Histamine-producing gut bacteria can trigger chronic abdomin
Researchers examined stool microbiota 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 study 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 the 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.

Source: https://www.science.org/doi/10.1126/scitranslmed.abj1895