Objectives: Promising results from clinical studies on the effect of probiotics as maintenance therapy in inflammatory bowel disease and in the prevention of onset of pouchitis ask for studies to unravel the still poorly understood mechanism of action of probiotics.
Methods: To evaluate whether the probiotic bacteria that were used in the clinical studies (VSL#3, Escherichia coli Nissle 1917, and Lactobacillus GG) are able to induce chemokine production in epithelial cells, HT29/19A monolayers were incubated with cell debris and cell extract fractions of single strains of the probiotic bacteria in doses ranging from 10(3) to 10(9) colony-forming units/ml for 32 h. Supernatants were measured for interleukin 8 by ELISA.
Results: Lactobacilli and bifidobacteria strains from VSL#3 and Lactobacillus GG did not induce interleukin 8, whereas both cell debris and cell extracts from E. coli Nissle 1917 induced interleukin 8 production in a dose-dependent way. Cell extracts from streptococcal strains induced interleukin 8 when applied at high concentrations.
Conclusions: Probiotic Gram-positive bacteria did not induce interleukin 8, whereas the nonpathogenic, Gram-negative E. coli Nissle 1917 strain induced interleukin 8 in a dose-dependent way in this culture model. These results suggest that probiotic Gram-positive bacteria and E. coli Nissle 1917 may exert their beneficial effects on the host by a different mechanism of action.