Combined effect of Lactobacillus acidophilus NCFM and cellobiose on composition of human gut microbiota and production of short-chain and branched-chain fatty acids: A randomized double-blinded cross-over trial

Background: The gut microbiota seems to play a role in host health and has received increasing attention. Probiotics, prebiotics and combinations thereof, have been reported to modulate the gut microbiota of humans thereby potentially exerting health beneficial effects. The objective of this study was to investigate the effects of a novel combination of probiotic bacteria and potential prebiotic on the composition and fermentation activity of human gut microbiota. Methods: Healthy volunteers (n =18) were enrolled in a double-blinded, randomized, placebo-controlled crossover trial and received synbiotic (Lactobacillus acidophilus NCFM (109 CFU) and cellobiose (5g)) or placebo daily for three weeks. Fecal samples were collected after each intervention period and Lactobacilli numbers were quantified by qPCR, and for the first time 454 tag encoded pyrosequencing was used to investigate the effect of synbiotic on the composition of the microbiota. The fermentation activity of the gut microbiota, i.e. production of short-chain and branched chain fatty acids, was measured by gas chromatography. Results and conclusions: The distribution of sequences was found to be in general agreement with previous studies. The synbiotic increased levels of Lactobacillus spp. and the relative abundance of genera Bifidobacterium, Collinsella and Eubacterium (p < 0.05). Also a decrease in relative abundance of genus Dialister (p = 0.03). In four volunteers the synbiotic was able to induce shifts in the abundances of Bacteroides, Prevotella and Ruminococcus, which are believed to form enterotypes of the human gut microbiota. No change in the production of short-chain fatty acids was seen, however the synbiotic increased concentrations of branched-chain fatty acids as compared to baseline. Therefore this novel combination shows potential as a synbiotic, and the findings of this study contribute to the understanding of how synbiotics affect the composition and activity of the human gut microbiota. Moreover the findings indicate that this novel synbiotic combination may be used to induce shifts in composition of the microbiota.