The term probiotics means "for life" and is currently used to name bacteria associated with beneficial effects for humans and animals.⁽¹⁾ They are live microbial feed supplement which beneficially affect the host by improving properties of indigenous flora.⁽²⁾

Prebiotics are dietary substances (mostly consisting of nonstarch polysaccharides and oligosaccharides poorly digested by human enzymes) that nurture a selected group of microorganisms living in the gut. They favor the growth of beneficial bacteria over that of harmful ones.⁽³⁾

More than 400 bacterial species are present normally in the gastrointestinal tract of humans.⁽⁴⁾ Normally the stomach contains few bacteria (103 colony forming units per ml of gastric juice) whereas the bacterial concentration increases throughout the gut resulting in a final concentration in the colon of 102 bacteria/gm. Bacterial colonization of gut begins at birth (before birth, the fetus is in a sterile environment) and continues throughout life.⁽⁵⁾ These intestinal microflora normally do not cause problems and some of them are necessary for maintaining well being of the host. These beneficial bacteria prevent colonization of gut with pathogens.⁽⁶⁾

Thus, it is assumed that dietary manipulation of gut flora in order to increase the relative number of "beneficial bacteria" by prebiotic or probiotic could contribute to the well being of the host.⁽⁷⁾

A number of health effects are associated with usage of probiotics. There are differing degrees of evidence supporting the verification of such effects.⁽¹⁾ The strongest evidence of beneficial effect of defined strains of probiotics has been established for lactobacillus rhamnosus GG and Bifidobacterium lactis BB-12 for prevention and treatment of acute diarrhea mainly caused by rotaviruses in children.^{(8, 12)} Probiotics have also shown beneficial effects in traveler's diarrhea where some of the pathogens are presumed to be bacterial in nature⁽¹³⁾ as well as in vitro studies have found that certain probiotics strains can inhibit growth of range of enteropathogens.^{(14, 15)} Also in antibiotic associated diarrhea, probiotics especially L. rhamnosus GG have been found to be useful as prophylaxis and also for treatment to reduce signs and symptoms once antibiotic associated diarrhea has occurred.^{(16, 17)}

Lactobacilli have been used for a prolonged time in humans without established risk.⁽¹⁸⁾ Also they do not have pathogenic or virulence properties.⁽¹⁹⁾ However there have been rare cases of bacteremia⁽¹⁸⁾ which have not been proven in other studies.⁽²⁰⁾ Also enterococcus is not recommended as probiotic for human use due to high level resistance to vancomycin.⁽²¹⁾

Species of lactobacillus, bifidobacterium, saccharomyces cerevisiae and some E coil & Bacillus species are used as probiotics.⁽³⁾ The most common forms of probiotics available are probiotic fortified food, probiotic sachets, tablets, capsules and probiotic fortified dairy products.⁽³⁾ The dose needed for probiotics varies with strain and product.⁽³⁾ Most products deliver in the range of 1-10 billion cfu/dose.

The concept of prebiotics is essentially the same as of probiotics which is to improve host health via modulation of the intestinal flora, although by a different mechanism.⁽¹⁾ Unlike probiotics, most prebiotics are used as food ingredients in biscuits, cereals, chocolate, spreads and dairy products. Commonly used prebiotics are: oligofructose, inulin, galacto-oligosaccharides, lactulose and breast milk oligosaccharides. Fermentation of oligofructose in the colon results in increasing the number of bifidobacteria (probiotic) in the colon, increasing fecal weight and shortening GI transit time. Increase in bifidobacteria results in inhibition of growth of potential pathogens.⁽³⁾ Also several prebiotics strains are useful in boosting the immune response.⁽²²⁾

Thus, scientific evidence is available that helps to determine health benefits of consuming probiotics and/or prebiotics.

1.		Joint FAO/WHO Expert Consultation on Evaluation of Health and Nutritional Properties of Probiotics in Food Including Powder Milk with Live Lactic Acid Bacteria. October 2001.
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3.		World Gastroenterology Organization Practice Guideline: Probiotics and Prebiotics. May 2008.
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