Candidaspecies fail to produce the immunosuppressive secondary metabolite gliotoxinin vitro

Immune Sensing of Candida albicans

Candida albicans infections range from superficial to systemic and are one of the leading causes of fungus-associated nosocomial infections. The innate immune responses during these various infection types differ, suggesting that the host environment plays a key role in modulating the host–pathogen interaction. In addition, C. albicans is able to remodel its cell wall in response to environmental conditions to evade host clearance mechanisms and establish infection in niches, such as the oral and vaginal mucosa. Phagocytes play a key role in clearing C. albicans, which is primarily mediated by Pathogen Associated Molecular Pattern (PAMP)–Pattern Recognition Receptor (PRR) interactions. PRRs such as Dectin-1, DC-SIGN, and TLR2 and TLR4 interact with PAMPs such as β-glucans, N-mannan and O-mannan, respectively, to trigger the activation of innate immune cells. Innate immune cells exhibit distinct yet overlapping repertoires of PAMPs, resulting in the preferential recognition of particular Candida morphotypes by them. The role of phagocytes in the context of individual infection types also differs, with neutrophils playing a prominent role in kidney infections, and dendritic cells playing a prominent role in skin infections. In this review, we provide an overview of the key receptors involved in the detection of C. albicans and discuss the differential innate immune responses to C. albicans seen in different infection types such as vulvovaginal candidiasis (VVC) and oral candidiasis.

Macrophages Maintain Epithelium Integrity by Limiting Fungal Product Absorption

The colon is primarily responsible for absorbing fluids. It contains a large number of microorganisms including fungi, which are enriched in its distal segment. The colonic mucosa must therefore tightly regulate fluid influx to control absorption of fungal metabolites, which can be toxic to epithelial cells and lead to barrier dysfunction. How this is achieved remains unknown. Here, we describe a mechanism by which the innate immune system allows rapid quality check of absorbed fluids to avoid intoxication of colonocytes. This mechanism relies on a population of distal colon macrophages that are equipped with "balloon-like" protrusions (BLPs) inserted in the epithelium, which sample absorbed fluids. In the absence of macrophages or BLPs, epithelial cells keep absorbing fluids containing fungal products, leading to their death and subsequent loss of epithelial barrier integrity. These results reveal an unexpected and essential role of macrophages in the maintenance of colon-microbiota interactions in homeostasis. VIDEO ABSTRACT.

Current Aspects in the Biology, Pathogeny, and Treatment of Candida krusei, a Neglected Fungal Pathogen

Fungal infections represent a constant and growing menace to human health, because of the emergence of new species as causative agents of diseases and the increment of antifungal drug resistance. Candidiasis is one of the most common fungal infections in humans and is associated with a high mortality rate when the fungi infect deep-seated organs. Candida krusei belongs to the group of candidiasis etiological agents, and although it is not isolated as frequently as other Candida species, the infections caused by this organism are of special relevance in the clinical setting because of its intrinsic resistance to fluconazole. Here, we offer a thorough revision of the current literature dealing with this organism and the caused disease, focusing on its biological aspects, the host-fungus interaction, the diagnosis, and the infection treatment. Of particular relevance, we provide the most recent genomic information, including the gene prediction of some putative virulence factors, like proteases, adhesins, regulators of biofilm formation and dimorphism. Moreover, C. krusei veterinary aspects and the exploration of natural products with anti-C. krusei activity are also included.

