Effect of diet and Lactobacillus acidophilus supplements on human fecal bacterial enzymes

Protection against gastrointestinal diseases--present facts and future developments

The importance of the intestinal microflora and, more specifically its composition, in physiological and pathophysiological processes in the human GIT is becoming more evident. Examples of such processes are translocation, the production and resorption of endotoxins, immune-modulation, and colonic motility. This leads to new possibilities for prevention and therapy of diseases, mainly of the gastrointestinal organs. New discoveries are specifically related to the beneficial effects of lactobacilli which have been discussed for decades. It is possible to increase the proportion of lactobacilli in the gastrointestinal microflora by consumption of fermented dairy products or by oral administration of specific non-digestible substrates such as oligofructose. Results from clinical trials and scientific studies have confirmed the preventive and therapeutic effects of selected strains of lactobacilli in viral- and bacterial-induced intestinal infections, in positively influencing immunological parameters, in normalizing the intestinal motility, and in inhibiting metabolic events in the gut lumen which promote colonic carcinogenesis. Nevertheless, there are still unresolved issues which can only be answered by well designed and well controlled clinical trials.

Overview of gut flora and probiotics

Scientific developments in recent years have opened new frontiers and enable a better understanding of the gastrointestinal tract (GIT) as a complex and delicately balanced ecosystem. This paper focuses on more recent information related to the microbial population of the GIT and its functional role in human physiology and health. Special attention is also given to modern approaches for improving or stabilising the intestinal system and its functioning by the deliberate application of viable microbial cultures, so-called 'probiotics', selected for special functional properties.

Cell-free whey from milk fermented with Bifidobacterium breve C50 used to modify the colonic microflora of healthy subjects

The ingestion of viable bacteria is thought to be required to modify intestinal microflora. In the present study, the effects on fecal flora of consumption of cell-free concentrated whey from milk that had been fermented with Bifidobacterium breve C50 was tested using 10 healthy human volunteers. Results were compared with effects of a commercial milk formula that had been fermented with Streptococcus thermophilus and B. breve C50 and given to 10 control subjects. Nitroreductase and beta-glucuronidase activities were assessed as risk indexes for colon carcinogenesis, and beta-galactosidase was measured as an indicator of the fermentation capacity of the colonic flora. Fecal excretion of Bacteroides fragilis, Clostridium perfringens, and clostridial spores decreased after 7 d of consumption of either preparation; however, counts of bifidobacteria only increased after intake of B. breve whey. Fecal pH was reduced from 7.1 +/- 0.2 to 6.6 +/- 0.3 after intake of whey that had been fermented with Bif. breve. Fecal nitroreductase and beta-glucuronidase significantly decreased, and beta-galactosidase activity increased, after consumption of either preparation. The results indicate that ingestion of viable bifidobacteria was not required to modify intestinal flora of humans. Repression of B. fragilis and clostridia seems to be independent of colonic bifidobacterial overgrowth in humans.

Probiotics: Functionality and commercial status

Probiotics in the form of fermented milk products have been consumed for centuries. In this century various health benefits have been purported to result from consumption of foods containing live microorganisms, particularly lactic acid bacteria (LAB). Probiotics can provide relief for lactose intolerant individuals and reduce bouts of diarrhea. Evidence for other claims such as lowering serum cholesterol, suppressing cancer and stimulating the immune system remains to be clearly established by conducting well-controlled, statistically-valid clinical trials. Although the benefits to healthy individuals are uncertain, many consumers especially in Japan and Europe, perceive probiotic products to be healthful, and sales are robust.

The effect of food restriction on the composition of intestinal microflora in rats

The effect of a food-restricted diet on the fecal microflora of rats was studied by determining total anaerobic bacteria, bacterial cellular fatty acids, and the predominant intestinal bacteria shown by polymerase chain reaction (PCR) primers specific for the 16S rRNA gene sequences of 12 bacterial species. Twenty-four female Fischer 344 rats, 57 days old were divided into two groups and maintained on an NIH-31 diet. One group was fed ad libitum while the other group received 60% of ad libitum food intake (40% food restriction supplemented with vitamins and minerals equal to the ad libitum animals). After 2, 10, and 20 weeks on this dietary regimen, groups of four animals were sacrificed and the intestinal contents analyzed for changes in the bacterial flora. The anaerobic population for two-week (short-term) food-restricted rats was 3.2 x 10(8) per gram, slightly less than the 9.1 x 10(8) per gram found in the ad libitum-fed rats. The anaerobic populations in 20-week food restricted and ad libitum fed rats were 1.9 x 10(9) and 2.7 x 10(9) per gram, respectively. The total anaerobic population did not change significantly in either group during the 20-week study. No statistically significant differences were observed in the bacterial cellular fatty acid profiles between the two groups as determined by gas-liquid chromatography. PCR analysis of the intestinal contents indicated no significant shifts in the predominant flora due to dietary changes. The results, using three different methods to detect changes in the rat intestinal microflora, suggest that long-term dietary restriction had little effect on the microflora of female Fischer 344 rats.

