Gastrointestinal microbiota in irritable bowel syndrome: present state and perspectives

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. IntroductionWe 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. Comparative microbiota analyses between multiple healthy subjects indicate that a limited proportion of phylotypes are shared between individuals, forming a common core microbiota that is assumed to be functionally redundant (Qin et al., 2010;Tap et al., 2009;Turnbaugh et al., 2009). Recent metagenomic sequence analysis of the GI tract microbiota has confirmed this and defined a reference set of over three million unique genes that vastly exceeds the coding capacity of the human genome (Qin et al., 2010). Insight into the microbiota of healthy subjects allows comparisons with that of compromised...

The Challenging Triad: Microbiota, Immune System and Anticancer Drugs

“…The last two of these were associated with changes in microbiota composition, but interestingly, no pattern of alteration was demonstrated [6][7][8][9][10]. Recent studies showed that the expression of the leukocyte antigen DQ2 is a strong risk factor for the development of celiac disease.…”

Postinfectious Chronic Gut Dysfunction: From Bench to Bedside

“…Recently, published data on the microbiota in IBS patients without a specifi ed history of a precipitating infection have not identifi ed a microbiotal " signature " other than a frequent reduction in Lactobacillus species. However, an emerging trend is a reduction in bacterial diversity and instability of the microbiota over time (for review see Salonen et al ( 29 )) Th e latter is of potential importance in that animal-based studies have shown that perturbation of a previously stable microbiota leads to changes in gut function ( 30 ) and behavior ( 31 ). Th e latter may be important given the association of psychiatric morbidity with postinfectious IBS.…”

Dysbiosis of the Intestinal Microbiota in IBS

“…and Veillonella sp., have been reported. Quantitative and qualitative microbial alterations in the GI tract of IBS subjects may have a functional role in the syndrome aetiology or merely reflect the status of the gut, but still have diagnostic or prognostic value in clinical practise and research (Kassinen, 2009; www.intechopen.com Salonen et al, 2010). In the following chapter, these IBS-related alterations within the human GI microbiota are reviewed.…”