Gut microbiota play a critical role in infant health. It is now accepted that breastmilk contains live bacteria from endogenous and exogenous sources, but it remains unclear whether these bacteria transfer to the infant gut and whether this process is influenced by breastmilk feeding practices. Here, we show that certain bacteria, including Streptococcus spp. and Veillonella dispar, co-occur in mothers’ milk and their infants’ stool, and co-occurrence is reduced when infants receive pumped breastmilk. The relative abundances of commonly shared species are positively correlated between breastmilk and stool. Overall, gut microbiota composition is strongly associated with breastfeeding exclusivity and duration but not breastmilk feeding mode (nursing versus pumping). Moreover, breastmilk bacteria contributed to overall gut microbiota variation to a similar extent as other modifiers of the infant microbiome, such as birth mode. These results provide evidence that breastmilk may transfer bacteria to the infant gut and influence microbiota development.

肠道菌群在婴儿健康中起关键作用。现在，人们公认母乳中含有来自内源性和外源性的活细菌，但目前尚不清楚这些细菌是否会转移到婴儿肠道，以及这一过程是否受到母乳喂养习惯的影响。在这里，我们显示了某些细菌，包括链球菌。和Veillonella dispar，母乳和婴儿粪便中共同出现，当婴儿接受抽乳时，共同发生减少。母乳和粪便之间常见物种的相对丰度呈正相关。总体而言，肠道菌群的组成与母乳喂养的排他性和持续时间密切相关，但与母乳喂养模式（护理与抽乳）无关。此外，母乳细菌与婴儿微生物组的其他修饰因子（例如分娩方式）相似，对肠道菌群整体变化的贡献程度相似。这些结果提供了证据，表明母乳可能会将细菌转移到婴儿肠道并影响微生物群的发育。