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Enterohemorrhagic Escherichia coli (EHEC) and enteropathogenic E. coli (EPEC) are bacterial pathogens that cause severe illnesses in humans. Citrobacter rodentium is a related mouse pathogen that serves as a small animal model for EPEC and EHEC infections. EPEC, EHEC and C. rodentium translocate bacterial virulence proteins directly into host intestinal cells via a type III secretion system (T3SS). Non-LEE-encoded effector A (NleA) is a T3SS effector that is common to EPEC, EHEC and C. rodentium. NleA interacts with and inhibits the mammalian COPII complex, impairing cellular secretion; this interaction is required for bacterial virulence. Although diarrhea is a hallmark of EPEC, EHEC and C. rodentium infections, the underlying mechanisms are not well characterized. One of the essential functions of the intestine is to maintain a barrier between the lumen and submucosa. Tight junctions seal the space between adjacent epithelial cells creating this barrier. Consequently, it is thought that the disruption of intestinal epithelial tight junctions by EPEC, EHEC, and C. rodentium could result in a loss of barrier function. In this study, we demonstrate that NleA mediated COPII inhibition is required for EPEC- and C. rodentium-mediated disruption of tight junction proteins and increases in fecal water content., (Copyright © 2013 Institut Pasteur. Published by Elsevier Masson SAS. All rights reserved.)

This study identified and characterized enteropathogenic Escherichia coli (EPEC) in the Canadian food supply. Eighteen of 450 E. coli isolates from food animal sources were identified as atypical EPEC (aEPEC). Several of the aEPEC isolates identified in this study possessed multiple virulence genes, exhibited adherence and attaching and effacing (A/E) lesion formation, disrupted tight junctions, and were coclassified with the extraintestinal pathogenic E. coli (ExPEC) and enterotoxigenic E. coli (ETEC) pathotypes.

Enteropathogenic Escherichia coli (EPEC) is a diarrhoeal pathogen that adheres to epithelial cells of the small intestine and uses a type III secretion system to inject effector proteins into host cells. EPEC infection leads to disruption of host intestinal tight junctions that are important for maintaining intestinal barrier function. This disruption is dependent on the bacterial type III secretion system, as well as the translocated effectors EspF and Map. Here we show that a third type III translocated bacterial effector protein, NleA, is also involved in tight junction disruption during EPEC infection. Using the drug Brefeldin A, we demonstrate that the effect of NleA on tight junction integrity is related to its inhibition of host cell protein trafficking through COPII-dependent pathways. These results suggest that NleA's striking effect on virulence is mediated, at least in part, via its role in disruption of intestinal barrier function.

Enterohemorrhagic and enteropathogenic Escherichia coli (EHEC and EPEC) maintain an extracellular lifestyle and use a type III secretion system to translocate effector proteins into the host cytosol. These effectors manipulate host pathways to favor bacterial replication and survival. NleA is an EHEC/EPEC- and related species-specific translocated effector protein that is essential for bacterial virulence. However, the mechanism by which NleA impacts virulence remains undetermined. Here we demonstrate that NleA compromises the Sec23/24 complex, a component of the mammalian COPII protein coat that shapes intracellular protein transport vesicles, by directly binding Sec24. Expression of an NleA-GFP fusion protein reduces the efficiency of cellular secretion by 50%, and secretion is inhibited in EPEC-infected cells. Direct biochemical experiments show that NleA inhibits COPII-dependent protein export from the endoplasmic reticulum. Collectively, these findings indicate that disruption of COPII function in host cells contributes to the virulence of EPEC and EHEC.