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Biomedical subjects

G R Gibson

Publications and source records attributed to G R Gibson.

At least 73 records · Page 4Linked to original sources
PubMed1997

Nutritional aspects of dissimilatory sulfate reduction in the human large intestine.

In contrast to other anaerobic ecosystems, such as marine and estuarine sediments, there is a lack of information on the nutritional requirements of human gut sulfate-reducing bacteria (SRB). Various substrates stimulated sulfate reduction in mixed culture, including short-chain fatty acids and other organic acids, alcohols, and amino acids (but not sugars or aromatic compounds). However, the use of sodium molybdate as a specific inhibitor of sulfate reduction caused an accumulation of ethanol and malonate only, and reduced the rate of utilization of lactate. This indicates the importance of these electron donors for sulfate reduction. Since ethanol and lactate are primarily utilized by members of the Desulfovibrio genus, the results suggest a physiologically important role for this group. Experiments with two strains of Desulfovibrio desulfuricans isolated from human feces demonstrated that both were able to reduce sulfite, thiosulfate or nitrate in the absence of sulfate. In addition, one strain (DsvUC1) was able to grow by fermentative metabolism, although the second strain (DsvFD1) showed more restricted fermentative growth. The data indicate that desulfovibrios are ecologically the most significant group of SRB in the human colon, and that colonic isolates belonging to this genus are versatile, in terms of both the electron acceptors and donors that they are able to utilize.

Acetates↗
PubMed1997

Modification of the intestinal microflora using probiotics and prebiotics.

Probiotics and prebiotics modulate the composition of the human gut microbiota. The beneficial effects may result from suppression of harmful microorganisms or stimulation of organisms which contribute in a positive way to the nutrition and health of the host. Both types of supplement represent an attempt to reconstitute the gut flora to its normal composition which has been adversely affected by dietary and environmental stresses.

Animals↗
PubMed1995

Growth, incidence and activities of dissimilatory sulfate-reducing bacteria in the human oral cavity.

Viable counts and activities of sulfate-reducing bacteria were determined in the oral cavities of 12 healthy volunteers. Of these, 10 harboured viable sulfate-reducing bacteria populations. Six separate sites were sampled: the posterior tongue, anterior tongue, mid buccal mucosa, vestibular mucosa, supragingival plaque and subgingival plaque. Sulfate-reducing bacteria occurred in all areas, with the highest incidence in supragingival plaque. Viable counts and sulfate-reducing activities in each of the regions varied from 0 to 10(8) cfu (g wet weight)-1 and from 0 to 50 nmol (g wet weight)-1 h-1, respectively. As sulfate-reducing bacteria can be detected in the oral cavity, they may potentially be involved in terminal oxidative processes carried out by the microflora of the mouth.

Adult↗
PubMed1995

Co-culture of Bifidobacterium adolescentis and Bacteroides thetaiotaomicron in arabinogalactan-limited chemostats: effects of dilution rate and pH.

The effects of dilution rate (D = 0.04-0.38/h) and pH (5.0-6.5) on co-cultures of Bifidobacterium adolescentis and Bacteroides thetaiotaomicron were studied in arabinogalactan-limited chemostats. B. thetaiotaomicron outcompeted B. adolescentis at all dilution rates at culture pH values between 5.0 and 6.0, although the bifidobacterium was always detected in the fermenters. At pH 6.5, however, B. adolescentis predominated in co-cultures at dilution rates above 0.24/h. Arabinogalactan degrading enzymes (beta-galactosidase, alpha-arabinofuranosidase) were strongly catabolite repressed in bacteroides at high dilution rates, but were constitutive and growth rate-associated in B. adolescentis. The increased competitiveness of B. adolescentis at high specific growth rates was not related to its ability to synthesise increased levels of depolymerising enzymes. Measurements of residual carbohydrate in pure and mixed culture chemostats showed that the bacteroides extensively digested the galactose backbone of the polymer, and to a lesser degree, the arabinose sidechains. Nevertheless, arabinose monomers and oligosaccharides (d.p. < 10) accumulated in these cultures under all growth conditions. In contrast, the bifidobacterium utilized considerably less arabinogalactan than the bacteroides, and this was reflected in the mixed culture studies. These experiments demonstrate that B. thetaiotaomicron was able to compete most successfully for this plant cell wall polysaccharide under nutritional, physiological and environmental conditions broadly similar to those encountered in the human colon, and indicate the existence of synergistic interactions between the two organisms that were growth rate dependent.

Journal Article↗
PubMed1995

Selective stimulation of bifidobacteria in the human colon by oligofructose and inulin.

