A synbiotic concept containing spore-forming Bacillus strains and a prebiotic fiber blend consistently enhanced metabolic activity by modulation of the gut microbiome in vitro

A standardized <i>in vitro</i> simulation of the human gastrointestinal tract (M-SHIME®) was used to assess the effect of repeated daily administration of a synbiotic formulation, containing five spore-forming <i>Bacillus</i> strains and a prebiotic fiber blend, on the microbial activity and composition of three simulated human subjects. Firstly, while confirming recent findings, deeper phylogenetic insight was obtained in the resident M-SHIME® microbiota, demonstrating that the model maintains a diverse and representative, colon region-specific luminal and mucosal microbial community. Supplementation of the synbiotic concept increased microbial diversity in the distal colon areas, whereas specific enhancement of <i>Bacillaceae</i> levels was observed in the ascending colon suggesting a successful engraftment of the <i>Bacillus</i> spores, which probably resulted in a stimulatory effect on, among others, <i>Bifidobacteriaceae</i>, <i>Lactobacillaceae, Prevotellaceae</i>, <i>Tannerellaceae</i> and <i>Faecalibacterium prausnitzii</i> contributing directly or indirectly to stimulation of acetate, propionate and butyrate production. When compared with a previous study investigating the <i>Bacillus</i> strains, the generated data suggest a synergistic effect on the intestinal microbiota for the synbiotic formulation. Given the fact that the probiotic strains have been shown to impact post-prandial metabolic endotoxemia in human individuals, it might be interesting to further investigate the efficacy of the synbiotic concept in protecting against obesity-related disorders.