Scientists from McMaster University and Queen’s University found a gut bacterial “super-producer” of histamine that can cause pain flare-ups in some patients with irritable bowel syndrome.
The culprit is what has now been named Klebsiella aerogenes, the McMaster-Queen (MQ) strain, identified in up to 25 percent of gut microbiota samples from patients with IBS.
The research is published in Science Translational Medicine and was conducted by Premysl Bercik et al.
In the study, researchers examined stool samples from both Canadian and American patient cohorts.
They followed up with 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.
The research team pinpointed the bacterium Klebsiella aerogenes as the key histamine producer by studying germ-free mice colonized with gut microbiota from patients with IBS.
They also colonized some mice with gut microbiota from healthy volunteers as a control group.
The team found that the bacterium Klebsiella aerogenes converts dietary histidine, an essential amino acid present in animal and plant protein, into histamine, a known mediator of pain.
The bacterial histamine then activates the gut immune system through histamine-4 receptor, which draws immune mast cells into the intestines.
These activated mast cells produce even more histamine and other pain-signaling mediators, triggering inflammation and pain.
The study found that when the mice colonized with histamine-producing bacteria were fed a diet low in fermentable carbohydrates, bacterial histamine production dramatically decreased.
This was due to changes in bacterial fermentation and acidity within the gut, which inhibited the bacterial enzyme responsible for histamine production.
These results explain the beneficial effects of a low fermentable diet in patients with IBS.
It is known that patients with IBS have more mast cells in their intestines, and that some of them improve with treatments targeting mast cells or histamine, such as mast cell stabilizers or antihistamines.
The new study explains why increased mast cells are found in IBS and suggest that H4 receptor pathway plays a major role in this process.
If you care about gut health, please read studies about big cause of leaky gut, fatty liver disease, and common blood pressure drug could increase your gut disease risk.
For more information about gut health, please see recent studies about diet that can reduce inflammation and improve gut health, and results showing a plant-based diet can give you a healthier gut.
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