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

<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

Effects of growth conditions on biofilm formation by Actinobacillus pleuropneumoniae

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

À propos de l’article de Alain-Marie Bassy, un point de vue québécois

Alain-Marie Bassy présente une analyse systémique susceptible de répondre aux interrogations de leaders éducatifs sur la lenteur que connaît l’adoption de l’innovation, reflet de nombre de résistances au changement non-perçu comme nécessaire ou, plutôt, de l’absence de conditions favorables, s’agisse-t-il des outils numériques ou des pratiques pédagogiques et organisationnelles qu’ils servent ou entraînent, dans les systèmes éducatifs francophones et autres. Nous retenons les cinq pistes de réflexion suivantes soumises par Bassy car elles trouvent écho au Québec : a) le modèle industriel (technologies, coûts de production) en évolution rapide ; b) le modèle de gouvernance : prééminence de l’État, centralisation et prescription ; c) le modèle social de l'École : de Jules Ferry au numérique, la mise en cause des dogmes ; d) le modèle pédagogique : les missions et le service de l'enseignant, immuables? e) le modèle éditorial et commercial : de l'imprimé au numérique, continuité ou rupture ? Notre réaction est ancrée dans les travaux que nous menons en tant que membres du Centre de recherche et d’intervention sur la réussite scolaire (CRIRES, crires.ulaval.ca) dont l’activité vise l’innovation sous l’éclairage, entre autres, du modèle d’Engeström (Engeström, 1987) ; (Engeström, 2010), en tant que membres du CEFRIO (cefrio.qc.ca), centre facilitant la recherche et l’innovation dans les organisations à l’aide des TIC, ou du CTREQ (ctreq.qc.ca), centre qui a pour mission de promouvoir l'innovation et le transfert de connaissances en vue d’accroître la réussite éducative du Québec