The neonatal and maternal nasal microbiomes are compositionally diverse and functionally distinct within 24 hours of birth.

BACKGROUND: The nasal microbiome provides a first line of defense at the respiratory mucosa, yet its composition immediately after birth and its relationship to the maternal nasal community remain poorly defined. METHODS: We used 16S rRNA gene sequencing to compare anterior nares swabs collected within 24 hours of delivery from mothers (n=25) and newborns (n=34), including 22 maternal-newborn dyads. RESULTS: The neonatal nasal microbiome was significantly more diverse than the maternal microbiome, with higher Shannon diversity, and the two communities were compositionally distinct by weighted UniFrac analysis. Maternal samples were dominated by Corynebacterium and Dolosigranulum, genera characteristic of a stable, healthy adult nares, whereas newborn samples were enriched for Lactobacillus, Burkholderia-Caballeronia-Paraburkholderia, Acinetobacter, and Streptococcus. Predicted functional profiling with PICRUSt2 indicated that, relative to mothers, neonatal communities had greater predicted capacity for degradation of aromatic and xenobiotic compounds, biosynthesis of antimicrobial secondary metabolites (including polyketides, β-lactams, and terpenoids), and lipid metabolism. CONCLUSIONS: Together, these findings show that the newborn nasal cavity is not a sparsely colonized niche but instead harbors a compositionally diverse and functionally versatile microbial community that is distinct from the maternal nares in both membership and predicted metabolic potential. These results identify the perinatal period as a critical window for nasal microbial colonization, with potential implications for the trajectory of infant respiratory health.