64 research outputs found

    Étude des gĂšnes d'Actinobacillus pleuropneumoniae exprimĂ©s en conditions d'infection

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    Actinobacillus pleuropneumoniae est l’agent Ă©tiologique de la pleuropneumonie porcine. La bactĂ©rie se transmet par voies aĂ©riennes et contacts directs. Plusieurs facteurs de virulence ont Ă©tĂ© identifiĂ©s, nommĂ©ment les polysaccharides capsulaires, les lipopolysaccharide, les exotoxines ApxI Ă  IV et de nombreux mĂ©canismes d’acquisition du fer. Aucun vaccin efficace contre tous les sĂ©rotypes de la bactĂ©rie n’a encore Ă©tĂ© Ă©laborĂ©. Afin de mieux comprendre de quelle façon A. pleuropneumoniae rĂ©gule la transcription de ses nombreux facteurs de virulence et de dĂ©couvrir de nouvelles cibles potentielles pour l’élaboration de vaccins efficaces, le profil transcriptomique de la bactĂ©rie a Ă©tĂ© Ă©tudiĂ© dans des conditions simulant l’infection ainsi qu’à la suite d’une infection naturelle aiguĂ« chez l’animal. Des biopuces de premiĂšre et de seconde gĂ©nĂ©ration (AppChip1 et AppChip2) comportant respectivement 2025 cadres de lecture ouverts (ORF) de la version prĂ©liminaire du gĂ©nome d’A. pleuropneumoniae sĂ©rotype 5b souche L20 et 2033 ORF de la version finale annotĂ©e du mĂȘme gĂ©nome ont Ă©tĂ© utilisĂ©es. Dans un premier temps, des expĂ©riences rĂ©alisĂ©es dans des conditions de concentration restreinte en fer ont permis d’identifier 210 gĂšnes diffĂ©rentiellement exprimĂ©s, dont 92 Ă©taient surexprimĂ©s. Plusieurs nouveaux mĂ©canismes d’acquisition du fer ont pu ĂȘtre identifiĂ©s, incluant un systĂšme homologue au systĂšme YfeABCD de Yersinia pestis, impliquĂ© dans l’acquisition du fer chĂ©latĂ©, ainsi que des gĂšnes homologues aux composantes du systĂšme HmbR de Neisseria meningitidis impliquĂ© dans l’acquisition du fer Ă  partir de l’hĂ©moglobine. Dans des conditions de culture permettant la formation de biofilms, les gĂšnes tadC et tadD d’un opĂ©ron tad (« tight adherence locus ») putatif, les gĂšnes pgaBC impliquĂ©s dans la synthĂšse d’un polysaccharide de la matrice du biofilm ainsi que deux gĂšnes prĂ©sentant de fortes homologies avec un gĂšne codant pour l’adhĂ©sine auto-transporteur Hsf retrouvĂ©e chez Haemophilus influenzae ont montrĂ© une surexpression significative. Plusieurs de ces gĂšnes ont Ă©galement Ă©tĂ© retrouvĂ©s lors d’expĂ©riences rĂ©alisĂ©es avec des cellules Ă©pithĂ©liales d’origine pulmonaire en culture, qui ont permis d’identifier 170 gĂšnes diffĂ©rentiellement exprimĂ©s aprĂšs la croissance planctonique au-dessus des cellules, et 131 autres suite Ă  l’adhĂ©sion Ă  ces cellules. Parmis les gĂšnes surexprimĂ©s, les gĂšnes tadB et rcpA de l’opĂ©ron tad putatif, les gĂšnes pgaBC ainsi que le gĂšne codant pour l’homologue d’Hsf ont Ă©tĂ© retrouvĂ©s. En prĂ©sence de liquide de lavage broncho-alvĂ©olaire (BALF), 156 gĂšnes ont montrĂ© un profil d’expression modifiĂ©, et le gĂšne apxIVA, identifiĂ© comme Ă©tant surexprimĂ©, a pu ĂȘtre dĂ©tectĂ© pour la premiĂšre fois dans des conditions de croissance in vitro. Finalement, des expĂ©riences visant Ă  dĂ©terminer les gĂšnes utilisĂ©s directement chez l’animal en phase aiguĂ« de la pleuropneumonie porcine ont permis d’identifier 150 gĂšnes qui Ă©taient diffĂ©rentiellement exprimĂ©s. En plus d’identifier des gĂšnes d’un possible opĂ©ron codant pour un fimbriae de type IV, 3 des 72 gĂšnes surexprimĂ©s sont conservĂ©s chez tous les sĂ©rotypes d’A. pleuropneumoniae et codent pour des