What intracellular receptors are involved in recognition of S. Typhimurium in mouse intestinal epithelial cells ?

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In vitro infection of intestinal finite and continuous cell lines by L monocytogenes

International audienc

Cell proliferation enhances entry of Listeria monocytogenes into intestinal epithelial cells by two proliferation-dependent entry pathways

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Involvement of c-Src tyrosine kinase upstream of class I phosphatidylinositol (PI) 3-kinases in <em>Salmonella</em> Enteritidis Rck protein-mediated invasion

International audienceThe Salmonella outer membrane protein Rck mediates a Zipper entry mechanism controlled by tyrosine phosphorylation and class I phosphatidylinositol 3-kinase (PI 3-kinase). However, the underlying mechanism leading to this signalling cascade remains unclear. The present study showed that using Rck-coated beads or Rck-overexpressing E. coli, Rck-mediated actin polymerization and invasion were blocked by PP2, a Src-family tyrosine kinase inhibitor. In addition, phosphorylation of Src-family kinases significantly increased after stimulation with Rck. The specific contribution of c-Src, one member of the Src-family kinases, was demonstrated using c-Src-deficient fibroblasts or c-Src siRNA transfected epithelial cells. We also observed that Rck-mediated internalization led to the formation of a complex between c-Src and at least one tyrosine phosphorylated protein. Furthermore, our results revealed that the c-Src signal molecule was upstream of PI 3-kinase during the Rck-mediated signalling pathway, as Rck-mediated PI 3-kinase activation was blocked by PP2, and PI 3-kinase inhibitor had no effect on the Src phosphorylation. These results demonstrate the involvement of c-Src upstream of the PI 3-kinase in the Zipper entry process mediated by Rck

Low persistence of a large-plasmid-cured variant of Salmonella enteritidis in ceca of chicks

International audienceIn order to estimate the contribution of Salmonella in the persistence of this bacterium in chicks, we compared the persistence of a Salmonella enteritidis strain and its plasmid-cured variant in a chicken asymptomatic carrier state model. After oral inoculation, colonization with the plasmid-cured strain was significantly reduced (P < 0.001) in the ceca of chicks from the third week postinoculation and persisted for a shorter period than the wild-type strain. Moreover, numbers of S. enteritidis-infected livers were also significantly lower (P < 0.01) for the plasmid-cured strain compared with the wild-type strain from the third to the seventh week postinoculation. No difference in spleen colonization was observed. These results did not correlate with any in vitro difference in attachment, entry to, or intracellular multiplication of bacteria within intestinal or macrophage avian cell lines.Con el objeto de estimar la persistencia de la Salmonella en los pollos, se comparó la persistencia de una cepa de Salmonella enteritidis y su variante privada de gran plásmido, en un modelo aviar de portador asintomático. Después de la inoculación oral, la colonización con el organismo sin el plásmido fue reducida significantemente (P < 0.001) en el ciego de pollos desde la tercera semana después de la inoculación y persistió por un corto período, comparado con la cepa normal. Además, el número de hígados infectados con S. enteritidis fue también significantemente menor (P < 0.01) para la cepa carente del plásmido comparada con la cepa normal, desde la tercera hasta la séptima semana después de la inoculación. No se observaron diferencias en la colonización del bazo. Estos resultados no mostraron correlación con ninguna diferencia in vitro en la adhesión, entrada o multiplicación intracelular de la bacteria dentro de líneas celulares aviares intestinales o macrófagos

Precise excision and secondary transposition of TnphoA in non-motile mutants of a Salmonella enterica serovar Enteritidis clinical isolate.

International audienceMutagenesis with TnphoA has been widely used in many bacteria. Here, we report the excision and secondary transposition of this transposon in three non-motile (fliC, fliF and motB) mutants of Salmonella enterica serovar Enteritidis (S. Enteritidis). Isolation of motile revertants showed that they were kanamycin resistant and conserved a copy of TnphoA in their genome in an insertion site different from the initial one. They also expressed an intact flagella. Characterization of the motile revertant derived from the fliC mutant showed that TnphoA excised precisely from the fliC gene, resulting in an equivalent amount of FliC secreted protein in the revertant compared to that of the wild-type strain. These results show that TnphoA mutants should be used with care and underline the value of using transposon derivatives lacking the transposase gene

Gene expression profile of enterocytes purified from two lines of chicken during the <em>Salmonella</em> carrier state

National audienc

<em>Salmonella enteritidis</em> Rck-mediated invasion requires activation of Rac1, which is dependent on the class I PI 3-kinases-Akt signaling pathway

International audienceThe Salmonella outer membrane protein Rck mediates a Zipper-like entry mechanism controlled by Rac, the Arp2/3 complex, and actin polymerization. However, little is known about the early steps leading to Rac activation and Rck-mediated internalization. The use of pharmacological inhibitors or PI 3-kinase dominant-negative mutant induced more than 80% less invasion without affecting attachment. Moreover, Rck-mediated internalization caused an increase in the association of p85 with at least one tyrosine-phosphorylated protein, indicating that class I PI 3-kinase activity was stimulated. We also report that this PI 3-kinase activity is essential for Rac1 activation. However, Rac recruitment at the Rck-mediated entry site was independent of its activation. Using a pharmacological approach or Akt-knockout cells, we also demonstrated that Akt was phosphorylated in response to Rck-mediated internalization as demonstrated by immunoblotting analysis and that all three Akt isoforms were required during this process. Overall, our results describe a signaling pathway involving tyrosine phosphorylation, class I PI 3-kinase, Akt activation, and Rac activation, leading to Rck-dependent Zipper entry. The specificity of this signaling pathway with regard to that of the type 3 secretion system, which is the other invasion process of Salmonella, is discussed

Multiplicity of Salmonella invasion mechanism

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Establishment and characterization of partially differentiated chicken enterocyte cell clones

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