Effects of lactic acid bacteria on binding and absorption of mutagenic heterocyclic amines

Effects of binding heterocyclic amines to cells of lactic acid bacteria on theirs absorption were investigated. Cells of Lactobacillus delbrueckii subsp. bulgaricus 2038 and Streptococcus thermophilus 1131 bind both 3-amino-1,4-dimethyl-5H-pyrido[4,3-b]indole (Trp-P-1) and 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx). The binding of strain 1131 cells to Trp-P-1 was maximum in the pHs from 4 to 8, but strain 2038 cells bound Trp-P-1 and MeIQx only slightly at pH 7. We investigated the absorption of heterocyclic amines by the small intestine of F344 rats in the presence of these bacterial cells, using an in situ loop technique. The absorption of Trp-P-1 by the small intestine was significantly lower in the presence of strain 1131 cells than in the absence of the cells, but the presence of strain 2038 cells had no effect on Trp-P-1 absorption. Perhaps strain 1131 cells bind to Trp-P-1 at the same pH as that of the small intestine (pH 6-7) and thus decrease its absorption.

Pattern of metabolism and composition of the fecal microflora in infants 10 to 18 months old from day care centers

BACKGROUND

From 5 months of age, infants are progressively introduced to a variety of foods which influence the equilibrium of the intestinal microflora.

METHODS

Thirty-five children age 10-18 months from 8 day care centers in France were studied. Fecal specimens were examined for their biochemical and microbiological criteria.

RESULTS

Bifidobacteria and Bacteroides belong to the predominant populations (9.7 and 8.6 log 10 cfu/g, respectively). The mean level of enterobacteria and enterococci were 8.0 and 7.8 log 10 cfu/g, respectively. Only 10% of the infants presented a lactobacilli amount above 6 log 10 cfu/g. Most feces had similar pH values (mean 6.4), percentage of water (mean 76.4%), and short chain fatty acid, ammonia and lactic acid concentrations (means 77, 6.7 and 2.3 mumol/g, respectively). beta-galactosidase had the highest activity (106 IU/g of protein) and nitroreductase, the lowest (0.1 IU/g of protein). alpha-glucosidase and nitrate reductase showed intermediate values of 17 and 4 IU/g of protein, respectively. With the exception of 4 infants, beta-glucosidase and beta-glucuronidase values were low (4 and 2 IU/g of protein). Age and day care center were not significant factors for most parameters studied, except that rotavirus was related to day care center, with detection in 5 infants from the same center.

CONCLUSIONS

Many biochemical parameters were comparable to those found in adults, with the exception of ammonia concentration and beta-galactosidase activity. The fecal bacterial profile was different than in adults, with more Bifidobacteria than Bacteroides and higher levels of facultative anaerobes. One infant suffering from gastroenteritis had distinctive biochemical and bacterial parameters.

Effects of a high-fat diet on azoxymethane-induced aberrant crypt foci and fecal biochemistry and microbial activity in rats

To shed light on the association of dietary fat with the development of colon cancer, we studied the ability of azoxymethane (AOM) to induce aberrant crypt foci (ACF) and biochemical changes in rats fed high- or normal-fat diets. Six-week-old male Fischer 344 rats were placed on a high-fat [7% (wt/wt) soybean oil + 15% (wt/wt) beef tallow] or a normal-fat (7% soybean oil, AIN-93G) diet. Rats fed each of these diets were given two weekly subcutaneous injections of AOM (15 mg/kg body wt) or saline at seven and eight weeks of age. Fecal samples were obtained at 10 weeks of age, and animals were sacrificed for ACF scoring and analysis of cecal contents at 13 weeks of age. We observed greater numbers of ACF in the high- than in the low-fat group. Biochemically, rats fed the high-fat diet showed dramatically elevated fecal and cecal long-chain free fatty acid levels and intestinal alkaline phosphatase activity. These animals also showed increased cholesterol and decreased coprostanol levels. We did not detect significant differences in the fecal and cecal concentrations of total and soluble bile acids or total neutral sterols (cholesterol + coprostanol) between the two groups. Thus a high-fat diet does show certain striking effects on colon biochemistry in rats.

Effects of lactulose and lactitol on colonic microflora and enzymatic activity

The effects of lactulose and lactitol (2 x 10 g/d) were studied in 36 healthy volunteers in comparison to placebo. All parameters studied were affected by both treatments, lactulose in general leading to more pronounced changes compared to lactitol. Probiotic bacteria were increased, and putrefactive bacteria and potential pathogens were significantly reduced. These variations in colonic flora had the following consequences: (i) a reduced activity of pro-carcinogenic enzymes: azoreductase, 7 alpha-dehydroxylase, beta-glucuronidase, nitroreductase and urease activity; (ii) a global increase of short-chain fatty acids in faeces; (iii) an effect on pH and moisture of faeces, and (iv) also on aromatic compounds such as phenol, cresol, indole and skatol. The findings suggest that lactulose and lactitol are not comparable in their effect on the colonic microflora, its metabolism, and the consequent probiotic effects on human health. The differences found may also be of clinical relevance suggesting that neither compound is equipotent.

