A Milk‐Oriented Microbiota (MOM) in Infants: Lessons from Your Other MOM

Human milk contains numerous components that shape the microbial content of the developing infant gastrointestinal tract. A prominent feature of milk is an array of complex free glycans and glycoconjugates that serve a passive immune function by deflecting pathogens while simultaneously enriching a protective microbiota often dominated by bifidobacteria. Human milk glycan structures are also host‐specific and these structural variations differentially influence the composition and function of the microbiota populations enriched. Infant‐borne bifidobacteria utilize human milk glycans as a carbon source for growth however the specific deconstruction mechanisms vary by glycan‐type. These bifidobacteria contain glycosidases and transport systems required to utilize milk glycans either by internalizing large glycans or degrading them extracellularly followed by import and catabolism of specific components. Growth on milk glycans also enhances bifidobacterial interaction with the host through direct and indirect routes—increasing bifidobacterial binding to epithelial cells and producing short chain fatty acids that beneficially modulate host immunity and barrier function. In aggregate, these studies suggest a co‐evolutionary relationship between mammalian milk glycans, infant‐borne bifidobacteria and the infant host that has enabled a programmed enrichment of a protective microbiota during a critical stage of infant development. Importantly, analysis of this natural system serves as a key model for design of probiotic and prebiotic‐based manipulation of the gut microbiota in a range of health settings.