Peanut allergy can be life-threatening, yet people with similar peanut-specific antibodies often react very differently. A new study suggests that bacteria in the mouth and upper gut may help explain why.
The research, published in Cell Host & Microbe, combined human sampling with preclinical experiments to examine whether specific microbes can break down peanut allergens and influence the severity of IgE-mediated reactions. The findings point to a biological pathway that could improve risk prediction in the future, but they do not show that altering the microbiome prevents anaphylaxis.
“Peanut allergies can cause serious reactions like difficulty breathing, and in some cases, can even be life threatening,” said Liam Rondeau, a postdoctoral fellow at McMaster University’s Farncombe Family Digestive Health Research Institute. “However, some people with peanut allergies can still eat small amounts without having a reaction. We were curious about why this happens, and we discovered the answer while studying the microbes in our mouth.”
Researchers analyzed saliva and upper gut samples from healthy volunteers and identified several bacterial species capable of breaking down major peanut allergens. Among them, Rothia species stood out for reducing the ability of peanut proteins to bind with IgE antibodies, a key step in triggering allergic reactions.
The team also examined a cohort of people with peanut allergies and found that those with a greater abundance of allergen-degrading bacteria tolerated higher amounts of peanut before reacting. The findings were validated in an external dataset of 120 children, where Rothia species were more abundant in children with higher peanut reaction thresholds.
In preclinical experiments, the bacteria reduced the amount of peanut allergen reaching the bloodstream, lowered activation of immune cells involved in anaphylaxis and led to milder reactions following exposure.
“Microbes in the mouth and gut play an important role in digestion,” said co-senior author Alberto Caminero Fenandez, an associate professor in McMaster’s Department of Medicine. “In our study, we found evidence that some of these microbes may help break down peanut components in ways that could influence allergic responses. These findings point to a newly identified pathway linking the oral and gut microbiome with food allergy, and they may help guide future work on prediction and treatment.”
The study did not test a probiotic or microbiome intervention in people with peanut allergy. It did not show that increasing Rothia or other bacteria will prevent severe reactions in real-world settings. Strict avoidance remains the standard management approach, and any changes to treatment should be guided by an allergist.
For now, the findings offer a clearer explanation for why antibody levels alone do not predict reaction severity and suggest the microbiome may be part of that equation.
Funding was provided by the New Frontiers in Research Fund, Natural Sciences and Engineering Research Council of Canada, the Farncombe Institute, Nutricia Research Foundation, the European Food Safety Authority, programs of the Spanish government and Instituto de Salud Carlos III, the Canadian Institutes of Health Research, Crohn’s and Colitis Canada and the Community of Madrid.