BACKGROUND/AIMS: Oligofructose and inulin are naturally occurring indigestible carbohydrates. In vitro they selectively stimulate the growth of species of Bifidobacterium, a genus of bacteria considered beneficial to health. This study was designed to determine their effects on the large bowel microflora and colonic function in vivo. METHODS: Eight subjects participated in a 45-day study during which they ate controlled diets. For the middle 15 days, 15 g.day-1 oligofructose was substituted for 15 g.day-1 sucrose. Four of these subjects went on to a further period with 15 g.day-1 inulin. Bowel habit, transit time, stool composition, breath H2 and CH4, and the predominant genera of colonic bacteria were measured. RESULTS: Both oligofructose and inulin significantly increased bifidobacteria from 8.8 to 9.5 log10 g stool-1 and 9.2 to 10.1 log10 g stool-1, respectively, whereas bacteroides, clostridia, and fusobacteria decreased when subjects were fed oligofructose, and gram-positive cocci decreased when subjects were fed inulin. Total bacterial counts were unchanged. Fecal wet and dry matter, nitrogen, and energy excretion increased with both substrates, as did breath H2. Little change in fecal short-chain fatty acids and breath CH4 was observed. CONCLUSIONS: A 15-g.day-1 dietary addition of oligofructose or inulin led to Bifidobacterium becoming the numerically predominant genus in feces. Thus, small changes in diet can alter the balance of colonic bacteria towards a potentially healthier microflora.

Adult↗
PubMed1995

Dietary modulation of the human colonic microbiota: introducing the concept of prebiotics.

Because the human gut microbiota can play a major role in host health, there is currently some interest in the manipulation of the composition of the gut flora towards a potentially more remedial community. Attempts have been made to increase bacterial groups such as Bifidobacterium and Lactobacillus that are perceived as exerting health-promoting properties. Probiotics, defined as microbial food supplements that beneficially affect the host by improving its intestinal microbial balance, have been used to change the composition of colonic microbiota. However, such changes may be transient, and the implantation of exogenous bacteria therefore becomes limited. In contrast, prebiotics are nondigestible food ingredients that beneficially affect the host by selectively stimulating the growth and/or activity of one or a limited number of bacterial species already resident in the colon, and thus attempt to improve host health. Intake of prebiotics can significantly modulate the colonic microbiota by increasing the number of specific bacteria and thus changing the composition of the microbiota. Nondigestible oligosaccharides in general, and fructooligosaccharides in particular, are prebiotics. They have been shown to stimulate the growth of endogenous bifidobacteria, which, after a short feeding period, become predominant in human feces. Moreover, these prebiotics modulate lipid metabolism, most likely via fermentation products. By combining the rationale of pro- and prebiotics, the concept of synbiotics is proposed to characterize some colonic foods with interesting nutritional properties that make these compounds candidates for classification as health-enhancing functional food ingredients.

Bacteria↗
PubMed1994

Enrichment of bifidobacteria from human gut contents by oligofructose using continuous culture.

Chemostat cultures of human faecal bacteria were used to determine the bifidogenic effect of oligofructose, a fermentable carbohydrate found in a number of plants. In single stage continuous culture, oligofructose preferentially enriched for bifidobacteria, in comparison to sucrose and inulin. This stimulatory effect was enhanced at a high dilution rate, high substrate concentration and low pH. These parameters are likely to approximate to those that occur in the proximal colon. Studies with a three-stage continuous culture model of the large intestine confirmed the bifidogenic effect of oligofructose. These in vitro data indicate that an increase in the concentration of fructose-based oligosaccharides in the diet may alter the balance of the gut microflora towards bifidobacteria, a purported health-promoting genus.

Anaerobiosis↗
PubMed1994

Isolation of Helicobacter pylori from feces of patients with dyspepsia in the United Kingdom.

BACKGROUND/AIMS: Epidemiological studies suggest that fecal-oral spread of Helicobacter pylori potentially represents an important route of infection. However, the bacterium has never been isolated from feces of adults in the developed world. This study attempted to isolate H. pylori from stool specimens donated by 36 adults from the United Kingdom who had dyspepsia. METHODS: Fresh fecal samples were obtained and, after centrifugation to harvest bacteria, cultured onto H. pylori selective growth media. Pure colonies of H. pylori were obtained by subculture and were then analyzed using polymerase chain reaction to confirm genotypic identity. RESULTS: H. pylori was isolated from feces in 12 of 25 subjects with dyspepsia proven to be H. pylori-positive at endoscopy and/or 14C urea breath test. Initial bacterial identification was made on the basis of various phenotypic methods. Genotypic confirmation that the bacterium was indeed H. pylori was also made. CONCLUSIONS: This study is the first to conclusively show that H. pylori can be isolated from feces obtained from adults in the United Kingdom. The implication of this finding is that transmission of H. pylori infection by the fecal-oral route is feasible.

Base Sequence↗
PubMed1994

Regulatory effects of bifidobacteria on the growth of other colonic bacteria.

