Oral probiotics are living microorganisms that, upon ingestion, affect the host in a beneficial manner by modulating mucosal and systemic immunity, as well as improving nutritional and microbial balance in the intestinal tract. The main probiotic preparations on the market belong to a large group of bacteria designated as lactic acid bacteria (Lactobacillus, Streptococcus, Bifidobacterium species) that are important and normal constituents of the human gastrointestinal microflora (Table 1). However, studies are also investigating the potential probiotic roles of other microbes, such as yeast (Saccharomyces boulardii), which are not normally found in the gastrointestinal tract.
Common probiotics, prebiotics and symbiotics
|Lactobacillus delbrueckii subsp bulgaricus|
|Lactis salivarius subsp thermophilus|
|Bifidobacterium species + FOS|
|Lactobacillus species + lactitol|
|Bifidobacterium species + GOS|
FOS Fructo-oligosaccharides; GOS Galacto-oligosaccharides
Prebiotics are nondigestible food ingredients that beneficially affect the host by selectively stimulating the growth and/or activity of one, or a limited number of, bacterial species already established in the colon. Substances that act as prebiotics cannot be hydrolyzed or absorbed in the upper part of the gastrointestinal tract but are available as substrates for the indigenous bacteria in the colon. Nondigestible oligosaccharides in general, and fructo-oligosaccharides (FOS) in particular, are prebiotics. These low molecular weight carbohydrates are found naturally in onions, garlic, leeks, chicory, artichokes and some cereals. Other oligosaccharides (raffinose and stachyose) are found in beans and peas. These molecules are also produced industrially, and a number of new prebiotic preparations are being developed for the market. The beneficial effect of prebiotic intake on the host may result from either suppression of the growth of harmful microorganisms or the stimulation of favourable organisms (mainly Lactobacillus species and Bifidobacterium species). For instance, in controlled dietary studies, intake of FOS (15 g/day) increased fecal Bifidobacterium species numbers 10-fold, while reducing Clostridia and Enterobacteria counts. However, it should be mentioned that intake of FOS at this dose may give some patients significant gastrointestinal symptoms, even apart from alterations in microbial flora.
A symbiotic is a product in which a probiotic and a pre-biotic are combined. The rationale for this combination is that survival of the probiotic bacteria is improved during the passage through the upper intestinal tract, implantation in the colon is more efficient, and the prebiotic has a stimulating effect on the growth of both the exogenous (probiotic) and endogenous bacteria.
Recent global marketing trends of probiotics and prebi-otics are based on numerous claims of various health benefits that have varying levels of supporting scientific evidence (Table 2). The emergence of microorganisms with acquired antibiotic resistance profiles, and increasing public concern about disease prevention and maintenance of health, are also driving the search for approaches to therapy that do not involve pharmaceutical agents. Thousands of different microbial preparations are available to the public. Traditionally, probiotic strains have been incorporated into fermented milk products, but dietary supplements containing Lactobacillus species, Bifidobacterium bifidum, Streptococcus thermophilus, or a combination of these microorganisms, are now available in capsules, tablets and enteric-coated formulations. However, it must be remembered that there is no substantial regulation in this area; thus, there is no guarantee that an over-the-counter product will contain the bacterial species listed on the label or that the bacteria will be viable. Indeed, a study performed by Hamilton-Miller et al showed that, of 52 probiotic products, very few actually contained what was listed on the label. Often, products contained lower numbers of bacteria than were listed on the label, contained extraneous bacterial strains not listed on the label, or did not contain the strains listed on the label. Thus, it is difficult to advise which products to purchase. Although probiotics and prebiotics have been used in humans and animals for centuries, only recently have these formulations been subjected to any type of controlled clinical research. The present review outlines various documented findings on the probiotics and prebiotics, with particular emphasis on gastrointestinal disease.
Alleged health claims for probiotics
|Intestinal disorders||Other disorders|
|Antibiotic-induced||Alcohol-induced liver disease|
|Salmonella and Shigella||Prevention of osteoperosis|
|species infections||Cystic fibrosis|
|Inflammatory bowel disease||Cystitis|