Alterations in Intestinal Microbial Flora and Human Disease

Mohamed Othman; Roberto Agüero; Henry C. Lin


Curr Opin Gastroenterol. 2008;24(1):11-16. 

In This Article

Gut Microbes and Intestinal Immune Response in Inflammatory Bowel Disease

Gastrointestinal inflammation overall is one of the most important factors that influence the quantity and quality of human intestinal flora. This interaction is illustrated by inflammatory bowel disease (IBD). For example, the dominant bacterial flora in patients with IBD differs from healthy patients; similarly, the dominant bacterial flora in patients with ulcerative colitis differs from those diagnosed with Crohn's disease.[38] Differences in microbiota were also found contrasting the bacteria isolated from mucosal biopsies of inflamed versus noninflamed tissue of newly diagnosed and untreated patients.[39••] The contribution of an abundance or reduction of bacteria such as those from the genus Clostridium or the phylum Bacteroidetes in the pathogenesis of these diseases remains to be established. The microflora of IBD patients produces greater amounts of metabolic products (e.g. ammonia and short-chain fatty acids) than the microflora of healthy controls.[40] The microflora isolated from inflamed mucosa of IBD patients was also found to trigger the production of interleukin (IL)-12, interferon-ϒ and IL-10, which are important mediators of inflammation in IBD.[41] Similarly, increased T-cell response to bacterial antigens has been reported.[42] Perhaps the strongest argument for the role of commensal gut microbes in IBD is that researchers were unable to demonstrate the development of colitis in knockout mouse models of IBD when the animals were kept germ free. Specifically, even IL-10 knockout mice would not develop their usual severe intestinal inflammation if raised in a germ-free environment.[43]

Probiotic organisms and the microflora itself have the ability to shift the inflammatory response in favor of the host; bacteria such as Bifidobacterium bifidum and Lactobacillus spp. have been shown to suppress T-cell responses in both an IBD animal model and in patients well as.[44••,45] A recent Cochrane review,[46•] however, suggested that probiotics did not have a statistically significant effect in maintaining remission in Crohn's disease patients. The use of probiotics has also been investigated in the setting of IBS in several RCTs,[47] with promising results reported by O'Mahony et al.[48] using B. infantis.


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