Impact of two human milk oligosaccharides and lactose on the faecal microbiome of infants with probable cow’s milk allergy

Cow's milk protein allergy (CMPA) in infancy is associated with intestinal microbial dysbiosis, characterised by low Bifidobacteriaceae levels. The present study aimed to investigate the impact of two human milk oligosaccharides (HMO), lactose (L), and their combination on the faecal microbiome and metabolome of infants with CMPA. Stool samples of 12 term infants with probable CMPA (mean age 4.3 months) were analysed using a validated intestinal fermentation assay (SIFR® technology). For each substrate (i.e. HMO (2'-fucosyllactose [2'-FL] and lacto-N-neotetraose [LNnT]), L and HMO + L), taxonomic microbiome characterisation and untargeted metabolite profiling were performed at multiple timepoints. At baseline, the tested faecal microbiota overall displayed low abundances of Bifidobacteriaceae. Fermentation with either HMO or lactose significantly enriched Bifidobacterium breve, Bifidobacterium longum, Bifidobacterium pseudocatenulatum and, for HMO + L, also Bifidobacterium bifidum. The increase in HMO-utilising bifidobacteria was associated with a significant rise in levels of short-chain fatty acids, aromatic lactic acids and N-acetylated amino acids, with additive effects being observed for HMO + L. The above data suggest that the combination of 2'-FL, LNnT and lactose helps to alleviate the previously reported CMPA-associated intestinal bacterial dysbiosis and induces the production of several beneficial metabolites. The clinical significance of these findings for infants with CMPA requires further investigation.