protĂ©ines ou lipoprotĂ©ines de surface. Nos expĂ©riences ont permis d’identifier plusieurs nouveaux facteurs de virulence potentiels chez A. pleuropneumoniae ainsi que plusieurs nouvelles cibles potentielles pour l’élaboration de vaccins efficaces contre tous les sĂ©rotypes.Actinobacillus pleuropneumoniae is the etiological agent of porcine pleuropneumonia. Transmission of the disease occurs through direct contact or aerosols. The bacteria possess many virulence factors, namely capsular polysaccharides, lipopolysaccharides, four Apx toxins and iron acquisition mechanisms. To this day, an efficient cross-serotype vaccine has yet to be developed. In order to investigate regulation mechanisms in A. pleuropneumoniae and to identify new potential targets for the synthesis of subunit vaccines, the transcriptomic profile of the bacteria under conditions that simulate the infection and following a natural acute infection in vivo were studied. The experiences relied on first and second generation microarrays (AppChip1 and AppChip2) designed using 2025 ORFs of the draft version of the A. pleuropneumoniae serotype 5b strain L20 genome and 2033 ORFs of the final and annotated version of the same genome respectively. First, experiments were conducted under iron-restricted conditions and 210 genes were deemed differentially expressed, 92 of which were up-regulated. Some new putative iron acquisition mechanisms were identified, including genes homologous to those of the Yersinia pestis YfeABCD chelated-iron acquisition system, as well as other genes homologous to components of the HmbR iron uptake from hemoglobin system of Neisseria meningitidis. When cultured in conditions promoting biofilm production, genes tadC and tadD from a putative tad (« tight adherence locus ») operon, genes pgaABC involved in the biosynthesis of a polysaccharide of the biofilm matrix as well as two ORFs encoding a putative autotransporter adhesins similar to the Haemophilus influenzae Hsf adhesin were all significantly overexpressed. Many of these genes were also overexpressed when lung epithelial cells were infected with A. pleuropneumoniae. While 170 genes were differentially expressed after planktonic growth in the culture medium above the cells, another 131 were identified following direct adhesion to the cells. Genes tadB and rcpA of the tad locus, as well as genes pgaBC and an ORF coding for the Hsf homolog where all found among overexpressed genes. When A. pleuropneumoniae was cultured in contact with broncho-alveolar lavage fluids (BALF), 156 genes were significantly differentially expressed and gene apxIVA, which was up-regulated, was detected for the first time during in in vitro growth conditions. Finally, experiments were conducted in vivo in animals naturally infected with A. pleuropneumoniae in the late stage of the acute phase in order to identify genes that are expressed during the infection of the natural host. While 150 genes were deemed differentially expressed, genes apxIVA as well as two genes from an operon coding for a putative type IV fimbriae were up-regulated. Out of those 72 genes that were overexpressed, 3 encode proteins or lipoproteins of the outer membrane which are conserved among all serotypes of the bacteria. Overall, we were able to identify several new potential virulence factors for A. pleuropneumoniae in the course of our experiments, as well as several new potential targets for the elaboration of an efficient cross-serotype vaccine

