The impact of widespread antibiotic use in the creation of drug-resistant bacteria has been widely discussed, but a recent study suggests another damaging side effect. The elimination of ‘good’ bacteria in the stomach and intestines could be a contributing cause to the heretofore mysterious rise in food allergies.
A class of bacteria commonly found in the guts of people — and rodents — appears to keep mice safe from food allergies, a study suggests. The same bacteria are among those reduced by antibiotic use in early childhood. The research fits neatly into an emerging paradigm that helps explain a recent alarming increase in food allergies and other conditions, such as obesity and autoimmune disease, and hints at strategies to reverse the trend.
Food allergies have increased about 50% in children since 1997. There are various theories explaining why. One is that the 21st century lifestyle, which includes a diet very different from our ancestors’, lots of antibiotic use, and even a rise in cesarean section deliveries, has profoundly changed the makeup of microbes in the gut of many people in developed countries. For example, the average child in the United States has taken three courses of antibiotics by the time he or she is 2 years old, says Martin Blaser, an infectious disease specialist and microbiologist at New York University in New York City.
Cathryn Nagler, an immunologist at the University of Chicago in Illinois, has spent years probing links between the immune system, intestinal bacteria, and the onset of allergies. Back in 2004, she and her colleagues reported that wiping out gut bacteria in mice led to food allergies. Since then, Nagler has continued trying to understand which bacteria offer allergy protection and how they accomplish that. In one of the latest efforts, Nagler’s team first confirmed that mice given antibiotics early in life were far more susceptible to peanut sensitization, a model of human peanut allergy. Then, they introduced a solution containing Clostridia, a common class of bacteria that’s naturally found in the mammalian gut, into the rodents’ mouths and stomachs. The animals’ food allergen sensitization disappeared, the team reports online today in the Proceedings of the National Academy of Sciences. When the scientists instead introduced another common kind of healthy bacteria, called Bacteroides, into similarly allergy-prone mice, they didn’t see the same effect. Studying the rodents more carefully, the researchers determined that Clostridia were having a surprising effect on the mouse gut: Acting through certain immune cells, the bacteria helped keep peanut proteins that can cause allergic reactions out of the bloodstream. “The bacteria are maintaining the integrity of the [intestinal] barrier,” Nagler says.