New research shows that healthy infants have intestinal bacteria that prevent the development of food allergies, findings that could impact the treatment of a disease that now affects 15 million Americans.

Researchers from the University of Chicago, Argonne National Laboratory and the University of Naples Federico II in Italy discovered that when gut microbes from healthy human infants were transplanted into germ-free mice, the animals were protected from an allergic reaction when exposed to cow’s milk.

Gut microbes from infants allergic to milk did not offer the same protection; mice receiving these bacteria suffered an allergic reaction when given cow’s milk. Cow’s milk allergy is the most common food allergy affecting children.

The study, published this week in Nature Medicine, also identifies a specific bacterial species that protects against allergic responses to food. “This study allows us to define a causal relationship and shows that the microbiota itself can dictate whether or not you get an allergic response,” said Cathryn Nagler, the Bunning Food Allergy Professor at UChicago and senior author of the study.

Nagler has been researching the physiological origins of tolerance to dietary antigens for more than 30 years. She is the co-founder and president of ClostraBio, an innovative startup company that is working to develop microbiome-based treatments for food allergies.