Intestinal colonization, microbiota, and probiotics

Presented as part of a symposium recognizing the 25th anniversary of the Bristol-Myers Squibb “Freedom to Discover” Nutrition Grants Program, University of Cincinnati, Cincinnati, OH, June 7-8, 2005.
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The human intestine is colonized by a large number of microorganisms that inhabit the intestinal tract and support a variety of physiological functions. The stepwise microbial colonization of the intestine begins at birth and continues during the early phases of life to form an intestinal microbiota that is different for each individual subject. This process facilitates the formation of a physical and immunologic barrier between the host and the environment, helping the gastrointestinal tract maintain a disease-free state. Probiotics are viable microbial food supplements that have a beneficial impact on human health. Health-promoting properties have been demonstrated for specific probiotic products. Scientific data are accumulating on these properties, especially in infants; the most significant effects include prevention and treatment of antibiotic-associated diarrhea and rotavirus diarrhea and allergy prevention. Bifidobacteria appear to be the most promising probiotic candidates, followed by defined lactic acid bacteria, which favor specific healthy bifidobacterial growth and species composition. Because viability appears to be important, probiotic properties also should be emphasized to meet this criterion. For future probiotics, the most important requirements include a demonstrated clinical benefit supported by mechanistic understanding of the effect on target population microbiota and immune functions. Genomic information and improved knowledge of microbiotic composition and its aberrancies should serve as a basis for selecting new probiotics for use in specific infant populations.

Section snippets

Source of Original Microbiota

The basis of the healthy gut microbiota is derived from the mother. The mother’s microbiotic composition and the original inoculum provided at birth depend on poorly understood genetic factors. Diet, environment, and stress factors during pregnancy and birth influence the mother’s fecal microbiota composition and, consequently, the inoculum transferred to the infant at birth.12, 13 The microbiota of a newborn develops rapidly after birth and is initially strongly dependent on feeding practices

Host–microbe interaction: from commensalism to mutualism

Normal intestinal microbiota are characterized as a complex collection and balance of microorganisms that normally inhabit the healthy GI tract. The indigenous bacteria sometimes have been classified as potentially harmful or health-promoting. Most of them, however, are part of the normal commensal flora. This term indicates a relationship between organisms of 2 or more different species in which 1 species derives benefits from the association while the other(s) remain(s) unharmed or

Role of probiotics

Probiotics have been defined by the International Life Sciences Institute Europe as “viable microbial food supplement[s] which when taken in the right dose beneficially influence the health of the host.”10 Practically the same definition of probiotics is used by the Food and Agriculture Organization of the United Nations and the World Health Organization.11 These definitions require that safety and efficacy be demonstrated scientifically for each strain and each product.

Aberrant gut microbiota: clinical consequences

Specific imbalances or deviations in the intestinal microbiota may make humans more vulnerable to intestinal inflammatory diseases and systemic diseases beyond the intestinal environment. Specific Bifidobacterium species in the healthy infant gut are the most predominant and metabolically active organisms; specific clostridia also are often present. Changes in their quantitative and qualitative composition appear to serve as useful indicators of deviations from the balanced microbiota. Other

Perspectives

Advancing genomic research will provide data on host–microbe interactions to identify key processes of microbiotic development and maintenance. These include nutrient–microbe interactions and a detailed knowledge of the transfer of microbial communities from parent to infant. Such data should provide the basis for the development of new probiotics.53

Probiotic genome analysis will predict their properties and interactions in human use, allowing their application to human studies of specific

Conclusion

The healthy infant microbiota acts as an organ to utilize nutrients and also as a defense mechanism against harmful environmental exposures. Deviations in composition can be related to multiple disease states within the intestine but also beyond it. Similarly, components of the human intestinal microbiota or organisms entering the intestine may have both harmful and beneficial effects on human health.

The current available information focuses mostly on the role of infant microbiota and the first

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    Seppo Salminen is a recipient of a Bristol Myers Squibb–Mead Johnson Unrestricted Nutrition Research grant. This is a Nutrition, Allergy, Mucosal Immunology, and Intestinal Microbiota (NAMI) research group report. Mead Johnson sponsored the symposium and provided an honorarium for conference attendance, presentation of the article, and submission of a manuscript. The authors are entirely and exclusively responsible for its content.

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