Ex vivo impact of human milk oligosaccharides and lactose on microbiome in infants with cow's milk protein allergy

Cow’s milk protein allergy (CMPA) is the most common food allergy in infancy. CMPA is associated with gut microbial dysbiosis, characterized by low Bifidobacteriaceae levels. This study investigated the impact of a human milk oligosaccharide (HMO) mixture of 2’-fucosyllactose (2’-FL) and lacto- N -neotetraose (LNnT), as well as lactose (L), on the fecal microbiome of infants with clinically diagnosed CMPA (n=12), using the ex vivo intestinal fermentation SIFR technology. The fecal microbiota displayed considerable heterogeneity, with low abundances of Bifidobacteriaceae found in most infants, except two breastfed infants. HMO and lactose both enriched Bifidobacteriaceae via stimulation of Operational Taxonomic Units (OTUs) related to B. breve , B. longum , B. pseudocatenulatum and, for HMO+L, also B. bifidum . All supplementations significantly boosted the production of acetate, propionate, aromatic lactic acids and N-acetylated amino acids, with additive effects observed for combining HMO+L. Additional contributors to HMO fermentation were OTUs related to Bacteroides fragilis, Blautia obeum/wexlerae and Ruminococcus gnavus, while OTUs related to Escherichia coli and Veillonella parvula were involved in lactose fermentation, suggesting involvement of substrate-specific fermentation pathways. In conclusion, the observed bifidogenic effect of HMO confirms the potential of 2’-FL and LNnT to ameliorate CMPA-associated dysbiosis, with additive effects found for the abundance of B. bifidum and bifidobacterial metabolite levels. The clinical significance of the partial reversal of fecal microbial dysbiosis and enhanced production of beneficial metabolites on the clinical course of CMPA requires further investigation.