Stool samples from patients with IBS have shown distinct differences in quality, quantity, and temporal stability compared with healthy individuals.3,14-17
Bacterial overgrowth and reduced bacterial diversity have been observed in cultures from the small intestine of patients with IBS compared with healthy individuals.9,10,18
In one study, small intestinal bacterial overgrowth was more commonly associated with IBS-D compared with other subtypes.18
Important note: Studies of microbial composition have been limited to small populations and often restricted to one geographic region.10,15-17 Results therefore may not be extrapolated to all patients with IBS. No specific bacterial species has been consistently linked to IBS, including IBS-D, but the body of evidence is growing.10,17,19
Research has uncovered a link between IBS and infectious enteritis.1 In a meta-analysis of 45 studies, 1 in nine individuals exposed to foodborne pathogens developed IBS, a rate nearly four times greater than those who were not exposed. The most common subtypes associated with infectious enteritis were IBS-M (mixed) and IBS-D (diarrhea-predominant). Risk factors included2:
The mechanism by which previous GI infection results in IBS is still being explored. Animal models suggest that acute gastroenteritis has long-term effects on the immune system and GI motility, leading to alterations in gut microbial composition and post-infectious IBS.11
Adapted, with permission, from: Casén C, Vebø HC, Sekelja M, et al. Deviations in human gut microbiota: a novel diagnostic test for determining dysbiosis in patients with IBS or IBD. Aliment Pharmacol Ther. 2015;42(1):71-83.
Adapted, with permission, from: Giamarellos-Bouboulis E, Tang J, Pyleris E, et al. Molecular assessment of differences in duodenal microbiome in subjects with irritable bowel syndrome. Scand J Gastroenterol. 2015;50(9):1076-1087.
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