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

Dietary modification of intestinal bacterial enzyme activities--potential formation of toxic agents in the gut

The bacterial population colonising the large intestine is able to metabolise a variety of ingested or endogenously produced substances to products, some of which possess toxic, mutagenic or carcinogenic properties. Dietary components, resistant to digestion and absorption in the upper alimentary tract, may influence these reactions by altering the environment of the gut or through the provision of nutrients to the flora. Evidence for the involvement of bacterial enzymes in the formation of toxic products in vivo has come largely from animal studies, particularly where fermentable plant cell-wall components are present in the diet. The role of diet in the modification of toxicologically important bacterial biotransformation processes will be discussed. Preliminary data will also be presented from a study demonstrating changes in the enzymic activity of the human faecal flora induced by pectin and bran. The significance of these changes to the disposition of chemicals in the gut will be discussed.

Studies on the chromatographic fractionation of metabolites of benzo[a]pyrene in faeces and urine from germfree and conventional rats

Rats, germfree and conventional, were dosed with 14C-labelled benzo[a]pyrene. Faeces and urine were collected. Metabolites in faeces were effectively extracted with a new method using a combination of solvents and solid sorbents. Metabolites in urine were extracted with octadecylsilane-bonded silica. The metabolites were fractionated into groups by chromatography on a cation exchanger (SP-LH-20 or SP-Sephadex C-25) and an anion exchanger (TEAP-LH-20). Some of the groups were further purified by column chromatography and analysed by HPLC and TLC. The analyses show a complex pattern of metabolism. A large part of the metabolites (9-24% depending on animal type and route of excretion) had amphoteric properties, e.g. like glutathione and cysteine conjugates. The abundance of conjugates sensitive to beta-glucuronidase and sulphatase was low. The relative amount of acidic conjugates in faeces was much higher in the germfree than in the conventional rats indicating the influence of the intestinal flora on the metabolism. The results support the view that the mercapturic acid pathway is a quantitatively important metabolic route for benzo[a]pyrene in rats. The methods of extraction and group fractionation were designed to be generally applicable to the analysis of lipophilic xenobiotics and their metabolites.

Overview of gastrointestinal microecology

In germ-free life many characteristics are not the consequence of living bacteria's metabolic activities but of bacteria acting as antigens. On the other hand, merely some bacteria species are able to activate the immune system. Noteworthy experimental results relate to inhibitory effects of dietary lactobacilli on intestinal carcinomas. Besides bacteria other components play a role within the very complex man-microbe ecosystem. Thus, protozoa, fungi, and viruses may be generally concerned with diseases in monogastric animals.

The human intestinal microflora

The major host defense mechanisms against bacterial overgrowth in the small bowel are the normal propulsive activity of the bowel itself and gastric acid secretion. Microbial interactions are a major factor in regulating the indigenous bacterial flora. Studies of the bacterial enzymes of the gut suggest that changes in diet may lead to marked changes in the colonic flora. Antibiotics affect the composition of the colonic microflora. The microflora also influence the degradation of mucin, the conversion of urobilin to urobilinogen, of cholesterol to coprostanol, and the production of short chain fatty acids. Current interests are focused on the bacterial flora of tropical sprue, the role of bacteria in colorectal cancer, and the involvement of intestinal microflora in the enterohepatic circulation of sex steroid hormones.

Dietary fiber and human cancer: critique of the literature

The relationship between dietary fiber consumption and risk of gastrointestinal cancer in humans is examined using representative studies of several types: international and intranational correlations, case-control analyses, metabolic investigations, cohort studies, and migrant studies. The strongest statistical association between diet and cancer is found in international studies in which numerous environmental variables differ. Studies on smaller groups within a single culture have not given strong support to the findings of international comparisons. Colon cancer rates within regions of the U.S. and other countries vary with sufficient magnitude that diet is unlikely to account for more than a minor proportion of risk. The evidence that a diet containing fiber-rich foods reduces risk of colon cancer must be considered tentative. Foods high in starch and fiber are statistically associated with a high rate of stomach cancer. Examination of the combined rates of colon and gastric cancer shows that the U.S. risk is low relative to countries in which a diet higher in fiber is consumed. It would be premature to suggest that a high fiber diet will confer protection against gastrointestinal cancer.

