Signal transduction and the physiological responses to infection with diarrheagenic Escherichia coli

grantor: University of TorontoInfection with enteropathogenic (EPEC) and Verotoxin-producing Escherichia coli (VTEC) is associated with a number of illnesses in humans. The pathogenic mechanisms of EPEC and VTEC infection are not well understood; therefore, the objectives of the studies presented in this thesis were to unravel the eukaryotic signal transduction responses following bacterial infection and to link these intracellular events to pathophysiological changes in epithelial function. Firstly, increased adherence of transformed strains of rabbit diarrheagenic E. coli (RDEC-1), the lapine counterpart of EPEC, was correlated with a number of signal transduction responses within infected host epithelial cells. The increased capability of transformed RDEC-1 to produce the morphologically distinct attaching and effacing (AE) lesion on epithelial cells was concomitant with the ability of these strains to stimulate increased levels of calcium as well as activate protein kinases within host cells. Next, since signal transduction responses could contribute to the induction of diarrhea following AE E. coli infection, changes in ion transport and permeability functions of epithelial cells infected with EPEC were examined. EPEC infection of a model intestinal epithelium, T84, resulted in a time-dependent decrease in barrier function due to alterations in the distribution of ZO-1 in the tight junction complex. These findings provide possible mechanisms for EPEC-induced diarrheal disease in vivo. Changes in epithelial function were then examined following VTEC infection, with the specific aim to link epithelial functional defects with intracellular signaling by VTEC. VTEC infection also decreased T84 resistance in a time-dependent fashion by altering intercellular tight junctions. Both protein kinase C and myosin light chain kinase played a role in the decreased barrier function induced by VTEC. In addition, VTEC infection resulted in an increase in chloride ion secretion in T84 cells. These findings suggest that the mechanisms for VTEC-induced diarrheal illness involve both increased epithelial permeability and ion transport. Finally, the possibility that VTEC-induced changes in T84 barrier function could provide a mechanism for Verotoxin-1 (VT-1) translocation across epithelial barriers was investigated. It was shown that the mechanism of VT-1 translocation involved a transcellular route in T84 cells. These findings impact on the general concept of bacterial toxin penetration of the intestinal mucosal barrier in the development of systemic illnesses in humans.Ph.D