The gastrointestinal tract of mammals hosts a high and diverse number of different microorganisms, known as intestinal microbiota. Many probiotics were originally isolated from the gastrointestinal tract, and they were defined by the Food and Agriculture Organization of the United Nations (FAO)/WHO as "live microorganisms which when administered in adequate amounts confer a health benefit on the host." Probiotics exert their beneficial effects on the host through four main mechanisms: interference with potential pathogens, improvement of barrier function, immunomodulation and production of neurotransmitters, and their host targets vary from the resident microbiota to cellular components of the gut-brain axis. However, in spite of the wide array of beneficial mechanisms deployed by probiotic bacteria, relatively few effects have been supported by clinical data. In this regard, different probiotic strains have been effective in antibiotic-associated diarrhea or inflammatory bowel disease for instance. The aim of this review was to compile the molecular mechanisms underlying the beneficial effects of probiotics, mainly through their interaction with the intestinal microbiota and with the intestinal mucosa. The specific benefits discussed in this paper include among others those elicited directly through dietary modulation of the human gut microbiota.

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Probiotics, gut microbiota, and their influence on host health and disease.

The intestinal tract is a diverse microenvironment where more than 500 species of bacteria thrive. A single layer of epithelium is all that separates these commensal microorganisms and pathogens from the underlying immune cells, and thus epithelial barrier function is a key component in the arsenal of defense mechanisms required to prevent infection and inflammation. The epithelial barrier consists of a dense mucous layer containing secretory IgA and antimicrobial peptides as well as dynamic junctional complexes that regulate permeability between cells. Probiotics are live microorganisms that confer benefit to the host and that have been suggested to ameliorate or prevent diseases including antibiotic-associated diarrhea, irritable bowel syndrome, and inflammatory bowel disease. Probiotics likely function through enhancement of barrier function, immunomodulation, and competitive adherence to the mucus and epithelium. This review summarizes the evidence about effects of the many available probiotics with an emphasis on intestinal barrier function and the mechanisms affected by probiotics.

https://www.physiology.org/doi/pdf/10.1152/ajpgi.00243.2009

Probiotic bacteria and intestinal epithelial barrier function

https://www.gastrojournal.org/article/S0016-5085(09)00293-5/pdf

Targeting the human microbiome with antibiotics, probiotics, and prebiotics: gastroenterology enters the metagenomics era.

Probiotics and prebiotics play an important role in human nutrition. In recent years there has been a significant increase in research on the characterization and verification potential health benefits associated with the use of probiotic and prebiotic. The main effects attributed to selected probiotics/prebiotic products have been proved by clinical trials, while others have been acquired on the basis of in vitro tests which require in vivo transposition in order to be validated. The main clinical reports in the literature for the application of probiotic have been done for the treatment of infectious diseases including viral, bacterial or antibiotic associated diarrhoea, relief of chronic bowel inflammatory diseases, immuno-modulation, lowering of serum cholesterol, decreased risk of colon cancer, improve lactose digestion, reduce allergies, and effect on intestinal microbiota. Although the large investigation for the health benefits, information on probiotic species, a specific strain-therapeutic application, and sufficient dosages, is not sufficiently studied to allow practical and rational consumption. Moreover, prebiotic oligosaccharides although provided curative and nutritional values, they are poorly understood in regard to their origin, the processes employed to generate them, their fermentation profiles, and dosages required for health effects. The present review summarizes guidelines reported on the literature in regard to clinician or therapeutic trials of probiotic and prebiotic.

An overview of the last advances in probiotic and prebiotic field

Commensal Bacteroides Species Induce Colitis in Host-Genotype-Specific Fashion in a Mouse Model of Inflammatory Bowel Disease

