Abstract
Comparing the genomes of O157 and non-O157 enterohemorrhagic Escherichia coli (EHEC) strains reveals the selective conservation of a large number of virulence determinants.
Highlights
Enterohemorrhagic Escherichia coli (EHEC) O157 causes severe food-borne illness in humans
The chromosome of O157 consists of 4.1 Mb backbone sequences shared by benign E. coli K-12, and 1.4 Mb O157-specific sequences encoding many virulence determinants, such as Shiga toxin genes and the locus of enterocyte effacement (LEE)
O157 and non-O157 EHECs have independently acquired a huge amount of serotype- or strain-specific genes by lateral gene transfer, they share an unexpectedly large number of virulence genes
Summary
Escherichia coli is a commensal intestinal inhabitant of vertebrates and rarely cause diseases except in compromised hosts. Most of the large S-loops are prophages and prophage-like elements, and O157 Sakai contains 18 prophages (Sp1-Sp18) and 6 prophage-like elements (SpLE1SpLE6; these elements contain phage integrase-like genes but no other phage-related genes) These Sps and SpLEs carry most of the virulence-related genes of O157, including the stx genes (stx1AB on Sp15 and stx2AB on Sp5). Numerous EHEC outbreaks have been attributed to strains of the O157 serotype (O157 EHEC), it has increasingly been more frequently recognized that EHEC strains belonging to a wide range of other serotypes cause similar gastrointestinal diseases in humans We selected 20 non-O157 EHEC strains, 8 of which belong to O26, six to O111, and six to O103 serotypes, and performed a whole genome comparison with O157 EHEC strains by O157 oligoDNA microarray and WGPScanning. Virulencerelated genes, those for non-LEE effectors and non-fimbrial adhesions, were relatively well conserved in the non-O157 EHEC strains
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