Feces intestinal bacteria

Vitamin Bjg is not synthesized by animals or by plants. Only a few species of bacteria synthesize this complex substance. Carnivorous animals easily acquire sufficient amounts of Bjg from meat in their diet, but herbivorous creatures typically depend on intestinal bacteria to synthesize Bjg for them. This is sometimes not sufficient, and certain animals, including rabbits, occasionally eat their feces in order to accumulate the necessary quantities of Big. 

Other bacteria. Intestinal bacteria may play a critical role in the metabolic activation of certain nitroaromatic compounds in animals (119) and several reports have appeared on the metabolism of nitro PAHs by rat and human intestinal contents and microflora (120-123). Kinouchi et al. (120) found that 1-nitropyrene was reduced to 1-aminopyrene when incubated with human feces or anaerobic bacteria. More recently, Kinouchi and Ohnishi (121) isolated four nitroreductases from one of these anaerobic bacteria (Bacteroides fragilis). Each nitroreductase was capable of converting 1-nitropyrene into 1-aminopyrene, and one form catalyzed the formation of a reactive intermediate capable of binding DNA. Howard ej al. (116) confirmed the reduction of 1-nitropyrene to 1-aminopyrene by both mixed and purified cultures of intestinal bacteria. Two additional metabolites were also detected, one of which appeared to be 1-hydroxypyrene. Recently, similar experiments have demonstrated the rapid reduction of 6-nitro-BaP to 6-amino-BaP (123). 

Much of the debate concerning the use of antibiotics in livestock feeds has centered on bacterial resistance. One of the first observations made early in the 1950s, was that the bacterial count in animal feces increased after a temporary decrease when antibiotics, such as tetracyclines, were fed (12). This was in contrast to the effect of sulfonamides, which reduce the count. Obviously, resistance had occurred because the intestinal bacteria were thriving in the presence of antibiotics. Simultaneously, the growth of the animals was increased. Therefore the resistance in itself was not harmful. 

Intestinal bacteria produce enzymes that can chemically alter the bile salts (4). The acid amide bond in the bile salts is cleaved, and dehydroxylation at C-7 yields the corresponding secondary bile acids from the primary bile acids (5). Most of the intestinal bile acids are resorbed again in the ileum (6) and returned to the liver via the portal vein (en-terohepatic circulation). In the liver, the secondary bile acids give rise to primary bile acids again, from which bile salts are again produced. Of the 15-30g bile salts that are released with the bile per day, only around 0.5g therefore appears in the feces. This approximately corresponds to the amount of daily de novo synthesis of cholesterol. 

For humans, the overall chromium(VI)-reducing/sequestering capacities were estimated to be 0.7-2.1 mg/day for saliva, 8.3-12.5 mg/day for gastric juice, 11-24 mg for intestinal bacteria eliminated daily with feces, 3,300 mg/hour for liver, 234 mg/hour for males and 187 mg/hour for females for whole blood, 128 mg/hour for males and 93 mg/hour for females for red blood cells, 0.1-1.8 mg/hour for ELF, 136 mg/hour for pulmonary alveolar macrophages, and 260 mg/hour for peripheral lung parenchyma. Although these ex vivo data provide important information in the conversion of chromium(VI) to reduced states, the values may over or under estimate the in vivo reducing capabilities (De Flora et al. 1997). 

E. histolytica exists in two forms cysts that can survive outside the body, and labile but invasive trophozoites that do not persist outside the body. Cysts, ingested through feces-contaminated food or water, pass into the intestine where trophozoites are liberated. The trophozoites multiply, and either invade and ulcerate the mucosa of the large intestine, or simply feed on intestinal bacteria. [Note One strategy for treating luminal amebiasis is to add antibiotics, such as tetra-... 

The hydrolysis of bile acid conjugates is probably the initial reaction catalyzed by intestinal bacteria. Therefore, primarily free bile acids are isolated from the feces of man and animals [1-5]. The bulk of the free bile acids in feces of man is deoxycholic acid and lithocholic acid which are generated by the 7 -dehydroxylation of cholic acid and chenodeoxycholic acid, respectively. A portion of fecal acids is absorbed from the intestinal tract, returned to the liver where they are conjugated and again secreted via biliary bile. Therefore, the final composition of biliary bile acids is the result of a complex interaction between liver enzymes and enzymes in intestinal bacteria. 

Intestinal bacteria capable of 7a-dehydroxylating bile acids have been isolated by several laboratories [16,50]. Most intestinal bacteria that carry out 7-dehydroxylation have been identified as members of the genera Clostridium [50-52] or Eubacterium [51,53]. Stellwag and Hylemon [52] and Ferrari et al. [54] demonstrated that the fecal population of 7 -dehydroxylating intestinal bacterial in man and rats is in the range of 10 -10 viable organisms/g wet weight feces. 

