ARS | Publication request: Identification and evolution of Shiga Toxin-producing Escherichia coli O157 genetic subtypes

Submitted to: International Dairy Federation, World Dairy Summit
Publication Type: Abstract Only
Publication Acceptance Date: August 16, 2012
Publication Date: N/A

Technical Abstract: INTRODUCTION Cattle are a major reservoir for Shiga toxin-producing Escherichia coli O157 (STEC O157) and harbour multiple genetic subtypes that do not all associate with human disease. A lack of genome sequence has hindered investigations on the evolution of human- and/or cattle-associated subtypes. The goals of this study were to identify nucleotide polymorphisms for STEC O157 genetic subtype detection, and to determine the order of STEC O157 genetic subtype evolution. BODY Materials & methods High-throughput 454 whole-genome sequencing was conducted on pooled STEC O157 strain DNAs from human clinical cases (n=87) and cattle (n=102). Putatively identified nucleotide polymorphisms were validated by independent genotyping assays in 426 STEC O157 strains. Resulting nucleotide polymorphism genotypes were subjected to phylogenetic analyses. Results &discussion A total of 762 nucleotide polymorphisms were validated in this study and used to identify 175 unique STEC O157 genetic subtypes. Eight major lineages of STEC O157 were identified, of which cattle are a reservoir for seven. Two lineages regularly harboured by cattle accounted for the majority of human disease in this study, whereas another was rarely represented in humans and may have evolved towards reduced human virulence. The base of the STEC O157 phylogenetic tree was represented by strains of human origin, not cattle. This result calls into question how cattle may have originally acquired STEC O157. CONCLUSIONS The nucleotide polymorphism-derived genotypes identified in this study are highly effective for identifying STEC O157 genetic subtypes and assessing their evolutionary relatedness.