Stepping Up to the Plate(let) against Candida albicans

Candida albicans is a pervasive commensal fungus that is the most common pathogen responsible for invasive fungal infection (IFI). With incidence of IFI on the rise due to increasing susceptible populations, it is imperative that we investigate how Candida albicans interacts with blood components. When stimulating either human or mouse whole blood with thrombin, we saw a significant decrease in C. albicans survival. We then repeated Candida killing assays with thrombin-stimulated or unstimulated washed platelets and saw a similar decrease in CFU. To investigate whether killing was mediated through surface components or releasable products, platelets were pretreated with an inhibitor of actin polymerization (cytochalasin D [CytoD]). CytoD was able to abrogate C. albicans killing. Moreover, dilution of releasates from thrombin-stimulated platelets showed that the toxicity of the releasates on C. albicans is concentration dependent. We then investigated C. albicans actions on platelet activation, granule release, and aggregation. While C. albicans does not appear to affect alpha or dense granule release, C. albicans exerts a significant attenuation of platelet aggregation to multiple agonists. These results illustrate for the first time that platelets can directly kill C. albicans through release of their granular contents. Additionally, C. albicans can also exert inhibitory effects on platelet aggregation.

Vaginal yeast colonisation: From a potential harmless condition to clinical implications and management approaches-A literature review

Vaginal yeast colonisation is a common clinical condition in premenopausal women. The potential pathogenicity and the circumstances under which it could evolve into infection are not fully clarified. Extensive review the literature regarding the definition of the vaginal yeast colonisation, its demographic features and causes as well as the risk factors favouring infection along with the necessity of treatment. Databases, namely PubMed-MEDLINE, Google Scholar, the University College London databases, e-journals, e-books and official Health Organisations websites were extensively searched in English, French, German and Greek language with no restriction in the type of publications during the last thirty years. In healthy women, vaginal yeast colonisation is an asymptomatic state with Candida albicans being the most prevalent species. Pregnant, HIV-positive and diabetic hosts are at higher risk. Other risk factors include oral contraceptives, hormonal replacement therapy and previous antibiotic use. Colonisation does not necessitate therapeutic intervention when asymptomatic. Prophylactic therapy during the third trimester of pregnancy is often recommended for reducing the risk of neonatal candidiasis. The distinction between commensalism and vaginitis is often complicated. Clinicians should be aware of the clinical context in order to decide the indicated therapeutic approach.

Host immune status-specific production of gliotoxin and bis-methyl-gliotoxin during invasive aspergillosis in mice

Delayed diagnosis in invasive aspergillosis (IA) contributes to its high mortality. Gliotoxin (GT) and bis-methyl-gliotoxin (bmGT) are secondary metabolites produced by Aspergillus during invasive, hyphal growth and may prove diagnostically useful. Because IA pathophysiology and GT's role in virulence vary depending on the underlying host immune status, we hypothesized that GT and bmGT production in vivo may differ in three mouse models of IA that mimic human disease. We defined temporal kinetics of GT and bmGT in serum, bronchoalveolar lavage fluid (BALF) and lungs of A. fumigatus-infected chronic granulomatous disease (CGD), hydrocortisone-treated, and neutropenic mice. We harvested lungs for assessment of fungal burden, histology and GT/bmGT biosynthetic genes' mRNA induction. GT levels were higher in neutropenic versus CGD or steroid-treated lungs. bmGT was persistently detected only in CGD lungs. GT, but not bmGT, was detected in 71% of sera and 50% of BALF of neutropenic mice; neither was detected in serum/BALF of CGD or steroid-treated mice. Enrichment of GT in Aspergillus-infected neutropenic lung correlated with fungal burden and hyphal length but not induction of GT biosynthetic genes. In summary, GT is detectable in mouse lungs, serum and BALF during neutropenic IA, suggesting that GT may be useful to diagnose IA in neutropenic patients.

Gliotoxin--bane or boon?

Gliotoxin (GT) is the most important epidithiodioxopiperazine (ETP)-type fungal toxin. GT was originally isolated from Trichoderma species as an antibiotic substance involved in biological control of plant pathogenic fungi. A few isolates of GT-producing Trichoderma virens are commercially marketed for biological control and widely used in agriculture. Furthermore, GT is long known as an immunosuppressive agent and also reported to have anti-tumour properties. However, recent publications suggest that GT is a virulence determinant of the human pathogen Aspergillus fumigatus. This compound is thus important on several counts - it has medicinal properties, is a pathogenicity determinant, is a potential diagnostic marker and is important in biological crop protection. The present article addresses this paradox and the ecological role of GT. We discuss the function of GT as defence molecule, the role in aspergillosis and suggest solutions for safe application of Trichoderma-based biofungicides.

