Induction of epithelial cell death including apoptosis by enteropathogenicEscherichia coli expressing bundle-forming pili

Infection with enteropathogenic Escherichia coli (EPEC) is a major cause of severe infantile diarrhea, particularly in parts of the developing world. The bundle-forming pilus (BFP) of EPEC is an established virulence factor e ncoded on the EPEC adherence factor plasmid (EAF) and has been implicated i n both localized adherence to host cells and bacterial autoaggregation. We investigated the role of BFP in the ability of EPEC binding to hill host ep ithelial cells. BFP-expressing strains killed all three cell lines tested, comprising HEp-2 (laryngeal), HeLa (cervical), and Caco-2 (colonic) cells. Analysis of phosphatidylserine expression, internucleosomal cleavage of hos t cell DNA, and morphological changes detected by electron microscopy indic ated evidence of apoptosis. The extent of cell death was significantly grea ter for BFP-expressing strains, including E2348/69, a wild-type clinical is olate, as well as for a laboratory strain, HB101, transformed with a bfp-ca rrying plasmid. Strains which did not express BFP induced significantly les s cell death, including a bfpA disruptional mutant of E2348/69, EAF plasmid -cured E2348/69, HB101, and HB101 complemented with the locus of enterocyte effacement pathogenicity island. These results indicate a direct correlati on between BFP expression and induction of cell death, including apoptosis, an event which may involve the targeting of host cell membrane phosphatidy lethanolamine.