title: Extensive genomic diversity and selective conservation of virulence-determinants in enterohemorrhagic Escherichia coli strains of O157 and non-O157 serotypes.
abstract: BACKGROUND
  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 (stx genes) and the locus of enterocyte effacement (LEE). Non-O157 EHECs belonging to distinct clonal lineages from O157 also cause similar illness in humans. According to the 'parallel' evolution model, they have independently acquired the major virulence determinants, the stx genes and LEE. However, the genomic differences between O157 and non-O157 EHECs have not yet been systematically analyzed.
  
  
  RESULTS
  Using microarray and whole genome PCR scanning analyses, we performed a whole genome comparison of 20 EHEC strains of O26, O111, and O103 serotypes with O157. In non-O157 EHEC strains, although genome sizes were similar with or rather larger than O157 and the backbone regions were well conserved, O157-specific regions were very poorly conserved. Around only 20% of the O157-specific genes were fully conserved in each non-O157 serotype. However, the non-O157 EHECs contained a significant number of virulence genes that are found on prophages and plasmids in O157, and also multiple prophages similar to, but significantly divergent from, those in O157.
  
  
  CONCLUSIONS
  Although 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. Independent infections of similar but distinct bacteriophages carrying these virulence determinants are deeply involved in the evolution of O157 and non-O157 EHECs.
authors: Division of Bioenvironmental Science, Frontier Science Research Center, University of Miyazaki, 5200 Kihara, Kiyotake, Miyazaki, Japan. y-ogura@med.miyazaki-u.ac.jp <y-ogura@med.miyazaki-u.ac.jp>
authors: Yoshitoshi
authors: Y
authors: Ogura
authors: Tadasuke
authors: T
authors: Ooka
authors: Asadulghani
authors: Jun
authors: J
authors: Terajima
authors: Jean-Philippe
authors: JP
authors: Nougayrède
authors: Ken
authors: K
authors: Kurokawa
authors: Kousuke
authors: K
authors: Tashiro
authors: Toru
authors: T
authors: Tobe
authors: Keisuke
authors: K
authors: Nakayama
authors: Satoru
authors: S
authors: Kuhara
authors: Eric
authors: E
authors: Oswald
authors: Haruo
authors: H
authors: Watanabe
authors: Tetsuya
authors: T
authors: Hayashi
mesh_terms: D001483:Base Sequence; D019453:Escherichia coli O157 / Q000235:genetics* / Q000472:pathogenicity; D019143:Evolution, Molecular; D014644:Genetic Variation; D016680:Genome, Bacterial / Q000235:genetics*; D023281:Genomics; D008969:Molecular Sequence Data; D020411:Oligonucleotide Array Sequence Analysis; D010957:Plasmids / Q000235:genetics; D039002:Prophages / Q000235:genetics; D037521:Virulence Factors / Q000235:genetics*
chemical_list: D037521:Virulence Factors
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