Technical problems related to in vitro study of colon flora

The complexity of colon flora and the technical problems encountered in the sampling techniques and their processing limit the study of its composition and activities. First, we list the main limitations related to the sampling procedure-transport and storage. We show that (i) use of a cryoprotective medium is necessary for sample storage and (ii) that storage has to be at -40 degrees C. Second, bacterial analysis and enzymatic activities are examined. The lack of specificity of the culture media generally used means that systematic studies are difficult to carry out and that bacterial identification at species level requires genetic techniques. Third, we show that activities of procarcinogenic enzymes are significantly affected by any kind of storage. Finally, for statistics, the problem of the size and the nutritional habits of the studied population is examined.

Tauroconjugation of cholic acid stimulates 7 alpha-dehydroxylation by fecal bacteria

We examined the effect of the type of cholic acid conjugation (taurine-conjugated, glycine-conjugated, or unconjugated cholic acid) on cholic acid 7 alpha-dehydroxylation by intestinal flora. Cholic acid 7 alpha-dehydroxylation in fecal cultures, in cultures of a defined limited flora consisting of a mixture of seven bacterial species isolated from the intestinal tract, and in a binary culture of a 7 alpha-dehydroxylating Clostridium species plus a cholic acid-deconjugating Bacteroides species was studied. We found that tauroconjugation of cholic acid significantly (P < 0.05) increased bacterial 7 alpha-dehydroxylation of cholic acid into deoxycholic acid from 34 to 55% in fecal cultures, from 45 to 60% in defined limited fecal cultures, and from 75 to 100% in binary cultures. Equimolar concentrations of free taurine did not stimulate 7 alpha-dehydroxylation in fecal cultures or in the defined limited flora, but free taurine did stimulate 7 alpha-dehydroxylation in the binary culture. In the binary culture of Clostridium species strain 9/1 plus Bacteroides species strain R1, the minimal flora capable of increased 7 alpha-dehydroxylation of taurocholic acid, strain R1 deconjugated taurine and rapidly reduced it to H2S. Bacteroides species strain R1 did not grow unless taurine or another appropriate reducible sulfur source was present. Clostridium species strain 9/1 did not grow or 7 alpha-dehydroxylate unless H2S or another source of reduced sulfur was present. We conclude that the increased 7 alpha-dehydroxylation of tauroconjugated cholic acid depends on the reduction of taurine to H2S, which is a necessary growth factor for the 7 alpha-dehydroxylating bacteria.

Effects of fish oil on fecal bacterial enzymes and steroid excretion in healthy volunteers: implications for colon cancer prevention

Diet-induced changes in fecal excretion of secondary bile acids, certain neutral sterols, and bacterial enzyme activities are known to play a role in colon cancer development. Dietary fish oil (FO) has been implicated as a protective agent in colon carcinogenesis. In the present study, the effects of FO and corn oil (CO) on these fecal parameters were investigated in 24 healthy volunteers consuming a low- or a high-fat diet (30% or 50% of energy derived from fat). After four weeks of FO or CO supplementation (4.4 g of n-3 fatty acids/day), no significant differences were noted for fecal activities of beta-glucuronidase, beta-glucosidase, and sulfatase, nor was fecal bile acid excretion significantly affected by FO or CO consumption. However, daily excretion of the putative colon carcinogen 4-cholesten-3-one was significantly lower in the FO than in the CO period during low- and high-fat experiments. This may be another biochemical mechanism by which FO exerts its protective effect on colon cancer development.

Effects of fructo-oligosaccharides ingestion on fecal bifidobacteria and selected metabolic indexes of colon carcinogenesis in healthy humans

Fructo-oligosaccharides (FOS) are a mixture of oligosaccharides consisting of glucose linked to fructose units. They are not digested in the human small intestine but fermented in the colon, where they could specifically promote the growth of some species of the indigenous microflora, especially bifidobacteria. We assessed in healthy humans the effects of FOS ingestion in fecal bifidobacteria and selected metabolic indexes potentially involved in colonic carcinogenesis. Twenty volunteers randomly divided into two groups were studied for three consecutive 12-day periods. During the ingestion period, they received 12.5 g/day FOS or placebo (saccharose) in three oral doses. Stools were regularly collected and analyzed. FOS ingestion led to an increase in fecal bifidobacterial counts [7.9 +/- 0.5 to 9.1 +/- 0.3 (SE) log colony-forming units/g wet wt, p < 0.01] and beta-fructosidase activity (9.6 +/- 1.9 to 13.8 +/- 1.9 IU/g dry wt, p < 0.01). In contrast, FOS ingestion had no significant effect on fecal total anaerobes, pH, the activities of nitroreductase, azoreductase, and beta-glucuronidase, and the concentrations of bile acids and neutral sterols. We conclude that ingestion of FOS, at a clinically tolerated dose of 12.5 g/day, led to an increase in colonic bifidobacteria. This effect was not associated in healthy humans with beneficial changes in various factors potentially involved in the pathogenesis of colonic cancer.

