This review of the subject of probiotics does not purport to be comprehensive, but rather merely an introduction.

The colonic microflora are important to health. The growth and metabolism of the many individual bacterial species inhabiting the large bowel depend primarily on the substrates available to them, most of which come from the diet. This has led to attempts to modify the structure and metabolic activities of the community through diet using probiotics and prebiotics. Probiotics are live microbial food supplements. The best known is the lactic acid bacteria (acidophilus, (ed)) and bifidobacteria in yoghurts or freeze-dried culture concentrates. These organisms are non-pathogenic and non-toxigenic, retain viability during storage, and survive passage through the stomach and small bowel. (Macfarlane G, Cummings J, BMJ, 318:999-1003, 1999)

Prebiotics are non-digestible food ingredients that selectively stimulate the growth or activities, or both, of lactobacilli or bifidobacteria in the colon, thereby improving health. The food ingredients most likely to be effective are the oligosaccharides, including artichokes, onions, chickory, garlic, leeks. Commercial probiotic preparations are usually mixtures of lactobacilli and bifidobacteria, although yeasts such as saccharomyces (as in Kombucha, (ed)) have also been used. (Macfarlane G, Cummings J, BMJ, 318:999-1003, 1999)

Acquisition of colonic microflora takes place early in life and is very much dependent on the nature of feeding. Compositional changes may also occur with disease or (certainly) after antibiotic therapy (Roberfroid M, et al, Nutritional Reviews, 53(5), 1995), the extensive use of which has led to a flourishing of antibiotic resistance in common pathogenic bacteria (Canganella F, et al, Microbiol Res, 151, 167-175, 1996), which become established when the integrity of the microbiota is impaired through antibiotic treatment (Macfarlane G, Cummings J, BMJ, 318:999-1003, 1999). The combination of probiotics and prebiotics in a synbiotic might improve the survival of the bacteria crossing the upper part of the gastrointestinal tract, enhancing their effects in the large bowel and their effects might be additive or even synergistic (Roberfroid M, Am J Clin Nutr, 17(6), 2000).

Several health-related effects associated with the intake of probiotics and their has been proposed as an alternative to antibiotics (McGroarty J, FEMS Immun Med Microbiol, 6 251-264, 1993); (Nader de Macias M, et al, J Food Prot, 56, 401-405, 1993); (Canganella F, et al, Microbiol Res, 151, 167-175, 1996). Probiotics, because of their role in the maintenance of normal gastrointestinal flora, can facilitate human resistance to opportunistic infection and positively impact the outcome in a variety of clinical situations. Probiotics have been used successfully to facilitate treatment of bacterial vaginosis, recurrent urinary infections, diarrhea, bladder cancer, complications of antibiotic therapy, dysbacteriosis and dyslipidemias (Catanzaro J, Green L, Alt Med Rev, 2(4), 1997).

A complex (normal) colonic microflora is likely to be crucial to both the development and homoeostasis of the intestinal immune system. Fermentation of non-digestible dietary substances as well as of endogenous mucus is a major metabolic function of colonic microflora. The primary functions of colonic microflora include nutritive, metabolic, immunologic, and protective, which functions support control of epithelial cell proliferation and differentiation, metabolism and enterohepatic circulation of xenobiotics, control of ion concentration and absorption and control of colonic pH and resistance to infection. (Roberfroid M, et al, Nutritional Reviews, 53(5), 1995)

The colonic microflora normally presents a barrier to invading organisms, but pathogens often become established when the integrity of the microbiota is impaired through stress, illness, antibiotic treatment, changes in diet, or physiological alterations in the gut. Bifidobacteria are known to be involved in resisting the colonisation of pathogens in the large bowel. Lactobacillus have been shown to colonise the gut and secrete antimicrobial products that are active against a range of other micro-organisms. Probiotics and prebiotics seem to be antimutagenic and or carcinogenic in several ways indicating the potential of prebiotics and probiotics to reduce or prevent carcinogenesis. (Macfarlane G, Cummings J, BMJ, 318:999-1003, 1999)

The colonic microbiota affects mucosal and systemic immunity in the host. Intestinal epithelial cells, blood leucocytes, B and T lymphocytes, and accessory cells of the immune system are all implicated. Lactobacilli (acidophilus, (ed)) bind in vitro to peripheral blood CD4 and CD8 T lymphocytes, while lactobacilli which adhere to human intestinal epithelial cells are capable of activating macrophages. Probiotic organisms interact with the immune system at many levels, including cytokine production, mononuclear cell proliferation, macrophage phagocytosis and killing, modulation of autoimmunity, and immunity to bacterial and protozoan pathogens. (Macfarlane G, Cummings J, BMJ, 318:999-1003, 1999)

Some evidence suggests a role for probiotics in reducing the risk of rotavirus-induced diarrhea and colon cancer. Among the most promising targets for functional foods are the gastrointestinal functions, including those that control transit time, bowel habits, and mucosal motility, alleviate lactose intolerance as well as those that modulate epithelial cell proliferation. Promising targets are also gastrointestinal functions that are associated with a balanced colonic microflora, that are associated with control of nutrient bioavailability (ions in particular), that modify gastrointestinal immune activity, or that are mediated by the endocrine activity of the gastrointestinal system. Finally, some systemic functions such as lipid homeostasis that are indirectly influenced by nutrient digestion or fermentation represent promising targets. (Roberfroid M, Am J Clin Nutr, 17(6), 2000)

Several health-related effects have been reported in human nutrition studies by different research groups in several countries. These effects may be used to justify either functional claims or claims of reduced disease risk. At present, claims about reduction of disease risk are only tentative and further research is needed. Among the claims are constipation relief, suppression of diarrhea, and reduction of the risks of osteoporosis, atherosclerotic cardiovascular disease associated with dyslipidemia and insulin resistance, obesity, and possibly type-2 diabetes. (Sanders M, J Diary Sci, 76:1819–28, 1993); (Roberfroid M, et al, Nutritional Reviews, 53(5), 1995); (Salminen S, et al, 70:347–58, 1996); (Mortomi M, Asia Pac J Clin Nutr, 5:29–30, 1996); (Catanzaro J, Green L, Alt Med Rev, 2(4), 1997); (Macfarlane G, Cummings J, BMJ, 318:999-1003, 1999); (Roberfroid M, Am J Clin Nutr, 17(6), 2000).

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