Clinical validity of bis(methylthio)gliotoxin for the diagnosis of invasive aspergillosis

Early and accurate diagnosis of invasive aspergillosis (IA) is one of the most critical steps needed to efficiently treat the infection and reduce the high mortality rates that can occur. We have previously found that the Aspergillus spp. secondary metabolite, bis(methylthio)gliotoxin (bmGT), can be detected in the serum from patients with possible/probable IA. Thus, it could be used as a diagnosis marker of the infection. However, there is no data available concerning the sensitivity, specificity and performance of bmGT to detect the infection. Here, we have performed a prospective study comparing bmGT detection with galactomannan (GM), the most frequently used and adopted approach for IA diagnosis, in 357 sera from 90 episodes of patients at risk of IA. Our results, involving 79 patients that finally met inclusion criteria, suggest that bmGT presents higher sensitivity and positive predictive value (PPV) than GM and similar specificity and negative predictive value (NPV). Importantly, the combination of GM and bmGT increased the PPV (100 %) and NPV (97.5 %) of the individual biomarkers, demonstrating its potential utility in empirical antifungal treatment guidance and withdrawal. These results indicate that bmGT could be a good biomarker candidate for IA diagnosis and, in combination with GM, could result in highly specific diagnosis of IA and management of patients at risk of infection.

Gliotoxin potentiates osteoblast differentiation by inhibiting nuclear factor-κB signaling

The differentiation of pluripotent mesenchymal stem cells to mature osteoblasts is crucial for the maintenance of the adult skeleton. In rheumatic arthritis, osteoblast differentiation is impaired by the overproduction of cytokine tumor necrosis factor (TNF)-α. It has been demonstrated that TNF-α is able to inhibit osteoblast differentiation through the activation of nuclear factor (NF)-κB signaling. As a result of the critical role of TNF-α and NF-κB in the pathogenesis of bone-loss associated diseases, these factors are regarded as key targets for the development of therapeutic agents. In the current study, the role of the NF-κB inhibitor gliotoxin (GTX) in the regulation of osteoblast differentiation was evaluated. The non-toxic GTX doses were determined to be ≤3 μg/ml. It was revealed that GTX was able to block TNF-α-induced inhibition of osteoblast differentiation, as indicated by alkaline phosphatase (ALP) activity and ALP staining assays, as well as the expression levels of osteoblast-associated genes Col I, Ocn, Bsp, Runx2, Osx and ATF4. Additionally, it was identified that gliotoxin directly promoted bone morphoge-netic protein-2-induced osteoblast differentiation. GTX was found to inhibit the accumulation of NF-κB protein p65 in the nucleus and reduce NF-κB transcriptional activity, suggesting that GTX potentiated osteoblast differentiation via the suppression of NF-κB signaling.

In Vitro Anti-Candida Activity of the Hydroalcoholic Extracts of Heracleum persicum Fruit Against Phatogenic Candida Species

BACKGROUND

Nowadays Candida albicans has become resistant to the toxic and expensive commercial anti-Candida drugs. Therefore, investigation for new anti-fungal agents is necessary.

OBJECTIVES

The purpose of this survey was to investigate the in vitro anti-Candida activity of the hydroalcoholic extracts of Heracleum persicum fruit.

MATERIALS AND METHODS

The plant ingredients were extracted using 80% ethanol and the extract was screened against 46 isolated pathogenic Candida species such as C. albicans, C. glabrata and C. tropicalis by agar well diffusion method.

RESULTS

The minimum inhibitory concentration (MIC) values at 24 and 48 hours were 0.625 - 20 µg/µL for C. albicans, 0.625 - 40 µg/µL for C. glabrata, and 5.0 - 20 µg/µL for C. tropicalis.

CONCLUSIONS

The results of this survey confirmed that tested plant extract had a potential anti-Candida activity. Hence, it is suggested to isolate and identify its active compounds in future.