In the intestine, bacteria deconjugate bilirubin diglucuronide and convert the bilirubin to urobilinogens (see Fig. 44.7). Some urobilinogen is absorbed into the blood and excreted in the urine. However, most of the urobilinogen is oxidized to urobilins, such as stercobilin, and excreted in the feces. These pigments give feces their brown color. 

Norman (3) demonstrated that the types of bile acids found in normal rat bile were not the same as those which were excreted in the feces. However, when the rats were fed high levels of antibiotics, the fecal bile acids were excreted essentially unchanged from the biliary bile acids (4). The intestinal bacteria were responsible for the hydrolysis of the biliary taurine-conjugated bile acids to the free bile acids found in the feces. Norman also showed that the dehydroxylation of cholic acid to deoxycholic acid could be prevented by Inhibiting the intestinal bacteria. The total amount of fecal bile acid excreted by conventional chicks has been found to be significantly lowered (5) by incorporation of an antibiotic into the diet. 

In the normal human being the excretion of porphyrins in the urine per day may amount to 100 jug., of which the coproporphyrin I isomer is the main component lesser amounts of coproporphyrin III and only traces of uroporphyrin are excreted. In the feces, per day, about 200-300 jug. of a mixture of coproporphyrin, protoporphyrin, and deuteropor-phyrin are excreted. The traces of deuteroporphyrin are assumed to be formed by the action of the intestinal bacteria on the excreted porphyrins and heme. 

A considerable amount of biotin is synthesized by human intestinal bacteria, as evidenced by the fact that 3 to 6 times more biotin is excreted in the urine and feces than is ingested. But synthesis in the gut may occur too late in the intestinal passage to be absorbed well and play much of a direct role as a biotin source. Also, several variables affect the microbial synthesis in the intestines, including the carbohydrate source of the diet (starch, glucose, sucrose, etc.), the presence of other B vitamins, and the presence or absence of antimicrobial drugs and antibiotics. 

Feces consist largely of mucous substances from the gastro-intestinal tract and remnants of intestinal bacteria. Their odor is due to indole and scatol their color is due to the bile pigments (Chapt. IX-5). 

More definite evidence that intestinal bacteria elaborated a nutritive factor was obtained by Osborne and Mendel (7) in 1911. They noted that rats on certain purified diets declined in weight and became coprophagous. The decline in weight could be arrested by incorporating in their diet feces from normal rats. When the rats were offered a choice between their own feces and those of normal rats, they invariably chose the latter. The superiority of the feces from the normal rats was attributed to the bacterial flora M hich, as was then well known, was greatly influenced by diet (8). Sterilization of the feces reduced their beneficial effect but did not abolish... 

The historical basis for this use of the sulfonamides is to be found in experiments dealing with the synthesis of vitamins by intestinal bacteria. For such a process to be of nutritional importance to rats or other animals, it is obvious that not only must needed vitamins be manufactured in this way but also they must be made available in significant amounts to the animals in question. It has been shown that both of these conditions are at times fulfilled. The first step was the demonstration, made some 30 years ago, that rats were benefited, under suitable experimental conditions, by the ingestion of feces. It thereafter was indicated by an orderly progression of researches that the benefits experienced were derived from vitamins in the feces, that these substances had been synthesized by intestinal bacteria, and finally that coprophagy was not essential in order for the animal harboring the micro-organisms to profit from their activity. 

There is no e idence to indicate that vitamin E can be synthesized by intestinal bacteria. This vitamin is not normally present in feces (101) and docs not appear to be synthesized by rumen microorganisms (102). 

The ring structure of cholesterol cannot be metabolized to C02 and HfeO in humans. Rather, the intact sterol nucleus is eliminated from the body by conversion to bile acids and bile salts, which are excreted in the feces, and by secretion of cholesterol into the bile, which transports it to the intestine for elimination. Some of the cholesterol in the intestine is modified by bacteria before excretion. The primary compounds made are the isomers coprostanol and cholestanol, which are reduced derivatives of cholesterol. Together with cholesterol, these compounds make up the bulk of (neutral fecal sterols. 

Bifidobacterium Fermentation. A unique form of lactic fermentation has been observed in members of the genus Bifidobacterium. These anaerobic bacteria are commonly found in the intestinal tract and feces of human infants and adults, as well as many animal species. Most Bifidobacterium spp. can acidify milk, and they produce acetic and lactic acids in an approximate 3 2 molar ratio when growing on glucose (Buchanan and Gibbons 1974). The Bifidobacterium fermentation (Fig-... 

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