    Analyse et Optimisation du Partage de Spectre dans les SystÚmes Mobiles Intégrés Satellite et Terrestre

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    Les technologies mobiles terrestre et satellite sont naturellement complĂ©mentaires. Les rĂ©seaux cellulaires terrestres sont adaptĂ©s aux villes oĂč la densitĂ© d’utilisateurs est maximale mais perdent leur rentabilitĂ© dans les zones peu peuplĂ©es. A l’inverse, les systĂšmes mobile satellite permettent de couvrir de vastes zones Ă  moindre coĂ»t mais n’assurent pas la couverture dans les zones urbaines car le signal est bloquĂ© par les constructions. En les combinant pour assurer la couverture en ville par le rĂ©seau terrestre et dans les zones moins denses avec le satellite, on obtient un systĂšme Ă  la couverture totale pour un coĂ»t optimal. Nous appelons un tel systĂšme intĂ©grant une composante satellite et une composante terrestres un « systĂšme intĂ©grĂ© » satellite/terrestre. Nul doute que d’ici quelques annĂ©es, le rĂȘve de la communautĂ© satellite de rendre tous les terminaux mobiles capables de se connecter Ă  un satellite sera accessible. Le satellite pourra ainsi ĂȘtre vu par les utilisateurs de terminaux portables comme une Ă©niĂšme technologie d’accĂšs Ă  un systĂšme « intĂ©grĂ© », aux cĂŽtĂ©s du Bluetooth, du Wifi et des technologies cellulaires (GSM, UMTS, LTE). La rĂ©utilisation du spectre satellite par les systĂšmes terrestres est un facteur dĂ©terminant dans le succĂšs de cette intĂ©gration car elle permet de justifier les investissements dans le systĂšme satellite qui ne peut ĂȘtre rentabilisĂ© par les abonnements seuls. Toutefois sa mise en Ɠuvre pose de nombreux problĂšmes : rĂšglementaires, commerciaux et bien entendu techniques. Cette thĂšse apporte des solutions sur ce dernier point et j’espĂšre qu’elle contribuera ainsi Ă  rendre possible ce rĂȘve d’intĂ©gration. Nous avons adoptĂ© une approche descendante du problĂšme du partage de spectre dans les systĂšmes mobiles satellite-terrestre. Nous avons tout d’abord Ă©tabli une synthĂšse sur les aspects recouverts par l’intĂ©gration des systĂšmes mobiles satellite et terrestre. Nous avons ensuite dressĂ© l’état de l’art sur la problĂ©matique de la rĂ©utilisation du spectre satellite par les systĂšmes terrestres, que nous avons complĂ©tĂ© par nos analyses. Nous avons dĂ©cidĂ© dans cette thĂšse de nous focaliser sur un des problĂšmes majeurs soulevĂ©s par cette rĂ©utilisation : les interfĂ©rences co-frĂ©quence du systĂšme terrestre sur le lien montant satellite. A partir de l’analyse d’une solution de partage statique de spectre par coordination des plans de frĂ©quence (principe de zone d’exclusion), nous avons Ă©laborĂ© puis analysĂ© les performances de mĂ©canismes innovants d’allocation de ressources dans le systĂšme terrestre qui permettent de rĂ©duire de façon importante les interfĂ©rences. De plus, nous proposons une mĂ©thode pour garantir au systĂšme satellite que les interfĂ©rences subies sur son lien montant soient infĂ©rieures Ă  une valeur limite. Enfin, nous dĂ©finissons une architecture et les mĂ©canismes associĂ©s qui permettent l’implantation des solutions proposĂ©es dans un systĂšme satellite-terrestre fondĂ© sur la technologie LTE. L’étude du sujet de partage de spectre dans les systĂšmes mobiles satellite-terrestre est relativement nouvelle et cette thĂšse constitue donc un travail novateur important qui pourra ĂȘtre utilisĂ© comme base Ă  de futurs travaux. ABSTRACT : Terrestrial and satellite mobile technologies are naturally complementary. Terrestrial cellular systems are adapted to urban areas where the user density is maximal but their cost-effectiveness is much lower in sparsely populated areas. On the contrary, mobile satellite systems cover large zones at a relatively low cost but they cannot ensure coverage in urban areas because of signal blockage due to buildings. By combining both systems for ensuring coverage in cities with terrestrial networks and in less dense areas with the satellite, we obtain a system with complete coverage for an optimal cost. Such a system is called mobile terrestrial and satellite “integrated system”. It is likely that in a few years, the dream of enabling satellite connectivity on all mobile terminals will be within reach. The satellite will then be perceived for mobile terminal users as an additional access technology to an “integrated network” comparable to Wifi, Bluetooth or cellular technologies (GSM, UMTS, LTE). The spectrum reuse by terrestrial systems is a key for the success of this integration because it justifies part of the investments in the satellite systems that cannot be supported by user subscriptions only. However, implementation of spectrum sharing generates many issues: regulatory, commercial and obviously technical. This thesis brings answers on the latter and I hope it will contribute to make this dream of integration become reality. We used a descending approach of the issue of spectrum sharing in terrestrial and satellite mobile systems. First, we establish a synthesis of all the aspects covered by the integration of mobile satellite and terrestrial systems. Then, we made the state of the art on the issue of satellite spectrum reuse by terrestrial systems and we completed it with our analysis. We decided to focus our work on one of the major issues raised by this reuse: co-frequency interference generated by the terrestrial system on the satellite uplink. From the analysis of a solution proposing a static spectrum sharing by coordination of frequency plans (the exclusion zone principle), we elaborated and analyzed performances of innovative mechanisms of resources allocation in the terrestrial system that allows to reduce significantly the interferences. Moreover, we proposed a method for guaranteeing to the satellite system that interferences from the terrestrial system will not exceed a given threshold. At last, we define an architecture and the associated mechanism that allow the implementation of our solution in an integrated terrestrial-satellite systems based on LTE technology. The study of spectrum sharing in terrestrial-satellite mobile systems is rather new and this thesis represents an innovative work that may serve as a basis for future studies on this issue

