Our study provides evidence that
Bacteroidaceae
strains present on infants’ skin within 10 min after birth, in meconium samples, and in fecal samples at 3 months of age in vaginally delivered infants are shared with their mothers. Using strain resolution analyses, we identified two strains, belonging to
Bacteroides caccae
and
Phocaeicola vulgatus
, as shared between mothers and their infants.