The role of the gastrointestinal microbiota in colorectal cancer

Both environmental and genetic factors contribute to cancers of the gastrointestinal tract including, the stomach, colon and rectum. The mechanisms associated with gastrointestinal cancer causation and prevention are largely unknown and the subject of much research. Many of the proposed mechanisms implicate the metabolic activities of the bacterial biota normally resident in the gastrointestinal tract. This review examines both the adverse and beneficial consequences of bacterial activity of the gastrointestinal tract focusing, in particularly on the stomach and large intestine. Studies on the role of the bacterial biota in colon carcinogenesis have also resulted in several useful biomarkers for use in human.

Profiling of composition and metabolic activities of the colonic microflora of growing pigs fed diets supplemented with prebiotic oligosaccharides

It is evident that quantitative information on different microbial groups and their contribution in terms of activity in the gastrointestinal (GI) tract of humans and animals is required in order to formulate functional diets targeting improved gut function and host health. In this work, quantitative information on levels and spatial distributions of Bacteroides spp, Eubacterium spp, Clostridium spp, Escherichia coli, Bifidobacterium spp and Lactobacillus/Enterococcus spp. along the porcine large intestine was investigated using 16S rRNA targeted probes and fluorescent in situ hybridisation (FISH). Caecum, ascending colon (AC) and rectum luminal digesta from three groups of individually housed growing pigs fed either a corn-soybean basal diet (CON diet) or a prebiotic diet containing 10 g/kg oligofructose (FOS diet) or trans-galactooligosaccharides (TOS diet) at the expense of cornstarch were analysed. DAPI staining was used to enumerate total number of cells in the samples. Populations of total cells, Bacteroides, Eubacterium, Clostridium and Bifidobacterium, declined significantly (P < 0.05) from caecum to rectum, and were not affected by dietary treatments. Populations of Lactobacillus/ Enterococcus and E coli did not differ throughout the large intestine. The relative percent (%) contribution of each bacterial group to the total cell count did not differ between caecum and rectum, with the exception of Eubacterium that was higher in the AC digesta. FISH analysis showed that the sum of all bacterial groups made up a small percentage of the total cells, which was 12.4%, 21.8% and 10.3% in caecum, AC and rectum, respectively. This supports the view that in swine, the diversity of GI microflora might be higher compared to other species. In terms of microflora metabolic activity, the substantially higher numerical trends seen in FOS and TOS treatments regarding total volatile fatty acid, acetate concentrations and glycolytic activities, it could be postulated that FOS and TOS promoted saccharolytic activities in the porcine colon. (c) 2006 Elsevier Ltd. All rights reserved.

An investigation of the expression and adhesin function of H7 flagella in the interaction of Escherichia coli O157: H7 with bovine intestinal epithelium

Enterohaemorrhagic Escherichia coli O157 : H7 is a bacterial pathogen that can cause haemorrhagic colitis and haemolytic uremic syndrome. In the primary reservoir host, cattle, the terminal rectum is the principal site of E. coli O157 colonization. In this study, bovine terminal rectal primary epithelial cells were used to examine the role of H7 flagella in epithelial adherence. Binding of a fliC(H7) mutant O157 strain to rectal epithelium was significantly reduced as was binding of the flagellated wild-type strain following incubation with H7-specific antibodies. Complementation of fliC(H7) mutant O157 strain with fliC(H7) restored the adherence to wild-type levels; however, complementation with fliC(H6) did not restore it. High-resolution ultrastructural and imunofluorescence studies demonstrated the presence of abundant flagella forming physical contact points with the rectal epithelium. Binding to terminal rectal epithelium was specific to H7 by comparison with other flagellin types tested. In-cell Western assays confirmed temporal expression of flagella during O157 interaction with epithelium, early expression was suppressed during the later stages of microcolony and attaching and effacing lesion formation. H7 flagella are expressed in vivo by individual bacteria in contact with rectal mucosa. Our data demonstrate that the H7 flagellum acts as an adhesin to bovine intestinal epithelium and its involvement in this crucial initiating step for colonization indicates that H7 flagella could be an important target in intervention strategies.