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Les micro-organismes du microbiote fromager survivent-ils à la digestion et peuvent-ils avoir un effet immunomodulateur sur l’hôte ?

Abstract : Worldwide, the Food Industry uses a broad range of microorganisms while making fermented products, like cheese, most of microorganisms being alive when the food is consumed. Our work aimed at studying the digestive stress response of the surface-ripened cheese microflora and at characterizing their potential immunomodulative properties.In the first part of this work, we investigated the resistance to digestive stress of a selection of 35 microorganisms (bacteria, yeasts and one fungus). We designed a three-step in vitro digestive batch experiment mimicking stresses encountered in (i) the stomach, (ii) the duodenum, (iii) the stomach followed by the duodenum. Alongside, we determined in vitro the microorganisms immunomodulating properties using PBMCs. Batch stress experiments results showed a strong resistance of yeasts to both gastric and duodenal stresses. Bacteria results were more contrasted. PBMCs profiles showed an overall anti-inflammatory response for yeasts (with the exception of one species) while bacteria profiles were fairly different, with both pro- and anti-inflammatory profiles among the same species.The second part of the work consisted in developing a Dynamic Gastro-Intestinal Digestive system (DIDGI) and to experiment on a reduced selection of microorganisms and to assess the influence of the growth under real ripening conditions on the ability of microorganisms to withstand digestive stress. Alongside, we tracked the microorganisms’ ability to survive the mouse digestive tract. Some microorganisms grown in cheeses showed fairly different responses during DIDGI experiments compared to lab-cultured microorganisms. A significant part of microorganisms was able to survive the digestive tract of mice.The third part of the work dealt with the microbial ecosystems' influence on the host's immune responses by (i) designing experimental smear-ripened cheeses with mix of microorganisms that had rather pro- or rather anti-inflammatory immunomodulatory profils and (ii) fed the ripened cheeses to mice with standardized microbiota. The effect of cheeses consumption on two different models of acute colitis was investigated. Results showed that both cheeses tend to exacerbate the symptoms in one of the colitis model and that the “pro-inflammatory” cheese significantly aggravated the symptoms of the second model of colitis.The fourth and last part of the work consisted in characterizing the molecular response to a similar in vitro batch digestive stress used in the first part of the work. Therefore, we selected a Gram-positive bacterium and a Gram-negative bacterium and used RNAseq for transcriptome analysis. A preliminary analysis of the results showed that both organisms were able to up- or down-regulate a major part of their metabolism, using both similar mechanisms and specific response per bacterium.
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Nadège Adouard. Les micro-organismes du microbiote fromager survivent-ils à la digestion et peuvent-ils avoir un effet immunomodulateur sur l’hôte ?. Alimentation et Nutrition. AgroParisTech, 2015. Français. ⟨NNT : 2015AGPT0012⟩. ⟨tel-03000970⟩

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