In the human large intestine bifidobacteria are a numerically important group of micro-organisms which are considered to exert a range of biological activities related to host health. One aspect is the inhibitory effect of these bacteria on other species, possibly excluding long term colonization by invasive pathogens. It has been suggested that the mechanism of inhibition carried out by bifidobacteria is related to the fermentative production of acids such as acetate and lactate. Experiments reported in this paper attempted to address this theory. Co-culture experiments whereby Bifidobacterium infantis was incubated with Escherichia coli and Clostridium perfringens, in a variety of fermentation systems, indicated that the bifidobacterium was able to exert an inhibitory effect not necessarily related to acid production. Further studies showed that eight species of bifidobacteria could variously excrete an anti-microbial substance with a broad spectrum of activity. Species belonging to the genera Salmonella, Listeria, Campylobacter and Shigella, as well as Vibrio cholerae, were all affected. These results show that bifidobacteria are able to exert more than one mechanism of inhibition, which may be of some importance with regard to protection against gastroenteritis.

Acetates↗
PubMed1993

Impaired hydrogen metabolism in pneumatosis cystoides intestinalis.

BACKGROUND: Pneumatosis cystoides intestinalis (PCI) is characterized by high levels of breath hydrogen. Clinical features of PCI may be due to abnormal H2 metabolism. METHODS: Breath levels of H2 and CH4 were measured in 3 patients and total gas in 2 patients with PCI on a polysaccharide-free (basal) diet and after administration of 15 g of lactulose. Metabolic activities and counts of methanogenic (MB) and sulfate-reducing (SRB) bacteria were measured in feces. Ten volunteers were also studied. RESULTS: Total H2 levels in patients were 383-420 mL/day on the basal diet and 1430-1730 mL/day after lactulose administration compared with 35 +/- 6 mL/day and 262 +/- 65 mL/day, respectively, in controls. Basal breath H2 levels in controls were 27 +/- 6 vs. 214 +/- 27 mL/day in patients and after lactulose ingestion, 115 +/- 18 vs. 370 +/- 72 mL/day. Four controls were methanogenic and had high fecal MB counts. The other controls had high SRB counts and sulfate reduction rates. All patients were nonmethanogenic and had low sulfate reduction rates. CONCLUSIONS: Patients with PCI excrete more H2 than controls. In normal subjects, H2 is consumed by MB or SRB; the activity of these bacteria is virtually absent in PCI. This may explain the gas accumulation in these patients.

Adult↗
PubMed1993

Effects of the in vitro fermentation of oligofructose and inulin by bacteria growing in the human large intestine.

The in vitro fermentability of oligofructose and inulin was compared with a range of reference carbohydrates by measuring bacterial end-product formation in batch culture. Short chain fatty acid and gas formation indicated that these substrates, which occur naturally in the diet and reach the colon in a largely intact form, were utilized by mixed populations of gut bacteria. Bacterial growth data showed that oligofructose and inulin exerted a preferential stimulatory effect on numbers of the health-promoting genus Bifidobacterium, whilst maintaining populations of potential pathogens (Escherichia coli, Clostridium) at relatively low levels. Pure culture studies confirmed the enhanced ability of bifidobacteria to utilize these substrates in comparison with glucose. Batch culture experiments demonstrated that the growth of Bifidobacterium infantis had an inhibitory effect towards E. coli and Clostridium perfringens. Potentially, an increase in the concentration of these substrates in the diet may therefore improve the composition of the large intestinal microflora and have positive effects on the quality of the Western diet.

Adult↗
PubMed1993

The biochemistry of oligofructose, a nondigestible fiber: an approach to calculate its caloric value.

Oligofructose, a natural food ingredient, is the product of partial enzymatic hydrolysis of inulin. This nondigestible oligosaccharide is fermented by colonic bacteria to produce mainly short-chain fatty acids, L-lactate, and CO2 and the energy necessary for bacterial growth. It also increases fecal mass. Based on biochemical balance charts for carbon atoms, metabolic pathways, and energy yield to the host, the caloric value of a fructosyl unit of oligofructose is calculated to be 25-35% that of a digested molecule of hexose. The caloric value of oligofructose is thus likely to be close to 1 kcal/g.

Animals↗
PubMed1992

Isolation of Helicobacter pylori from human faeces.

Helicobacter pylori is arguably the commonest chronic infection in man. However, its route of transmission is unknown. We have isolated viable H pylori from the faeces of an infected individual from The Gambia. The organism was cultured on selective media after concentration of faecal bacteria by centrifugation in a buffer equilibrated with a microaerophilic gas mixture. Growth characteristics, microscopic appearances, and enzyme activities were the same as those of a typical gastric isolate of H pylori. Protein preparations derived from the new isolate and the typical strain were antigenically similar, and had very similar electrophoretic profiles (including two major protein bands of 62 and 26 kDa, corresponding to the urease enzyme subunits). With the same technique, organisms with the colony morphology, growth requirements, enzyme activities, and microscopic appearances of H pylori were isolated from the faeces of 9 of 23 randomly selected children aged 3-27 months from a Gambian village with a high prevalence of H pylori infection in early life. Faecal-oral transmission is probably important in the spread of infection in such communities.

Adult↗