It seems counterintuitive that breastmilk would be anything but sterile—human infants have a naïve and immature immune system and their first food should be free of potential pathogenic organisms, right? But study after study demonstrates that milk indeed contains microbes. Precisely where these microbes originate and how they make their way into human milk, however, is still being worked out. There are two, non-mutually exclusive hypotheses to explain their origins: one argues that milk microbes originate from the mother’s gut and are passed to the mammary gland (entero-mammary translocation) and the other that bacteria from the infant’s oral cavity move back into the mammary gland and influence the types and quantities of bacteria passed via milk (retrograde inoculation). Because not all milk microbes are equally beneficial for the infant, finding support for one or both of these hypotheses offers the potential of modifying the milk microbiome in ways that could improve infant outcomes. Read More...

Proteins in food often suffer from mistaken identity. Instead of being seen as the innocuous food items they are, immune systems instead take these proteins for harmful invaders and mount a response. To understand why some immune systems are sensitized to cow milk protein whereas others have an inappropriate reaction, researchers are turning to gut bacteria. In animal models and in humans, food allergies have been associated with a lack of diversity in gut bacteria species. And specific research on cow’s milk allergy (CMA) suggests that there might be particular species of gut bacteria that can prevent the development of allergy or allow for complete resolution of CMA in late infancy or early childhood. Read More...