans in an ex vivo murine model of oral infection

The oral cavity is a primary target for opportunistic infections, particularly oral candidiasis caused by Candida albicans. A commensal fungus commonly colonizing mucosal surfaces, under conditions of immune dysfunction, C. albicans can become a pathogen causing recurrent infections. Yet, the role of host oral innate immunity in the development of candidiasis is not fully elucidated. Specifically, the host salivary antimicrobial peptide histatin-5 (Hst-5) has been proposed to play a protective role in the oral cavity against C. albicans. However, investigations demonstrating its efficacy on oral tissue have been lacking. To this end, in this study, an ex vivo murine model of oral infection was developed. Viable C. albicans counts and histopathological analyses demonstrated a significant protective effect for Hst-5 on mouse oral tissue against C. albicans. More importantly, host saliva exerted a comparable anticandidal effect. However, this effect was neutralized upon treatment of saliva with proteases and C. albicans, previously shown to degrade Hst-5, indicating that Hst-5 is likely the salivary component responsible for the observed protection. Combined, the findings from this study demonstrate for the first time the efficacy of salivary Hst-5 in protecting host oral tissue against C. albicans infection, thereby affirming the therapeutic potential of this natural host peptide.

The Candida albicans ESCRT pathway makes Rim101-dependent and -independent contributions to pathogenesis

Candida albicans is an opportunistic pathogen that colonizes diverse mucosal niches with distinct environmental characteristics. To adapt to these different sites, C. albicans must activate and attenuate a variety of signal transduction pathways. A mechanism of signal attenuation is through receptor endocytosis and subsequent vacuolar degradation, which requires the endosomal sorting complex required for transport (ESCRT) pathway. This pathway comprises several polyprotein complexes (ESCRT-0, -I, -II, -III, and -DS) that are sequentially recruited to the endosomal membrane. The ESCRT pathway also activates the Rim101 transcription factor, which governs expression of genes required for virulence. Here, we tested the hypothesis that the ESCRT pathway plays a Rim101-independent role(s) in pathogenesis. We generated deletion mutants in each ESCRT complex and determined that ESCRT-I, -II, and -III are required for Rim101 activation but that ESCRT-0 and ESCRT-DS are not. We found that the ESCRT-0 member Vps27 and ESCRT-DS components are required to promote epithelial cell damage and, using a murine model of oral candidiasis, found that the vps27Delta/Delta mutant had a decreased fungal burden compared to that of the wild type. We found that a high-dose inoculum can compensate for fungal burden defects but that mice colonized with the vps27Delta/Delta strain exhibit less morbidity than do mice infected with the wild-type strain. These results demonstrate that the ESCRT pathway has Rim101-independent functions for C. albicans virulence.

Safety and efficacy of activated transfected killer cells for neutropenic fungal infections

BACKGROUND

Invasive fungal infections cause considerable morbidity and mortality in neutropenic patients. White blood cell transfusions are a promising treatment for such infections, but technical barriers have prevented their widespread use.

METHODS

To recapitulate white blood cell transfusions, we are developing a cell-based immunotherapy using a phagocytic cell line, HL-60. We sought to stably transfect HL-60 cells with a suicide trap (herpes simplex virus thymidine kinase), to enable purging of the cells when desired, and a bioluminescence marker, to track the cells in vivo in mice.

RESULTS

Transfection was stable despite 20 months of continuous culture or storage in liquid nitrogen. Activation of these transfected cells with retinoic acid and dimethyl sulfamethoxazole enhanced their microbicidal effects. Activated transfected killer (ATAK) cells were completely eliminated after exposure to ganciclovir, confirming function of the suicide trap. ATAK cells improved the survival of neutropenic mice with lethal disseminated candidiasis and inhalational aspergillosis. Bioluminescence and histopathologic analysis confirmed that the cells were purged from surviving mice after ganciclovir treatment. Comprehensive necropsy, histopathology, and metabolomic analysis revealed no toxicity of the cells.

CONCLUSIONS

These results lay the groundwork for continued translational development of this promising, novel technology for the treatment of refractory infections in neutropenic hosts.