    Analyse et Optimisation du Partage de Spectre dans les SystÚmes Mobiles Intégrés Satellite et Terrestre

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    Les technologies mobiles terrestre et satellite sont naturellement complĂ©mentaires. Les rĂ©seaux cellulaires terrestres sont adaptĂ©s aux villes oĂč la densitĂ© d'utilisateurs est maximale mais perdent leur rentabilitĂ© dans les zones peu peuplĂ©es. A l'inverse, les systĂšmes mobile satellite permettent de couvrir de vastes zones Ă  moindre coĂ»t mais n'assurent pas la couverture dans les zones urbaines car le signal est bloquĂ© par les constructions. En les combinant pour assurer la couverture en ville par le rĂ©seau terrestre et dans les zones moins denses avec le satellite, on obtient un systĂšme Ă  la couverture totale pour un coĂ»t optimal. Nous appelons un tel systĂšme intĂ©grant une composante satellite et une composante terrestres un "systĂšme intĂ©grĂ©" satellite/terrestre. Nul doute que d'ici quelques annĂ©es, le rĂȘve de la communautĂ© satellite de rendre tous les terminaux mobiles capables de se connecter Ă  un satellite sera accessible. Le satellite pourra ainsi ĂȘtre vu par les utilisateurs de terminaux portables comme une Ă©niĂšme technologie d'accĂšs Ă  un systĂšme "intĂ©grĂ©", aux cĂŽtĂ©s du Bluetooth, du Wifi et des technologies cellulaires (GSM, UMTS, LTE). La rĂ©utilisation du spectre satellite par les systĂšmes terrestres est un facteur dĂ©terminant dans le succĂšs de cette intĂ©gration car elle permet de justifier les investissements dans le systĂšme satellite qui ne peut ĂȘtre rentabilisĂ© par les abonnements seuls. Toutefois sa mise en Ɠuvre pose de nombreux problĂšmes : rĂšglementaires, commerciaux et bien entendu techniques. Cette thĂšse apporte des solutions sur ce dernier point et j'espĂšre qu'elle contribuera ainsi Ă  rendre possible ce rĂȘve d'intĂ©gration. Nous avons adoptĂ© une approche descendante du problĂšme du partage de spectre dans les systĂšmes mobiles satellite-terrestre. Nous avons tout d'abord Ă©tabli une synthĂšse sur les aspects recouverts par l'intĂ©gration des systĂšmes mobiles satellite et terrestre. Nous avons ensuite dressĂ© l'Ă©tat de l'art sur la problĂ©matique de la rĂ©utilisation du spectre satellite par les systĂšmes terrestres, que nous avons complĂ©tĂ© par nos analyses. Nous avons dĂ©cidĂ© dans cette thĂšse de nous focaliser sur un des problĂšmes majeurs soulevĂ©s par cette rĂ©utilisation : les interfĂ©rences co-frĂ©quence du systĂšme terrestre sur le lien montant satellite. A partir de l'analyse d'une solution de partage statique de spectre par coordination des plans de frĂ©quence (principe de zone d'exclusion), nous avons Ă©laborĂ© puis analysĂ© les performances de mĂ©canismes innovants d'allocation de ressources dans le systĂšme terrestre qui permettent de rĂ©duire de façon importante les interfĂ©rences. De plus, nous proposons une mĂ©thode pour garantir au systĂšme satellite que les interfĂ©rences subies sur son lien montant soient infĂ©rieures Ă  une valeur limite. Enfin, nous dĂ©finissons une architecture et les mĂ©canismes associĂ©s qui permettent l'implantation des solutions proposĂ©es dans un systĂšme satellite-terrestre fondĂ© sur la