ABSTRACTThe gastrointestinal pathogen enteropathogenic E. coli (EPEC) causes diarrhea and is responsible forsignificant morbidity and mortality in children under five years of age in developing countries. There arekey gaps in our understanding of how EPEC causes diarrhea. The bacteria use a syringe-like type IIIsecretion system to deliver key virulence effectors directly into host intestinal epithelial cells. In theinitial phase of infection EPEC delivers proteins that promote host cell survival. Later in infectionhowever secretion of more cytotoxic proteins results in host cell death. The studies proposed in thisapplication focus on two EPEC effector molecules that are secreted at discrete times post-infectionand that have contrasting impacts on mitochondria and on host cell survival. We hypothesize that theorchestrated and intersecting actions of effector proteins on host mitochondrial stability and functionare critical for EPEC colonization and virulence. This hypothesis will be tested in three Aims where wewill: (1) Mechanistically define the impact of two EPEC effectors on host mitochondrial structure (2)Characterize effector-dependent alterations in mitochondrial function in infected intestinal epithelialcells in vitro and (3) Establish the impact of EPEC secreted virulence effectors on mitochondrialfunction in vivo using a rabbit model of infection. The proposed studies will establish the precise role ofkey secreted virulence factors and of host mitochondrial perturbations in EPEC virulence. In the futurewe anticipate our studies to inform the development and use of host cell-targeted molecules as adjunctsto standard therapies for treating the diarrhea caused by EPEC and related bacteria.