by American Society for Microbiology

Relative abundance of bacterial taxa in the stool samples obtained from irritable bowel syndrome patients and healthy controls. Four box plots are shown, representing the range of the relative abundance values of each taxon across individual samples in healthy control (HC), irritable bowel syndrome (IBS), diarrheal IBS (IBS-D), and nondiarrheal IBS (IBS-ND) subjects. The color scheme was used to aid distinction among the sample groups as well as the cases with significant differences (see the visual legend inside the figure). Significance was tested for a given taxon by performing t test and Wilcoxon ranked sum test for comparisons between the healthy control group and each IBS category. A taxon was considered to be differentially abundant when the fold difference of abundance between the groups was above a certain threshold (5-fold for families, 10-fold for genera, 100-fold for operational taxonomic units [OTUs], and 500-fold for amplicon sequence variants [ASVs], adjusted for each rank to control the number of taxa to visualize), and P < 0.05 from t test or Wilcoxon test. Upward and downward arrows are placed above the taxon in the given patient group. These indicate the relative enrichment and depletion, respectively, compared with abundance in HCs. Panel A-D show the selected families (A), genera (B), OTUs (C), and ASVs (D). Credit: Microbiology Spectrum (2023). DOI: 10.1128/spectrum.02125-22

People with irritable bowel syndrome (IBS) have lower bacterial diversity in the intestine than do healthy people, according to a team of Korean investigators. The investigators believe that theirs is the first analysis to find a clear association between IBS and reduced diversity in the microbiota of the gut. The research appears in Microbiology Spectrum, an open-access journal of the American Society for Microbiology.

Normally, "More than 10,000 species of microorganism live in the human intestine," said corresponding author Jung Ok Shim, M.D., Ph.D., professor of Pediatric Gastroenterology, Hepatology, and Nutrition, Department of Pediatrics, Korea University College of Medicine, Seoul. Disruption of the microbiome of the human gastrointestinal tract can trigger IBS. Typically, IBS causes bloating, diarrhea, and stomach pain or cramps.

Previous studies of gut bacteria in patients with IBS have been controversial, with inconsistent results, due to small sample size and lack of consistent analytical methods used among these studies, said Shim. The investigators combined their own dataset with 9 published, shared datasets, encompassing 576 IBS patients and 487 healthy controls, analyzing them with a "unified data processing and analytical method."

The researchers found that the gut bacterial community is less diverse in IBS patients than in healthy people, said Shim. Additionally, the abundance of 21 bacterial species differed between IBS patients and healthy controls. However, the findings were not statistically significant in the pediatric cohort due to small sample size.

The investigators proved that the disturbed gut bacterial community "is associated with IBS, though this does not mean that the relationship is causal," said Shim. "Functional studies are needed to prove whether the change in gut micro-organisms contributes to development of IBS."

Even though IBS is a common disorder, its pathogenesis remains unknown, and as yet there is no effective treatment strategy. "Based on the epidemiological studies of IBS patients, altered gut microbiota was proposed as one of the possible causes of IBS," the researchers write. "Acute bacterial gastroenteritis can cause chronic, asymptomatic, low-grade intestinal wall inflammation sufficient to alter neuromuscular and epithelial cell function."

More information: Gun-Ha Kim et al, Gut Bacterial Dysbiosis in Irritable Bowel Syndrome: a Case-Control Study and a Cross-Cohort Analysis Using Publicly Available Data Sets, Microbiology Spectrum (2023). DOI: 10.1128/spectrum.02125-22

Provided by American Society for Microbiology