technologie LTE. L'Ă©tude du sujet de partage de spectre dans les systĂšmes mobiles satellite-terrestre est relativement nouvelle et cette thĂšse constitue donc un travail novateur important qui pourra ĂȘtre utilisĂ© comme base Ă  de futurs travaux.Terrestrial and satellite mobile technologies are naturally complementary. Terrestrial cellular systems are adapted to urban areas where the user density is maximal but their cost-effectiveness is much lower in sparsely populated areas. On the contrary, mobile satellite systems cover large zones at a relatively low cost but they cannot ensure coverage in urban areas because of signal blockage due to buildings. By combining both systems for ensuring coverage in cities with terrestrial networks and in less dense areas with the satellite, we obtain a system with complete coverage for an optimal cost. Such a system is called mobile terrestrial and satellite "integrated system". It is likely that in a few years, the dream of enabling satellite connectivity on all mobile terminals will be within reach. The satellite will then be perceived for mobile terminal users as an additional access technology to an "integrated network" comparable to Wifi, Bluetooth or cellular technologies (GSM, UMTS, LTE). The spectrum reuse by terrestrial systems is a key for the success of this integration because it justifies part of the investments in the satellite systems that cannot be supported by user subscriptions only. However, implementation of spectrum sharing generates many issues: regulatory, commercial and obviously technical. This thesis brings answers on the latter and I hope it will contribute to make this dream of integration become reality. We used a descending approach of the issue of spectrum sharing in terrestrial and satellite mobile systems. First, we establish a synthesis of all the aspects covered by the integration of mobile satellite and terrestrial systems. Then, we made the state of the art on the issue of satellite spectrum reuse by terrestrial systems and we completed it with our analysis. We decided to focus our work on one of the major issues raised by this reuse: co-frequency interference generated by the terrestrial system on the satellite uplink. From the analysis of a solution proposing a static spectrum sharing by coordination of frequency plans (the exclusion zone principle), we elaborated and analyzed performances of innovative mechanisms of resources allocation in the terrestrial system that allows to reduce significantly the interferences. Moreover, we proposed a method for guaranteeing to the satellite system that interferences from the terrestrial system will not exceed a given threshold. At last, we define an architecture and the associated mechanism that allow the implementation of our solution in an integrated terrestrial-satellite systems based on LTE technology. The study of spectrum sharing in terrestrial-satellite mobile systems is rather new and this thesis represents an innovative work that may serve as a basis for future studies on this issue.TOULOUSE-INP (315552154) / SudocSudocFranceF

    Transcriptional profiling of Actinobacillus pleuropneumoniae during the acute phase of a natural infection in pigs

