title: Salmonella enterica isolated from infections in Australian livestock remain susceptible to critical antimicrobials.
abstract: Salmonella enterica is a zoonotic pathogen causing a variety of diseases in humans and animals. Many countries are reporting an increase in the prevalence of multidrug-resistant (MDR) S. enterica in food animals. The aim of this study was to determine whether S. enterica isolated from livestock in New South Wales, Australia, have similar resistance traits to those reported internationally. Salmonella enterica (n=165) from clinical infections in food animals between 2007 and 2011 were serotyped and tested for susceptibility to 18 antimicrobials. Also, 22 antimicrobial resistance genes (ARGs), 3 integrons and 18 plasmid replicon types were screened for using PCR. Most isolates (66.1%) remained susceptible to all antimicrobials; 8.5% of the isolates were resistant to four or more antimicrobials. Antimicrobials with the highest prevalence of resistance were sulfafurazole (28.5%), ampicillin (17.0%), tetracycline (15.8%) and trimethoprim (8.5%). There was no resistance to fluoroquinolones or third-generation cephalosporins. The most common ARGs were blaTEM (15.2%), sul2 (10.3%), tetB (9.1%), tetA (5.5%), aphA1 (4.8%) and dhfrV (4.8%). Class 1 integrons (7.9%) and IncFIIA (69.7%) were the most commonly detected integron and plasmid replicon types, respectively. Class 1 integrons were positively associated with MDR phenotypes and ARG carriage (P≤0.001). Internationally prominent MDR serovars associated with severe disease in humans (e.g. AmpC-positive Salmonella Newport) were not detected. Overall, the comparatively favourable resistance status of S. enterica in Australian livestock represents minimal public health risk associated with MDR strains and supports a conservative approach to the registration of antimicrobial drug classes in food-producing animals.
authors: School of Animal and Veterinary Sciences, The University of Adelaide, Mulda Wirra Road, Roseworthy, SA 5371, Australia; New South Wales Department of Primary Industries, Woodbridge Road, Menangle, NSW 2568, Australia.
authors: Sam
authors: S
authors: Abraham
authors: New South Wales Department of Primary Industries, Woodbridge Road, Menangle, NSW 2568, Australia; School of Agriculture and Food Sciences, The University of Queensland, Gatton Campus, QLD 4343, Australia.
authors: Mitchell D
authors: MD
authors: Groves
authors: School of Animal and Veterinary Sciences, The University of Adelaide, Mulda Wirra Road, Roseworthy, SA 5371, Australia.
authors: Darren J
authors: DJ
authors: Trott
authors: New South Wales Department of Primary Industries, Woodbridge Road, Menangle, NSW 2568, Australia.
authors: Toni A
authors: TA
authors: Chapman
authors: New South Wales Department of Primary Industries, Woodbridge Road, Menangle, NSW 2568, Australia.
authors: Bernadette
authors: B
authors: Turner
authors: New South Wales Department of Primary Industries, Woodbridge Road, Menangle, NSW 2568, Australia.
authors: Michael
authors: M
authors: Hornitzky
authors: New South Wales Department of Primary Industries, 1243 Bruxner Highway, Wollongbar, NSW 2477, Australia. Electronic address: david.jordan@dpi.nsw.gov.au.
authors: David
authors: D
authors: Jordan
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D004269:DNA, Bacterial / Q000235:genetics; D005798:Genes, Bacterial; D032023:Integrons; D058751:Livestock; D008826:Microbial Sensitivity Tests; D009517:New South Wales; D010957:Plasmids / Q000032:analysis; D016133:Polymerase Chain Reaction; D012481:Salmonella Infections, Animal / Q000382:microbiology*; D019779:Salmonella enterica / Q000145:classification / Q000187:drug effects* / Q000235:genetics / Q000302:isolation & purification*; D012703:Serotyping
chemical_list: D000900:Anti-Bacterial Agents; D004269:DNA, Bacterial
keywords: Animals; Antimicrobial resistance; Australia; Plasmid replicon; Salmonella