Effect of Probiotic Administration on Gut Flora Composition

Healthy human gut contains a large number of bacteria, which belong to several different species. Some genes in these bacteria encode enzymes that the human body cannot produce. These enzymes can catalyze metabolic reactions in the distal small bowel. For instance, bacterial enzymes can breakdown indigestible dietary constituents, making available extra energy to the host. The current paradigm treats the human body as a 'metagenome', i.e. a composite of Homo sapiens genes and genes in the genomes of the colonizing bacteria. Till recently, accurate determination of bacterial gut flora was not possible. Recent development of multi-parallel sequencing techniques has allowed unbiased determination of profile of gut flora. These techniques have revealed changes in gut flora in several disease conditions, including those of the gastrointestinal tract and liver. This has prompted the use of drugs, such as probiotics to restore the gut flora. Probiotics contain living microorganisms, and are administered in an attempt to obtain health benefits by restoring normal gut flora. These preparations provide benefit to patients with several diseases, including childhood diarrhea, antibiotic-associated diarrhea, inflammatory bowel disease, vaginitis, etc. However, the mechanisms of their beneficial effects remains unclear. Gut microbiota appear to modulate the development of immune system and maintain a balance between Th17 and T regulatory cells in animals. However, it is not known whether administration of probiotics changes the profile (nature and relative density of various species) of gut flora, and whether these changes are short-lasted or persistent. This proposal aimed to study whether probiotic administration influences the gut bacterial profile and host immune responses. In addition, we wished to determine whether the changes in gut flora and immune responses persist after probiotic administration is stopped.