Virulence attenuation of Candida albicans genetic variants isolated from a patient with a recurrent bloodstream infection

The incidence of Candida albicans infections and the relapse episodes after antifungal treatment have increased in recent decades. Recurrences are mainly due to the persistence of the original infecting strain that may present genetic and genomic rearrangements during interaction with the host, reflecting strain adaptation. In this study, four isolates recovered from a patient during recurrent candidemia episodes were genotyped by microsatellite length polymorphism (MLP) and by multilocus sequence typing (MLST) and found to be genetic variants of the same strain. Using experimental mouse infections, a progressive reduction in the virulence of the four isolates was observed, with the first two isolates more virulent than the third and fourth. Additionally, in the mouse model, the first isolate resisted host control more efficiently, resulting in higher kidney fungal burdens and necrosis as compared to the third isolate. The resolution of inflammation was delayed in mice challenged with the first isolate and the message for IFN-gamma and TNF-alpha in the spleen was lower within the first few hours post-infection. Original and recurrent isolates also displayed different phenotypes regarding activity of secreted enzymes and response to stress agents. Overall, the comparative analysis indicated that the virulence decrease of these isolates was related to a lower ability to resist to the host anticandida effector mechanisms. We showed for the first time that C. albicans genetic variants of the same strain, sequentially isolated from an immunocompromised patient, underwent adaptations in the human host that resulted in virulence attenuation when tested in mice.

Microsatellite typing identifies the major clades of the human pathogen Candida albicans

Candida albicans population studies showed that this species could be divided into sub-groups of closely related strains, designated by clades. Since the emergence of microsatellite analysis as a PCR based method, this technique has been successfully used as a tool to differentiate C. albicans isolates but has never been tested regarding clustering of the five major clades. In this study we tested microsatellite length polymorphism (MLP) ability to group 29 C. albicans strains previously defined as belonging to clades I, II, III, E and SA, nine atypical strains from Angola and Madagascar, and 78 Portuguese clinical isolates. MLP typing of the total 116 strains analyzed yielded 87 different multilocus allelic combinations which resulted in a high discriminatory power index, of 0.987, with only two markers, CA1 and CEF3. Cluster analysis of the 29 previously defined strains grouped them according to their clade designation with a matrix cophenetic correlation of r=0.963 after a normalized Mantel statistic. Clustering analysis of the 116 strains maintained the same groupings, clearly defining the five major C. albicans clades. The cophenetic value obtained was of r=0.839, and the one-tail probability of the normalized Mantel statistic out of 1000 random permutations was P=0.0020. The proportion of Portuguese isolates in the groups I, II, III and SA was of 2.7%, 15.4%, 3.8% and 0%, respectively. None of the isolates co-clustered with the atypical strains. These results confirm MLP typing as a good method both to type and differentiate C. albicans isolates and to group isolates, identifying the major C. albicans clades, similarly to Ca3 fingerprinting and multilocus sequence typing (MLST).

Epidemiology of invasive mycoses in North America

The incidence of invasive mycoses is increasing, especially among patients who are immunocompromised or hospitalized with serious underlying diseases. Such infections may be broken into two broad categories: opportunistic and endemic. The most important agents of the opportunistic mycoses are Candida spp., Cryptococcus neoformans, Pneumocystis jirovecii, and Aspergillus spp. (although the list of potential pathogens is ever expanding); while the most commonly encountered endemic mycoses are due to Histoplasma capsulatum, Coccidioides immitis/posadasii, and Blastomyces dermatitidis. This review discusses the epidemiologic profiles of these invasive mycoses in North America, as well as risk factors for infection, and the pathogens' antifungal susceptibility.

Effect of serum and surface characteristics on Candida albicans biofilm formation

Candida spp. biofilms can be established on a wide range of materials, including implanted medical devices, and can display a resistant phenotype to antifungal drugs. Several factors, including host and surface properties, may influence the establishment and the development of Candida albicans biofilms on biotic and abiotic surfaces. We therefore selected a collection of C. albicans clinical isolates to evaluate the effect of surface and serum on biofilm attachment and development. Disc coupons from the CDC biofilm reactor were used in a well plate assay to study biofilm production on six different surfaces with or without the addition of serum: polycarbonate, polystyrene, stainless steel, Teflon, polyvinyl chloride or hydroxyapatite. Our results showed that serum increases in vitro C. albicans biofilm formation on a wide range of distinct surfaces including metallic and non-metallic materials, and that roughness and hydrophobicity can modulate C. albicans biofilm formation. These findings were also confirmed by scanning electron microscopy and it revealed the deposition of extracellular material on hyphae attached to a solid surface. Interestingly, adhesion can be significantly increased in the early stages of colonisation when serum is provided as a conditioning film in a surface-dependent manner.

