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Category: Clinical Microbiology
Probiotics in Gastrointestinal Diseases, Page 1 of 2
< Previous page | Next page > /docserver/preview/fulltext/10.1128/9781555815462/9781555814038_Chap20-1.gif /docserver/preview/fulltext/10.1128/9781555815462/9781555814038_Chap20-2.gifAbstract:
A large and diverse community of commensal bacteria is harbored in the human gut, in a symbiotic arrangement that influences both the physiology and pathology of the host. Microbial ecology in the gut can be modulated by pharmacological and nutritional interventions with probiotics and prebiotics, and a balanced microbial environment would likely promote symbiotic functions of bacteria and enhance human health. In controlled human studies, probiotics and prebiotics have been used for improving certain metabolic functions of the microbiota, for protection against infections, and for modulation of the immune system. This chapter summarizes the recommendation grades for the use of probiotics in gastroenterology according to the criteria of evidence-based medicine. Current clinical research is focused mainly at establishing the role and efficacy of probiotics and prebiotics in the prevention and control of inflammatory bowel disease (IBD) and colon cancer. Experimental studies have yielded convincing evidence of their potential utility for these indications. However, human studies have failed in some attempts to provide effective therapeutic strategies with probiotics and prebiotics. It is likely that the development of improved tools to investigate gut colonization will provide a more complete picture of the actual scenario in inflammatory disorders and colon cancer. As a consequence, new interventions will aim towards more robust modifications or remodeling of intestinal microbial populations with applications for improving gut health.
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The specialized lymphoid follicles of the gut mucosa are major sites for induction and regulation of immune responses. Multiple and diverse interactions between microbes, epithelium, and gut lymphoid tissues are constantly reshaping local and systemic mechanisms of immunity. Gut microbes stimulate clonal expansion of lymphocytes in follicles, and the mechanisms which determine the phenotype differentiation of T-helper cells are not fully understood. However, experimental evidence indicates that innate recognition of bacteria by epithelial cells and/or antigen-presenting cells may play critical roles in the induction of either effector or regulatory pathways. Costimulatory signals (cytokines) released by these cell types dictate polarization of the adaptive immune response.
Relative risks (and 95% confidence intervals) of diarrhea in subjects on antibiotics and probiotics as normalized by the incidence of diarrhea in control subjects on antibiotics and placebo in 14 controlled clinical trials. Twelve studies estimated a relative risk lower than 1, and in seven of these studies the upper limit of the 95% confidence interval was also below 1. Overall, the combined relative risk is significantly reduced, as determined in published meta-analyses ( Cremonini et al., 2002 ; D’Souza et al., 2002 ; Szajewska and Mrukowicz, 2005 ; Sazawal et al., 2006 ). LGG, L. rhamnosus GG.
Colorectal cancer is induced by a series of mutational events in a number of critical genes of epithelial stem cells in the mucosa. The presence in the colonic lumen of DNA-damaging agents could represent an important risk factor for colonic cancer. Diet and gut bacteria are likely to play a role in the production and/or elimination of genotoxic compounds in the colonic lumen. The SYNCAN study found a decrease in genotoxicity indexes in colonic mucosal biopsy samples from patients taking a synbiotic (prebiotic plus two probiotic strains), whereas this change was not observed in subjects taking a placebo (data from Rafter et al., 2007 ). This finding suggests a decreased mucosal exposure to genotoxins associated with the consumption of the synbiotic.
Pathological conditions associated with dysfunction of the gut microbiota
Clinical studies investigating the efficacy of probiotics in the treatment of IBSa
Clinical studies investigating the efficacy of probiotics in maintenance of remission in ulcerative colitisa
Clinical studies investigating the efficacy of probiotics in maintenance of remission in Crohn’s disease
Probiotics in evidence-based medicine