Speakers: Giovanni Barbara (Italy), Magnus Simren (Sweden)
Prof. Barbara highlighted the fact that there is increasing evidence indicating that the gut microbiota may be involved in the pathogenesis and pathophysiology of functional gastrointestinal disorders (FGIDs). FGIDs are a group of disorders characterised by recurrent GI symptoms that cannot be explained by other pathologically-based disease. Of these, irritable bowel syndrome (IBS) is one of the most frequently reported and the most studied. IBS is multifactorial in origin, and may be associated with stress, anxiety or depression, food hypersensitivity, changes in the gut such as an increase in mucosal permeability, and changes in the gut microbiota.
Bidirectional interplay occurs between the gut microbiota and the host, affecting many physiological aspects both inside and outside the intestinal tract. Several mechanisms are proposed by which the microbiota can modulate gut motor function: some are related to the release of neurotransmitters and proteases, another is related to the production of end products from bacterial fermentation e.g. the production of short chain fatty acids (such as butyrate) from carbohydrate metabolism, while other mechanisms relate to the activation of toll-like receptors (TLRs).
Post-infectious IBS may develop after a severe case of gastroenteritis, and accounts for 10% of all IBS cases. Among an Italian population of school children and teachers who were exposed to salmonella infection the use of antibiotics was associated with an increased risk of developing post-infectious IBS in children. Previously, a decrease in lactobacilli and bifidobacteria has been identified in culture-based assessment of faecal microbiota from IBS patients, but there may be many more microbial species involved that cannot be identified using culture-techniques. We don’t yet know whether changes in the microbiota are the cause or an effect of some GI symptoms. Longitudinal studies to see how the microbiota change over time in a patient and how this correlates with fluctuations in symptoms and the disease state would provide some insight into this relationship. There are many factors that can influence the microbiota including those related to bowel dysfunction such as gut transit time, medications such as proton pump inhibitors and antibiotics, probiotics and diet.
Prof. Barbara also discussed evidence that the gut sensorimotor dysfunction of IBS can be adaptively transferred; this is mediated through changes in visceral hypersensitivity, enteric nervous system dysfunction, and altered mucosal permeability.
Prof. Simren presented the clinician’s view of the role of microbiota in functional bowel disease (FBD). Small intestinal bacterial overgrowth (SIBO) and altered intestinal microbiota are implicated in subgroups of FBD patients, although the clinical relevance of these findings is unclear at present. The use of hydrogen breath tests to measure SIBO is controversial as the tests have not been validated. The lactulose breath test has poor sensitivity and poor specificity for bacteria resident in the large intestine, while the glucose hydrogen breath test gives better sensitivity and specificity for microbial activity in the upper GI tract.
A relationship between the use of antibiotics and an increase in functional GI symptoms 4 months after treatment has been demonstrated. Conversely, the use of a 2-week course of the non-absorbable antibiotic rifaximin has been shown to provide sustained relief from IBS symptoms for up to 10 weeks post-treatment in one study. However, the idea of using antibiotics for the treatment of chronic illness met with some scepticism amongst the GFMH audience.
Some studies have demonstrated a benefit from the use of probiotics to alleviate symptoms of IBS, in particular gas-related symptoms such as bloating. Further, meta-analyses demonstrate an overall benefit from the use of probiotics; however, evidence for the benefits of specific probiotic strains is limited. In conclusion, Prof. Simren stated that we need more high quality, large-scale, randomised controlled trials of probiotics and head-to-head studies to determine the effects and comparative efficacy of probiotics. We also need to better understand the mechanisms involved, so that in future we will be able to select the right treatment for the right patient.
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