Enterohaemorrhagic and enteropathogenic Escherichia coli use a different Tir-based mechanism for pedestal formation

Enterohaemorrhagic Escherichia coli (EHEC) adheres to the host intestinal e pithelium, resulting in the formation of actin pedestals beneath adhering b acteria. EHEC and a related pathogen, enteropathogenic E. coli (EPEC), inse rt a bacterial receptor, Tir, into the host plasma membrane, which is requi red for pedestal formation. An important difference between EPEC and EHEC T ir is that EPEC but not EHEC Tir is tyrosine phosphorylated once delivered into the host. In this study, we assessed the role of Tir tyrosine phosphor ylation in pedestal formation by EPEC and EHEC. In EPEC, pedestal formation is absolutely dependent on Tir tyrosine phosphorylation and is not complem ented by EHEC Tir. The protein sequence surrounding EPEC Tir tyrosine 474 i s critical for Tir tyrosine phosphorylation and pedestal formation by EPEC. In contrast, Tir tyrosine phosphorylation is not required for pedestal for mation by EHEC. EHEC forms pedestals with both wild-type EPEC Tir and the n ontyrosine-phosphorylatable EPEC Tir Y474F. Pedestal formation by EHEC requ ires the type III delivery of additional EHEC factors into the host cell. T hese findings highlight differences in the mechanisms of pedestal formation by these closely related pathogens and indicate that EPEC and EHEC modulat e different signalling pathways to affect the host actin cytoskeleton.