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    <p>Abstract</p> <p>Background</p> <p><it>Actinobacillus pleuropneumoniae </it>is the etiological agent of porcine pleuropneumonia, a respiratory disease which causes great economic losses worldwide. Many virulence factors are involved in the pathogenesis, namely capsular polysaccharides, RTX toxins, LPS and many iron acquisition systems. In order to identify genes that are expressed <it>in vivo </it>during a natural infection, we undertook transcript profiling experiments with an <it>A. pleuropneumoniae </it>DNA microarray, after recovery of bacterial mRNAs from serotype 5b-infected porcine lungs. AppChip2 contains 2033 PCR amplicons based on the genomic sequence of <it>App </it>serotype 5b strain L20, representing more than 95% of ORFs greater than 160 bp in length.</p> <p>Results</p> <p>Transcriptional profiling of <it>A. pleuropneumoniae </it>recovered from the lung of a pig suffering from a natural infection or following growth of the bacterial isolate in BHI medium was performed. An RNA extraction protocol combining beadbeating and hot-acid-phenol was developed in order to maximize bacterial mRNA yields and quality following total RNA extraction from lung lesions. Nearly all <it>A. pleuropneumoniae </it>transcripts could be detected on our microarrays, and 150 genes were deemed differentially expressed <it>in vivo </it>during the acute phase of the infection. Our results indicate that, for example, gene <it>apxIVA </it>from an operon coding for RTX toxin ApxIV is highly up-regulated <it>in vivo</it>, and that two genes from the operon coding for type IV fimbriae (APL_0878 and APL_0879) were also up-regulated. These transcriptional profiling data, combined with previous comparative genomic hybridizations performed by our group, revealed that 66 out of the 72 up-regulated genes are conserved amongst all serotypes and that 3 of them code for products that are predicted outer membrane proteins (genes <it>irp </it>and <it>APL_0959</it>, predicted to code for a TonB-dependent receptor and a filamentous hemagglutinin/adhesin respectively) or lipoproteins (gene <it>APL_0920</it>). Only 4 of 72 up-regulated genes had previously been identified in controled experimental infections.</p> <p>Conclusions</p> <p>These genes that we have identified as up-regulated in <it>vivo</it>, conserved across serotypes and coding for potential outer membrane proteins represent potential candidates for the development of a cross-protective vaccine against porcine pleuropneumonia.</p

    malT knockout mutation invokes a stringent type gene-expression profile in Actinobacillus pleuropneumoniae in bronchoalveolar fluid

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    Actinobacillus pleuropneumoniae causes contagious pleuropneumonia, an economically important disease of commercially reared pigs throughout the world. To cause this disease, A. pleuropneumoniae must rapidly overcome porcine pulmonary innate immune defenses. Since bronchoalveolar fluid (BALF) contains many of the innate immune and other components found in the lungs, we examined the gene expression of a virulent serovar 1 strain of A. pleuropneumoniae after exposure to concentrated BALF for 30 min.Peer reviewed: YesNRC publication: Ye

    Truncation of the lipopolysaccharide outer core affects susceptibility to antimicrobial peptides and virulence of Actinobacillus pleuropneumoniae serotype 1.

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    Abstract We reported previously that the core oligosaccharide region of the lipopolysaccharide (LPS) is essential for optimal adhesion of Actinobacillus pleuropneumoniae, an important swine pathogen, to respiratory tract cells. Rough LPS and core LPS mutants of A. pleuropneumoniae serotype 1 were generated by using a mini-Tn10 transposon mutagenesis system. Here we performed a structural analysis of the oligosaccharide region of three core LPS mutants that still produce the same O-antigen by using methylation analyses and mass spectrometry. We also performed a kinetic study of proinflammatory cytokines production such as interleukin (IL)-6, tumor necrosis factor-α, IL1-ÎČ, MCP-1, and IL8 by LPS-stimulated porcine alveolar macrophages, which showed that purified LPS of the parent strain, the rough LPS and core LPS mutants, had the same ability to stimulate the production of cytokines. Most interestingly, an in vitro susceptibility test of these LPS mutants to antimicrobial peptides showed that the three core LPS mutants were more susceptible to cationic peptides than both the rough LPS mutant and the wild type parent strain. Furthermore, experimental pig infections with these mutants revealed that the galactose (Gal I) and d,d-heptose (Hep IV) residues present in the outer core of A. pleuropneumoniae serotype 1 LPS are important for adhesion and overall virulence in the natural host, whereas deletion of the terminal GalNAc-Gal II disaccharide had no effect. Our data suggest that an intact core-lipid A region is required for optimal protection of A. pleuropneumoniae against cationic peptides and that deletion of specific residues in the outer LPS core results in the attenuation of the virulence of A. pleuropneumoniae serotype 1

    Effects of growth conditions on biofilm formation by Actinobacillus pleuropneumoniae

