Systematic deletion of type III secretion system effectors in enteropathogenic E. coli unveils the role of non-LEE effectors in A/E lesion formation

Enteropathogenic E. coli (EPEC) is a diarrheagenic human pathogen. The hallmark of EPEC infection is the formation of the attachment and effacement (A/E) lesion in intestinal epithelial cells, characterized by the effacement of brush border microvilli and the intimate bacterial attachment to the enterocyte in actin-rich pedestal-like structures. The locus of enterocyte effacement (LEE) in the EPEC genome encodes a type III protein secretion system (T3SS) that translocates multiple effector proteins into the host cell to subvert cellular functions for the benefit of the pathogen. These effectors are encoded both within the LEE and outside the LEE. In vitro cell culture infections have shown that LEE effectors are required for intimate bacterial attachment to epithelial cells whereas non-LEE effectors mostly play a role in modulating inflammation and cell apoptosis in the gut epithelium. We constructed a set of EPEC mutant strains harbouringving deletions in the complete repertoire of genes encoding T3SS-effectors. Infection of human intestinal in vitro organ cultures (IVOC) with these mutant strains surprisingly revealed that non-LEE effectors are also needed to induce efficient A/E lesion formation in intestinal mucosal tissue.