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Category: Microbial Genetics and Molecular Biology
Pathogenicity Islands and Other Mobile Genetic Elements of Diarrheagenic Escherichia coli, Page 1 of 2
< Previous page | Next page > /docserver/preview/fulltext/10.1128/9781555818173/9781555811617_Chap03-1.gif /docserver/preview/fulltext/10.1128/9781555818173/9781555811617_Chap03-2.gifAbstract:
This chapter focuses on diarrheagenic Escherichia coli strains and the various pathogenicity islands (PAIs) and other mobile genetic elements that differentiate these pathogens from normal-flora E. coli. At least six categories of diarrheagenic E. coli strains have been defined. Five of these categories, enteropathogenic E. coli (EPEC), enterohemorrhagic E. coli (EHEC), enteroaggregative E. coli (EAEC), enterotoxigenic E. coli (ETEC), and enteroinvasive E. coli (EIEC), are reviewed in the chapter. A sixth category, diffusely adherent E. coli (DAEC), is a heterogeneous group of organisms, and epidemiological studies have given conflicting results about the true clinical significance of these strains. Mobile genetic elements encoding virulence factors in human diarrheagenic E. coli are listed in the chapter. The majority of EPEC strains associated with diarrhea possess the EPEC adherence factor (EAF) plasmid and are referred to as typical EPEC strains, while EPEC strains that do not possess EAF plasmids are referred to as atypical EPEC strains. The majority of genes within this region have homology to transposons and insertion elements (IS elements), although these elements are apparently incomplete and nonfunctional. The great variety of mobile genetic elements present in diarrheagenic E. coli , including plasmids, bacteriophages, transposons, and PAIs, on a K-12 backbone with so many horizontally transferred regions indicates an enormous genomic plasticity that complicates the efforts to categorize the existing subgroups into sharply delineated pathotypes and the attempts to predict what novel combination of virulence factors may emerge in the future.
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Diagram of the LEE PAIs of EPEC E2348/69 (O127:H6) ( 27 ) and EHEC EDL933 (O157:H7) ( 88 ). The different patterns of the large arrows indicate the nucleotide divergence between the EPEC and EHEC genes. Small arrows indicate operons within the LEE; the four polycistronic operons demonstrated for the LEE are designated LEE1 through LEE4. The 933L prophage on the right side of the LEE is present in EHEC O157:H7 but not in EPEC OI27:H6.
Diagram of the LEE PAIs of EPEC E2348/69 (O127:H6) ( 27 ) and EHEC EDL933 (O157:H7) ( 88 ). The different patterns of the large arrows indicate the nucleotide divergence between the EPEC and EHEC genes. Small arrows indicate operons within the LEE; the four polycistronic operons demonstrated for the LEE are designated LEE1 through LEE4. The 933L prophage on the right side of the LEE is present in EHEC O157:H7 but not in EPEC OI27:H6.
EspC pathogenicity islet from EPEC E2348/69.
EspC pathogenicity islet from EPEC E2348/69.
Map of the pO157 plasmid based on the complete sequence determination by Makino et al. ( 68 ) and Burland et al. ( 14 ). Solid boxes indicate locations of major IS elements.
Map of the pO157 plasmid based on the complete sequence determination by Makino et al. ( 68 ) and Burland et al. ( 14 ). Solid boxes indicate locations of major IS elements.
Proposed model for the clonal evolution of EPEC and EHEC strains showing the hypothesized insertion of the LEE PAI, the EAF and pO157 plasmids, the Stx phage, the espC islet, and the rfb genes encoding the O157 lipopolysaccharide.
Proposed model for the clonal evolution of EPEC and EHEC strains showing the hypothesized insertion of the LEE PAI, the EAF and pO157 plasmids, the Stx phage, the espC islet, and the rfb genes encoding the O157 lipopolysaccharide.
Map of the PAA2 plasmid from EAEC 042. AAF/II-related proteins are represented by solid black arrows. Secreted proteins are designated by hatching.
Map of the PAA2 plasmid from EAEC 042. AAF/II-related proteins are represented by solid black arrows. Secreted proteins are designated by hatching.
Mobile genetic elements encoding virulence factors in human diarrheagenic E. coli
Mobile genetic elements encoding virulence factors in human diarrheagenic E. coli
Major gene products of the EPEC LEE a
Major gene products of the EPEC LEE a
Putative virulence genes in EAEC
Putative virulence genes in EAEC