Topic Highlight
Copyright ©2014 Baishideng Publishing Group Inc. All rights reserved.
World J Gastroenterol. Oct 21, 2014; 20(39): 14105-14125
Published online Oct 21, 2014. doi: 10.3748/wjg.v20.i39.14105
Irritable bowel syndrome: A microbiome-gut-brain axis disorder?
Paul J Kennedy, John F Cryan, Timothy G Dinan, Gerard Clarke
Paul J Kennedy, Timothy G Dinan, Gerard Clarke, 1.15 Biosciences Institute, Department of Psychiatry, Alimentary Pharmabiotic Centre, University College Cork, Cork, Ireland
John F Cryan, Department of Anatomy and Neuroscience, Alimentary Pharmabiotic Centre, University College Cork, Cork, Ireland
Author contributions: Clarke G, Dinan TG and Cryan JF devised the study; Clarke G, Dinan TG, Cryan JF and Kennedy PJ reviewed and evaluated the literature for inclusion in the review; Clarke G and Kennedy PJ prepared the initial draft of the manuscript; Clarke G, Dinan TG, Cryan JF and Kennedy PJ reviewed, edited and approved the final version of the manuscript.
Supported by Science Foundation Ireland, No. SFI/12/RC/2272, No. 02/CE/B124, No. 07/CE/B1368; Health Research Board No. HRA_POR/2011/23; Brain and Behaviour Research Foundation No. 20771
Correspondence to: Gerard Clarke, PhD, 1.15 Biosciences Institute, Department of Psychiatry, Alimentary Pharmabiotic Centre, University College Cork, Cork, Ireland.
Telephone: +353-21-4901408 Fax: +353-21-4901722
Received: February 28, 2014
Revised: April 18, 2014
Accepted: May 26, 2014
Published online: October 21, 2014

Irritable bowel syndrome (IBS) is an extremely prevalent but poorly understood gastrointestinal disorder. Consequently, there are no clear diagnostic markers to help diagnose the disorder and treatment options are limited to management of the symptoms. The concept of a dysregulated gut-brain axis has been adopted as a suitable model for the disorder. The gut microbiome may play an important role in the onset and exacerbation of symptoms in the disorder and has been extensively studied in this context. Although a causal role cannot yet be inferred from the clinical studies which have attempted to characterise the gut microbiota in IBS, they do confirm alterations in both community stability and diversity. Moreover, it has been reliably demonstrated that manipulation of the microbiota can influence the key symptoms, including abdominal pain and bowel habit, and other prominent features of IBS. A variety of strategies have been taken to study these interactions, including probiotics, antibiotics, faecal transplantations and the use of germ-free animals. There are clear mechanisms through which the microbiota can produce these effects, both humoral and neural. Taken together, these findings firmly establish the microbiota as a critical node in the gut-brain axis and one which is amenable to therapeutic interventions.

Keywords: Irritable bowel syndrome, Microbiome, Anxiety, Tryptophan, Abdominal pain, Gastrointestinal motility, Cognition

Core tip: A dysregulated gut-brain axis may be responsible for the main features of irritable bowel syndrome (IBS). However, the role of the gut microbiota is an underappreciated but critical node in this construct. Numerous clinical studies have documented various alterations in the composition of the gut microbiota in IBS, indicating defects in stability and diversity of this virtual organ. Manipulation of the gut microbiome influences the symptom profile in IBS and clear mechanisms have been elucidated to explain these interactions. This has important clinical implications and may offer hope for future treatment options to alleviate the suffering caused by this debilitating disorder.