The EspD protein of enterohemorrhagic Escherichia coli is required for theformation of bacterial surface appendages and is incorporated in the cytoplasmic membranes of target cells

The formation of EspA-containing surface appendages in pathogenic Escherich ia coli strains, both enteropathogenic E, coli (EPEC) and Shiga toxin-produ cing E, coil strains, is essential for critical events in the infective pro cess, e.g., localized bacterial adherence to host cells with formation of m icrocolonies and induction of attaching and effacing lesions. It has been r eported that EPEC mutants deficient in the production of EspD, which is enc oded by the esp operon, are unable to accumulate actin underneath adherent bacteria but exhibit an attachment similar to that of the wild type. Here, we report the construction and characterization of an in-frame espD deletio n mutant of the enterohemorrhagic E, coli (EHEC) strain EDL933, In contrast to what was observed in EPEC mutants, the EDL933 espD mutant not only lack ed the capacity to accumulate actin but also exhibited an impaired attachme nt to HeLa cells. The synthesis of the EspD protein was also essential for the formation of EspA-containing filaments, Finally, localization studies d emonstrated that the EspD protein is transferred to the cytoplasm and integ rated into the cytoplasmic membranes of infected cells. These results help to elucidate the underlying molecular events in infections caused by EHEC.