Activation of NF-kappaB in intestinal epithelial cells by E. coli strains isolated from the colonic mucosa of IBD patients.

Katia La Ferla, Dirk Seegert, Stefan Schreiber
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International journal of colorectal disease
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Our results indicate that E. coli strains can be found in the mucosa of some IBD patients which are able to activate NF-kappaB similar to known pathogenic strains. The absence of several virulence genes in these cells suggests that they are members of the luminal flora which acquire as yet unidentified virulence determinants and are therefore involved in the pathophysiology of IBD.Fifteen bacterial strains from inflamed and six from noninflamed colonic tissues from IBD patients. Their ability to induce NF-kappaB activation was examined in vitro by gel-shift assays. The activation of the TNF-alpha promoter was determined by reporter gene assays. Bacterial isolates were characterized by invasion assays, electron microscopy, and PCR.Four of 15 E. coli bacterial isolates from inflamed IBD tissues induced NF-kappaB activity in intestinal epithelial cells as determined by gel-shift assays. NF-kappaB activation was only seen with living bacteria but not with heat-inactivated cells. Isolates from noninflamed tissues and a wild-type E. coli control strain induced a weaker or no activation. Reporter gene assays with a construct comprising a luciferase gene driven by the TNF-alpha promoter revealed that isolates from Crohn''s disease patients induced a stronger activation of the TNF-alpha gene than isolates from ulcerative colitis patients. The isolated bacteria invaded HT-29 cells, although typical virulence genes for enteropathogenic, enterhemorrhagic, or enteroinvasive E. coli, i.e., eae, tir, EspA, Per (A-C), ipaC, were not detected in these cells. Bacterial invasion was additionally confirmed by electron microscopy examination.The involvement of bacteria in the pathogenesis of inflammatory bowel disease has been discussed for several years. In this study we evaluated the ability of E. coli isolates from inflamed and noninflamed colonic mucosa to activate NF-kappaB.