B-201. Differences in the Locus of Enterocyte Effacement (LEE) Pathogenicity Island of the Closely Related Escherichia coli Serotypes O157:H7, O55:H7 and O145:NM

Y. Zhang, G. Golds, S. J. John, C. Laing, E. Taboada, V. P. J. Gannon;
Pub. Hlth. Agency of Canada, Lethbridge, AB, CANADA.

Background: The LEE pathogenicity island encodes a type III secretion system and various effectors required by EHEC and EPEC to produce attaching and effacing lesions in host enterocytes. Microarray-based comparative genomic hybridization studies have shown that strains of EHEC E. coli O157:H7 and O145:NM and EPEC O55:H7 are more closely related to each other than members of other EHEC serotypes. In this study, the LEE pathogenicity islands of strains from these E. coli serotypes were compared. Methods: Cosmid libraries of the genomes of E. coli O157:H7 lineage II strain EC970520, EPEC O55:H7 strain EDS-58 and EHEC O145:NM strain ECI-142 were constructed. Cosmid clones containing LEE from these libraries were identified using PCR primers specific for the Sakai ecsV gene. LEE sequences for each strain were assembled from the cosmid clones. Results: As expected, LEE was inserted downstream of the tRNA selC gene in E. coli O157:H7 lineage II strain EC970520, EHEC O145:NM ECI-142, and EPEC O55:H7 EDS-58. EPEC O55:H7 EDS-58 and EHEC O145:NM ECI-142 were missing three IS-related genes (ECs4545, ECs4546, ECs4547) upstream of LEE4 (CP-933L phage region in E. coli O157:H7 Sakai). This region was replaced by a phage-related DNA with homology to Shigella boydii Sb227 genes SBO_4170 through SBO_4165 and the putative transcriptional activator gene in the E. coli O157:H7 EC970520 and EHEC O145:NM ECI-142. Genes within LEE were highly conserved with 41/43 (95%) having >97.4% identity to E. coli O157:H7 Sakai and 56% (24/43) of the genes encoding identical proteins. The espF gene in LEE of EPEC O55:H7 EDS-58 showed the lowest similarity (80.7%) to E. coli O157:H7 Sakai and EC970520 and EHEC O145:NM ECI-142. However, the tir gene was the most divergent among these four E. coli strains. Conclusion: The phage-related region upstream of LEE4 was divergent among these E. coli strains. While the LEEs of EHEC O157:H7 and O145:NM and EPEC O55:H7 strains were highly homologous, significant differences in tir and espF genes were noted. These differences may influence host specificity, colonization and virulence.