The triad of maternal gut-breast milk-infant gut microbial transmission in early life as a critical pathway for microbial inheritance.

Although maternal microbial inheritance is recognized, the temporal dynamics of how the maternal gut microbiota shapes the infant gut microbiota via specific routes remain unexplored. We performed longitudinal, multi-site microbiota sampling in 30 mother-infant pairs (including 14 exclusive breastfeeding and 16 mixed breastfeeding) from birth to one month, stratified by lactation stages. To trace the origin of breast milk microbiota, we also analyzed colostrum and gut samples from 8 postpartum mothers separated from their infants. Using 16S RNA sequencing, we analyzed microbial diversity and correlations across lactation stages. The results demonstrated that the gut microbiota of exclusively breastfed newborns on the first day primarily originated from breast milk and exhibited remarkably high diversity. We identified maternal gut-breast milk-infant gut transfer as a key pathway for microbial inheritance, with Bifidobacteria being a compelling example. These findings provide evidence for this route as a mechanism for inherited microbial diversity.