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Appl. Environ. Microbiol. doi:10.1128/AEM.02821-07
Copyright (c) 2008, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Genotypic characterization and prevalence of virulence factors among Canadian Escherichia coli O157:H7 strains

Laboratory for Foodborne Zoonoses, Public Health Agency of Canada, Guelph, ON, Canada, N1G 3W4; Laboratory for Foodborne Zoonoses, Public Health Agency of Canada, Lethbridge, AB, Canada, T1J 3Z4; Department of Food Science and Technology, University of Nebraska, Lincoln, NE, USA, 68583-0919; Department of Population Medicine, University of Guelph, Guelph, ON, Canada N1G 2W1; Ontario Ministry of Health and Long–Term Care, Hamilton Public Health Laboratory, Hamilton, ON, L8N 3R5

^* To whom correspondence should be addressed. Email: gannonv{at}inspection.gc.ca.

	Abstract

In this study, the association between genotypic and selected phenotypic characteristics was examined in a collection of Canadian Escherichia coli O157:H7 strains isolated from humans and cattle in the provinces of Alberta, Ontario, Saskatchewan and Quebec. In a subset of 69 strains selected on the basis of specific phage types (PTs), a strong correlation between the lineage specific polymorphism assay (LSPA6) genotype and PT was observed with all strains of PTs 4, 14, 21, 31, 33, and 87 belonging to the LSPA6 lineage I (LSPA6-LI) genotype while those of PTs 23, 45, 67, and 74 belonged to LSPA6 lineage II (LSPA6-LII) genotypes. This correlation was maintained when additional strains of each PT were tested. E. coli O157:H7 strains having the LSPA6-LI genotype were much more common in the collection than were the LSPA6-LII or the lineage I/II (LSPA6-LI/II)-related genotypes (82.6%, 11.2% and 5.8%, respectively). Of the strains tested, proportionately more LSPA6-LI than LSPA6-LII genotype strains were isolated from humans (52.7% versus 19.7%) than from cattle (47.8% versus 80.2%). In addition, 96.7% of the LSPA6-LII strains carried the stx_2c variant gene while only 50.0% of LSPA6-LI/II and 2.7% of LSPA6-LI strains carried this gene. LSPA6-LII strains were also significantly more likely to possess colD157 genes (50.8% versus 23.2%) and have combined resistance to streptomycin, sulfisoxazole and tetracycline (72.1% versus 0.9%) than were LSPA6-LI strains. The LSPA6 genotype- and PT-related characteristics identified may be important markers of specific ecotypes of E. coli O157:H7 that have unique epidemiological and virulence characteristics.

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