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Journal of Bacteriology, September 2008, p. 5832-5840, Vol. 190, No. 17
0021-9193/08/$08.00+0     doi:10.1128/JB.00480-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Genomic O Island 122, Locus for Enterocyte Effacement, and the Evolution of Virulent Verocytotoxin-Producing Escherichia coli{triangledown} ,{dagger}

Paulina Konczy,1 Kim Ziebell,1 Mariola Mascarenhas,1 Aileen Choi,1 Corinne Michaud,1 Andrew M. Kropinski,1 Thomas S. Whittam,2 Mark Wickham,3 Brett Finlay,3 and Mohamed A. Karmali1*

Laboratory for Foodborne Zoonoses, Public Health Agency of Canada, Guelph, Ontario N1G 3W4, Canada,1 Microbial Evolution Laboratory, National Food Safety and Toxicology Center, Michigan State University, East Lansing, Michigan 48824,2 The University of British Columbia, Michael Smith Laboratories, 301-2185 East Mall, Vancouver, British Columbia V6T 1Z4, Canada3

Received 8 April 2008/ Accepted 17 June 2008

The locus of enterocyte effacement (LEE) and genomic O island 122 (OI-122) are pathogenicity islands in verocytotoxin-producing Escherichia coli (VTEC) serotypes that are associated with outbreaks and serious disease. Composed of three modules, OI-122 may occur as "complete" (with all three modules) or "incomplete" (with one or two modules) in different strains. OI-122 encodes two non-LEE effector (Nle) molecules that are secreted by the LEE type III secretion system, and LEE and OI-122 are cointegrated in some VTEC strains. Thus, they are functionally linked, but little is known about the patterns of acquisition of these codependent islands. To examine this, we conducted a population genetics analysis, using multilocus sequence typing (MLST), with 72 VTEC strains (classified into seropathotypes A to E) and superimposed on the results the LEE and OI-122 contents of these organisms. The wide distribution of LEE and OI-122 modules among MLST clonal groups corroborates the hypothesis that there has been lateral transfer of both pathogenicity islands. Sequence analysis of a pagC-like gene in OI-122 module 1 also revealed two nonsynonymous single-nucleotide polymorphisms that could help discriminate a subset of seropathotype C strains and determine the presence of the LEE. A nonsense mutation was found in this gene in five less virulent strains, consistent with a decaying or inactive gene. The modular nature of OI-122 could be explained by the acquisition of modules by lateral transfer, either singly or as a group, and by degeneration of genes within modules. Correlations between clonal group, seropathotype, and LEE and OI-122 content provide insight into the role of genomic islands in VTEC evolution.

* Corresponding author. Mailing address: Laboratory for Foodborne Zoonoses, Public Health Agency of Canada, 110 Stone Rd. West, Guelph, Ontario, Canada N1G 3W4. Phone: (519) 822-3300. Fax: (519) 822-2280. E-mail: Mohamed_Karmali{at}phac-aspc.gc.ca

{triangledown} Published ahead of print on 27 June 2008.

{dagger} Supplemental material for this article may be found at http://jb.asm.org/.

Journal of Bacteriology, September 2008, p. 5832-5840, Vol. 190, No. 17
0021-9193/08/$08.00+0     doi:10.1128/JB.00480-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.



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