Abstract/Summary

Aims The present study aimed to explore microbial production of neurotransmitters related to cognitive function in the faecal microbiota of healthy older adults, and assess whether a multi-strain probiotic formula may influence production of these neuroactive metabolites, short-chain fatty acids, and the bacterial community. Method and results The current study employed a three-stage continuous culture system with faecal microbiota from three healthy older adult donors. Neuroactive compounds were quantified using liquid chromatography mass spectroscopy, SCFAs using gas chromatography, and the bacterial community was assessed using fluorescence in situ hybridization with flow cytometry and 16S rRNA sequencing. Addition of the probiotic supplement (Bifidobacterium lactis W51, Bifidobacterium lactis W52, Lactobacillus acidophilus W37, Lactobacillus salivarius W24, Lactobacillus casei W56, Bifidobacterium bifidum W23, Lactobacillus brevis W63, Lactococcus lactis W19, Lactococcus lactis W58) significantly increased the relative abundance of Lactococcus lactis in the transverse region, alongside a trend for increased Roseburia across the three colon regions modelled, valerate in the distal region, and GABA in the proximal region. Conclusions While administration of the probiotic only had a small effect of trending increases in the synthesis of GABA and valerate, this highlights important mechanisms by which probiotics could be involved in the gut-brain axis. The model also enabled the observation of limited microbial production of other neurotransmitters. Further exploration in human studies is therefore warranted. Probiotics were confirmed to lead to microbial changes, both directly (Lactococcus) and indirectly (Roseburia). This research helps to support mechanistic understanding of probiotics and the gut-brain axis.