By Pat Anson, PNN Editor

Canadian researchers have identified one of the primary causes of Irritable Bowel Syndrome (IBS), a frustrating intestinal condition that causes abdominal pain, cramps, bloating, gas and diarrhea.

The culprit appears to be Klebsiella aerogenes, a strain of bacteria that causes white blood cells to produce excess amounts of histamine, a chemical that triggers a painful immune system response. Gut bacteria have long been suspected as a likely cause of IBS, but this is the first time a specific bacterial strain has been identified.  

Researchers at McMaster University and Queen’s University studied stool samples from both Canadian and American IBS patients, and found Klebsiella aerogenes in about 25 percent of them.

“We followed up these patients for several months and found high levels of stool histamine at the time when the patients reported severe pain, and low stool histamine when they were pain-free,” said senior author Premysl Bercik, MD, a gastroenterologist and professor at McMaster’s Michael G. DeGroote School of Medicine.

Further tests on laboratory mice that were colonized with gut microbes from IBS patients showed that several types of bacteria produced histamine, but Klebsiella aerogenes was a “super-producer.” The chemical is produced when histidine, an essential amino acid in animal and plant protein, is converted into histamine, triggering pain and inflammation.

“Now that we know how the histamine is produced in the gut, we can identify and develop therapies that target the histamine producing bacteria,” said first author Giada de Palma, an assistant professor of medicine at McMaster.

Researchers found that when mice colonized with histamine producing bacteria were fed a diet low in carbohydrates, histamine production dramatically decreased. That would explain the benefits of diets low in carbohydrates and high in dietary fiber, which are often recommended to IBS patients. Allergy medications that block histamine production may also be useful in treating IBS.

“Many but not all IBS patients will benefit from therapies targeting this histamine driven pathway,” said co-first author David Reed, assistant professor of medicine at Queen’s University.

The McMaster-Queens study was funded by the Canadian Institutes of Health Research and published in the journal Science Translational Medicine.