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Gut Microbes. 2019 Nov 4:1-10. doi: 10.1080/19490976.2019.1667722. [Epub ahead of print]

Origins of human milk microbiota: new evidence and arising questions.

Moossavi S1,2,3,4, Azad MB2,3,5.

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Department of Medical Microbiology and Infectious Diseases, University of Manitoba, Winnipeg, MB, Canada.
Children's Hospital Research Institute of Manitoba, Winnipeg, MB, Canada.
Developmental Origins of Chronic Diseases in Children Network (DEVOTION), Winnipeg, MB, Canada.
Digestive Oncology Research Center, Digestive Disease Research Institute, Tehran University of Medical Sciences, Tehran, Iran.
Pediatrics and Child Health, University of Manitoba, Winnipeg, MB, Canada.


Human milk contains a diverse community of bacteria. The growing appreciation of commensal microbes and increasing availability of high-throughput technology has set the stage for a theory-driven approach to the study of milk microbiota, and translation of this knowledge to improve maternal and child health. We recently profiled the milk microbiota of healthy Canadian mothers and applied theory-driven causal modeling, finding that mode of breast milk feeding (nursing directly at the breast vs. pumping and feeding breast milk from a bottle) was significantly associated with milk microbiota composition. This observation could reflect an increased exposure to pumps and/or a decreased exposure to the infant mouth. Either way, it provides evidence for the retrograde mechanism of milk inoculation. Here, we discuss the implications of this research and related controversies, and raise new questions about the origins and function of milk bacteria.


Breastfeeding; CHILD cohort; entero-mammary pathway; milk microbiota; pump; retrograde inoculation

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