Differential Establishment of Bifidobacteria in the Breastfed Infant Gut.

The composition of an infant's gut microbiome can impact their immediate and long-term health. Bifdobacteria play a major role in structuring the gut microbiome of breastfed infants due to their ability to consume oligosaccharides found in human milk. However, recent studies have revealed that bifidobacteria are often absent in the gut microbiome of breastfed infants in some locations. This lack of colonization may be due either to differences in the environmental conditions in the gastrointestinal tract of uncolonized infants which prohibit the growth of bifidobacteria or a dearth of sources from which infants may acquire these specialized bacterial species. Potential mechanisms by which these broad factors may lead to lower colonization of infants by bifidobacteria are discussed herein. Environmental conditions which may select against bifidobacteria include low rates/duration of breastfeeding, milk glycan composition, and antimicrobial use. Routes of colonization by bifidobacteria which may be disrupted include maternal transfer via vaginal birth, fecal-oral routes, or via breast milk itself. A careful contemplation of the conditions experienced by bifidobacteria over human evolutionary history may lead to further hypotheses as to the causative factors of the differential colonization by this foundation genus in some contemporary locations.