The breast milk and childhood gastrointestinal microbiotas and disease outcomes: a longitudinal study

We aimed to characterize breast milk microbiota and define associations with saliva and fecal microbiota and selected diseases in preschool children.

In a longitudinal cohort study, the microbiotas from breast milk, mouth, and fecal samples were characterized by 16S rRNA gene sequencing. Questionnaires and medical records provided information on demographics, medical, and dental data.

The phylogeny in breast milk, saliva swabs, and feces differed at all levels (p < 0.0003), though all harbored species in Streptococcus, Veillonella, and Haemophilus. Species richness was highest in breast milk with increasing resemblance with the oral swab microbiota by increasing age. Caries-affected children at age 5 had been fed breast milk with tenfold higher abundance of caries-associated bacteria, e.g., Streptococcus mutans, than caries-free children (p < 0.002). At that age, taxa, e.g., Neisseria sicca were overrepresented in saliva swabs of children with otitis media (LDA score >2, p < 0.05). Gut symbionts, e.g., Bacteroides, were underrepresented in 3-month fecal samples in children later diagnosed with allergic disease (LDA score >2, p < 0.05).

Distinct microbiotas for the three sources were confirmed, though resemblance between milk and oral swab microbiota increased by age. Future studies should evaluate if the observed associations with disease outcomes are causal.

Few studies have studied the association between breast milk microbiota and gastrointestinal microbiota beyond early infancy. The present study confirms distinct microbiota profiles in breast milk, saliva swabs, and feces in infancy and indicates increasing resemblance between breast milk and the oral microbiota by increasing age. The fecal microbiota at 3 months was associated with later allergic disease; the saliva microbiota by age 5 differed between children with and without otitis media at the same age; and children with caries by age 5 had been fed breast milk with a higher abundance of caries-associated bacteria.