Effect of probiotics on enterocyte bacterial translocation in vitro

Enteral probiotics such as Lactobacillus casei GG (LGG) have been used in t he treatment of a variety of intestinal disorders in infants and children, including diarrhea, malabsorption, and Clostridium difficile colitis. We ha ve previously demonstrated that the probiotic bacterium LGG has an inhibito ry effect on bacterial translocation (BT) in a neonatal rabbit model. Howev er, this in-vivo model is limited for investigating the cellular and molecu lar mechanisms responsible for probiotic inhibition of BT. The purpose of t his study was to determine the efficacy of LGG in reducing the rate of Esch erichia coli C25 (E. coli C25) translocation using an in-vitro enterocyte c ell-culture model. Human colonic carcinoma (Caco-2) enterocytes were seeded in porous filters in the apical chamber of a two-chamber cell-culture syst em and grown for 14 days to confluence. The monolayers were incubated at 37 degreesC with LGG for 180 min. Non-adherent LGG was washed away prior to a 120-min incubation period with 10(5) CFU E. coli C25. E. coli that had tra nslocated across the enterocyte monolayer were quantified by growing basal- chamber media samples on gram-negative bacteria-specific MacConkey's agar. In order to determine monolayer integrity, transepithelial electrical resis tance (TEER) was measured across Caco-2 cells treated with LGG and E. coli. Statistical analysis was by ANOVA with P < 0.05 considered significant. LG G inhibited E. coli translocation at all LGG concentrations tested. The TEE R ratio was not significantly altered by addition of LGG or E, coli (0.9 +/ - 0.03 vs 0.8 +/- 0.05). These results demonstrate that the probiotic bacte rium LGG inhibits BT of E. coli C25 in a dose-dependent manner in an invitr o cell-culture model. This model should be valuable in investigating the ce llular and molecular mechanisms involved in the inhibition of pathological enteral bacteria by probiotic agents.