Abstract
In July 2014, an outbreak of Shiga toxin–producing Escherichia coli (STEC) O55:H7 in England involved 31 patients, 13 (42%) of whom had hemolytic uremic syndrome. Isolates were sequenced, and the sequences were compared with publicly available sequences of E. coli O55:H7 and O157:H7. A core-genome phylogeny of the evolutionary history of the STEC O55:H7 outbreak strain revealed that the most parsimonious model was a progenitor enteropathogenic O55:H7 sorbitol-fermenting strain, lysogenized by a Shiga toxin (Stx) 2a–encoding phage, followed by loss of the ability to ferment sorbitol because of a non-sense mutation in srlA. The parallel, convergent evolutionary histories of STEC O157:H7 and STEC O55:H7 may indicate a common driver in the evolutionary process. Because emergence of STEC O157:H7 as a clinically significant pathogen was associated with acquisition of the Stx2a-encoding phage, the emergence of STEC O55:H7 harboring the stx2a gene is of public health concern.
Highlights
In July 2014, an outbreak of Shiga toxin–producing Escherichia coli (STEC) O55:H7 in England involved 31 patients, 13 (42%) of whom had hemolytic uremic syndrome
Previous studies postulated that the common STEC O157:H7 clone evolved from enteropathogenic E. coli (EPEC) serotype O55:H7 [2,3]
In the United Kingdom, STEC is regarded as a substantial threat to public health, and enhanced surveillance systems are in place [32]
Summary
In July 2014, an outbreak of Shiga toxin–producing Escherichia coli (STEC) O55:H7 in England involved 31 patients, 13 (42%) of whom had hemolytic uremic syndrome. The first outbreak of Shiga toxin–producing Escherichia coli (STEC) O55:H7 in the United Kingdom occurred in the county of Dorset, England, in July 2014 [1]. The genes encoding the toxins, stx and stx, are harbored on lambdoid prophage and are the targets of commercial and in-house diagnostic PCR assays [9]. The inability to ferment sorbitol or to produce β-glucuronidase differentiates STEC O157 from ≈90% of other gastrointestinal bacteria [5,12] These characteristics, along with resistance to tellurite, facilitate the detection and identification of STEC O157:H7 on selective media. Initial PCRs detected the presence of stx and the intimin gene
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