Dietary fat and colon cancer

Dietary fat in general, and perhaps animal and polyunsaturated fats in particular, appear to increase colon carcinogenesis in animal models and epidemiologic studies. This observation holds the potential to shed light on the underlying mechanisms of colorectal carcinogenesis and reduce morbidity and mortality from the disease by dietary and chemoprevention. While research continues into the relationship between prostglandins and other putative mediators of the effects of fats on the colon, we can suggest that a diet which protects against colorectal cancer would be low in fat with most of that fat coming from vegetable sources. Prospective dietary trials are ongoing which may strengthen or modify these preliminary recommendations.

Effect of milks inoculated with Lactobacillus acidophilus or a yogurt starter culture in lactose-maldigesting children

Dairy products containing live bacteria that possess lactase activity are used for dietary management of lactose maldigestion. The efficacy of acidophilus milk and the effect of consuming unfermented milk that had been inoculated with yogurt bacteria have not been examined in children. We compared scores for breath H2 excretion and symptoms of 20 lactose-maldigesting children following ingestion of 250 ml of uninoculated milk with two identical milks inoculated with 10(10) cells of Lactobacillus acidophilus or with a commercial yogurt starter culture containing 10(8) cells of Lactobacillus lactis and 10(10) cells of Streptococcus thermophilus. Nine of 10 subjects who were symptomatic following ingestion of uninoculated milk experienced a reduction in symptoms following ingestion of milk inoculated with L. acidophilus, without a decline in H2 excretion. Five of 6 subjects who were symptomatic following uninoculated milk had decreased symptoms and a significant reduction in H2 excretion following milk inoculated with the yogurt culture. For lactose-maldigesting children, milks inoculated with L. acidophilus or with a yogurt culture were associated with decreased symptoms compared with those with uninoculated milk.

Effects of three microbial probiotics on postprandial porto-arterial concentration differences of glucose, galactose and amino-nitrogen in the young pig

Postprandial kinetics of porto-arterial concentration differences of glucose (G), galactose (Gal), L-lactic acid (LA) and amino-N (AN) were studied in the piglet after the ingestion of 10(7) colony-forming units (cfu) Sporolactobacillus P44 (SP), or 10(6) cfu Bacillus cereus IP5832 (AC), or 10(6) cfu of a combination of Lactobacillus acidophilus, L. fermentum and L. brevis (AB)/g feed. Sixteen fistulated piglets (portal vein and brachiocephalic trunk; mean body weight 22 (SD 2) kg) were used. The diet was based on skimmed milk (320 g/kg), barley (300 g/kg), wheat bran (110 g/kg), maize (100 g/kg) and lactose (70 g/kg). The postprandial blood kinetics, four measurements per animal at 1-week intervals, were studied for 6 h after the ingestion of test meals of 400 g basal diet (BD) or this diet supplemented with the bacteria (SP, AC and AB respectively). Areas of porto-arterial concentration differences (APACD) of G, Gal and LA were not influenced by the bacteria supplements. APACD of AN was significantly higher after the ingestion of the SP diet than that estimated for BD.

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.

Anticarcinogenic, hypocholesterolemic, and antagonistic activities of Lactobacillus acidophilus

Lactobacillus acidophilus is considered to possess health-promoting attributes. These include anticarcinogenic and hypocholesterolemic properties and antagonistic action against intestinal and food-born pathogens. L. acidophilus can also survive the hostile environment and establish in the complex ecosystem of the gastrointestinal tract. Therefore, the beneficial effects of ingesting L. acidophilus accrue over a longer period than those organisms that cannot colonize the gut. However, the exact mechanisms of these attributes are not known. Presumably, the anticarcinogenic activity may be attributed to production of compounds and/or conditions that inhibit the proliferation of tumor cells, suppression of microorganisms that convert procarcinogens to carcinogens, and degradation of carcinogens formed. They hypocholesterolemic effect is probably exerted by inhibition of 3-hydroxy-3-methylglutaryl CoA reductase, which is a rate-limiting enzyme in endogenous cholesterol biosynthesis in the body and by promoting the excretion of dietary cholesterol in feces as a result of coprecipitation in the presence of deconjugated bile acids in the intestine and/or adsorption by the organisms. The antagonistic effect against pathogens and other organisms is possibly mediated by competition for nutrients and adhesion sites, formation of metabolites such as organic acids, hydrogen peroxide, and production of antibiotic-like compounds and bacteriocins.