Objective To evaluate whether probiotics maintain remission in patients with Crohn’s disease (CD). Design A meta-analysis of controlled clinical trials. Methods PUBMED and Cochrane Central Register of Controlled Trials were searched for clinical trial studies investigated the efficacy of probiotics for the maintenance of remission in Crohn’s disease. Clinical relapse and endoscopic relapse were the key outcomes of interest. Data were searched within the time period of 1966 through may 2007. Result Eight randomized placebo-controlled clinical trials met our criteria and were included in the analysis. Seven determined clinical relapse and three evaluated endoscopic relapse among patients with CD received probiotics for maintenance of remission. Pooling of seven trials for the outcome of clinical relapse yielded an odds ratio of 0.92 (95% confidence interval of 0.52–1.62, P = 0.8853), a nonsignificant odds ratio. The odds ratio for three studies for the outcome of endoscopic relapse was 0.97 (95% confidence interval of 0.54–1.78, P = 0.93), a nonsignificant odds ratio. Conclusion This meta-analysis fails to demonstrate the efficacy of probiotics in maintaining remission and preventing clinical and endoscopic recurrence in CD. It is suggested to use probiotic preparations containing a mixture of lactobacillus with E. coli or Saccharomyces.

A Meta-Analysis on the Efficacy of Probiotics for Maintenance of Remission and Prevention of Clinical and Endoscopic Relapse in Crohn’s Disease

This study was designed to evaluate whether probiotics improve symptoms in patients with irritable bowel syndrome. PubMed, Embase, Scopus, Web of Science, and Cochrane Central Register of Controlled Trials were searched for studies that investigated the efficacy of probiotics in the management of irritable bowel syndrome. Clinical improvement was the key outcome of interest. Data were searched within the time period of 1966 through September 2007. Eight randomized, placebo-controlled, clinical trials met our criteria and were included in the analysis. Pooling of eight trials for the outcome of clinical improvement yielded a significant relative risk of 1.22 (95 percent confidence interval, 1.07–1.4; P = 0.0042). Probiotics may improve symptoms of irritable bowel syndrome and can be used as supplement to standard therapy.

Efficacy of probiotics in irritable bowel syndrome: a meta-analysis of randomized, controlled trials.

The objective of this study was to evaluate and collect current evidence on the effect of probiotics in preventing pouchitis after restorative ileal pouch anal anastomosis (IPAA). The Pubmed, Medline, EMbase, CINAHL, Web of Science, and Scopus bibliographic, and Google Scholar databases were searched between 1966 and May 2007, and relevant controlled clinical trials were extracted, reviewed, and validated according to the study protocol. The outcome of interest was for pouchitis defined by a pouchitis disease activity index (PDAI) ≥7. Five randomized, placebo-controlled clinical trials were included in the meta-analysis. Pooling of the results from these trials yielded an odds ratio (OR) of 0.04 with a 95% CI of 0.01–0.14 (P < 0.0001) in the treatment group in comparison with the placebo group. In conclusion, the benefit of probiotics in the management of pouchitis after IPAA operation was confirmed by the meta-analysis.

On the Benefit of Probiotics in the Management of Pouchitis in Patients Underwent Ileal Pouch Anal Anastomosis: A Meta-analysis of Controlled Clinical Trials

The aim of the study was to evaluate and collect current evidence on the effect of antibiotics in pretreatment of pouchitis after restorative ileal pouch anal anastomosis (IPAA). Pubmed, Embase, Web of Science, Scopus, and Cochrane Library databases were searched between 1966 and July 2008; and relevant clinical trials extracted, reviewed, and validated according to the study protocol. The outcome of interest was clinical improvement after treatment. Nine randomized, placebo-controlled clinical trials were found relevant and studied but 3 of them with 70 patients were entered into meta-analysis. Pooling of the results from these trials yielded an odds ratio of 15.96 with a 95% CI of 4.20–60.70, indicating a significant OR (p<0.0001) in treatment group in comparison to the placebo group. In conclusion, the meta-analysis confirms benefit of antibiotics in management of pouchitis after IPAA operation.

Saeed Derakhshani

Papers

A Meta-Analysis on the Efficacy of Probiotics for Maintenance of Remission and Prevention of Clinical and Endoscopic Relapse in Crohn’s Disease

Efficacy of probiotics in irritable bowel syndrome: a meta-analysis of randomized, controlled trials.

On the Benefit of Probiotics in the Management of Pouchitis in Patients Underwent Ileal Pouch Anal Anastomosis: A Meta-analysis of Controlled Clinical Trials

Benefit of antibiotic therapy on pouchitis after ileal pouch anal anastomosis: A systematic review and meta-analysis of clinical trials

A meta-analysis on the efficacy of probiotics in irritable bowel syndrome