Pathobionts are microorganisms that live harmlessly in a balanced microbiome but become harmful when conditions change. H. pylori, Clostridioides difficile, and certain E. coli strains exist in small numbers in many healthy guts without causing problems. Dysbiosis from antibiotics, illness, or dietary change can allow pathobionts to overgrow rapidly and cause conditions like C. difficile colitis, SIBO, and IBS.
