333 research outputs found

    Distributed Recoloring of Interval and Chordal Graphs

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    Natriuretic peptides modify Pseudomonas fluorescens cytotoxicity by regulating cyclic nucleotides and modifying LPS structure

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    <p>Abstract</p> <p>Background</p> <p>Nervous tissues express various communication molecules including natriuretic peptides, <it>i.e</it>. Brain Natriuretic Peptide (BNP) and C-type Natriuretic Peptide (CNP). These molecules share structural similarities with cyclic antibacterial peptides. CNP and to a lesser extent BNP can modify the cytotoxicity of the opportunistic pathogen <it>Pseudomonas aeruginosa</it>. The psychrotrophic environmental species <it>Pseudomonas fluorescens </it>also binds to and kills neurons and glial cells, cell types that both produce natriuretic peptides. In the present study, we investigated the sensitivity of <it>Pseudomonas fluorescens </it>to natriuretic peptides and evaluated the distribution and variability of putative natriuretic peptide-dependent sensor systems in the <it>Pseudomonas </it>genus.</p> <p>Results</p> <p>Neither BNP nor CNP modified <it>P. fluorescens </it>MF37 growth or cultivability. However, pre-treatment of <it>P. fluorescens </it>MF37 with BNP or CNP provoked a decrease of the apoptotic effect of the bacterium on glial cells and an increase of its necrotic activity. By homology with eukaryotes, where natriuretic peptides act through receptors coupled to cyclases, we observed that cell-permeable stable analogues of cyclic AMP (dbcAMP) and cyclic GMP (8BcGMP) mimicked the effect of BNP and CNP on bacteria. Intra-bacterial concentrations of cAMP and cGMP were measured to study the involvement of bacterial cyclases in the regulation of <it>P. fluorescens </it>cytotoxicity by BNP or CNP. BNP provoked an increase (+49%) of the cAMP concentration in <it>P. fluorescens</it>, and CNP increased the intra-bacterial concentrations of cGMP (+136%). The effect of BNP and CNP on the virulence of <it>P. fluorescens </it>was independent of the potential of the bacteria to bind to glial cells. Conversely, LPS extracted from MF37 pre-treated with dbcAMP showed a higher necrotic activity than the LPS from untreated or 8BcGMP-pre-treated bacteria. Capillary electrophoresis analysis suggests that these different effects of the LPS may be due, at least in part, to variations in the structure of the macromolecule.</p> <p>Conclusion</p> <p>These observations support the hypothesis that <it>P. fluorescens </it>responds to natriuretic peptides through a putative sensor system coupled to a cyclase that could interfere with LPS synthesis and thereby modify the overall virulence of the micro-organism.</p

    Pseudomonas fluorescens alters epithelial permeability and translocates across Caco-2/TC7 intestinal cells

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    <p>Abstract</p> <p>Background</p> <p><it>Pseudomonas fluorescens </it>has long been considered as a psychrotrophic microorganism. Recently, we have shown that clinical strains of <it>P. fluorescens </it>(biovar 1) are able to adapt at a growth temperature of 37°C or above and induce a specific inflammatory response. Interestingly, a highly specific antigen of <it>P. fluorescens</it>, I2, is detected in the serum of patients with Crohn's disease but the possible role of this bacterium in the disease has not yet been explored. In the present study, we examined the ability of a psychrotrophic and a clinical strain of <it>P. fluorescens </it>to modulate the permeability of a Caco-2/TC7 intestinal epithelial model, reorganize the actin cytoskeleton, invade the target cells and translocate across the epithelium. The behaviour of these two strains was compared to that of the well known opportunistic pathogen <it>P. aeruginosa </it>PAO1.</p> <p>Results</p> <p>Both strains of <it>P. fluorescens </it>were found to decrease the transepithelial resistance (TER) of Caco-2/TC7 differentiated monolayers. This was associated with an increase in paracellular permeability and F-actin microfilaments rearrangements. Moreover, the invasion and translocation tests demonstrated that the two strains used in this study can invade and translocate across the differentiated Caco-2/TC7 cell monolayers.</p> <p>Conclusions</p> <p>The present work shows for the first time, that <it>P. fluorescens </it>is able to alter the intestinal epithelial barrier function by disorganizing the F-actin microfilament network. Moreover, we reveal that independently of their origins, the two <it>P. fluorescens </it>strains can translocate across differentiated Caco-2/TC7 cell monolayers by using the transcellular pathway. These findings could, at least in part, explain the presence of the <it>P. fluorescens </it>specific I2 antigen in the serum of patients with Crohn's disease.</p

