Model of the development of PAI of pathogenic E. coli. Model of the development of PAI of pathogenic E. coli. In this basic model, foreign DNA is acquired by an ancient nonpathogenic E. coli strain, e.g., a normal inhabitant of the gut of vertebrates. In EHEC, a virulence-associated plasmid and at least one Stx-converting phage and several PAI have been acquired and maintained due to the specific adaptation to different environments. Genomic islands, which are present in a specific live environment may specialize and are involved in the development of disease such as (A), diarrhea and hemolytic-uremic syndrome after colonization of the large intestine (A), watery diarrhea after colonization of the small intestine (B), and UTI after survival and colonization of E. coli in the bladder (C). Such events probably have led to the development of specific pathotypes of E. coli, examples of which are EHEC (A), EPEC (B), and UPEC (C). In the model described here, the evolutionary sequence of uptake and incorporation of mobile genetic elements has not been considered. tRNA genes and bacterial phage attachment sites are depicted by grey rectangles with dots and hatched dark grey rectangles, respectively. stx, Shiga toxin gene; OI, O-island; espC, E. coli secreted protease gene. Herbert Schmidt, and Michael Hensel Clin. Microbiol. Rev. 2004; doi:10.1128/CMR.17.1.14-56.2004