Cover of Probiotic Microbes: The Scientific Basis

The American Academy for Microbiology convened a colloquium Nov. 5-7, 2005, in Baltimore, Md., to deliberate the current state of knowledge regarding probiotics. Participants with expertise in microbiology, medicine, periodontics, animal science, immunology, nutrition and other relevant fields conferred on potential applications of probiotic therapies, regulatory issues, the human acquisition of normal microbiota, interactions between commensal microorganisms and their hosts, interactions among commensal microorganisms and the identification of prospective probiotic organisms. Recommendations for ensuring the safety and efficacy of probiotic therapies were made.

The definition of "probiotic" set forth by the United Nations Food and Agricultural Organization and the World Health Organization in a joint report on the topic identifies probiotics as "live microorganisms, which, when administered in adequate amounts, confer a health benefit on the host" (FAO/WHO, 2001). This definition was adopted by the colloquium participants and is the 1 used in this report.

In theory, microorganisms could be used to combat pathogenic microorganisms and the diseases they cause. They could also conceivably be used to prevent infectious diseases and immune dysfunction. Some probiotic formulations have been subjected to more scientific scrutiny than others, and many of these applications show considerable promise for alleviating certain illnesses. Many combinations of therapies are being evaluated for the treatment and prevention of various diseases and conditions.

Humans are colonized by bacteria, viruses and other microbes from birth; we live with a suite of commensal microorganisms from that moment on. Neonatal gut colonization is strongly affected by the mode of birth. In vaginally born infants, colonization follows a more or less predictable course, starting with certain groups of facultative anaerobic bacteria, then obligate anaerobes. The distribution of microorganisms within the adult gastrointestinal tract is difficult to determine given the current technical limitations on sampling and analysis. Studies indicate that the gut microbiota is relatively stable in an individual over time and that great variability in the composition of these microbial communities exists between individuals.

Interactions between a host and its commensal microorganisms, and the interplay between the commensal microorganisms themselves, can be critical to the health of a host. Proper development of the human immune system is reliant on microbial stimulation. Probiotic organisms may have the potential to interact with both the innate and acquired immune systems with possible benefits to the host.

In identifying prospective probiotic organisms for use in humans, particular attention must be placed on the safety of the organism for a wide variety of individuals, including the immunocompromised, the very young, and the aged. A number of in vitro test systems and in vivo models are now available for studying probiotics prior to their use in human subjects, although relevance of the resulting data may not be predictable.


Richard Walker, Merry Buckley. 2006. Probiotic microbes: the scientific basis.

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