The effect of diet on the mammalian gut flora and its metabolic activities

The review will encompass the following points: A brief introduction to the role of the gut flora in the toxicology of ingested food components, contaminants, and additives, including known pathways of activation and detoxication of foreign compounds and the implication of the flora in enterohepatic circulation of xenobiotics. The advantages and disadvantages of the various methods of studying the gut flora (classical bacteriological techniques, metabolic and enzymological methods) will be critically discussed with special reference to their relevance to dietary, toxicological, and biochemical studies. Sources of nutrients available to the gut flora will be described including host products (mucus, sloughed mucosal cells, hormones, proteins) and exogenous nutrients derived from diet. An account of the problems involved in studies of dietary modification with special reference to the use of stock laboratory animal diets, purified diets, and human dietary studies. The influence of dietary modification on the flora will be assessed on the basis of changes in numbers and types of bacteria and their metabolic activity, drawing on data from human and animal studies. The effects of manipulation of the quantity and quality of protein, fat, and indigestible residues (fiber) of the diet will be described together with their possible implications for toxicity of ingested compounds.

The intestinal microflora and its colon cancer connection

Epidemiologic studies suggest that the incidence of colon cancer is influenced by environmental factors, especially diet. The high beef-high fat-low fiber diet of Western societies is associated with a high risk of colon cancer. The intestinal microflora may play a role in colon cancer by metabolic activation of procarcinogens in the lumen of the large bowel. The link between diet and colon cancer can be explained, in part, by the alterations in fecal bacterial enzyme activity induced by a Western-style diet. For example, fecal bacterial beta-glucuronidase, nitroreductase, azoreductase and steroid 7-alpha-dehydroxylase activities are increased in animals or humans consuming a high beef diet. These enzyme activities can be reduced by eating a grain diet, by the addition of Lactobacillus acidophilus to the diet, or by administration of low dose antibiotics. In experimental animals these three measures to reduce the activity of the microflora also produce few colon tumors in animals given the chemical carcinogen dimethylhydrazine. Further studies are needed to establish whether alterations in the metabolism of the colonic microflora can reduce the risk of large bowel cancer in humans.

Mutagens in human faeces. Are they relevant to cancer of the large bowel?

1. Mutagenic activity has been detected in faecal extracts, prepared by a number of methods, from donors living under widely differing geographical, cultural and dietary circumstances. Faecal extracts cause point mutations in bacteria and chromosomal damage in cultured mammalian cells. 2. The claims that nitroso compounds are present in human faeces have been retracted, and the chemical nature of faecal mutagens is still unknown. Indirect evidence suggests the presence of several classes of mutagen. 3. The use of different methods of mutation assay gives conflicting estimates of the proportion of people who excrete mutagenic faeces. There is wide variation in mutagenic activity between different stool samples from one person, and between different stool samples from different people. There is conflicting evidence for inhibition or enhancement of the mutagenicity of reference mutagens by faecal extracts. The effects of air oxidation on the mutagenicity of faecal extracts have not been investigated in detail. 4. It has been claimed that the proportion of people excreting mutagenic faeces is higher in groups representing populations at high risk of large-bowel cancer than in groups at low risk of large-bowel cancer. For the reasons given in paragraph 3, these claims must be regarded as premature. 5. The part played by faecal mutagens in the aetiology of large-bowel cancer has yet to be determined.

Growth Characteristics, Bile Sensitivity, and Freeze Damage in Colonial Variants of Lactobacillus acidophilus

Rough (R) and smooth (S) colonial variants were isolated from a heterogeneous culture of Lactobacillus acidophilus RL8K. R and S types were stable upon repeated transfer on agar, but revertant colonies did appear after broth transfers. When propagated in commercial MRS broth, R and S cultures showed similar growth characteristics, and both cell types were insensitive to freezing and frozen storage at −20°C. Alternatively, during growth in scratch MRS broth, R cultures shifted to a reduced rate of growth during the late logarithmic phase. R cells grown under these conditions were susceptible to death by freezing and injury at −20°C. Microscopically, R cells were observed as long gram-positive rods with small nonstainable blebs protruding from the cell wall. In bile sensitivity studies of R and S cells plated on MRS agar plus oxgall, the S culture was resistant to 1% bile, whereas the R culture was sensitive to 0.6% bile. Differences in the bile resistance and freeze damage of R and S cells suggest that colonial and cellular morphologies are important considerations for the selection of Lactobacillus strains as dietary adjuncts and for the development of growth conditions for preparing frozen concentrated cultures from either cell type.