Background : Pathogenic adherent–invasive Escherichia coli have been isolated from ileal lesions of Crohn's disease.

Aim : To investigate the non-pathogenic E. coli strain Nissle 1917 (Mutaflor) as possible maintenance therapy in inflammatory bowel disease by testing its ability to prevent adherent–invasive E. coli strains from adhering to and invading human intestinal epithelial cells in vitro.

Methods : Bacterial adhesion to and invasion of intestinal epithelial cells (Intestine-407) were assessed by counting the colony-forming units. The inhibitory effect of E. coli Nissle 1917 was determined after co-incubation with adherent–invasive E. coli strains or after pre-incubation of the intestinal epithelial cells with this probiotic strain prior to infection with adherent–invasive E. coli strains.

Results : Strain Nissle 1917 exhibited dose- and time-dependent adherence to intestinal epithelial cells and inhibited the adhesion and invasion of various adherent–invasive E. coli strains. In co-infection experiments, the inhibitory effect on adherent–invasive E. coli adhesion reached 78–99.9%. Pre-incubation of intestinal epithelial cells with strain Nissle 1917 reduced adherent–invasive E. coli adhesion by 97.2–99.9%. The inhibitory effect on adherent–invasive E. coli invasion paralleled that on adhesion.

Conclusion : As strong and significant inhibitory effects on adherent–invasive E. coli adhesion and invasion were observed in co-infection and pre-infection experiments, E. coli Nissle 1917 could be efficient for preventive or curative probiotic therapy in patients with Crohn's disease.