In vitro effects of Bifidobacterium lactis-based synbiotics on human faecal bacteria

Synbiotic supplements contain pre- and probiotics and are used to modulate gut microbiota composition. This study aimed to investigate effects of two synbiotic mixtures on human faecal bacteria in vitro. Short chain fructooligosaccharides (FOS) (1% w/v) combined with either Bifidobacterium lactis Bb12 or Bifidobacterium lactis HN019 (10⁶ colony-forming units (CFU)/mL)] were added to pH-controlled anaerobic batch cultures inoculated with human faeces. Maltodextrin (1% w/v), FOS (1% w/v) and the probiotic strains were also tested individually. Effects on bacteria, short-chain fatty acids (SCFAs) and branched-chain fatty acids (BCFAs) were assessed over 48 h. With maltodextrin, FOS and the synbiotic mixtures, there was a significant increase in total bacteria and bifidobacteria numbers, compared to the negative control or probiotics alone. Increases in Atopobium cluster and Clostridium coccoides-Eubacterium rectale group occurred with FOS and maltodextrin, respectively. Additionally, maltodextrin, FOS and synbiotics resulted in a greater production of acetate and butyrate (SCFAs) compared to the negative control and probiotics alone, whereas concentrations of iso-valerate (BCFA) were lower with these treatments. In conclusion, synbiotic-induced in vitro bacterial changes and changes in SCFAs concentrations were not different from those observed with FOS alone. These data suggest that metabolic effects of these synbiotics are largely driven by the prebiotic component.