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    Biofilm formation is an important virulence trait of many bacterial pathogens. It has been reported in the literature that only two of the reference strains of the swine pathogen Actinobacillus pleuropneumoniae, representing serotypes 5b and 11, were able to form biofilm in vitro. In this study, we compared biofilm formation by the serotype 1 reference strain S4074 of A. pleuropneumoniae grown in five different culture media. We observed that strain S4074 of A. pleuropneumoniae is able to form biofilms after growth in one of the culture conditions tested brain heart infusion (BHI medium, supplier B). Confocal laser scanning microscopy using a fluorescent probe specific to the poly-N-acetylglucosamine (PGA) polysaccharide further confirmed biofilm formation. In accordance, biofilm formation was susceptible to dispersin B, a PGA hydrolase. Transcriptional profiles of A. pleuropneumoniae S4074 following growth in BHI-B, which allowed a robust biofilm formation, and in BHI-A, in which only a slight biofilm formation was observed, were compared. Genes such as tadC, tadD, genes with homology to autotransporter adhesins as well as genes pgaABC involved in PGA biosynthesis and genes involved in zinc transport were up-regulated after growth in BHI-B. Interestingly, biofilm formation was inhibited by zinc, which was found to be more present in BHI-A (no or slight biofilm) than in BHI-B. We also observed biofilm formation in reference strains representing serotypes 3, 4, 5a, 12 and 14 as well as in 20 of the 37 fresh field isolates tested. Our data indicate that A. pleuropneumoniae has the ability to form biofilms under appropriate growth conditions and transition from a biofilm-positive to a biofilm-negative phenotype was reversible

    Microarray-based comparative genomic profiling of reference strains and selected Canadian field isolates of Actinobacillus pleuropneumoniae

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    <p>Abstract</p> <p>Background</p> <p><it>Actinobacillus pleuropneumoniae</it>, the causative agent of porcine pleuropneumonia, is a highly contagious respiratory pathogen that causes severe losses to the swine industry worldwide. Current commercially-available vaccines are of limited value because they do not induce cross-serovar immunity and do not prevent development of the carrier state. Microarray-based comparative genomic hybridizations (M-CGH) were used to estimate whole genomic diversity of representative <it>Actinobacillus pleuropneumoniae </it>strains. Our goal was to identify conserved genes, especially those predicted to encode outer membrane proteins and lipoproteins because of their potential for the development of more effective vaccines.</p> <p>Results</p> <p>Using hierarchical clustering, our M-CGH results showed that the majority of the genes in the genome of the serovar 5 <it>A. pleuropneumoniae </it>L20 strain were conserved in the reference strains of all 15 serovars and in representative field isolates. Fifty-eight conserved genes predicted to encode for outer membrane proteins or lipoproteins were identified. As well, there were several clusters of diverged or absent genes including those associated with capsule biosynthesis, toxin production as well as genes typically associated with mobile elements.</p> <p>Conclusion</p> <p>Although <it>A. pleuropneumoniae </it>strains are essentially clonal, M-CGH analysis of the reference strains of the fifteen serovars and representative field isolates revealed several classes of genes that were divergent or absent. Not surprisingly, these included genes associated with capsule biosynthesis as the capsule is associated with sero-specificity. Several of the conserved genes were identified as candidates for vaccine development, and we conclude that M-CGH is a valuable tool for reverse vaccinology.</p

    Physical Methods for the Preparation of Hybrid Nanocomposite Polymer Latex Particles

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    In this chapter, we will highlight conceptual physical approaches towards the fabrication of nanocomposite polymer latexes in which each individual latex particle contains one or more "hard" nanoparticles, such as clays, silicates, titanates, or other metal(oxides). By "physical approaches" we mean that the "hard" nanoparticles are added as pre-existing entities, and are not synthesized in situ as part of the nanocomposite polymer latex fabrication process. We will narrow our discussion to focus on physical methods that rely on the assembly of nanoparticles onto the latex particles after the latex particles have been formed, or its reciprocal analogue, the adhesion of polymer onto an inorganic nanoparticle. First, will discuss the phenomenon of heterocoagulation and its various driving forces, such as electrostatic interactions, the hydrophobic effect, and secondary molecular interactions. We will then address methods that involve assembly of nanoparticles onto or around the more liquid precursors (i.e., swollen/growing latex particles or monomer droplets). We will focus on the phenomenon of Pickering stabilization. We will then discuss features of particle interaction with soft interfaces, and see how the adhesion of particles onto emulsion droplets can be applied in suspension, miniemulsion, and emulsion polymerization. Finally, we will very briefly mention some interesting methods that make use of interface-driven templating for making well-defined assembled clusters and supracolloidal structures
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