The effect of prebiotics, probiotics, synbiotics and zinc carnosine on bacterial metabolism in an in vitro gut model fermentation system

In Western populations up to one in four individuals meet the criteria for functional gastrointestinal disorder. Modulation of the gut microbiota composition and bacterial metabolism may improve this and the main driver for these alterations is through dietary components. Prebiotics, probiotics and synbiotics have previously been shown to modulate the gut microbiota. Therefore the aim was to investigate the bacterial metabolism following a wheat dextrin, partially hydrolysed guar gum, inulin, Bifidobacterium lactis HN019, Lactobacillus acidophilus NCFM and zinc carnosine intervention in an in vitro batch culture and three stage continuous culture gut model system. A secondary aim was to investigate impact of the interventions on Irritable Bowel Syndrome-Diarrhoea and compare this to healthy donors. The third aim was to assess the impact of zinc carnosine on the gut microbiota. Samples were collected at multiple time points and used to enumerate bacteria through fluorescence in situ hybridisation flow-cytometry, organic acid production via gas chromatography and neurotransmitter gamma-aminobutyric acid through liquid chromatography-mass spectrometry. The main findings were that partially hydrolysed guar gum and wheat dextrin were metabolised by Bacteroides and Clostridium cluster IX and produced propionate with partially hydrolysed guar gum being fermented to a greater extent. The addition of a probiotic strain led to no changes in bacterial metabolism. Inulin led to an increase in Bifidobacterium spp., which was prolonged by a synbiotic. The production of gamma-aminobutyric acid was significantly increased in healthy donor inocula following prebiotic and synbiotic interventions but this was not seen in the Irritable Bowel Syndrome-Diarrhoea group. Additionally, zinc carnosine may promote Bifidobacterium spp., and lactic acid bacteria but further research is required as some bacterium in the Clostridium histolyticum group are pathogenic and these were also elevated. Overall, the prebiotic had a greater impact on the gut microbiota although, synbiotics did have positive influences on the gut microbiota of both healthy and Irritable Bowel Syndrome-Diarrhoea donors