The Gut Microbiome and DiseaseBrain–Gut Microbiome Interactions and Functional Bowel Disorders
Section snippets
Alterations in the Intestinal Microbiome of Patients With IBS
Advances in analytic techniques have helped to better characterize different aspects of the gut microbiome.22, 23, 24 Only 20%–30% of microbes identified in the human colon can be cultured (mostly Firmicutes, Bacteroidetes, Proteobacteria, and Actinobacteria); these new techniques can be used to assess diversity and functional groups.12 Culture-independent approaches include 16S ribosomal RNA gene-based analyses (to identify microbes in the GI tract), metagenomic approaches (to determine which
Possible Causes of Dysbiosis in Patients With IBS
A small percentage of patients (8%–15%) have persistent IBS-like symptoms after an initial documented episode of enteric bacterial or viral infection, called postinfectious IBS. This observation supports a role for a perturbed intestinal microbiome in the development of altered brain–gut interactions associated with IBS-like symptoms. Common bacterial causes of traveler’s diarrhea (Escherichia coli, Salmonella, and Campylobacter) strongly are associated with postinfectious IBS, and biological
The Intestinal Microbiota and the Central Nervous System
The central nervous system (CNS) modulates the GI tract via the sympathetic and parasympathetic branches of the ANS and the HPA axis. These can affect the enteric microbiota indirectly by altering its environment, and directly via signaling molecules (reviewed by Rhee et al2). Both branches of the ANS regulate gut functions such as regional motility, secretion of acid, production of bicarbonates and mucus, maintenance of epithelial fluid, permeability of the intestine, and the mucosal immune
Gut Microbiota Modulate Gut–Brain Interactions
There are multiple ways, levels, and signaling mechanisms by which the microbiota can influence interactions between the gut and the nervous system, including the brain. Such influences may occur early in life and affect the development of the nervous system, the brain’s interaction with the intestine, and the HPA axis, or in adults act on fully developed circuits (reviewed by Forsythe and Kunze,5 Cryan and Dinan,8 and Bercik et al9). There have been more review articles and news stories on
Future Directions
There have been many exciting studies providing new insights into the complex interactions between the microbiota, intestinal cells, the ENS, and the CNS, but little is known about their role in the development of IBS or the maintenance of IBS symptoms. Studies in rodents and healthy individuals have provided evidence that the intestinal microbiota can be modulated by the ANS, and possibly by the HPA axis. On the other hand, other preclinical studies, and a recent clinical study,20 have shown
Acknowledgment
The authors thank Dr J. Versalovic for valuable scientific advice and C. Liu for invaluable editorial assistance.
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Conflicts of interest The authors disclose the following: Dr Emeran A. Mayer is a member of the International Danone Advisory Board. The remaining authors disclose no conflicts.