Submitted to: International Journal of Medical Microbiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/24/2010
Publication Date: 1/1/2011
Publication URL: http://handle.nal.usda.gov/10113/56083
Citation: Fratamico, P.M., Yan, X., Caprioli, A., Esposito, G., Needleman, D.S., Pepe, T., Tozzoli, R., Cortesi, M.L., Morabito, S. 2011. The complete DNA sequence and analysis of the virulence plasmid and of five additional plasmids carried by Shiga toxin-producing Escherichia coli O26:H11 strain H30. Journal of Medical Microbiology. 301:192-203. Interpretive Summary: Escherichia coli strains that produce Shiga toxins and belong to serogroup O26 are important human pathogens that cause hemorrhagic colitis and hemolytic uremic syndrome. These bacteria cause a similar type of food-borne illness as Shiga toxin-producing E. coli (STEC) O157:H7; however, it is not known if STEC O26 and E. coli O157:H7 possess the same set of genes (virulence genes) that are important for causing illness. STEC O157:H7 possesses a large plasmid (circular DNA that is not part of the chromosome) that carries important virulence genes; however it is not known if E. coli O26 strains that cause human illness also possess a large virulence plasmid. Therefore, the DNA sequence of the large virulence plasmid of a STEC O26 strain (O26:H11) was determined and analyzed. The E. coli O26 strain had the same set of virulence genes as the large plasmid of E. coli O157:H7, and in addition, it carried genes for tetracycline resistance and genes that help this pathogenic strain to persist in the environment. Moreover, the O26:H11 strain contained 5 smaller plasmids, in addition to the virulence plasmid. This study underscores the diversity among the STEC virulence plasmids and provides insights into the evolution of these plasmids in STEC strains causing serious human illness.
Technical Abstract: Shiga toxin-producing Escherichia coli (STEC) strains belonging to serogroup O26 have been associated with sporadic cases and outbreaks of hemorrhagic colitis and hemolytic uremic syndrome. STEC strains usually harbor a large plasmid carrying genes associated with virulence. The objective of this study was to determine the DNA sequence of the large plasmid of STEC O26:H11 strain H30 and to compare it with that of the virulence plasmid from E. coli O157:H7, pO157. In addition to the large virulence plasmid (pO26-Vir), 168 kb in size, strain H30 carries five additional plasmids. Four are small cryptic plasmids, pO26-S1 (1.5 kb), pO26-S2 (3.1 kb), pO26-S3 (4.2 kb), and pO26-S4 (5.8 kb) that carry very little genetic information but inexplicably reside in O26:H11 strain H30 while the second largest plasmid, pO26-L, (73 kb) carries the tetracycline resistance gene and has regions that show homology to the Escherichia coli conjugative resistance plasmid NR1. pO26-Vir possesses a mosaic structure, showing homology to plasmid pSERB1 found in clinical strain C1096 and shares several highly conserved syntenic regions with pO157, as well. pO26-Vir carries important virulence genes, including toxB, katP, espP, and the hly gene cluster. In addition, preliminary molecular features analyses of the virulence plasmid reveal the presence of the type IV pilus gene cluster conferring to E. coli O26:H11 H30 the potential to form biofilms. This study underscores the diversity among the STEC virulence plasmids and provides insights into the evolution of these plasmids in STEC strains causing serious human illness.