Metabolism of 7-nitrobenz[a]anthracene by intestinal microflora

Pure cultures of anaerobic intestinal bacteria and mixed fecal microflora from human, rat, mouse, and pig were screened for the ability to metabolize 7-nitrobenz[a]anthracene (7-NO2BA). Based on analysis by high-performance liquid chromatography (HPLC) and by ultraviolet (UV), mass, and nuclear magnetic resonance (NMR) spectral techniques, the compounds were identified as 7-aminobenz[a]anthracene (7-NH2BA) and benz[a]anthracene 7,12-dione (dione). Identification of 7-NH2BA as a metabolite of 7-NO2BA indicates that the anaerobic intestinal bacteria are capable of reducing 7-NO2BA to potentially bioactive intermediates. The reductive capacities of the mixed intestinal microflora were generally greater than those of pure cultures. Thus, metabolism of 7-NO2BA in the intestinal tract may be underestimated if pure cultures are used as the sole method for evaluating the potential hazard.

High concentrations of conjugated bile acids inhibit bacterial growth of Clostridium perfringens and induce its extracellular cholylglycine hydrolase

To investigate the effects of conjugated bile acid on bacterial growth and cholylglycine hydrolase activity, Clostridium perfringens from human feces was exposed to varying concentrations of taurine- or glycine-conjugated chenodeoxycholic acid. Extracellular enzyme activity was determined by deconjugation of radiolabeled taurocholic acid and viable cells were counted after anaerobic culture at 37 degrees C for 24 h. Viable cells were decreased with more than 1.0 mg of conjugated chenodeoxycholic acid per mL and there were no viable cells with 10.0 mg of bile acid per mL. Although total enzyme activity was decreased according to the bile acid concentration, enzyme activity per bacterium was increased between 1.0 and 4.0 mg/mL. There were no statistically significant differences between the types of conjugation. It was concluded that conjugated bile acids may exert inhibitory effect on bacterial growth and extracellular cholylglycine hydrolase activity in Clostridium perfringens. However, under the physiologic condition in the human intestine, conjugated bile acid might induce production of extracellular cholyglycine hydrolase per bacterium.

A note on lactobacilli and beta-glucuronidase activity in the intestinal contents of mice

A comparison was made of caecal beta-glucuronidase activity in the caecal contents of mice with or without lactobacilli as members of the normal microflora. Male mice that did not have lactobacilli as intestinal inhabitants had approximately 52% more caecal beta-glucuronidase activity than their female counterparts. Colonization of male mice by lactobacilli reduced the beta-glucuronidase activity to that of female mice.

An uncooked vegan diet shifts the profile of human fecal microflora: computerized analysis of direct stool sample gas-liquid chromatography profiles of bacterial cellular fatty acids

The effect of an uncooked extreme vegan diet on fecal microflora was studied by direct stool sample gas-liquid chromatography (GLC) of bacterial cellular fatty acids and by quantitative bacterial culture by using classical microbiological techniques of isolation, identification, and enumeration of different bacterial species. Eighteen volunteers were divided randomly into two groups. The test group received an uncooked vegan diet for 1 month and a conventional diet of mixed Western type for the other month of the study. The control group consumed a conventional diet throughout the study period. Stool samples were collected. Bacterial cellular fatty acids were extracted directly from the stool samples and measured by GLC. Computerized analysis of the resulting fatty acid profiles was performed. Such a profile represents all bacterial cellular fatty acids in a sample and thus reflects its microflora and can be used to detect changes, differences, or similarities of bacterial flora between individual samples or sample groups. GLC profiles changed significantly in the test group after the induction and discontinuation of the vegan diet but not in the control group at any time, whereas quantitative bacterial culture did not detect any significant change in fecal bacteriology in either of the groups. The results suggest that an uncooked extreme vegan diet alters the fecal bacterial flora significantly when it is measured by direct stool sample GLC of bacterial fatty acids.

Diet and colon cancer in Los Angeles County, California

The diets of 746 colon cancer cases in Los Angeles County, California (USA) were compared with those of 746 controls matched on age, sex, race, and neighborhood. In both genders, total energy intake was associated with significantly increased risk, and calcium intake was associated with significantly decreased risk. These effects were reduced only slightly after adjustment for the nondietary risk factors (weight, physical activity, family history, and, if female, pregnancy history). In men, total fat and alcohol intakes were responsible for the calorie effect; in women, no individual source of calories was associated independently with risk. Neither saturated fat nor fat from animal sources was responsible for the fat effect. There were no additional independent significant effects for sucrose, fiber, cruciferous vegetables, beta-carotene, other vitamins, or any other nutrient or micronutrient. In univariate analyses, meats, poultry, breads, and sweets were associated with excess risk, and yogurt was protective. After adjustment for sources of calories, no individual food was associated with excess risk, but yogurt remained significantly protective. Total calories were associated with excess risk throughout the colon while the effects of calcium, fat, and alcohol appeared somewhat stronger in the distal colon. After adjustment, crude fiber was significantly protective in the ascending colon but not even weakly protective in the distal colon.

