Genomic diversity of pathogenic Escherichia coli of the EHEC 2 clonal complexReportar como inadecuado

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BMC Genomics

, 10:296

First Online: 03 July 2009Received: 18 December 2008Accepted: 03 July 2009


BackgroundEvolutionary analyses of enterohemorrhagic Escherichia coli EHEC have identified two distantly related clonal groups: EHEC 1, including serotype O157:H7 and its inferred ancestor O55:H7; and EHEC 2, comprised of several serogroups O26, O111, O118, etc

These two clonal groups differ in their virulence and global distribution. Although several fully annotated genomic sequences exist for strains of serotype O157:H7, much less is known about the genomic composition of EHEC 2. In this study, we analyzed a set of 24 clinical EHEC 2 strains representing serotypes O26:H11, O111:H8-H11, O118:H16, O153:H11 and O15:H11 from humans and animals by comparative genomic hybridization CGH on an oligoarray based on the O157:H7 Sakai genome.

ResultsBackbone genes, defined as genes shared by Sakai and K-12, were highly conserved in EHEC 2. The proportion of Sakai phage genes in EHEC 2 was substantially greater than that of Sakai-specific bacterial non-phage genes. This proportion was inverted in O55:H7, reiterating that a subset of Sakai bacterial genes is specific to EHEC 1. Split decomposition analysis of gene content revealed that O111:H8 was more genetically uniform and distinct from other EHEC 2 strains, with respect to the Sakai O157:H7 gene distribution. Serotype O26:H11 was the most heterogeneous EHEC 2 subpopulation, comprised of strains with the highest as well as the lowest levels of Sakai gene content conservation. Of the 979 parsimoniously informative genes, 15% were found to be compatible and their distribution in EHEC 2 clustered O111:H8 and O118:H16 strains by serotype. CGH data suggested divergence of the LEE island from the LEE1 to the LEE4 operon, and also between animal and human isolates irrespective of serotype. No correlation was found between gene contents and geographic locations of EHEC 2 strains.

ConclusionThe gene content variation of phage-related genes in EHEC 2 strains supports the hypothesis that extensive modular shuffling of mobile DNA elements has occurred among EHEC strains. These results suggest that EHEC 2 is a multiform pathogenic clonal complex, characterized by substantial intra-serotype genetic variation. The heterogeneous distribution of mobile elements has impacted the diversification of O26:H11 more than other EHEC 2 serotypes.

Electronic supplementary materialThe online version of this article doi:10.1186-1471-2164-10-296 contains supplementary material, which is available to authorized users.

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Autor: Galeb S Abu-Ali - David W Lacher - Lukas M Wick - Weihong Qi - Thomas S Whittam


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