An <i>in vitro</i> batch culture study to assess the fermentation of human milk oligosaccharides by faecal microbiota from healthy and irritable bowel syndrome stool donors

This study explored the effects of different human milk oligosaccharides (HMOs), solely and in combination, on gut microbiota composition and metabolic activity (organic acid production), using anaerobic <i>in vitro</i> batch culture fermenters. The aim was to compare prebiotic effects of HMOs (2'FL, 3'FL, 3'SL, 6'SL, LNT, LNnT, and 1:1 ratio mixes of 2'FL/3'SL and 3'SL/LNT) in faecal samples from irritable bowel syndrome (IBS) donors and healthy controls, and to determine the best-performing HMO in IBS. Fluorescent <i>in situ</i> hybridisation coupled with flow cytometry was utilised to study microbiota changes in major colonic genera, and organic acid production was assessed by gas chromatography. IBS donors had different starting microbial profiles compared to healthy controls and lower levels of organic acids. In response to HMOs, there were alterations in both the control and IBS faecal microbiomes. In IBS donor fermenters, <i>Bifidobacterium</i>, <i>Faecalibacterium</i>, total bacterial numbers, and organic acid production significantly increased post-HMO intervention. When comparing the effect of HMO interventions on the microbiota and organic acid production, a mix of 3'SL/LNT HMOs may be the most promising intervention for IBS patients.