The prevalence and genomic context of Shiga toxin 2a genes in E. coli found in cattle

PLoS One. 2020 Aug 12;15(8):e0232305. doi: 10.1371/journal.pone.0232305. eCollection 2020.

Abstract

Shiga toxin-producing Escherichia coli (STEC) that cause severe disease predominantly carry the toxin gene variant stx2a. However, the role of Shiga toxin in the ruminant reservoirs of this zoonotic pathogen is poorly understood and strains that cause severe disease in humans (HUSEC) likely constitute a small and atypical subset of the overall STEC flora. The aim of this study was to investigate the presence of stx2a in samples from cattle and to isolate and characterize stx2a-positive E. coli. In nationwide surveys in Sweden and Norway samples were collected from individual cattle or from cattle herds, respectively. Samples were tested for Shiga toxin genes by real-time PCR and amplicon sequencing and stx2a-positive isolates were whole genome sequenced. Among faecal samples from Sweden, stx1 was detected in 37%, stx2 in 53% and stx2a in 5% and in skin (ear) samples in 64%, 79% and 2% respectively. In Norway, 79% of the herds were positive for stx1, 93% for stx2 and 17% for stx2a. Based on amplicon sequencing the most common stx2 types in samples from Swedish cattle were stx2a and stx2d. Multilocus sequence typing (MLST) of 39 stx2a-positive isolates collected from both countries revealed substantial diversity with 19 different sequence types. Only a few classical LEE-positive strains similar to HUSEC were found among the stx2a-positive isolates, notably a single O121:H19 and an O26:H11. Lineages known to include LEE-negative HUSEC were also recovered including, such as O113:H21 (sequence type ST-223), O130:H11 (ST-297), and O101:H33 (ST-330). We conclude that E. coli encoding stx2a in cattle are ranging from strains similar to HUSEC to unknown STEC variants. Comparison of isolates from human HUS cases to related STEC from the ruminant reservoirs can help identify combinations of virulence attributes necessary to cause HUS, as well as provide a better understanding of the routes of infection for rare and emerging pathogenic STEC.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Cattle / microbiology*
  • Disease Reservoirs / microbiology
  • Escherichia coli Infections / epidemiology
  • Escherichia coli Infections / microbiology
  • Genetic Variation
  • Genome, Bacterial
  • Hemolytic-Uremic Syndrome / epidemiology
  • Hemolytic-Uremic Syndrome / microbiology
  • Humans
  • Multilocus Sequence Typing
  • Norway / epidemiology
  • Prevalence
  • Real-Time Polymerase Chain Reaction
  • Shiga Toxin 2 / genetics*
  • Shiga-Toxigenic Escherichia coli / cytology
  • Shiga-Toxigenic Escherichia coli / genetics*
  • Shiga-Toxigenic Escherichia coli / isolation & purification
  • Sweden / epidemiology
  • Virulence / genetics
  • Zoonoses / epidemiology
  • Zoonoses / microbiology

Substances

  • Shiga Toxin 2

Grant support

The work performed in Sweden was funded by the Swedish Board of Agriculture and the Swedish Civil Contingencies Agency. The work performed in Norway was funded by The Research Council of Norway (Project no 221663; Pathogens in the food chain) and the Norwegian Veterinary Institute. The Norwegian samples were collected in a survey funded by the Norwegian Food Safety Authority. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.