    PHYSICAL AGING OF EMULSIONS CONTAINING COATED TIO2-NANOPARTICLES: INTERACTION BETWEEN NANOPARTICLES AND OTHER INGREDIENTS

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    International audienceTiO2-nanoparticles (NPs) are usually added to cosmetic emulsions because they procure a good UV-protection1. In this study, two natures of NPs surfaces were explored: a hydrophilic silica-coated particle and a hydrophobic one covered with a large organic coating. During emulsion aging and depending on their surfacenature and properties, NPs might interact with the formula by inducing adsorption of formula’s compounds2 or by undergoingcoatings damages. These phenomenamay change the nanoparticle surface properties, their behavior in emulsion, and finally, led to the emulsionsdestabilization. The impact of TiO2-NP surfaces on the physical aging of emulsions was here studied.For this purpose, threeemulsions were formulated differing only by the presence and type of NPs: one NP-free as blank, and two containing hydrophilic and hydrophobic commercial TiO2-NPs, respectively.The emulsification process was optimized to obtain a blank emulsion physically stable and to improve the NPs dispersions. Effects of coatings on fresh emulsions were depicted on the micro and macro scales by several physico-chemical methods.Then, emulsions physical evolutions onnormal or accelerate aging conditionswere monitored.Droplets sizes were similar between the three fresh emulsions, whereas slight differences in term of networksorganization highlighted the impact of the coating nature on the emulsion microstructure. However, initial emulsions properties looked similar by applying rheological and textural analyses. Although the blank emulsion and the one with hydrophilic NPs remained similar after the aging step, the microstructure of the emulsion with hydrophobic NPsquickly evolved: aggregates of both droplets and NPs made the formula less homogeneous. As will be illustrated, this evolution in term of colloids sizes strongly affects the functional properties, as viscosity, consistency or spreading quality of this aged emulsion. These results revealed the impact of coating nature in this kind of complex media. Afterinnovative NPs extractions3 from fresh and aged formulae, their surfaces were characterized. By an original physico-chemical approach, quick surface modifications appeared and changed the surface charges and wettability of particles. These variations might cause the differences in term of stability between emulsions.(1) Serpone, N.; Dondi, D.; Albini, A. Inorganica Chim. Acta2007, 360 (3), 794–802.(2) Rossano, M.; Hucher, N.; Picard, C.; Colleta, D.; Le Foll, F.; Grisel, M. Int. J. Pharm.2014, 461 (1-2), 89–96.(3) Rossano, M. Ph.D thesis: Utilisation des nanoparticules de dioxyde de titane dans les émulsions cosmétiques : impact sur la santé humaine et l’environnement, Université du Havre: Le Havre, 2014

    The Hidden Face of Nitrogen Oxides Species: From Toxic Effects to Potential Cure?