Bis(methyl)gliotoxin proves to be a more stable and reliable marker for invasive aspergillosis than gliotoxin and suitable for use in diagnosis

The virulence factor gliotoxin (GT) and its inactive derivative, bis(methylthio)gliotoxin (bmGT), are produced by pathogens of the genus Aspergillus. Here we report the detection of GT and bmGT in serum of humans at risk of invasive aspergillosis (IA) as well as in cultures of fungal isolates derived from patients with proven infection with A. fumigatus. Although both compounds are readily recoverable from spiked human serum or plasma, only bmGT is retained in whole blood, indicating that bmGT may be the better marker for in vivo detection. Accordingly, bmGT was found more frequently than GT in samples from patients at risk of IA and incultures of clinical isolates of A. fumigatus. In some cases, bmGT was detected before mycologic evidence ofinfection was gained. Importantly, neither GT nor bmGT was found in serum from healthy donors or from neutropenic patients without any sign of infection. Thus, bmGT presence might provide a more reliable indicator of A. fumigatus infections than GT. Due to its simplicity and sensitivity, a diagnostic technology based on this test could be easily adopted in clinical laboratories to help in the diagnosis of this often fatal fungal infection.

Antifungal activity of microbial secondary metabolites

Secondary metabolites are well known for their ability to impede other microorganisms. Reanalysis of a screen of natural products using the Caenorhabditis elegans-Candida albicans infection model identified twelve microbial secondary metabolites capable of conferring an increase in survival to infected nematodes. In this screen, the two compound treatments conferring the highest survival rates were members of the epipolythiodioxopiperazine (ETP) family of fungal secondary metabolites, acetylgliotoxin and a derivative of hyalodendrin. The abundance of fungal secondary metabolites indentified in this screen prompted further studies investigating the interaction between opportunistic pathogenic fungi and Aspergillus fumigatus, because of the ability of the fungus to produce a plethora of secondary metabolites, including the well studied ETP gliotoxin. We found that cell-free supernatant of A. fumigatus was able to inhibit the growth of Candida albicans through the production of a secreted product. Comparative studies between a wild-type and an A. fumigatus ΔgliP strain unable to synthesize gliotoxin demonstrate that this secondary metabolite is the major factor responsible for the inhibition. Although toxic to organisms, gliotoxin conferred an increase in survival to C. albicans-infected C. elegans in a dose dependent manner. As A. fumigatus produces gliotoxin in vivo, we propose that in addition to being a virulence factor, gliotoxin may also provide an advantage to A. fumigatus when infecting a host that harbors other opportunistic fungi.

Detection of coagulase activity in pathogenic Candida species

The coagulase activities of various Candida spp were assessed using a classical tube test. A total of 125 clinical Candida isolates representing eight species (C. albicans, C. parapsilosis, C. tropicalis, C. glabrata, C. kefyr, Geotrichum candidum, C. krusei and C. guilliermondii) were incubated with rabbit, sheep or human plasma. After 24 h incubation, 29/64 (45.3%) C. albicans isolates and 23/61 (37.7%) non-albicans Candida strains were positive for coagulase in rabbit plasma, whereas 20/64 (31.2%) C. albicans and 6/61 (9.8%) non-albicans Candida isolates were positive for coagulase in sheep plasma. None of the tested Candida isolates reacted positively in human plasma. These results suggest that rabbit plasma is the most appropriate medium for detection of coagulase activity in Candida spp. Variations in coagulase production by Candida spp may be related to their pathogenicity. It is concluded that the laboratory detection of coagulase activity in clinical isolates of Candida spp may help the diagnosis of Candida-related infections.

