A gut bacterium protected mice from cow's milk allergy

The team collected stool from infants who were healthy and from infants diagnosed with a cow's milk allergy, then gave each type of bacteria to separate groups of germ-free mice before exposing the mice to the same milk protein.

Mice colonized with bacteria from healthy infants were protected from anaphylactic reactions to the cow's milk protein, while mice given bacteria from allergic infants were not. Sequencing pointed to a single species, Anaerostipes caccae, a member of the Clostridiales group, as doing much of the protective work.

The finding suggested that a missing or altered strain of gut bacteria in infancy, rather than the food protein itself, could be a root cause of some food allergies. The work was done entirely in mice colonized with human-derived bacteria, and whether a bacterial supplement could prevent or treat allergy in infants directly has not been settled.

One missing bacterium, one allergic reaction.