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    Nitrogen oxide (NOx) species represent ones of the most threatening air pollutants due to their prevalence and harmful impact on the environment and human health. The term NOx gathers mainly nitric oxide (NO) and nitrogen dioxide (NO2), mostly produced by anthropogenic activities such as transport and industries. Several cellular constituents were already described as NOx targets. These include membranes, proteins, respiratory chain enzymes, lipids, and DNA. Such damages lead to pathologies of lungs, cardiovascular system, and skin because these organs represent the first barrier toward the environment. On the other hand, NOx is also naturally synthetized by several organisms, playing a mediator role in essential cellular functions. However, few data are yet available on NOx activity toward microorganisms. Here, we review data concerning the double face of NOx, including their use in the medical field against pathogens’ infections that highlight the versatility of these compounds

    Involvement of a phospholipase C in the hemolytic activity of a clinical strain of Pseudomonas fluorescens

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    <p>Abstract</p> <p>Background</p> <p><it>Pseudomonas fluorescens </it>is a ubiquitous Gram-negative bacterium frequently encountered in hospitals as a contaminant of injectable material and surfaces. This psychrotrophic bacterium, commonly described as unable to grow at temperatures above 32°C, is now considered non pathogenic. We studied a recently identified clinical strain of <it>P. fluorescens </it>biovar I, MFN1032, which is considered to cause human lung infection and can grow at 37°C in laboratory conditions.</p> <p>Results</p> <p>We found that MFN1032 secreted extracellular factors with a lytic potential at least as high as that of MF37, a psychrotrophic strain of <it>P. fluorescens </it>or the mesophilic opportunistic pathogen, <it>Pseudomonas aeruginosa </it>PAO1. We demonstrated the direct, and indirect – through increases in biosurfactant release – involvement of a phospholipase C in the hemolytic activity of this bacterium. Sequence analysis assigned this phospholipase C to a new group of phospholipases C different from those produced by <it>P. aeruginosa</it>. We show that changes in PlcC production have pleiotropic effects and that <it>plcC </it>overexpression and <it>plcC </it>extinction increase MFN1032 toxicity and colonization, respectively.</p> <p>Conclusion</p> <p>This study provides the first demonstration that a PLC is involved in the secreted hemolytic activity of a clinical strain of <it>Pseudomonas fluorescens</it>. Moreover, this phospholipase C seems to belong to a complex biological network associated with the biosurfactant production.</p

    Cell-associated hemolysis activity in the clinical strain of Pseudomonas fluorescens MFN1032

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    <p>Abstract</p> <p>Background</p> <p>MFN1032 is a clinical <it>Pseudomonas fluorescens </it>strain able to grow at 37°C. MFN1032 cells induce necrosis and apoptosis in rat glial cells at this temperature. This strain displays secretion-mediated hemolytic activity involving phospholipase C and cyclolipopeptides. Under laboratory conditions, this activity is not expressed at 37°C. This activity is tightly regulated and is subject to phase variation.</p> <p>Results</p> <p>We found that MFN1032 displays a cell-associated hemolytic activity distinct from the secreted hemolytic activity. Cell-associated hemolysis was expressed at 37°C and was only detected <it>in vitro </it>in mid log growth phase in the presence of erythrocytes. We studied the regulation of this activity in the wild-type strain and in a mutant defective in the Gac two-component pathway. GacS/GacA is a negative regulator of this activity. In contrast to the <it>Pseudomonas fluorescens </it>strains PfO-1 and Pf5, whose genomes have been sequenced, the MFN1032 strain has the type III secretion-like genes <it>hrc</it>RST belonging to the <it>hrpU </it>operon. We showed that disruption of this operon abolished cell-associated hemolytic activity. This activity was not detected in <it>P.fluorescens </it>strains carrying similar <it>hrc </it>genes, as for the <it>P. fluorescens </it>psychrotrophic strain MF37.</p> <p>Conclusions</p> <p>To our knowledge this the first demonstration of cell-associated hemolytic activity of a clinical strain of <it>Pseudomonas fluorescens</it>. Moreover, this activity seems to be related to a functional <it>hrpU </it>operon and is independent of biosurfactant production. Precise link between a functional <it>hrpU </it>operon and cell-associated hemolytic activity remains to be elucidated.</p
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