Breast milk contains more than 700 bacteria species

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Humans carry around loads of living bacteria that are crucial for good health, and through breastfeeding, 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.

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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 breastfed.

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.

Fort their study, researchers examined both colostrum, which is the first secretion of the mammary glands after birth, and breast milk from one to six months after birth. The latter samples contained bacteria typically found in the mouth, such as Veillonella,Leptotrichia and Prevotella, the scientists found.

"We are not yet able to determine if these bacteria colonise 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 of mothers who have a planned caesarean contains a lesser diversity of bacteria species. (Mothers who have an unplanned caesarean have a breast milk composition is very similar to that of mothers who have 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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