title: Comparison of antimicrobial resistance phenotypes and genotypes in enterotoxigenic Escherichia coli isolated from Australian and Vietnamese pigs.
abstract: This study aimed to compare the antibiogram phenotype and carriage of antimicrobial resistance genes (ARGs) of 97 porcine multidrug-resistant (MDR) enterotoxigenic Escherichia coli (ETEC) isolates obtained from Vietnam and 117 porcine MDR-ETEC obtained from Australia, two countries with different antimicrobial regulation systems. An antimicrobial resistance index (ARI) was calculated to quantify their potential significance to public health. Both Vietnamese and Australian isolates had moderate to high levels of resistance to commonly used antibiotics (ampicillin, tetracycline and sulphonamides). None of the Australian isolates were resistant to fluoroquinolones or third-generation cephalosporins and none possessed associated plasmid-mediated ARGs. However, 23.1% of Australian isolates were resistant to gentamicin owing to ARGs associated with apramycin or neomycin resistance [e.g. aac(3)-IV] that impart cross-resistance to gentamicin. Whilst Vietnamese isolates carried aminoglycoside ARGs, 44.4% of commercial pig isolates were resistant to gentamicin in comparison with 0% of village pig isolates. The plasmid-mediated fluoroquinolone ARG qnrB was commonly detected in Vietnamese isolates (52.3% commercial, 44.1% village), but phenotypic resistance was low (3.2% and 11.8%, respectively). The mean ARI for Vietnamese isolates (26.0) was significantly different (P<0.001) from the mean ARI for Australian isolates (19.8), primarily reflecting fluoroquinolone resistance in the former collection. This comparison suggests the effectiveness of regulations that slow the dissemination of 'critical' resistance by restricting the availability of important classes of antimicrobials.
authors.affiliation: The University of Queensland, School of Veterinary Science, Gatton, QLD 4343, Australia.
authors.forename: M
authors.initials: M
authors.lastname: Smith
authors.affiliation: National Institute of Veterinary Research (NIVR), 86 Truong Chinh, Hanoi, Vietnam.
authors.forename: T N
authors.initials: TN
authors.lastname: Do
authors.affiliation: The University of Queensland, School of Veterinary Science, Gatton, QLD 4343, Australia. Electronic address: gibson.j@uq.edu.au.
authors.forename: J S
authors.initials: JS
authors.lastname: Gibson
authors.affiliation: New South Wales Department of Primary Industries, Wollongbar, NSW 2477, Australia.
authors.forename: D
authors.initials: D
authors.lastname: Jordan
authors.affiliation: The University of Queensland, School of Veterinary Science, Gatton, QLD 4343, Australia.
authors.forename: R N
authors.initials: RN
authors.lastname: Cobbold
authors.affiliation: School of Animal and Veterinary Sciences, The University of Adelaide, Mudla Wirra Road, Roseworthy, SA 5371, Australia.
authors.forename: D J
authors.initials: DJ
authors.lastname: Trott
keywords: Aminoglycoside; Antimicrobial resistance; Enteric colibacillosis; Enterotoxigenic Escherichia coli; Fluoroquinolone; Third-generation cephalosporin