Impact of Bifidobacterium longum on human fecal microflora

The effects of Bifidobacterium longum feedings for five weeks on the fecal microflora, water contents, pH values, ammonia concentration, and beta-glucuronidase activity were investigated in five healthy human volunteers. Although numbers of major bacterial groups of the fecal microflora were not changed by the bifidobacteria feedings, a remarkably decreasing number of lecithinase-negative clostridia was observed. The percentage of lecithinase-negative clostridia and bacteroides to the total bacterial numbers isolated were decreased during the feedings and numbers of C. paraputrificum and C. innocuum were reduced. A significant reduction of fecal pH values for the last week of the feeding was observed. Ammonia concentration and beta-glucuronidase activity in the feces during the feedings were significantly lower than those before or after the feedings. The oral supplement of B. longum may be introduced to improve the fecal properties such as fecal ammonia concentration and beta-glucuronidase activity, but not the composition of fecal flora.

The reduction of azo dyes by the intestinal microflora

Azo dyes are widely used in the textile, printing, paper manufacturing, pharmaceutical, and food industries and also in research laboratories. When these compounds either inadvertently or by design enter the body through ingestion, they are metabolized to aromatic amines by intestinal microorganisms. Reductive enzymes in the liver can also catalyze the reductive cleavage of the azo linkage to produce aromatic amines. However, evidence indicates that the intestinal microbial azoreductase may be more important than the liver enzymes in azo reduction. In this article, we examine the significance of the capacity of intestinal bacteria to reduce azo dyes and the conditions of azo reduction. Many azo dyes, such as Acid Yellow, Amaranth, Azodisalicylate, Chicago Sky Blue, Congo Red, Direct Black 38, Direct Blue 6, Direct Blue 15, Direct Brown 95, Fast Yellow, Lithol Red, Methyl Orange, Methyl Red, Methyl Yellow, Naphthalene Fast Orange 2G, Neoprontosil, New Coccine, Orange II, Phenylazo-2-naphthol, Ponceau 3R, Ponceau SX, Red 2G, Red 10B, Salicylazosulphapyridine, Sunset Yellow, Tartrazine, and Trypan Blue, are included in this article. A wide variety of anaerobic bacteria isolated from caecal or fecal contents from experimental animals and humans have the ability to cleave the azo linkage(s) to produce aromatic amines. Azoreductase(s) catalyze these reactions and have been found to be oxygen sensitive and to require flavins for optimal activity. The azoreductase activity in a variety of intestinal preparations was affected by various dietary factors such as cellulose, proteins, fibers, antibiotics, or supplementation with live cultures of lactobacilli.

In vivo and in vitro models of the human colonic flora

The study of colonic flora composition and metabolism presents considerable methodological problems. Attempts to circumvent these problems have led to the development of numerous in vitro and in vivo models to simulate the human colon and its microbial population. In terms of in vivo models, conventional laboratory animals have many limitations. Data of greater relevance to man can be obtained by using germ-free rodents associated with human colonic bacteria. The applications of such animals to studies of toxicity of chemicals and gastrointestinal infections are discussed. The advantages and disadvantages of the various in vitro systems for studying gut microflora and its metabolic activity (from simple static cultures to the more sophisticated continuous and semicontinuous flow models) are reviewed. The apparatus involved is described together with practical information on media, running conditions, and sampling. The bacteriological and metabolic criteria for establishing the similarity of the models to the in situ colonic flora are also discussed. The final sections of the review are devoted to the major applications (current and future) of the models, including fermentation studies on dietary fiber, metabolism of nutrients and foreign compounds (including carcinogens) in food, and the investigation of colonization resistance.

Survival of Lactobacillus species (strain GG) in human gastrointestinal tract

A newly isolated strain of a species of Lactobacillus of human origin, designated GG (Lactobacillus GG), has been studied to determine its ability to survive in the human gastrointestinal tract. When fed to 76 volunteers as a frozen concentrate or as a fermented preparation in milk or whey, Lactobacillus GG was recovered in the feces of all subjects receiving the fermented milk or whey and in 86% receiving the frozen concentrate when a single fecal specimen was cultured. The organism was also present in the feces of subjects concurrently receiving ampicillin. After terminating feeding of the organism, Lactobacillus GG persisted in the feces of 87% of volunteers four days later and in 33% of subjects seven days later. Lactobacillus GG lowered fecal bacterial beta-glucuronidase activity by approximately 80% in volunteers given the organism for four weeks. These studies demonstrate that Lactobacillus GG can survive and temporarily colonize the human gastrointestinal tract and can affect the metabolic activity of the resident microflora.

