Breast Milk Contains Over 700 Bacteria Species

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Humans carry around loads of living bacteria that are crucial for good health, and through breast-feeding, infants make some of their first contact with beneficial microorganisms that will colonize their body. Scientists have discovered that breast milk contains more species of bacteria than originally expected — more than 700 varieties.

The bacteria's exact role is still unclear, but this microbial diversity could help the baby to digest the milk or to give the infant's immune system a boost, researchers say. And further investigations could lead to nutrition strategies for babies who cannot be breast-fed.

The microbiome of breast milk was mapped out using a DNA sequencing technique known as pyrosequencing, which generates extremely large numbers of small DNA "tags" copied from the genes of organisms being examined. Scientists can sort out different species by looking at variations in DNA sequences that code for a molecule universal among all living cells.

For their study, researchers examined both colostrum, which is the first secretion of the mammary glands after birth, and breast milk from mothers from one to six months after giving birth. The latter samples contained bacteria typically found in the mouth, such as Veillonella, Leptotrichia and Prevotella, the scientists found. [8 Odd Facts About Breasts]

"We are not yet able to determine if these bacteria colonize the mouth of the baby or whether oral bacteria of the breast-fed baby enter the breast milk and thus change its composition," researchers María Carmen Collado of the Institute of Agrochemistry and Food Technology and Alex Mira of the Higher Public Health Research Center, both in Spain, said in a statement.

Among other findings of the study, the breast milk of overweight mothers and mothers who had planned caesareans contained a lower diversity of bacteria species compared with that of other moms. (Mothers who had unplanned caesareans showed breast milk composition that was very similar to that of mothers who had a vaginal birth, the researchers noted.)

"If the breast milk bacteria discovered in this study were important for the development of the immune system, its addition to infant formula could decrease the risk of allergies, asthma and autoimmune diseases," the authors conclude.

The results have been published in the American Journal of Clinical Nutrition.

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