In vitro selection criteria for probiotic bacteria of human origin: correlation with in vivo findings

The enteric flora comprises approximate to 95% of the total number of cells in the human body and can elicit immune responses while protecting against microbial pathogens. However, the resident bacterial flora of the gastroin testinal tract may also be implicated in the pathogenesis of diseases such as inflammatory bowel disease (ulcerative colitis and Crohn disease). The o bjectives of the Probiotic Research Group based at University College Cork were to isolate and identify lactic acid bacteria exhibiting beneficial pro biotic traits, such as bile tolerance in the absence of deconjugation activ ity, acid resistance, adherence to host epithelial tissue, and in vitro ant agonism of pathogenic microorganisms or those suspected of promoting inflam mation. To isolate potentially effective probiotic bacteria, we screened th e microbial population adhering to surgically resected segments of the gast rointestinal tract (the environment in which they may subsequently be reint roduced and required to function). In total, 1500 bacterial strains from re sected human terminal ilea were assessed. From among these organisms, Lacto bacillus salivarius subsp. salivarius strain UCC118 was selected for furthe r study. In mouse feeding trials, milk-borne L. salivarius strain UCC118 co uld successfully colonize the murine gastrointestinal tract. A human feedin g study conducted in 80 healthy volunteers showed that yogurt can be used a s a vehicle for delivery of strain UCC118 to the human gastrointestinal tra ct with considerable efficacy in influencing gut flora and colonization. In summary, we developed criteria for in vitro selection of probiotic bacteri a that may reflect certain in vivo effects on the host such as modulation o f gastrointestinal tract microflora.