Abstract
Irritable bowel syndrome (IBS) is a functional gastrointestinal disorder that has been associated with aberrant microbiota. This review focuses on the recent molecular insights generated by analysing the intestinal microbiota in subjects suffering from IBS. Special emphasis is given to studies that compare and contrast the microbiota of healthy subjects with that of IBS patients classified into different subgroups based on their predominant bowel pattern as defined by the Rome criteria. The current data available from a limited number of patients do not reveal pronounced and reproducible IBS-related deviations of entire phylogenetic or functional microbial groups, but rather support the concept that IBS patients have alterations in the proportions of commensals with interrelated changes in the metabolic output and overall microbial ecology. The lack of apparent similarities in the taxonomy of microbiota in IBS patients may partially arise from the fact that the applied molecular methods, the nature and location of IBS subjects, and the statistical power of the studies have varied considerably. Most recent advances, especially the finding that several uncharacterized phylotypes show non-random segregation between healthy and IBS subjects, indicate the possibility of discovering bacteria specific for IBS. Moreover, tools are being developed for the functional analysis of the relationship between the intestinal microbiota and IBS. These approaches may be instrumental in the evaluation of the ecological dysbiosis hypothesis in the gut ecosystem. Finally, we discuss the future outlook for research avenues and candidate microbial biomarkers that may eventually be used in IBS diagnosis.
Highlights
We are colonized from birth by a complex microbiota that affects health and disease
This review focuses on recent GI microbiota research in Irritable bowel syndrome (IBS) patients, with a special emphasis on mining the subtype-specific findings obtained using culture-independent methods, as the initial culture-based studies had various limitations and have already been thoroughly reviewed in the existing literature (Lee & Tack, 2010; Parkes et al, 2008; Quigley, 2009; Ringel & Carroll, 2009)
Lachnospira and family- or genus-level representatives of the gammaproteobacteria and bacilli were enriched in IBSD, while Bacteroides and Ruminococcus spp., as well as three genera assigned to the Actinobacteria, were depleted
Summary
We are colonized from birth by a complex microbiota that affects health and disease. By far the greater part of this microbiota resides in the gastrointestinal (GI) tract, and can be considered as an organ within an organ (Bocci, 1992). As many of the GI tract microbes have not yet been cultured and are only recognized based on their 16S rDNA sequences, molecular high-throughput approaches have been developed to study the diversity and functionality of the thousands of phylotypes that have been predicted to be present in the GI tract (for a full review, see Zoetendal et al, 2008). These studies have revealed that the composition of the microbiota in healthy adults is highly subject-specific and stable, indicating an individual core. The presence of low-level inflammation in the GI mucosa of IBS patients has been observed in several studies, including those reported by Aerssens et al (2008), Chadwick et al (2002) and Macsharry et al (2008)
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