The possible role of probiotics as dietary antimutagen

Possible antimutagenic actions of probiotics--mainly lactic acid bacteria--were examined using in vitro and in vivo test systems. In the Ames test with Salmonella typhimurium TA1538 beef extract and nitrosated beef extract were used as mutagens. L. casei showed high antimutagenic activity on mutagenicity induced by nitrosated beef extract only without S9 mix, whereas Omniflora (a lyophilized preparation of lactobacilli and E. coli) and its cell-free culture broth exhibited antimutagenic action only on beef extract. The actions of probiotics were more homogeneous when living animals were used in the tests. Using busulfan as a mutagen both the chromosome aberration test (with Chinese hamster bone marrow cells) and the micronucleus test (with bone marrow cells of Chinese hamsters and mice) showed strong anticlastogenic action when L. casei, Omniflora or yoghurt (with living bifiobacteria) were given orally at the same time as the mutagen. Lactobacilli were effective also after i.p. injection. Cell-free culture broths had no or only weak antimutagenic effects. Mutagen-induced chromosome aberrations and micronuclei were reduced by up to 80% by the lactobacilli.

Relation of meat, fat, and fiber intake to the risk of colon cancer in a prospective study among women

BACKGROUND

The rates of colon cancer in various countries are strongly correlated with the per capita consumption of red meat and animal fat and, to a lesser degree, inversely associated with the consumption of fiber.

METHODS

We conducted a prospective study among 88,751 women 34 to 59 years old and without a history of cancer, inflammatory bowel disease, or familial polyposis who completed a dietary questionnaire in 1980. By 1986, during 512,488 person-years of follow-up, 150 incident cases of colon cancer had been documented.

RESULTS

After adjustment for total energy intake, animal fat was positively associated with the risk of colon cancer (P for trend = 0.01); the relative risk for the highest as compared with the lowest quintile was 1.89 (95 percent confidence interval, 1.13 to 3.15). No association was found for vegetable fat. The relative risk of colon cancer in women who ate beef, pork, or lamb as a main dish every day was 2.49 (95 percent confidence interval, 1.24 to 5.03), as compared with those reporting consumption less than once a month. Processed meats and liver were also significantly associated with increased risk, whereas fish and chicken without skin were related to decreased risk. The ratio of the intake of red meat to the intake of chicken and fish was particularly strongly associated with an increased incidence of colon cancer (P for trend = 0.0005); the relative risk for women in the highest quintile of this ratio as compared with those in the lowest quintile was 2.49 (95 percent confidence interval, 1.50 to 4.13). A low intake of fiber from fruits appeared to contribute to the risk of colon cancer, but this relation was not statistically independent of meat intake.

CONCLUSIONS

These prospective data provide evidence for the hypothesis that a high intake of animal fat increases the risk of colon cancer, and they support existing recommendations to substitute fish and chicken for meats high in fat.

Shift from a mixed diet to a lactovegetarian diet: influence on some cancer-associated intestinal bacterial enzyme activities

This investigation studied the effects of a shift from a mixed diet to a lactovegetarian diet on some cancer-associated bacterial enzymes in human feces (beta-glucuronidase, beta-glucosidase, and sulphatase). Three months after the shift to the lactovegetarian diet, there was a significant decrease in beta-glucuronidase, beta-glucosidase, and sulphatase activities per gram feces wet weight (p less than 0.05, less than 0.05, and less than 0.001, respectively). In contrast, glucuronide and glucoside hydrolysis remained unchanged per gram dry weight, although sulphatase activity was still significantly lowered when expressed this way (p less than 0.01). However, the fecal excretion increased significantly (p less than 0.05). Part of the explanation for the decreased enzyme activities is obviously a dilution effect, because much of the increased fecal weight after the shift in diet was associated with a higher water content. The higher water content was probably due to a higher fiber intake (p less than 0.001). Thus, the results in this paper indicate that a change from a mixed diet to a lactovegetarian diet leads to a decrease in certain enzyme activities proposed to be risk factors for colon cancer.

The search for the causes of breast and colon cancer

Epidemiological studies of breast and colon cancers implicate diet as a causative factor but the evidence is stronger for colon cancer, the occurrence of which may be reduced by diets with less animal fat and more fruit and vegetables.

Control of Escherichia coli populations by a combination of indigenous clostridia and lactobacilli in gnotobiotic mice and continuous-flow cultures

