title: First detection of extended-spectrum cephalosporin- and fluoroquinolone-resistant Escherichia coli in Australian food-producing animals.
abstract: This study aimed to define the frequency of resistance to critically important antimicrobials (CIAs) [i.e. extended-spectrum cephalosporins (ESCs), fluoroquinolones (FQs) and carbapenems] among Escherichia coli isolates causing clinical disease in Australian food-producing animals. Clinical E. coli isolates (n=324) from Australian food-producing animals [cattle (n=169), porcine (n=114), poultry (n=32) and sheep (n=9)] were compiled from all veterinary diagnostic laboratories across Australia over a 1-year period. Isolates underwent antimicrobial susceptibility testing to 18 antimicrobials using the Clinical and Laboratory Standards Institute disc diffusion method. Isolates resistant to CIAs underwent minimum inhibitory concentration determination, multilocus sequence typing (MLST), phylogenetic analysis, plasmid replicon typing, plasmid identification, and virulence and antimicrobial resistance gene typing. The 324 E. coli isolates from different sources exhibited a variable frequency of resistance to tetracycline (29.0-88.6%), ampicillin (9.4-71.1%), trimethoprim/sulfamethoxazole (11.1-67.5%) and streptomycin (21.9-69.3%), whereas none were resistant to imipenem or amikacin. Resistance was detected, albeit at low frequency, to ESCs (bovine isolates, 1%; porcine isolates, 3%) and FQs (porcine isolates, 1%). Most ESC- and FQ-resistant isolates represented globally disseminated E. coli lineages (ST117, ST744, ST10 and ST1). Only a single porcine E. coli isolate (ST100) was identified as a classic porcine enterotoxigenic E. coli strain (non-zoonotic animal pathogen) that exhibited ESC resistance via acquisition of blaCMY-2. This study uniquely establishes the presence of resistance to CIAs among clinical E. coli isolates from Australian food-producing animals, largely attributed to globally disseminated FQ- and ESC-resistant E. coli lineages.
authors.affiliation: School of Animal and Veterinary Sciences, University of Adelaide, Adelaide, SA, Australia; School of Veterinary and Life Sciences, Murdoch University, Perth, WA, Australia. Electronic address: s.abraham@murdoch.edu.au.
authors.forename: Sam
authors.initials: S
authors.lastname: Abraham
authors.affiliation: New South Wales Department of Primary Industries, Wollongbar, NSW, Australia.
authors.forename: David
authors.initials: D
authors.lastname: Jordan
authors.affiliation: School of Animal and Veterinary Sciences, University of Adelaide, Adelaide, SA, Australia.
authors.forename: Hui S
authors.initials: HS
authors.lastname: Wong
authors.affiliation: Veterans Affairs Medical Center and University of Minnesota, Minneapolis, MN, USA.
authors.forename: James R
authors.initials: JR
authors.lastname: Johnson
authors.affiliation: Cardiff Institute of Infection & Immunity, Cardiff University, Cardiff, UK.
authors.forename: Mark A
authors.initials: MA
authors.lastname: Toleman
authors.affiliation: School of Veterinary Science, The University of Queensland, Gatton, QLD, Australia.
authors.forename: David L
authors.initials: DL
authors.lastname: Wakeham
authors.affiliation: Australian National University, Canberra, ACT, Australia.
authors.forename: David M
authors.initials: DM
authors.lastname: Gordon
authors.affiliation: Australian Commission on Safety and Quality in Health Care, Sydney, NSW, Australia.
authors.forename: John D
authors.initials: JD
authors.lastname: Turnidge
authors.affiliation: Department of Agriculture and Fisheries, Coopers Plains, QLD, Australia.
authors.forename: Joanne L
authors.initials: JL
authors.lastname: Mollinger
authors.affiliation: School of Veterinary Science, The University of Queensland, Gatton, QLD, Australia.
authors.forename: Justine S
authors.initials: JS
authors.lastname: Gibson
authors.affiliation: School of Animal and Veterinary Sciences, University of Adelaide, Adelaide, SA, Australia.
authors.forename: Darren J
authors.initials: DJ
authors.lastname: Trott
keywords: Antimicrobial resistance; Critically important antimicrobials; Escherichia coli; Extended-spectrum cephalosporins; Fluoroquinolones; Food-producing animals