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Pathotypes and pathogenic clones
Enteropathogenic E. coli
A plasmid-encoded, type IV bundle-forming pilus critical for virulence.
A chromosomal pathogenicity island encoding a type III secretion system and the ability to alter the host cytoskeleton.
A 35-kb genetic element known as the locus of enterocyte effacement (LEE) is necessary for this effect and, when cloned from EPEC strain E2348/69 #into a nonpathogenic E. coli strain, is sufficient to confer attaching and effacing activity (18). The LEE is considered to be a pathogenicity island because it contains virulence loci, it is not found in nonpathogenic E. coli strains, it is inserted into the genome of E. coli at specific sites (tRNA genes), and finally because its distinctive G+C content (38%) indicates its origin in another species. The LEE is inserted near different tRNA loci in different EPEC strains (18). The LEE from strain E2348/69 carries 41 genes, which encode a type III secretion system and various proteins secreted via this system, including an adhesin and its cognate receptor, a regulator, and several proteins of unknown function. Type III secretion systems are found in bacteria from several Gram-negative genera that have close relationships with eukaryotic hosts (19). These systems can transport bacterial proteins across the inner and outer membranes of the bacteria and the host cell plasma membrane and can deliver effector proteins to the surface or interior of host cells.
A large toxin that inhibits lymphocyte activation.
Two divergent groups of EPEC
Enterohemorrhagic E. coli
Production of Shiga toxins.
The EHEC LEE.
Evolution of EHEC groups.
Stepwise evolution of E. coli O157:H7.
A second group of EHEC.
Conclusions
Acknowledgments
References
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