Composition and Variation of the Human Milk Microbiota Are Influenced by Maternal and Early-Life Factors.
Moossavi S, Sepehri S, Robertson B, Bode L, Goruk S, Field CJ, Lix LM, de Souza RJ, et al.
Cell Host Microbe. 2019 Feb 13;25(2):324-335.e4
COMMENT: The breastmilk contains a complex community of bacteria but the determinants of milk microbiota are mostly unknown. This study uses multiple analytic approaches to analyze the human milk microbiota in a large population cohort and provides evidence that its composition and diversity are influenced by maternal factors, early life events, breastfeeding practices, and other milk components. The impact of milk microbiota on infant gut microbiota and health could have important implications for microbiota-based strategies for early-life prevention of chronic conditions.
The objective of this study was to profile the milk microbiota in a large sample of healthy mother-infant dyads and examine the association of maternal, infant, early-life, and milk factors with milk microbiota composition.
Milk microbiota is dominated by inversely correlated Proteobacteria and Firmicutes with high inter-individual variability
18 unique phyla were detected, with the majority of taxa detected belonging to Proteobacteria, Firmicutes, Actinobacteria and Bacteroidetes.
At the genus level, the most abundant taxa were Streptococcus, Ralstonia and Staphylococcus.
We identified four main clusters within the milk microbiota and found that mode of breastfeeding was significantly associated with milk microbiota composition.
we used hierarchical clustering to identify inherent patterns in the milk microbial community, finding four main clusters. While C1 was dominated by Enterobacteriaceae, Moraxellaceae, and Pseudomonadaceae, C2 had the highest relative abundances of Streptococcaceae and Staphylococcaceae as well as low abundance of potential reagent contaminants.
Indirect breastfeeding was independently associated with lower milk bacterial richness and diversity
Among the many factors examined, only mode of breastfeeding was associated with differential relative abundance for a few individual taxa (…) Gemellaceae, Vogesella, and Nocardioides had higher relative abundances with direct breastfeeding whereas Enterobacteriaceae and Pseudomonas were relatively more abundant with indirect breastfeeding.
additional factors including exclusive breastfeeding, lactation stage, parity, maternal BMI, ethnicity, and infant sex were significantly associated with the milk microbiota composition, albeit with very low redundancy values (each accounting for <1% of the variation in the milk microbiota). The fact that these factors were associated with overall microbiota composition, but not with cluster membership, suggests their influence on the non-core (inter-individual variable) component of the milk microbiota
Structural Equation Modeling Identifies Mode of Breastfeeding as a Key Determinant of Milk Microbiota, and Defines Other Causal Pathways Influencing Milk Composition
..mode of breastfeeding was the only consistent factor directly associated with the milk microbiota composition.
Overall, the CFA (confirmatory factor analysis) suggests that (1) mode of breastfeeding directly influences the milk microbiota, and (2) maternal diet influences BMI, which affects non-bacterial milk components that do not directly influence milk microbiota.
Indirect Breastfeeding Is Associated with Enrichment of Potential Pathogens and Depletion of Bifidobacteria in Milk Microbiota
The results suggest that direct breastfeeding facilitates acquisition of oral microbiota while indirect breastfeeding leads to enrichment by environmental (pump-associated) bacteria.
Notably, the many factors that were evaluated collectively explained less than a third of the total variation observed in milk microbiota composition, indicating that other unmeasured factors are contributing to the large inter-individual variation in milk microbiota profiles.
Our results suggest that multiple maternal, infant, and environmental factors interactively influence milk microbiota composition.
Most strikingly, indirect breastfeeding and pump expression were consistently associated with milk microbiota composition, highlighting the importance of breastfeeding practices.
Infant sex differences were also identified, as well as potential associations between microbiota and other milk components.