[The intestinal microbiota in inflammatory bowel diseases].

backgroundThe intestinal microbiota comprises all living microorganisms in the gastrointestinal tract and is crucial for its function. Clinical observations and laboratory findings confirm a central role of the microbiota in chronic inflammatory bowel diseases (IBD). However, many mechanistic details remain unclear.

objectivesChanges in the microbiota and the causal relationship with the pathogenesis of IBD are described and current and future diagnostic and therapeutic options are discussed. MATERIALS AND

methodsNarrative review.

resultsThe intestinal microbiota is altered in composition, diversity, and function in IBD patients, but specific (universal) IBD-defining bacteria have not been identified. The healthy microbiota has numerous anti-inflammatory functions such as the production of short-chain fatty acids or competition with pathogens. In contrast, the IBD microbiota promotes inflammation through the destruction of the intestinal barrier and direct interaction with the immune system. The balance between pro- and anti-inflammatory effects of the microbiota appears to be crucial for the development of intestinal inflammation. Microbiota-based IBD diagnostics show promise but are not yet ready for clinical use. Probiotics and fecal microbiota transplantation have clinical effects, especially in ulcerative colitis, but the potential of microbiota-based therapies is far from being fully realized.

conclusionIBD dysbiosis remains undefined so far. It is unclear how the many parallel pro- and anti-inflammatory mechanisms contribute to IBD pathogenesis. An inadequate mechanistic understanding hinders the development of microbiota-based diagnostics and therapies.