Exploration du potentiel probiotique de la bactérie lactique Streptococcus thermophilus : évalutation du potentiel probiotique et de sa variabilité : mise au point et validation de l'outil R-IVET (Recombinase based in vivo Expression Technology) pour l'étude de l'état physiologique de la bactérie dans le tractus gastro-intestinal

Abstract : Streptococcus thermophilus is a lactic acid bacterium used after Lactococcus lactis in the dairy industry for the production of yogurt and cheeses like Emmental, Gruyere, Mozarella and Cheddar. It is the only streptococcus to have the GRAS (Generally Recognized As Safe) status. In this work, the probiotic potential of 30 S. thermophilus strains from different origins was tested by studying their ability to resist different stress conditions encountered during their passage through the GIT (low pH, bile salts and oxidative stress), their ability to adhere to intestinal epithelial cells and their immunomodulatory properties. Majority of the strains reduced the production of interleukin IL-8 (pro-inflammatory) and induced the production of interleukin IL-10 (anti-inflammatory) and IL-12 (pro-inflammatory). On the basis of the ratio IL-10/IL-12 which allows to evaluate the anti-inflammatory potential of a probiotic, several strains appeared to have a high the anti-inflammatory potential. Principal Component Analysis (PCA) allowed us to classify strains in 6 different categories with different properties. Within each class, variability and interesting features were observed, but none of the classes could be considered as containing the perfect probiotic. Following this study and on the basis of its resistance to gastric stress and its adhesion capacity and knowing that its genome sequence is available, the strain LMD-9 was selected for the second part of this work, namely the construction of a tool based on R-IVET to study the physiological state of S. thermophilus in the digestive tract. This tool is composed of two elements: a plasmid vector (pULNcreB), carrying the gene cre encoding a site-specific recombinase without its promoter and a chromosomal cassette composed of a gene of resistance to spectinomycin flanked by loxP sites which are recognized by the recombinase Cre. The functionality of the tool R-IVET was then tested by cloning three different promoters of S. thermophilus (PprtS, Pshsp and Plac) upstream of cre. System was valid in vitro with all the three promoters and in vivo by using the lactose operon promoter Plac
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Maïra Junjua. Exploration du potentiel probiotique de la bactérie lactique Streptococcus thermophilus : évalutation du potentiel probiotique et de sa variabilité : mise au point et validation de l'outil R-IVET (Recombinase based in vivo Expression Technology) pour l'étude de l'état physiologique de la bactérie dans le tractus gastro-intestinal. Alimentation et Nutrition. Université de Lorraine, 2013. Français. ⟨NNT : 2013LORR0034⟩. ⟨tel-01749566⟩

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