title: Colistin resistance in Salmonella and Escherichia coli isolates from a pig farm in Great Britain.
abstract: The objective of this study was to characterize colistin-resistant bacteria isolated from pigs on a farm in Great Britain following identification of a plasmid-borne colistin resistance mechanism in Escherichia coli from China.
  
  
  
  Phenotypic antimicrobial susceptibility testing was undertaken by broth dilution and WGS was performed to detect the presence of genes encoding resistance and virulence. Transferable colistin resistance was investigated by conjugation.
  
  
  
  Two E. coli and one Salmonella Typhimurium variant Copenhagen were shown to be MDR, including resistance to colistin, with one E. coli and the Salmonella carrying the mcr-1 gene; all three harboured chromosomal mutations in genes conferring colistin resistance and both E. coli harboured β-lactamase resistance. The Salmonella mcr-1 plasmid was highly similar to pHNSHP45, from China, while the E. coli mcr-1 plasmid only had the ISApII and mcr-1 genes in common. The frequency of mcr-1 plasmid transfer by conjugation to recipient Enterobacteriaceae from Salmonella was low, lying between 10(-7) and 10(-9) cfu/recipient cfu. We were unable to demonstrate mcr-1 plasmid transfer from the E. coli. Plasmid profiling indicated transfer of multiple plasmids from the Salmonella resulting in some MDR transconjugants.
  
  
  
  Identification of the mcr-1 gene in Enterobacteriaceae from pigs confirms its presence in livestock in Great Britain. The results suggest dissemination of resistance through different horizontally transferable elements. The in vitro transfer of multiple plasmids carrying colistin and other resistances from the Salmonella isolate underlines the potential for wider dissemination and recombination.
authors.affiliation: Animal and Plant Health Agency, Weybridge, New Haw, Addlestone, Surrey KT15 3NB, UK muna.anjum@apha.gsi.gov.uk.
authors.forename: Muna F
authors.initials: MF
authors.lastname: Anjum
authors.affiliation: Animal and Plant Health Agency, Weybridge, New Haw, Addlestone, Surrey KT15 3NB, UK.
authors.forename: Nicholas A
authors.initials: NA
authors.lastname: Duggett
authors.affiliation: Animal and Plant Health Agency, Weybridge, New Haw, Addlestone, Surrey KT15 3NB, UK.
authors.forename: Manal
authors.initials: M
authors.lastname: AbuOun
authors.affiliation: Animal and Plant Health Agency, Weybridge, New Haw, Addlestone, Surrey KT15 3NB, UK.
authors.forename: Luke
authors.initials: L
authors.lastname: Randall
authors.affiliation: Animal and Plant Health Agency, Weybridge, New Haw, Addlestone, Surrey KT15 3NB, UK.
authors.forename: Javier
authors.initials: J
authors.lastname: Nunez-Garcia
authors.affiliation: Animal and Plant Health Agency, Weybridge, New Haw, Addlestone, Surrey KT15 3NB, UK.
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Ellis
authors.affiliation: Animal and Plant Health Agency, Weybridge, New Haw, Addlestone, Surrey KT15 3NB, UK.
authors.forename: Jon
authors.initials: J
authors.lastname: Rogers
authors.affiliation: Animal and Plant Health Agency, Weybridge, New Haw, Addlestone, Surrey KT15 3NB, UK.
authors.forename: Robert
authors.initials: R
authors.lastname: Horton
authors.affiliation: Animal and Plant Health Agency, Weybridge, New Haw, Addlestone, Surrey KT15 3NB, UK.
authors.forename: Camilla
authors.initials: C
authors.lastname: Brena
authors.affiliation: Animal and Plant Health Agency, Weybridge, New Haw, Addlestone, Surrey KT15 3NB, UK.
authors.forename: Susanna
authors.initials: S
authors.lastname: Williamson
authors.affiliation: Animal and Plant Health Agency, Weybridge, New Haw, Addlestone, Surrey KT15 3NB, UK.
authors.forename: Francesca
authors.initials: F
authors.lastname: Martelli
authors.affiliation: Animal and Plant Health Agency, Weybridge, New Haw, Addlestone, Surrey KT15 3NB, UK.
authors.forename: Robert
authors.initials: R
authors.lastname: Davies
authors.affiliation: Animal and Plant Health Agency, Weybridge, New Haw, Addlestone, Surrey KT15 3NB, UK.
authors.forename: Christopher
authors.initials: C
authors.lastname: Teale
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D003091:Colistin / Q000494:pharmacology*; D003227:Conjugation, Genetic; D024881:Drug Resistance, Bacterial; D004926:Escherichia coli / Q000187:drug effects* / Q000302:isolation & purification; D000072480:Farms; D022761:Gene Transfer, Horizontal; D005798:Genes, Bacterial; D016680:Genome, Bacterial; D008826:Microbial Sensitivity Tests; D010957:Plasmids / Q000032:analysis; D012475:Salmonella / Q000187:drug effects* / Q000302:isolation & purification; D017422:Sequence Analysis, DNA; D013552:Swine / Q000382:microbiology*; D006113:United Kingdom
chemical_list: D000900:Anti-Bacterial Agents; D003091:Colistin