Gastrointestinal tract normal flora

Hill M Normal and pathological microbial flora of the upper gastrointestinal tract. Scand J Gastroenterol Suppl 1985 111 1-6. 

These antibiotics are partially absorbed from the stomach and upper gastrointestinal tract. Food impairs absorption of all tetracyclines except doxycycline and minocycline. Absorption of doxycycline and minocy-cbne is improved with food. Since the tetracyclines form insoluble chelates with calcium (such as are found in many antacids), magnesium, and other metal ions, their simultaneous administration with milk (calcium), magnesium hydroxide, aluminum hydroxide, or iron will interfere with absorption. Because some of the tetracyclines are not completely absorbed, any drug remaining in the intestine may inhibit sensitive intestinal microorganisms and alter the normal intestinal flora. 

Common Sites of Invasion Anaerobes colonize the mouth, gastrointestinal tract and skin of all persons. Infections develop when anaerobes penetrate poorly oxygenated tissues (e.g., the diabetic foot) or tissues that are normally sterile (e.g., peritoneum). When broad spectrum antibiotics diminish normal bowel flora, C. difficile proliferates and releases a toxin that causes pseudomembranous colitis. 

The most common cause of yeast infections is Candida albicans, which is part of the normal flora in a significant portion of the population where it resides in the oropharynx, gastrointestinal tract, vagina, and surrounding skin (4). It is the principal cause of vaginal yeast infections and oral yeast infections (thrush). These commonly occur in mucosal tissue when the normal population of flora has been disturbed by treatment of a bacterial infection with an antibiotic or when growth conditions are... 

Vitamin B12 is synthesized in large quantities by the intestinal flora, particularly in ruminants. The exact amount of vitamin B12 required by the normal human is not known. The absorption of vitamin B12 from the gastrointestinal tract is dependent on the presence of a gastric mucoprotein called intrinsic factor. Calcium ions seem to be necessary for the interaction of vitamin B12 with this intrinsic factor. Vitamin B12, which is absorbed only in the ileum, is stored in the liver. There are two transport proteins for vitamin Bj2 transcobalamin I and II, the latter being physiologically more important. Vitamin B12 plays an important role in the metabolism of functional groups with one carbon atom such as the methyl group... 

For animal feed, biotin is also of high importance. [110] Whereas ruminants have normally a sufficient supply of biotin provided by their fodder and by the amounts of biotin synthesised in the gastrointestinal tract, deficiencies occur more often in pigs, especially in piglets. Poultry tends to underutilise the biotin in their feed, and their enteral biotin synthesis is poor. Turkeys have an especially high demand for biotin. The use of sulfonamides and other antibiotics in animal husbandry affects the intestinal flora and may necessitate biotin-fortified feed (Tab. 7.4). 

Most bacterial nosocomial lower respiratory tract infections occur by aspiration of bacteria that colonize the oropharynx or upper gastrointestinal tract of the child. Both intubation and mechanical ventilation alter or circumvent some of the patient s natural barrier defenses against infection. These interventions allow organisms from the oropharyngeal or upper gastrointestinal tract greater access to the lower respiratory tract. The aspiration of contaminated materials may be obvious or, more commonly, it is subclinical. The normal respiratory flora of children admitted to a hospital consists of both gram-positive and... 

Example 2 Chloramphenicol and Tetracycline—Sparingly soluble broad-spectrum antibiotics like chloramphenicol and tetracycline found to damage the gastrointestinal epithelium besides changing the normal micro-flora in the Gl-tract that are required for normal good health. 

Nosocomially acquired fungal infections may arise from either exogenous or endogenous flora. Endogenous flora may include normal commensals of the skin, gastrointestinal (GI), genitourinary, or respiratory tract. C. albicans is found as a normal commensal of the GI tract in 20% to 30% of humans. ... 

The competitive exclusion concept was originated by Nurmi and Rantala (1973), based on the study of Salmonella in chickens. Newly hatched birds in modern hatcheries are not able to obtain the normal gut flora of adult birds. As a result, the intestines of chicks can be easily colonized by foodbome pathogens when present. When the chickens were inoculated immediately after birth with the intestinal content of a Salmonella-free adult bird, the frequency of Salmonella infections was radically reduced and the number of Salmonella needed to colonize the ceca of chicks increased. Hence, the normal gastrointestinal microflora of adult chickens can competitively exclude Salmonella from colonizing the naive intestinal tract of chicks. 

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