Comparison of inhibitory mold agar to Sabouraud dextrose agar as a primary medium for isolation of fungi

Clinical specimens cultured on two selective fungal media, inhibitory mold agar (IMA) and Sabouraud dextrose agar (SDA), were compared with respect to recovery of fungi. Of the 840 fungal isolates recovered, 69.3% grew on both IMA and SDA; 24.9% grew only on IMA; and 5.8% grew only on SDA, showing that IMA is superior (P=0.003).

New polymorphic microsatellite markers able to distinguish among Candida parapsilosis sensu stricto isolates

Among the Candida species causing bloodstream infections, Candida parapsilosis is one of the most frequently isolated. The objective of the present work was the identification of new microsatellite loci able to distinguish among C. parapsilosis isolates. DNA sequences with trinucleotide repeats were selected from the C. parapsilosis genome database. PCR primer sets flanking the microsatellite repeats were designed and tested with 20 independent isolates. On the basis of the amplification efficiency, specificity, and observed polymorphism, four of the sequences were selected for strain typing. Two hundred thirty-three independent C. parapsilosis sensu stricto isolates were genotyped by using these markers. The polymorphic loci exhibited from 20 to 42 alleles and 39 to 92 genotypes. In a multiplex analysis, 192 genotypes were obtained and the combined discriminatory power of the four microsatellites was 0.99. Reproducibility was demonstrated by submission of subcultures of 4 isolates each, in triplicate, interspersed with unique numbers among a group of 30 isolates for blind testing. Comparison of the genotypes obtained by microsatellite analysis and those obtained by randomly amplified polymorphic DNA analysis, restriction fragment length polymorphism analysis, and internal transcribed sequence grouping was performed and showed that the microsatellite method could distinguish individual isolates; none of the other methods could do that. Related species, C. orthopsilosis and C. metapsilosis, were not confused with C. parapsilosis sensu stricto. These new microsatellites are a valuable tool for use for the differentiation of C. parapsilosis sensu stricto strains, vital in epidemiology to answer questions of strain relatedness and determine pathways of transmission.

Treatment strategies for oropharyngeal candidiasis

BACKGROUND

Oropharyngeal candidiasis (OPC) is a common oral disease that may cause oral symptoms, lead to regional infection (e.g., esophageal candidiasis) and increase the risk of systemic fungal infection in the compromised host.

OBJECTIVE

Critical review of the literature of prevention and therapy.

METHODS

The literature was reviewed using PubMed, and specific keywords from the MeSH Database were used.

RESULTS/CONCLUSION

Management of OPC requires that the underlying risk factors of infection be diagnosed and managed whenever possible. Antimicrobials may be provided as topical or systemic therapy. Topical therapies may provide effective management for candidiasis in the non-compromised host and increase the control of colonization in the compromised host. Advances in prevention and management include new agents and improved mechanisms of topical drug delivery.

Candida glabrata tryptophan-based pigment production via the Ehrlich pathway

Pigments contribute to the pathogenicity of many fungi, mainly by protecting fungal cells from host defence activities. Here, we have dissected the biosynthetic pathway of a tryptophan-derived pigment of the human pathogen Candida glabrata, identified key genes involved in pigment production and have begun to elucidate the possible biological function of the pigment. Using transcriptional analyses and a transposon insertion library, we have identified genes associated with pigment production. Targeted deletion mutants revealed that the pigment is a by-product of the Ehrlich pathway of tryptophan degradation: a mutant lacking a tryptophan-upregulated aromatic aminotransferase (Aro8) displayed significantly reduced pigmentation and a recombinantly expressed version of this protein was sufficient for pigment production in vitro. Pigment production is tightly regulated as the synthesis is affected by the presence of alternative nitrogen sources, carbon sources, cyclic AMP and oxygen. Growth of C. glabrata on pigment inducing medium leads to an increased resistance to hydrogen peroxide, an effect which was not observed with a mutant defective in pigmentation. Furthermore, pigmented yeast cells had a higher survival rate when exposed to human neutrophils and caused increased damage in a monolayer model of human epithelia, indicating a possible role of pigmentation during interactions with host cells.