Live Candida albicans suppresses production of reactive oxygen species in phagocytes

Production of reactive oxygen species (ROS) is an important aspect of phagocyte-mediated host responses. Since phagocytes play a crucial role in the host response to Candida albicans, we examined the ability of Candida to modulate phagocyte ROS production. ROS production was measured in the murine macrophage cell line J774 and in primary phagocytes using luminol-enhanced chemiluminescence. J774 cells, murine polymorphonuclear leukocytes (PMN), human monocytes, and human PMN treated with live C. albicans produced significantly less ROS than phagocytes treated with heat-killed C. albicans. Live C. albicans also suppressed ROS production in murine bone marrow-derived macrophages from C57BL/6 mice, but not from BALB/c mice. Live C. albicans also suppressed ROS in response to external stimuli. C. albicans and Candida glabrata suppressed ROS production by phagocytes, whereas Saccharomyces cerevisiae stimulated ROS production. The cell wall is the initial point of contact between Candida and phagocytes, but isolated cell walls from both heat-killed and live C. albicans stimulated ROS production. Heat-killed C. albicans has increased surface exposure of 1,3-beta-glucan, a cell wall component that can stimulate phagocytes. To determine whether surface 1,3-beta-glucan exposure accounted for the difference in ROS production, live C. albicans cells were treated with a sublethal dose of caspofungin to increase surface 1,3-beta-glucan exposure. Caspofungin-treated C. albicans was fully able to suppress ROS production, indicating that suppression of ROS overrides stimulatory signals from 1,3-beta-glucan. These studies indicate that live C. albicans actively suppresses ROS production in phagocytes in vitro, which may represent an important immune evasion mechanism.

An investigation on the anticandidal activity of some traditional medicinal plants in Turkey

Methanol and chloroform extracts obtained from eight plant species belonging to six families, which were selected depending on their use in Turkish folk medicine, including Mentha longifolia L. (Labiatae), Mentha piperita L. Hudson (Labiatae), Prongos ferulaceae (Umbelliferae), Galium verum L. (Rubiaceae), Salvia limbata C. A Meyer (Labiatae), Artemisia austriaca Jacq. (Artemiceae), Plantago lanceolata L. (Plantaginaceae) and Urtica dioica L. (Urticaceae) were evaluated for their in vitro anticandidal activity. The anticandidal activity of extracts against 99 human pathogenic clinical isolates belonging to 35 Candida albicans, 33 Candida tropicalis and 31 Candida glabrata and standard strains of Candida spp. (C. albicans ATCC 10231, C. glabrata ATCC 80030 and C. tropicalis ATCC 22019) were tested by disc diffusion method and the active extracts were assayed for the minimal inhibitory concentration (MIC). Chloroform extracts of plants have no inhibitory effect against both clinical and standard strains of Candida spp., whereas methanol extracts exhibited good activity. Among the plants tested, M. piperita showed the highest anticandidal activity with 12.3 mm inhibition zone and 1.25 mg ml(-1) MIC value against C. albicans, M. longifolia, P. lanceolata and A. austriaca also displayed activity against C. albicans and C. tropicalis.

Superantigen-like effects of a Candida albicans polypeptide

The amino terminal sequence of the Candida albicans cell wall protein Int1 exhibited partial identity with the major histocompatibility complex (MHC) class II binding site of the Mycoplasma arthritidis superantigen MAM. Int1-positive C. albicans blastospores activated human T lymphocytes and expanded Vbeta subsets 2, 3, and/or 14; Int1-negative strains were inactive. Release of interferon-gamma (IFN-gamma) but not of tumor necrosis factor-alpha or interleukin-6 was Int1 dependent; interleukin-4 and interleukin-10 were not detected. T lymphocyte activation, Vbeta expansion, and IFN-gamma release were associated with a soluble polypeptide that encompassed the first 263 amino acids of Int1 (Pep(263)). Monoclonal antibody 163.5, which recognizes an Int1 epitope that overlaps the region of identity with MAM, significantly inhibited these activities when triggered by Int1-positive blastospores or Pep(263) but not by staphylococcal enterotoxin B. Histidine(263) was required. Pep(263) bound to T lymphocytes and MHC class II and was detected in the urine of a patient with C. albicans fungemia. These studies identify a candidal protein that displays superantigen-like activities.