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Appl Environ Microbiol. 2020 Mar 20. pii: AEM.02730-19. doi: 10.1128/AEM.02730-19. [Epub ahead of print]

Prebiotics inhibit proteolysis by gut bacteria in a host diet-dependent manner: a three stage continuous in vitro gut model experiment.

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Department of Food and Nutritional Sciences, University of Reading, Reading RG6 6AP, United Kingdom.
BENEO-Institute, Obrigheim, Germany.
Department of Food and Nutritional Sciences, University of Reading, Reading RG6 6AP, United Kingdom


Dietary protein residue can result in microbial generation of various toxic metabolites in the gut, such as ammonia. A prebiotic is "a substrate that is selectively utilised by host microorganisms conferring a health benefit". Prebiotics are carbohydrates that may have the potential to reverse the harmful effects of gut bacterial protein fermentation.Three-stage continuous colonic model systems were inoculated with faecal samples from omnivore and vegetarian volunteers. Casein (equivalent to 105g protein consumption per day) was used within the systems as a fermentab274; le protein source. Two different doses of inulin type fructans (Synergy1) were later added (equivalent to 10g per day in vivo and 15g per day) to assess whether this influenced protein fermentation. Bacteria were enumerated by fluorescence in situ hybridisation with flow cytometry. Metabolites from bacterial fermentation (short chain fatty acid (SCFA), ammonia, phenol, indole and p-cresol) were monitored to further analyse proteolysis and the prebiotic effect. A significantly higher number of bifidobacteria was observed with the addition of inulin, together with reduction of Desulfovibrio spp. Furthermore, metabolites from protein fermentation such as branched chain fatty acids (BCFA) and ammonia were significantly lowered with Synergy1. Production of p-cresol varied among donors as we recognised four high producing models and two low producing models. Prebiotic addition reduced its production only in vegetarian high p-cresol producers.Importance: Dietary protein levels are generally higher in Western populations than the world average. We challenged three-stage continuous colonic model systems containing high protein levels and confirmed the production of potentially harmful metabolites from proteolysis, especially replicates of the transverse and distal colon. Fermentations of proteins with a prebiotic supplementation resulted in a change in the human gut microbiota and inhibited the production of some proteolytic metabolites. Moreover, we observed both bacterial and metabolic differences between faecal bacteria from omnivore donors and vegetarian donors. Proteins with prebiotic supplementation showed higher Bacteroides spp. and inhibited clostridial cluster IX in omnivore models while in vegetarian modes, clostridial cluster IX were higher and Bacteroides spp. lowered with high protein plus prebiotic supplementation. Synergy1 addition inhibited p-cresol production in vegetarian high p-cresol producing models while the inhibitory effect was not seen in omnivore models.


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