INITIAL BINDING OF SHIGA TOXIN-PRODUCING ESCHERICHIA-COLI TO HOST-CELLS AND SUBSEQUENT INDUCTION OF ACTIN REARRANGEMENTS DEPEND ON FILAMENTOUS ESPA-CONTAINING SURFACE APPENDAGES

Shiga toxin-producing Escherichia coli (STEC) induce so-called attachi ng and effacing lesions that enable the tight adherence of these patho gens to the gut epithelium. All of the genes necessary for this proces s are present in the locus of enterocyte effacement, which encodes a t ype III secretion system, the secreted Esp proteins and the surface pr otein intimin. In this study we sequenced the espA gene of STEC, gener ated and characterized a corresponding deletion mutant and raised EspA -specific monoclonal antibodies to analyse the functional role of this protein during infection. EspA was detected in often filament-like st ructures decorating all bacteria that had attached to Hela cells. Thes e appendages were especially prominent on bacteria that had not yet in duced the formation of actin pedestals, indicating that they mediate t he initial contact of STEC to their target cells. Consistently, a dele tion of the espA gene completely abolished the capacity of such STEC m utants to bind to HeLa cells and to induce actin rearrangements. Surfa ce appendages similar to those described in this study are also formed by Pseudomonas syringae and may represent a structural element common to many bacterial pathogens that deliver proteins into their target c ells via a type ill secretion system.