THE INFANT microbiome, the community of microbes living in a baby’s gut, is crucial for immune, metabolic, and digestive development. While it is well established that mothers seed much of this microbiome around birth, new research suggests that nursery life quickly becomes just as influential, with babies extensively sharing gut microbes with one another during their first year.
Peer Contact and the Infant Microbiome
In a detailed study tracking gut bacteria in babies, families, and nursery staff, researchers found that baby-to-baby transmission plays a major role in shaping the infant microbiome. Using over 1,000 stool samples collected across the first year of nursery attendance, the team showed that within just 1 month, babies were already acquiring microbial strains from peers in their nursery group.
By the end of the first term, microbes picked up at nursery made up a proportion of the infant microbiome comparable to those acquired from family members. Over time, peer-derived strains became even more prominent, sometimes exceeding maternal and household contributions.
What this Means for Gut Health
For clinicians, the key message is that the infant microbiome is highly social. Close contact between babies (shared spaces, toys, and daily interactions) creates dense networks of microbial exchange. Some bacterial strains spread widely within a class, in patterns resembling outbreaks, but without causing disease.
Notably, many of these shared microbes included beneficial early-life gut colonisers such as Bifidobacterium species, which are linked to healthy digestion and immune development. The findings reinforce that not all microbial spread is harmful; some may support healthy microbiome maturation.
Antibiotics, Siblings, and Resilience
The study also highlights factors that influence how the infant microbiome develops. Babies with siblings had higher microbial diversity and were less likely to acquire strains from nursery peers, suggesting early exposure at home offers some protection. In contrast, antibiotic use was the strongest driver of change, temporarily disrupting the microbiome but followed by rapid re-colonisation through new strain acquisition.
This fast recovery was more pronounced in babies than adults, underlining both the vulnerability and adaptability of the infant microbiome during early life.
Real-World Implications
Overall, the findings reposition social interaction as a central driver of infant microbiome development. While they do not suggest changes to infection control practices, they may inform future thinking about antibiotic stewardship, nursery environments, and early-life health: recognising that everyday peer contact helps build, not just challenge, a healthy gut ecosystem.
Reference
Ricci L et al. Baby-to-baby strain transmission shapes the developing gut microbiome. Nature. 2026;DOI:10.1038/s41586-025-09983-z.
