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ABSTRACTEnteropathogenic Escherichia coli(EPEC) and enterohemorrhagic E. coliare extracellular pathogens that employ a type III secretion system to export translocator and effector proteins, proteins which facilitates colonization of the mucosal surface of the intestine via formation of attaching and effacing (A/E) lesions. The genes encoding the proteins for A/E lesion formation are located on a pathogenicity island, termed the locus of enterocyte effacement (LEE), which contains eaeencoding intimin as well as the type III secretion system and effector genes. Many type III secreted proteins are stabilized and maintained in a secretion-competent conformation in the bacterial cytosol by specific chaperone proteins. Three type III chaperones have been described thus far within the EPEC LEE region: CesD, for the translocator proteins EspB and EspD; CesT, for the effector proteins Tir and Map; and CesF, for EspF. In this study we report the characterization of CesD2 (previously Orf27), a second LEE-encoded chaperone for EspD. We show specific CesD2-EspD protein interaction which appears to be necessary for proper EspD secretion in vitro and pathogenesis in vivo as demonstrated in the A/E-lesion-forming mouse pathogen Citrobacter rodentium.

Enteropathogenic Escherichia coli(EPEC) encode a type III secretion system located on a pathogenicity island known as the locus for enterocyte effacement. Four proteins are known to be exported by this type III secretion system – EspA, EspB and EspD required for subversion of host cell signal transduction pathways and a translocated intimin receptor protein (Tir) required for intimin‐mediated intimate attachment and attaching and effacing lesion formation. The espAgene is located within the locus for enterocyte effacement and the EspA polypeptide from the prototype EPEC strain E2348/69 (O127:H6) has recently been shown to be a component of a filamentous structure involved in bacteria‐host cell interaction and locus for enterocyte effacement‐encoded protein translocation involved in attaching and effacing lesion formation. In this study we have extended our investigation of EspA to strains belonging to other classical EPEC serotypes. DNA sequencing demonstrated that the espAgene from the different EPEC strains share at least 65% DNA identity. In addition, we detected morphologically and antigenically similar EspA filaments in all but one of the bacterial strains examined including recombinant, non‐pathogenic E. coliexpressing espAfrom a cloned locus for enterocyte effacement region (HB101(pCVD462)).

Parenteral immunization with either formalin‐fixed whole cells of the fimbriate Bgd17 strain or purified fimbriae protected against Vibrio choleraeO1 infection in rabbits, independent of biotype and serotype. Parenteral immunization of adult rabbits with purified fimbriae prior to V. choleraeO1 challenge resulted in a reduction of 2 to 3 orders of magnitude in the number of bacteria recovered from the small intestines of immunized rabbits in comparison to non‐immunized controls. IgG and IgA antibodies against fimbrillin of V. choleraeO1 were detected in the convalescent sera of patients with cholera; however, little fimbrial antigen was detected in the commercially available cholera vaccines when examined by polyclonal and monoclonal antibodies against fimbriae. These data suggest that fimbrial hemagglutinin is a major adhesin of V. choleraeO1 and that parenteral immunization with fimbriae generates a specific immune response in the gut that may serve as one means of mitigating subsequent V. choleraeO1 gut infection.