Observational study finds maternal breast milk contains beneficial bacteria for infant gut microbiome — Evidence Review
Published in Nature Communications, by researchers from University of Chicago, University of Minnesota, Oklahoma University Health Sciences Center
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Table of Contents
Scientists have found that specific gut-friendly bacteria in human breast milk, notably Bifidobacterium longum, are transmitted to infants and help seed the developing gut microbiome. Related research broadly supports these findings, consistently showing that breast milk microbiota contribute directly to infant gut colonization and overall health.
- Multiple studies confirm that the microbial communities in breast milk play a significant role in establishing the infant gut microbiome, with Bifidobacterium species frequently highlighted as dominant and beneficial 1 2 5.
- Evidence suggests both direct (vertical) transfer of specific bacterial strains from mother to infant via breastfeeding, and influences from maternal body sites and infant oral contact during nursing 2 3 5.
- The new study’s use of metagenomic analysis provides strain-level detail, building on earlier work that used less precise methods, and aligns with emerging evidence that breast milk bacteria are critical for healthy gut development and immune maturation 1 4 12.
Study Overview and Key Findings
Understanding the origins and development of the infant gut microbiome is central to advancing pediatric health, as early microbial colonization influences metabolism, nutrition, and immune system function. This new study addresses longstanding analytical challenges in characterizing the breast milk microbiome by applying metagenomic sequencing to a large, well-phenotyped cohort. By linking specific bacterial strains in breast milk to those found in infant stool, the research offers some of the clearest evidence yet for vertical microbial transmission through breastfeeding and refines our understanding of the bacterial species involved.
| Property | Value |
|---|---|
| Study Year | 2025 |
| Organization | University of Chicago, University of Minnesota, Oklahoma University Health Sciences Center |
| Journal Name | Nature Communications |
| Authors | Pamela Ferretti, Mattea Allert, Kelsey E. Johnson, Marco Rossi, Timothy Heisel, Sara Gonia, Dan Knights, David A. Fields, Frank W. Albert, Ellen W. Demerath, Cheryl A. Gale, Ran Blekhman |
| Population | Mother-infant pairs |
| Sample Size | n=507 breast milk and infant stool samples from 195 pairs |
| Methods | Observational Study |
| Outcome | Bacterial strains in mother's milk and their link to infant gut microbiome |
| Results | Milk contained B. longum, found in over 98% of infants' gut microbiomes. |
Literature Review: Related Studies
To contextualize these findings, we searched the Consensus paper database, using over 200 million research papers, to identify studies relevant to breast milk microbial transmission, infant gut microbiome development, and related health outcomes. The following search queries were used:
- breast milk gut bacteria transmission
- B. longum infant microbiome development
- breastfeeding microbiome health outcomes
Table: Key Topics and Findings from Related Studies
| Topic | Key Findings |
|---|---|
| How does breast milk contribute to infant gut microbiome development? | - Breast milk directly seeds the infant gut microbiome, with vertical transfer of specific bacterial taxa, notably Bifidobacterium species 1 2 5. - The composition and diversity of the infant gut microbiome are closely linked to breastfeeding practices and the proportion of breast milk intake 1 3 11. |
| What is the role of specific bacteria (e.g., Bifidobacterium longum) in infant health? | - B. longum and other Bifidobacterium species are prevalent in breastfed infants and are associated with healthy gut function, improved immune maturation, and reduced disease risks 6 7 9. - Supplementation or natural abundance of B. longum can lead to persistent colonization and beneficial metabolic effects 7 9. |
| What factors influence the breast milk and infant gut microbiota? | - Breastfeeding mode, maternal health, delivery method, diet, and environmental exposures can shape both breast milk and infant gut microbiota composition 3 6 12. - Retrograde flow during nursing and the entero-mammary pathway may contribute to microbial transfer from maternal sites to milk and then to the infant 2 5 12. |
| What are the broader health impacts of breast milk-derived microbes in infants? | - Exposure to breast milk microbiota is linked to reduced gut dysbiosis, decreased risk of necrotizing enterocolitis, and improved neurodevelopmental outcomes, especially in preterm infants 11 13. - Manipulating or supplementing breast milk microbiota shows potential for improving infant health outcomes 4 13. |
How does breast milk contribute to infant gut microbiome development?
Related studies consistently demonstrate that breast milk is both a source and vector for beneficial microbes that establish and shape the infant gut microbiome. The new study’s direct identification of strain-level transmission of B. longum and other bacteria aligns with earlier evidence, but adds precision about which strains are shared and how frequently this occurs.
