甲烷呼气摘要.doc

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are fermented principally to short chain fatty acids hydrogen and carbon dioxide Microbial disposal of the hydrogen generated during anaerobic fermentation in the human colon is critical to optimal functioning of this ecosystem However our understanding of microbial hydrogenotrophy is fragmented and at least as it occurs in the colon is mostly theoretical in nature Thorough investigation and integration of knowledge on the diversity of hydrogenotrophic microbes their metabolic variation and activities as a functional group as well as the nature of their interactions with fermentative bacteria are necessary to understand hydrogen metabolism in the human colon Here we review the limited data available on the three major groups of H 2 consuming microorganisms found in the human colon methanogens sulfate reducing bacteria SRB and acetogens as well as evidence that end products of their metabolism have an important impact on colonic health BMC Microbiol 2008 May 20 8 79 doi 10 1186 1471 2180 8 79 Human methanogen diversity and incidence in healthy and diseased colonic groups using mcrA gene analysis Scanlan PD Shanahan F Marchesi JR Source Alimentary Pharmabiotic Centre National University of Ireland University College Cork Cork Ireland paulinescanlan yahoo co uk Abstract BACKGROUND The incidence and diversity of human methanogens are insufficiently characterised in the gastrointestinal tract of both health and disease A PCR and clone library methodology targeting the mcrA gene was adopted to facilitate the two fold aim of surveying the relative incidence of methanogens in health and disease groups and also to provide an overview of methanogen diversity in the human gastrointestinal tract RESULTS DNA faecal extracts 207 in total from a group of healthy controls and five gastrointestinal disease groups were investigated Colorectalcancer polypectomised irritable bowel syndrome and the control group had largely equivalent numbers of individuals positive for methanogens range 45 50 Methanogen incidence in the inflammatory bowel disease groups was reduced 24 for ulcerative colitis and 30 for Crohn s disease Four unique mcrA gene restriction fragment length polymorphism profiles were identified and bioinformatic analyses revealed that the majority of all sequences 94 retrieved from libraries were 100 identical to Methanobrevibacter smithii mcrA gene In addition mcrA gene sequences most closely related to Methanobrevibacter oralis and members of the order Methanosarcinales were also recovered CONCLUSION The mcrA gene serves as a useful biomarker for methanogen detection in the human gut and the varying trends of methanogen incidence in the human gut could serve as important indicators of intestinal function Although Methanobrevibacter smithii is the dominant methanogen in both the distal colon of individuals in health and disease the diversity of methanogens is greater than previously reported In conclusion the low incidence of methanogens in Inflammatory Bowel Disease the functionality of the methanogens and impact of methaneproduction in addition to competitive interactions between methanogens and other microbial groups in the human gastrointestinal tract warrants further investigation J Clin Gastroenterol 2005 Feb 39 2 98 109 Diet anaerobic bacterial metabolism and colon cancer a review of the literature McGarr SE Ridlon JM Hylemon PB Source Department of Internal Medicine Gastroenterology Virginia Commonwealth University VCU Medical Center Richmond VA 23298 0341 USA Abstract Epidemiologic studies have demonstrated variations in the incidence of colon cancer between populations and socioeconomic groups Differences in dietary habits have been implicated in the risk of developing colon cancer Diet appears to influence our colonic microflora Such variations may allow for future utilization of the fecal flora as markers for screening and diagnosis of colon cancer The composition of the diet not only dictates the available substrates for the flora but also helps to establish predictable and competitive relationships between intestinal bacteria To appreciate the significance of populations deemed high and low risk based on host flora an understanding of several dynamic microbial relationships and metabolites produced is necessary In this review we explore the critical relationships between bile acid 7 alpha dehydroxylation sulfidogenesis methanogenesis and how they relate to carbohydrate and bile acid metabolism We summarize the chemopreventative anticarcinogenic and detoxifying activity of probiotics and prebiotics as well as potential mechanisms for protection against colon cancer Wei Sheng Wu Xue Bao 1991 Dec 31 6 473 8 Methanogens from feces of patients with intestine disorder Article in Chinese Xu B Zhang D Su W Xiao S Source Shanghai Technical Teacher s College Abstract Fecal specimens from 10 colorectal cancer 1 duodenum