Clostridia encompasses about 100 bacterial species, some of which live harmlessly in the gut. Others are responsible for gangrene, tetanus, botulism food poisoning and hospital infections caused by Clostridium difficile.
The new study suggests that "friendly" Clostridia have a unique ability to block the harmful immune response behind food allergies. Tests on "sterile" mice sensitised to peanuts showed that introducing a Clostridia cocktail into their bacteria-free guts reversed their allergy.
Re-introduction of another major group of gut bacteria, Bacteroides, did not have the same effect. Tests indicated that Clostridia caused immune cells to produce high levels of a signalling molecule known to decrease permeability of the intestinal lining.This in turn reduced the chances of allergens - molecules that trigger an allergic reaction - leaking into the bloodstream.
US lead scientist Professor Cathryn Nagler, from the University of Chicago, said: "We've identified a bacterial population that protects against food allergen sensitisation.
"The first step in getting sensitised to a food allergen is for it to get into your blood and be presented to your immune system. The presence of these bacteria regulates that process." Severe food allergy can cause anaphylaxis, an extreme immune reaction that may prove fatal.
The findings appear in the journal Proceedings of the National Academy of Sciences.