Comparative genomics of two super-shedder isolates of Escherichia coli O157:H7

PLoS One. 2017 Aug 10;12(8):e0182940. doi: 10.1371/journal.pone.0182940. eCollection 2017.

Abstract

Shiga toxin-producing Escherichia coli O157:H7 (O157) are zoonotic foodborne pathogens and of major public health concern that cause considerable intestinal and extra-intestinal illnesses in humans. O157 colonize the recto-anal junction (RAJ) of asymptomatic cattle who shed the bacterium into the environment through fecal matter. A small subset of cattle, termed super-shedders (SS), excrete O157 at a rate (≥ 104 CFU/g of feces) that is several orders of magnitude greater than other colonized cattle and play a major role in the prevalence and transmission of O157. To better understand microbial factors contributing to super-shedding we have recently sequenced two SS isolates, SS17 (GenBank accession no. CP008805) and SS52 (GenBank accession no. CP010304) and shown that SS isolates display a distinctive strongly adherent phenotype on bovine rectal squamous epithelial cells. Here we present a detailed comparative genomics analysis of SS17 and SS52 with other previously characterized O157 strains (EC4115, EDL933, Sakai, TW14359). The results highlight specific polymorphisms and genomic features shared amongst SS strains, and reveal several SNPs that are shared amongst SS isolates, including in genes involved in motility, adherence, and metabolism. Finally, our analyses reveal distinctive patterns of distribution of phage-associated genes amongst the two SS and other isolates. Together, the results of our comparative genomics studies suggest that while SS17 and SS52 share genomic features with other lineage I/II isolates, they likely have distinct recent evolutionary histories. Future comparative and functional genomic studies are needed to decipher the precise molecular basis for super shedding in O157.

MeSH terms

  • Animals
  • Bacterial Shedding*
  • Cattle / microbiology*
  • Cattle Diseases / microbiology*
  • Escherichia coli Infections / microbiology
  • Escherichia coli Infections / veterinary*
  • Escherichia coli O157 / genetics*
  • Escherichia coli O157 / isolation & purification
  • Escherichia coli O157 / physiology*
  • Genome, Bacterial
  • Humans
  • Polymorphism, Single Nucleotide

Grants and funding

RK, RC, VK, CD: The authors received no specific funding for this work. ITK: USDA-ARS CRIS project 5030-32000-100-00D. TMA: USDA-ARS CRIS project 3040-42000-180-00D. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.