| Adhesion of bacteria to host epithelial cells is a critical primary step in the pathogenesis of diarrheal disease. Bacteria demonstrating attaching and effacing (AE) adhesion include enteropathogenic Escherichia coli (EPEC), Verocytotoxin-producing E. coli (VTEC), and certain isolates of Hafnia alvei. The AE lesion is characterized by focal destruction of microvilli followed by intimate contact between the bacteria and the host membrane with recruitment of underlying cytoskeletal elements.;By immunofluorescence microscopy, it was shown that detection of alpha-actinin, an actin binding and crosslinking protein, accumulation in infected epithelial cells is a consistent and specific manifestation of AE response. Therefore, the detection of alpha-actinin in eukaryotic cells could serve as a reliable and non-toxic alternative to fluorescent F-actin staining test utilizing phalloidin, a highly toxic mushroom-derived poison, to detect AE bacteria.;Selected signal transduction responses to VTEC O157:H7 infection were examined. Similar to EPEC, VTEC infection of epithelial cells leads to an activation of phoshatidylinositol cascade as determined by elevations in inositol trisphosphate and release of intracellular Ca2+. In contrast to EPEC, multiple VTEC O157:H7 strains consistently failed to induce a detectable phosphotyrosine response. However, the phosphotyrosine response and the ability of VTEC to induce their internalization into ion into non-phagocytic cells, an event dependent on tyrosine phosphorylation, could be induced in VTEC-infected cells if coinfected with an EPEC. Using recombinant laboratory E. coli overexpressing intiminO157, and double immunofluorescence labeling, it was demonstrated that VTEC can signal for the accumulation of cytoskeletal proteins in the absence of phosphotyrosine response. Taken together, these findings show that VTEC O157:H7 pathogenesis may involve signal transduction pathways distinct from those induced by EPEC.;Eleven Canadian clinical isolates of H. alvei were examined for the AE characteristics. These organisms failed to induce cytoskeletal rearrangement or form AE lesions. None of the organisms possessed the eae gene. These results demonstrate that not all diarrheagenic H. alvei are AE. Together with profiles of outer membrane protein extracts, chromosomal macrorestriction fragments and plasmids, these findings indicate that there is heterogeneity in phenotypic and genotypic characteristics among strains of H. alvei. |