- Breast milk supplies a significant proportion of the bacteria colonizing the infant gut, particularly in exclusively breastfed infants 1.
- Vertical transfer of viable, gut-associated anaerobes from mother to infant via breastfeeding has been documented, suggesting a direct link between maternal and infant microbial populations 2.
- The extent of transfer and resulting gut microbial diversity is influenced by breastfeeding exclusivity and duration, supporting a dose-dependent relationship 1 11.
- The use of advanced metagenomic methods in the new study allows for more detailed strain-level tracking, confirming and building upon prior findings 1 2 5.
What is the role of specific bacteria (e.g., Bifidobacterium longum) in infant health?
The predominance of B. longum in both breast milk and infant gut microbiomes observed in the new study is echoed by several prior studies. These bacteria are associated with beneficial metabolic activity, immune system development, and overall gut health.
- B. longum and related species are early colonizers of the infant gut, often independent of delivery mode or other factors 6.
- Supplementation with B. longum subsp. infantis can result in persistent colonization and improved fermentation of human milk oligosaccharides, with downstream health benefits 7.
- Specific B. longum clades are linked to improved early growth and reduced incidence of childhood diarrhea, highlighting their functional importance 9.
- The presence and abundance of Bifidobacterium species may vary by geography, feeding practices, and population, but their health-promoting effects are broadly supported 6 9 11.
What factors influence the breast milk and infant gut microbiota?
The composition of both breast milk and infant gut microbiota is shaped by a range of maternal, infant, and environmental factors. The new study’s identification of oral-associated bacteria in milk also reflects dynamic interactions during breastfeeding.
- Feeding practices, including the proportion of breast milk and the mode of feeding (direct vs. pumped), impact microbial transmission and co-occurrence in mother-infant pairs 3.
- Maternal health, delivery mode, and environmental exposures (e.g., antibiotics, diet) influence the diversity and composition of both breast milk and infant gut microbiota 6 12.
- Proposed mechanisms for microbial transfer include retrograde flow during breastfeeding and the entero-mammary pathway, both of which are supported by molecular evidence 2 5 12.
- The complexity and variability of these factors underscore the need for further research using robust, multi-omic approaches 12.
What are the broader health impacts of breast milk-derived microbes in infants?
Exposure to breast milk microbiota has been associated with significant short- and long-term health benefits, particularly in vulnerable populations such as preterm infants. The new study strengthens the case for the importance of early microbial exposures via breastfeeding.
- Exclusive breastfeeding is linked to reduced gut dysbiosis, lower rates of diarrhea, and more stable gut microbiota, with benefits persisting beyond infancy 11.
- In preterm infants, maternal breast milk reduces risks of necrotizing enterocolitis and improves neurodevelopmental outcomes, effects thought to be mediated in part by microbiome modification 13.
- Breast milk-derived microbes may also act as natural probiotics, and there is growing interest in supplementing or manipulating these communities for health benefits 4 13.
- The diversity and health-promoting properties of breast milk microbiota offer potential targets for future nutritional and therapeutic interventions 4.
Future Research Questions
Ongoing research is needed to clarify the mechanisms of microbial transfer, the functional roles of specific strains, and the long-term health implications of early-life microbial exposures. Addressing these questions will help optimize infant feeding strategies and inform potential interventions to promote healthy microbiome development.
| Research Question | Relevance |
|---|---|
| How do different strains of Bifidobacterium in breast milk affect infant health outcomes? | Understanding strain-specific effects could guide probiotic development and targeted nutritional interventions to improve infant health 7 9. |
| What is the relative contribution of breast milk, maternal skin, and infant oral microbiota to the infant gut microbiome? | Clarifying the sources of infant gut bacteria will help refine strategies for optimizing early microbial exposures and understanding transmission pathways 1 3 5. |
| How do environmental factors (e.g. antibiotics, PFAS) influence the breast milk microbiome and infant gut microbiome? | Environmental exposures may alter microbial communities in both milk and infants, with potential health implications that require further investigation 12. |
| Does the presence of pathobionts in breast milk impact infant health, and under what conditions could these bacteria cause harm? | While some potentially pathogenic bacteria are found in healthy pairs, their role and risk factors for pathogenicity in infants need clarification 10 12. |
| Can modifying the breast milk microbiome through maternal diet or probiotics improve infant gut health and development? | Interventions targeting the maternal or breast milk microbiome may offer ways to enhance infant outcomes, but robust evidence for efficacy and safety is needed 4 13. |