In vitro susceptibility testing in fungi: a global perspective on a variety of methods

Candida and Aspergillus species are the most common causes of invasive fungal infections in immunocompromised patients. The introduction of new antifungal agents and recent reports of resistance emerging during treatment have highlighted the need for in vitro susceptibility testing. For some drugs, there is a supporting in vitro-in vivo correlation available from studies of clinical efficacy. Both intrinsic and emergent antifungal drug resistance are encountered. Various testing procedures have been proposed, including macrodilution and microdilution, agar diffusion, disk diffusion and Etest. Early recognition of infections caused by pathogens that are resistant to one or more antifungals is highly warranted to optimise treatment and patient outcome.

A proteomic analysis of the salt, cadmium and peroxide stress responses in Candida albicans and the role of the Hog1 stress-activated MAPK in regulating the stress-induced proteome

Stress responses are important for the virulence of the major fungal pathogen of humans, Candida albicans. In this study we employed a 2-DE approach to examine the impact of exposure to peroxide (5 mM H(2)O(2)), salt (300 mM NaCl) or cadmium stress (0.5 mM Cd(2+)) upon the C. albicans proteome. Highly reproducible changes in the C. albicans proteome were observed in response to each stress condition. Significantly more proteins were up-regulated in response to cadmium (77) than to the salt (35) or peroxide stresses (35). These proteomic changes displayed minimal overlap with those observed in the transcriptome under equivalent conditions and, importantly, revealed functional categories that respond to stress at the protein level but not the transcript level. Six proteins were up-regulated by all three conditions: Adh1, Atp2, Cip1, Eft2, Ssa1 and Ssb1, which is consistent with the concept that a core stress response exists in C. albicans. This is the first time that a fungal core stress response has been defined at the proteomic level. We have also shown that the Hog1 stress-activated mitogen-activated protein kinase, which is activated in response to the stresses examined in this study, makes a major contribution to the C. albicans stress proteome.

Immunological reactivity of blood from healthy humans to the rAls3p-N vaccine protein

We determined reactivity of human blood to a vaccine based on the recombinant N-terminus of candidal Als3p (rAls3p-N) in preparation for future clinical trials. Healthy donor plasma had high immunoglobulin G titers (median, 1:51,200) and lower immunoglobulin A (median, 1:3,200) and immunoglobulin E (median, 1:128) titers to rAls3p-N by enzyme-linked immunosorbent assay. rAls3p-N stimulated interferon gamma (IFN-gamma) and interleukin (IL)-17, but not IL-4, from donor lymphocytes by enzyme-linked immunosorbent spot assay and IL-12 p70, IFN-gamma, IL-17, and IL-10 by cytometric bead array. Donors reacted to diverse immunodominant epitopes. Thus, facile humoral and cellular assays can monitor immune responses to the rAls3p-N vaccine in planned clinical trials.

Impact of the transcriptional regulator, Ace2, on the Candida glabrata secretome

Candida glabrata is a major fungal pathogen of humans, and the virulence of C. glabrata is increased by inactivation of the transcription factor, Ace2. Our previous examination of the effects of Ace2 inactivation upon the intracellular proteome suggested that the hypervirulence of C. glabrata ace2 mutants might be caused by differences in the secretome. Therefore in this study we have characterised the C. glabrata secretome and examined the effects of Ace2 inactivation upon this extracellular proteome. We have identified 31 distinct proteins in the secretome of wild-type C. glabrata cells by MS/MS of proteins that were precipitated from the growth medium and enriched by affinity chromatography on concanavalin A. Most of these proteins are predicted to be cell wall proteins, cell wall modifying enzymes and aspartyl proteinases. The endochitinase Cts1 and the endoglucanase Egt2 were not detected in the C. glabrata secretome following Ace2 inactivation. This can account for the cell separation defect of C. glabrata ace2 cells. Ace2 inactivation also resulted in the detection of new proteins in the C. glabrata secretome. The release of such proteins might contribute to the hypervirulence of ace2 cells.