Does bacteria in maternal breast milk and on areolar skin around the nipple transfer to the guts of infants? A new article published by JAMA Pediatrics examined the association and the results suggest bacteria in mother’s breast milk may help to seed the infant gut.

The microbial colonization of the infant gut is a complex process and it plays an important role in lifelong health. But little is known about the transfer of breast milk microbes from mother to infant.

Grace M. Aldrovandi, M.D., of the University of California, Los Angeles, and coauthors conducted a study of 107 healthy mother-infant pairs where bacterial composition was identified with sequencing of the 165 ribosomal RNA gene in breast milk, areolar skin and infant stool samples.

Distinct and diverse bacterial communities were found in breast milk, areolar skin and stool. The infant gut microbial communities were more closely related to an infant’s mother’s milk and skin compared with a random mother, the authors report.

Estimates suggest that during the first 30 days of life, infants who breastfeed to get 75 percent of more of their daily milk intake received an average of nearly 28 percent of the bacteria from breast milk and about 10 percent from areolar skin, with the remaining nearly 62 percent coming from sources the authors did not characterize.

Changes in the infant gut bacterial community were associated with the proportion of breast feeding in a dose-dependent way, where the effect changes with the amount, according to the results.

Limitations of the study include that the origin of breast milk bacteria is unclear and that authors did not sequence other bacterial communities from the mother which may have contributed to additional bacteria in infants.

“Our study confirms a bacterial community in breast milk and tracks that community from mothers into the infant gut. Breast milk bacteria influence the establishment and development of the infant microbiome with continued impact after solid food introduction. … Our results emphasize the importance of breastfeeding in the assembly of the infant gut microbiome,” the article concludes.

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