Composition of the human milk microbiome in the GUSTO cohort is shaped by intrapartum antibiotic prophylaxis and breastfeeding exclusivity

Abstract

Human milk exposes infants to a constant source of maternal bacteria that may influence the development of the infant immune system and gut microbiome. However, compared to other body niches, the human milk microbiome is relatively under-studied, and there is limited consensus on the factors driving variance in these bacterial communities. In this study, we performed in-depth microbiome profiling of milk samples from 208 mothers in a diverse Asian population, finding a high level of variation between individuals and over time. We found that factors such as delivery-related antibiotics, breastfeeding practices, and maternal lifestyle can influence which bacteria are present in milk. These findings suggest that the milk microbiome is not static, but dynamic and shaped by both medical and social factors. Understanding what drives variance in the milk microbiome could help inform strategies to support maternal and infant health, especially in the critical early months of life when microbial exposures can have long-term effects.