Molecular Epidemiology of Escherichia coli Producing CTX-M and pAmpC β-Lactamases from Dairy Farms Identifies a Dominant Plasmid Encoding CTX-M-32 but No Evidence for Transmission to Humans in the Same Geographical Region

Jacqueline Findlay, Oliver Mounsey, Winnie W Y Lee, Nerissa Newbold, Katy Morely, Hannah Schubert, Virginia Gould, Tristan A Cogan, Kristen K Reyher, Matthew B Avison*

*Corresponding author for this work

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Abstract

Third-generation cephalosporin resistance (3GC-R) in Escherichia coli is a rising problem in human and farmed animal populations. We conducted whole genome sequencing analysis of 138 representative 3GC-R isolates previously collected from dairy farms in South West England and confirmed by PCR to carry acquired 3GC-R genes. This analysis identified blaCTX-M (131 isolates: encoding CTX-M-1, -14, -15, -32 and the novel variant, CTX-M-214), blaCMY-2 (6 isolates) and blaDHA-1 (one isolate). A highly conserved plasmid was identified in 73 isolates, representing 27 E. coli sequence types. This novel ∼220 kb IncHI2 plasmid carrying blaCTX-M-32 was sequenced to closure and designated pMOO-32. It was found experimentally to be stable in cattle and human transconjugant E. coli even in the absence of selective pressure and was found by multiplex PCR to be present on 26 study farms representing a remarkable range of transmission over 1500 square kilometres. However, the plasmid was not found amongst human urinary E. coli we have recently characterised from people living in the same geographical location, collected in parallel with farm sampling. There were close relatives of two blaCTX-M plasmids circulating amongst eight human and two cattle isolates, and a closely related blaCMY-2 plasmid found in one cattle and one human isolate. However, phylogenetic evidence of recent sharing of 3GC-R strains between farms and humans in the same region was not found.
Importance Third-generation cephalosporins (3GCs) are critically important antibacterials and 3GC-resistance (3GC-R) threatens human health, particularly in the context of opportunistic pathogens such as Escherichia coli. There is some evidence for zoonotic transmission of 3GC-R E. coli through food, but little work has been done examining possible transmission (e.g. via interaction of people with the local near-farm environment). We characterised acquired 3GC-R E. coli found on dairy farms in a geographically restricted region of the United Kingdom and compared these with E. coli from people living in the same region, collected in parallel. Whilst there is strong evidence for recent farm-to-farm transmission of 3GC-R strains and plasmids – including one epidemic plasmid that has a remarkable capacity to transmit – there was no evidence that 3GC-R found on study farms had a significant impact on circulating 3GC-R E. coli strains or plasmids in the local human population.
Original languageEnglish
Article numbere01842-20
Pages (from-to)1-9
Number of pages9
JournalApplied and Environmental Microbiology
Volume87
Issue number1
Early online date17 Dec 2020
DOIs
Publication statusPublished - 1 Jan 2021

Keywords

  • antibiotic resistance
  • phylogenetic analysis
  • plasmid analysis
  • zoonotic infections

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