diverticulosis and 2 healthy adults were examined Nine fecal enrichments contained Methanobrevibacter The percentage of methanogen positive individuals was 69 Methanobrevibacter were isolated from fecal enrichments of 4 colorectal cancer and 1 duodenum diverticulosis The percentage of breath methane positive individuals and methane production had significantly increased in colorectal cancer patients It will be hopeful that methane production in breath samples at the end of exhalation will became a rapid simple and non penetrative method for monitoring precancerous colonic or rectal carcinogenesis and monitoring the relapse of individuals with carcinosectomy Proc Nutr Soc 1990 Jul 49 2 153 71 Mechanisms and experimental and epidemiological evidence relating dietary fibre non starch polysaccharides and starch to protection against large bowel cancer Bingham SA Source MRC Dunn Clinical Nutrition Centre Cambridge Abstract The cause of human colo rectal cancer is unknown although international and racial comparisons suggest that diet may be important Within populations risk of cancer is also affected by genetic factors which remain to be elucidated Dietary fibre and NSP consumption is not always high in populations at low risk of colo rectal cancer but rates are fast increasing with westernization and meat and fat consumption in Japan The suggestion that dietary fibre is protective in colo rectal cancer is based on the fact that cereal fibre from bran increases faecal weight dilutes large intestinal contents and speeds up transit time In animal models bran reduces the number of tumours induced by chemical carcinogens and cellulose may have a similar effect The faeces of some individuals contain mutagens some of which have been identified as fecapentaenes and heterocyclic amines Bran reduces faecal mutagenicity although the mutagen concerned is unknown Most dietary fibre is fermented in the large gut by anaerobic bacteria and little remains in faecal matter Recent observations have shown that substantial amounts of starch survive digestion in the small bowel and are available also for fermentation in the large gut The metabolic consequences of fermentation may be important in carcinogenesis via altered N metabolism SCFA production and pH reduction Methane is also produced in some individuals but contrary to previous findings is not a risk factor for large bowel cancer Starch appears to be beneficial as a substrate for fermentation because yields of the SCFA butyrate are increased both in vitro and in vivo Butyrate is an energy substrate for the colonic mucosa and an anti proliferative and differentiating agent in cell culture lines Possible mechanisms whereby starch and NSP may protect against colo rectal cancer therefore exist The majority of individual case control epidemiological studies suggest that fibre containing foods are protective in colo rectal cancer although this effect is largely due to vegetable rather than cereal consumption Case control studies of diet and large bowel cancer may however reflect the effect rather than the cause of the disease so that confirmation of the possible protective effects of starch and NSP is needed from accurate prospective studies both of diet and associated risk factors Dig Dis Sci 1990 Feb 35 2 221 4 Methane excretion and experimental colonic carcinogenesis Flick JA Hamilton SR Rosales FJ Perman JA Source Department of Pediatrics Johns Hopkins University School of Medicine Baltimore Maryland 21205 Abstract To examine the association between methane CH4 excretion and experimental colonic carcinogenesis we measured CH4 excretion in rats treated with the colonic carcinogen azoxymethane AOM 7 mg kg weekly for 10 weeks and paired controls CH4 excretion was not initially detected in either experimental or control groups but all animals acquired positive CH4 excretion status by time of sacrifice week 26 There was no difference between groups or among AOM treated animals with and without tumors in the median time to onset of detectable CH4 excretion or in the amount of CH4 excreted Our results fail to provide support for a link between CH4 excretion and experimental colonic dysplasia or adenocarcinoma Digestion 1975 13 4 232 40 The colon Absorptive seccretory and metabolic functions Cummings JG Abstract The role which the human colon fulfils in digestion and metabolism remains largely undocumented Its capacity to conserve water and electrolytes is well known although how this is controlled is uncertain In the animal kingdom calcium and magnesium absorption from the colon are improtant as are absorption and synthesis of vitamins The abundant microflora of the human colon gives it unique properties Dietary residue is metabolised forming short chain fatty acids hydrogen carbon dioxide and methane whilst 20 of urea synthesised in man is broken down in the colon to ammonia which is reabsorbed and carbonic acid The microflora also degrades a wide variety of organic c