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Category: Clinical Microbiology
How Noninvasive Pathogens Induce Disease: Lessons from Enteropathogenic and Enterohemorrhagic Escherichia Coli, Page 1 of 2
< Previous page | Next page > /docserver/preview/fulltext/10.1128/9781555817848/9781555812614_Chap23-1.gif /docserver/preview/fulltext/10.1128/9781555817848/9781555812614_Chap23-2.gifAbstract:
A novel focus of the work has been on defining the molecular and cellular mechanisms underlying the interactions between bacterial pathogens and host cells. During infection, enteropathogenic Escherichia coli (EPEC) and enterohemorrhagic E. coli (EHEC) induce a characteristic ‘‘attaching and effacing’’ (A/E) histopathology on gut enterocytes. Since studies investigating the function of EPEC’s virulence factors are the most advanced, this chapter deals with EPEC as the prototype for the family of A/E-inducing pathogens. EPEC infection is estimated to cause the deaths of several hundred thousand children per year owing to dehydration and other complications. First widely recognized as the causative agent of hamburger disease, EHEC is a zoonotic pathogen that appears to be asymptomatically carried by various ruminants. Mutants lacking the bundle-forming pilus (BFP) plasmid still attach to host cells, but do not form microcolonies and produce fewer A/E lesions than wild-type EPEC. Immunofluorescence studies have shown that in addition to membrane-bound Tir, the tips of EPEC pedestals contain predominantly filamentous (F)-actin, as well as talin, α- actinin, ezrin, and several other cytoskeletal proteins. Diarrhea is undoubtedly the most prominent and widespread symptom associated with both EPEC and EHEC infection. Approaches using molecular biology, genetics, and cell biology have provided many new insights into how EPEC and related pathogens interact with and exploit host cells during the course of infection and how this ultimately leads to disease.
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Transmission electron micrograph of A/E lesions in rabbit intestinal epithelial tissue (Peyer's patch) caused by the REPEC O103. Bacteria are labeled with “B”; pedestals are labeled with “P.” (×20,000.) (Photograph courtesy of Ursula Heczko, Biotechnology Laboratory, University of British Columbia, modified with permission from reference 36 .)
Transmission electron micrograph of A/E lesions in rabbit intestinal epithelial tissue (Peyer's patch) caused by the REPEC O103. Bacteria are labeled with “B”; pedestals are labeled with “P.” (×20,000.) (Photograph courtesy of Ursula Heczko, Biotechnology Laboratory, University of British Columbia, modified with permission from reference 36 .)
The structure of the EPEC-induced pedestal. EPEC intimately attaches to the host cell through intimin-Tir binding. Several cytoskeletal proteins including α-actinin, talin, and Nck are recruited to the tip of the pedestal. Talin binds to Tir, but to which region is unknown; however, α-actinin binds to the N terminus of Tir, while Nck binds to the phosphotyrosine 474 at the C terminus of Tir. Binding of Nck is required for the recruitment of N-WASP and the Arp 2/3 complex, resulting in the nucleation of actin. F-actin, as well as many other host proteins, is found along the length of the pedestal while non-muscle myosin II and tropomyosin are found at the pedestal base. (Modified with permission from reference 36 .)
The structure of the EPEC-induced pedestal. EPEC intimately attaches to the host cell through intimin-Tir binding. Several cytoskeletal proteins including α-actinin, talin, and Nck are recruited to the tip of the pedestal. Talin binds to Tir, but to which region is unknown; however, α-actinin binds to the N terminus of Tir, while Nck binds to the phosphotyrosine 474 at the C terminus of Tir. Binding of Nck is required for the recruitment of N-WASP and the Arp 2/3 complex, resulting in the nucleation of actin. F-actin, as well as many other host proteins, is found along the length of the pedestal while non-muscle myosin II and tropomyosin are found at the pedestal base. (Modified with permission from reference 36 .)
Putative mechanisms underlying EPEC-induced diarrhea include increased epithelial permeability and alterations in Cl- and HCO3 − ion secretion. Contributing structural changes include loss of absorptive surfaces, while the translocated EPEC effector EspF has been implicated in the loss of tight junction integrity. Signaling events within infected cells may also play a role in diarrhea, including increased MAP kinase activity and IL-8 production, causing the recruitment of neutrophils resulting in tissue damage. (Modified with permission from reference 36 .)
Putative mechanisms underlying EPEC-induced diarrhea include increased epithelial permeability and alterations in Cl- and HCO3 − ion secretion. Contributing structural changes include loss of absorptive surfaces, while the translocated EPEC effector EspF has been implicated in the loss of tight junction integrity. Signaling events within infected cells may also play a role in diarrhea, including increased MAP kinase activity and IL-8 production, causing the recruitment of neutrophils resulting in tissue damage. (Modified with permission from reference 36 .)