The function of indigenous lactobacilli in the control of other intestinal microbial species is not clear. Still more controversial is the effect of dietary bacterial supplements containing lactobacilli or other species. This situation is unlikely to change unless the mechanisms that control the colonization of ingested bacteria are better understood, and until more detailed information becomes available on the mechanisms by which certain populations of indigenous bacteria can affect the population sizes of other species. We used gnotobiotic mice and a continuous-flow culture system to study the interactions between Escherichia coli and (i) clostridia (in chloroform-treated cecal suspensions from conventional mice) and (ii) three strains of lactobacilli isolated from conventional mice. In gnotobiotic mice, the lactobacilli suppressed E. coli multiplication in the stomach and the small intestine, but had no demonstrable effect on E. coli multiplication in the large intestine. In contrast, clostridia were most effective in controlling E. coli multiplication in the large intestine. In the presence of both lactobacilli and clostridia, E. coli populations in the various regions of the gastrointestinal tract resembled those found in conventionalized control animals. The control of E. coli populations was not related to changes in pH or intestinal motility. In vitro stimulation of the above-described in vivo interactions required a two-stage continuous-flow culture in which the effluent from the first stage represented the influx to the second. The first stage was inoculated with lactobacilli, and the second stage was inoculated with either a pure culture of E. coli or E. coli and clostridia. In these instances, the E. coli populations in the second stage of the culture resembled in size those found in the large intestine of gnotobiotic mice harboring a similar flora. Although there are some current shortcomings of this in vitro model, we expect that a multistage continuous-flow culture can be developed to satisfactorily model the interactions among bacterial populations along the entire gastrointestinal tract.

Impact of Lactobacillus acidophilus on the normal intestinal microflora after administration of two antimicrobial agents

Twenty healthy volunteers participated in a comparative study concerning the influence of Lactobacillus acidophilus supplements on the normal intestinal microflora after the administration of two antimicrobial agents, enoxacin and clindamycin, respectively. L. acidophilus NCFB 1748 was given as a fermented milk product containing 5 x 10(8)-2 x 10(9) CFU/ml to ten of the volunteers immediately after the administration of the antimicrobial agents. On the seventh day of enoxacin administration enterobacteria were eliminated in nine of ten subjects. Enterococci disappeared or decreased significantly in five subjects. During the L. acidophilus supplementation, there was a significant increase in the number of Escherichia coli in one subject, while enterococci returned to the same level as before enoxacin administration in all subjects.

The influence of nutrition on the systemic availability of drugs. Part II: Drug metabolism and renal excretion

Plasma concentrations of an active compound vary between individuals and within a subject, even if the same drug dosage is used. These differences are related to variations of drug absorption from the gastrointestinal tract, of presystemic drug metabolism in the intestine or the liver, and of drug elimination from the systemic circulation, for instance by hepatic metabolism or renal excretion. All of these processes can be modified by nutrition. However it is necessary to emphasize the significance of the pharmaceutical formulation for variations of both drug absorption and elimination. The role of nutrition should receive adequate attention during therapeutic use of drugs as well as in drug disposition studies. Recent guidelines for the assessment of the systemic availability of drugs therefore do recommend nutrition to be controlled.

The multicomponent analysis of estrogens in urine by ion exchange chromatography and GC-MS--II. Fractionation and quantitation of the main groups of estrogen conjugates

A method for the metabolic profiling of estrogen conjugates in urine is described. It mainly involves protection of carbonyl functions by ethoximation, solid extraction on Sep-Pak C18 cartridges, a number of ion exchange chromatographic steps and quantitation by capillary GC or GC-MS. The acetate form of DEAE-Sephadex is used to initially separate estrogen conjugates into four groups; unconjugated, monoglucuronides, monosulfates and double conjugates. Monoglucuronides are further subfractionated to A- and D-ring glucuronides by carbodiimide methylation of the carboxylic functions and chromatography on the free base form of DEAE-Sephadex. Double conjugates are subfractionated to disulfates and sulfoglucuronides by solvolysis and chromatography on the acetate form of DEAE-Sephadex. After the appropriate enzymatic hydrolysis or solvolysis procedures the liberated free estrogens are purified and fractionated by a series of anion exchange chromatographic steps. Finally, following trimethylsilyl ether derivatization estrogens are analysed by capillary GC or GC-MS. The method permits the quantitation of the main conjugates of all the important estrogen metabolites including catechol estrogens. The method is precise, the sensitivity depending on the quantitation mode employed GC or SIM GC-MS. The method was applied to seven late pregnancy urines the values of which are presented.

Diet and the excretion and enterohepatic cycling of estrogens

Urinary and fecal excretion and plasma levels of estrogens were measured in pre- and postmenopausal women eating different diets. When premenopausal U.S. women eating a "Western diet," comprising high fat (40% of calories) and low fiber, were compared with age-matched vegetarians eating a moderate-fat (30%), high-fiber diet, it was found that the vegetarians excreted threefold more estrogen in their feces, had lower urinary excretion, and had 15-20% lower plasma estrogen levels. When U.S. pre- and postmenopausal women eating a Western diet were compared with recent Asian immigrants eating a very low-fat diet (20-25% of calories), similar results were obtained except that plasma estrogen levels were 30% lower among Orientals compared with those among Western omnivore women. Correlation analysis of dietary components and plasma estrogen showed that plasma estrogen was positively associated with fat and was negatively associated with fiber. The results indicate that diet can alter the route of excretion of estrogen by influencing the enterohepatic circulation and that this, in turn, influences plasma estrogen levels.