Berg R. The indigenous gastrointestinal microflora. Trends Microbiol 1996;4(11):430-435.

The indigenous gastrointestinal (GI) tract microflora has profound effects on the anatomical, physiological and immunological development of the host.

The indigenous microflora stimulates the host immune system to respond more quickly to pathogen challenge and, through bacterial antagonism, inhibits colonization of the GI tract by overt exogenous pathogens.

Indigenous GI bacteria are also opportunistic pathogens and can translocate across the mucosal barrier to cause systemic infection in debilitated hosts.

Douglas L, Sanders E. Probiotics and Prebiotics in Dietetics Practice. J Am Diet Assn 2008;108(3):510-521.

Probiotics and prebiotics share a unique role in human nutrition, largely centering on manipulation of populations or activities of the bacteria that colonize our bodies.

Benefits of regular consumption of probiotics or prebiotics include enhanced immune function, improved colonic integrity, decreased incidence and duration of intestinal infections, down-regulated allergic response, and improved digestion and elimination.

Research has shown that probiotics and prebiotics may be useful in achieving these and other positive effects, provided that proper strain, product selection, and dosing guidelines of commercial products are followed. There is a need to consolidate the basic and applied research on probiotics and prebiotics into useful tools for food and nutrition professionals.

Information on probiotic species, applications for specific strains, dosages and forms, safety, and shelf life is not sufficiently summarized to allow practical and consistent recommendations to be made by most food and nutrition professionals. In addition, prebiotic fibers—although providing nutraceutical and nutritional value—are a group of diverse carbohydrate ingredients that are poorly understood in regard to their origin, fermentation profiles, and dosages required for health effects.

The science and practice-based guidelines presented here will enhance clinician and client understanding of probiotics and prebiotics, with the aim of improving appropriate recommendation and informed use of these emerging dietary ingredients and the products containing them.

Salminen S, Bouley C, Boutron-Rualt M, et al. Functional food science and gastrointestinal physiology and function. Br J Nutr 1998;80(1):S147-S171.

The gut is an obvious target for the development of functional foods, acting as it does as the interface between diet and the metabolic events which sustain life.

The key processes in digestive physiology which can be regulated by modifying diet are satiety, the rate and extent of macronutrient breakdown and absorption from the small bowel, sterol metabolism, the colonic microflora, fermentation, mucosal function and bowel habit, and the gut immune system. The intestinal microflora is the main focus of many current functional foods.

Probiotics are foods which contain live bacteria which are beneficial to health whilst prebiotics, such as certain non-digestible oligosaccharides which selectively stimulate the growth of bifidobacteria in the colon, are already on the market. Their claimed benefits are to alleviate lactose maldigestion, increase resistance to invasion by pathogenic species of bacteria in the gut, stimulate the immune system and possibly protect against cancer. There are very few reports of well-designed human intervention studies with prebiotics as yet. Certain probiotic species have been shown to shorten the duration of rotavirus diarrhoea in children but much more work is needed on the mechanism of immunomodulation and of competitive exclusion and microflora modification.

The development of functional foods for the gut is in its infancy and will be successful only if more fundamental research is done on digestive physiology, the gut microflora, immune system and mucosal function.

Goldin B, Gorbach S, Saxelin M, et al. Survival of Lactobacillus species (strain GG) in human gastrointestinal tract. Digestive Dis Sci 1992;37(1):121-128.

A newly isolated strain of a species of Lactobacillus of human origin, designated GG (Lactobacillus GG), has been studied to determine its ability to survive in the human gastrointestinal tract.

When fed to 76 volunteers as a frozen concentrate or as a fermented preparation in milk or whey, Lactobacillus GG was recovered in the feces of all subjects receiving the fermented milk or whey and in 86% receiving the frozen concentrate when a single fecal specimen was cultured. The organism was also present in the feces of subjects concurrently receiving ampicillin.

After terminating feeding of the organism, Lactobacillus GG persisted in the feces of 87% of volunteers four days later and in 33% of subjects seven days later. Lactobacillus GG lowered fecal bacterial -glucuronidase activity by approximately 80% in volunteers given the organism for four weeks.

These studies demonstrate that Lactobacillus GG can survive and temporarily colonize the human gastrointestinal tract and can affect the metabolic activity of the resident microflora.

Gopal, P, Prasad J, Gill H. Effects of the consumption of Bifidobacterium lactis HN019 (DR10TM) and galacto-oligosaccharides on the microflora of the gastrointestinal tract in human subjects. Nutrition Research 2003;23(10):1313-1328.

The effects of dietary consumption of milk derived oligosaccharides and a probiotic bacterium Bifidobacterium lactis HN019 (also known as DR10TM) on the microbial composition of the gastrointestinal tract of human subjects was examined using a randomized, double blind, placebo-controlled study design.

Thirty subjects (age range 20–60 years) were divided randomly into three groups. After two weeks of a pre-intervention period, volunteers in group one consumed a reconstituted milk containing 2.4 g of galacto-oligosaccharides per day, volunteers in group two consumed reconstituted milk containing 3 × 1010 CFU of B. lactis HN019 per day, and group three volunteers consumed reconstituted milk without galacto-oligosaccharides or probiotic bacteria. The feeding period continued for four weeks followed by a wash out period of two weeks. Faecal samples were collected at weekly intervals and analysed for eight major groups of microbes associated with human gastrointestinal tract.

Subjects receiving reconstituted milk containing either galacto-oligosaccharides or probiotic bacteria (B. lactis HN019) exhibited a significant increase in the faecal counts of both lactobacilli (p < 0.004) and bifidobacteria (p < 0.0002). In comparison, little or no changes were observed in lactobacilli and bifidobacteria counts in subjects who consumed reconstituted milk without supplementation with either galacto-oligosaccharides or probiotic B. lactis HN019 (placebo control group).

Furthermore, B. lactis HN019 survived the digestion through human gastrointestinal tract and colonised transiently. It is believed that desirable bacteria including members of the genera bifidobacterium and lactobacillus, have a positive impact on human health.

The results presented in this study demonstrate that dietary supplementation with B. lactis HN019 or galacto-oligosaccharides increases the proportion of bifidobacterium and lactobacillus in the human gastrointestinal tract and hence may improve human health.