Probiotic strains:: survival under simulated gastrointestinal conditions, in vitro adhesion to Caco-2 cells and effect on cytokine secretion

This study evaluated three probiotic strains (Lactobacillus paracasei subsp. paracasei LC-01, L. acidophilus LA-5, Bifidobacterium lactis Bb-12) and two yoghurt strains (L. delbrueckii subsp. bulgaricus LBY-27 and Streptococcus thermophilus STY-31) with regard to their resistance to simulated gastrointestinal stress, and their ability to interact with human intestinal epithelial cells. The viability of strains was analyzed by measurements of fluorescence-stained cells and their growth by plate colony-counts. The results reveal that for all tested strains, gastric emptying (above pH 3.0) would release a large number of viable cells ranging from 91% for L. paracasei to 53% for S. thermophilus into the intestinal tract, and that between 12 and 23% of them subsequently survive intestinal stress. Among them L. paracasei showed the highest resistance to gastric stress. All the bacteria adhered to the Caco-2 cell line, with the highest adhesions being observed for L. delbrueckii subsp. bulgaricus (9%) and L. acidophilus (7%). Binding of all strains to Caco-2 cells did not result in a significant increase in the production of IL-6 and IL-8 cytokines, suggesting that these bacteria do not trigger an overt inflammatory response in human intestine epithelial cells.