Perinatal factors influencing the earliest establishment of the infant microbiome

Background: While extensive research exists on the human microbiome, a number of outstanding questions remain regarding the infant microbiome in the initial stages of life. This study aimed to determine the timing of very early microbial colonization in humans, assess the contribution of maternal microbial sources to their offspring and examine the effects of perinatal factors such as delivery mode, gestational age, and feeding practices on the maternal and infant microbiota in early life. Methods: Using a cohort of 18 healthy mother-infant dyads, maternal saliva (within 24 h postpartum), vaginal (1 h prepartum), and placental (1 h postpartum) samples were collected. From their corresponding infants, saliva (within 24 h postpartum) and meconium (within 96 h postpartum) samples were collected. 16S rRNA amplicon sequencing was utilized to assess the taxonomic and inferred functional compositions of the bacterial communities from both mothers and infants. Results: Our results consolidate and corroborate recent findings addressing the existence of a meconium microbiome and the absence of a placental microbiome. We show that significant sharing of microbiota, primarily Streptococcus and Veillonella species, between the maternal oral cavity and the infant oral cavity occurs in early life. Perinatal factors such as vaginal delivery and exclusive breastfeeding were strongly associated with enhanced microbial richness and diversity in infants. Conclusions: This study provides information on the relationship between health and delivery factors and the first establishment of the infant microbiota. These findings could offer valuable guidance to clinicians and mothers in optimizing the infant microbiota toward health during infancy and later life.