While the differential association ofEscherichia coliO157 genotypes with animal and human hosts has recently been well documented, little is known about their distribution between countries and how this might affect regional disease rates. Here, we used a 48-plex single nucleotide polymorphism (SNP) assay to segregate 148E. coliO157 isolates from Australia, Argentina, and the United States into 11 SNP lineages. We also investigated the relationship between SNP lineages, Shiga toxin (Stx) gene profiles, and total Stx production.E. coliO157 isolates clearly segregated into SNP lineages that were differentially associated with each country. Of the 11 SNP lineages, seven were detected among isolates from a single country, two were detected among isolates from all three countries, and another two were detected only among U.S. and Argentinean isolates. A number of Australian (30%) and Argentinean (14%) isolates were associated with novel, previously undescribed SNP lineages that were unique to each country. Isolates within SNP lineages that were strongly associated with the carriage ofstx2aproduced comparatively more Stx on average than did those lacking thestx2asubtype. Furthermore, the proportion of isolates instx2a-associated SNP lineages was significantly higher in Argentina and the United States than Australia (P< 0.05). This study provides evidence for the geographic divergence ofE. coliO157 and for a prominent role ofstx2ain total Stx production. These results also highlight the need for more comprehensive studies of the global distribution ofE. coliO157 lineages and the impacts of regionally predominantE. coliO157 lineages on the prevalence and severity of disease.
Genome Sequences of Eight Shiga Toxin-Producing Escherichia coli Strains Isolated from a Produce-Growing Region in California