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International audience; Background:Adherent-invasive Escherichia coli (AIEC), which colonize the ileal mucosa of patients with Crohn's disease (CD), are able to adhere to and invade intestinal epithelial cells. Overexpression of the glycoprotein CEACAM6 on host cells favors AIEC attachment and inflammation. We investigated the ability of Saccharomyces cerevisiae CNCM I-3856 to inhibit AIEC adhesion and to reduce colitis.Methods:Adhesion experiments were performed on T84 cells and on enterocytes from patients with CD with AIEC LF82 in the presence of S. cerevisiae. Colonization and symptoms of colitis were assessed in LF82-infected transgenic CEABAC10 mice treated with live S. cerevisiae or S. cerevisiae derivatives. Proinflammatory cytokines were quantified by enzyme linked immunosorbent assay. Intestinal permeability was assessed by measuring the 4 kDa dextran-FITC flux in the serum.Results:S. cerevisiae strongly inhibited LF82 adhesion to T84 cells and to the brush border of CD enterocytes. Yeasts decreased LF82 colonization and colitis in CEABAC10 mice and restored barrier function through prevention of the LF82-induced expression of pore-forming tight junction claudin-2 at the plasma membrane of intestinal epithelial cells. These effects were accompanied by a decrease in proinflammatory cytokines IL-6, IL-1, and KC release by the gut mucosa. Yeast derivatives exerted similar effects on LF82 colonization and colitis demonstrating that yeast viability was not essential to exert beneficial effects.Conclusions:S. cerevisiae yeasts reduce colitis induced by AIEC bacteria in CEACAM6-expressing mice. Such a probiotic strategy could be envisaged in a subgroup of patients with CD abnormally expressing CEACAM6 at the ileal mucosa and therefore susceptible to being colonized by AIEC bacteria.

AIM: To evaluate the in vitro immunomodulation capacity of various non-pathogenic yeast strains and to investigate the ability of some of these food grade yeasts to prevent experimental colitis in mice. METHODS: In vitro immunomodulation was assessed by measuring cytokines [interleukin (IL)-12p70, IL-10, tumor necrosis factor and interferon γ] released by human peripheral blood mononuclear cells after 24 h stimulation with 6 live yeast strains (Saccharomyces ssp. ) and with bacterial reference strains. A murine model of acute 2-4-6-trinitrobenzene sulfonic acid (TNBS)-colitis was next used to evaluate the distinct prophylactic protective capacities of three yeast strains compared with the performance of prednisolone treatment. RESULTS: The six yeast strains all showed similar non-discriminating anti-inflammatory potential when tested on immunocompetent cells in vitro . However, although they exhibited similar colonization patterns in vivo , some yeast strains showed significant anti-in flammatory activities in the TNBS-induced colitis mod el, whereas others had weaker or no preventive effect at all, as evidenced by colitis markers (body-weight loss, macroscopic and histological scores, myeloperoxidase activities and blood inflammatory markers). CONCLUSION: A careful selection of strains is required among the biodiversity of yeasts for specific clinical studies, including applications in inflammatory bowel disease and other therapeutic uses.