{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,9]],"date-time":"2026-10-09T21:47:05Z","timestamp":1791582425833,"version":"4.3.4"},"reference-count":45,"publisher":"Public Library of Science (PLoS)","issue":"7","license":[{"start":{"date-parts":[[2023,7,7]],"date-time":"2023-07-07T00:00:00Z","timestamp":1688688000000},"content-version":"vor","delay-in-days":0,"URL":"http:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100000933","name":"Department of Agriculture, Fisheries and Forestry, Australian Government","doi-asserted-by":"publisher","award":["IRMA 19178"],"award-info":[{"award-number":["IRMA 19178"]}],"id":[{"id":"10.13039\/501100000933","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/501100009313","name":"Australian Eggs","doi-asserted-by":"crossref","award":["IRMA 19178"],"award-info":[{"award-number":["IRMA 19178"]}],"id":[{"id":"10.13039\/501100009313","id-type":"DOI","asserted-by":"crossref"}]}],"content-domain":{"domain":["www.plosone.org"],"crossmark-restriction":false},"short-container-title":["PLoS ONE"],"abstract":"<jats:p>Controlling the use of the most critically important antimicrobials (CIAs) in food animals has been identified as one of the key measures required to curb the transmission of antimicrobial resistant bacteria from animals to humans. Expanding the evidence demonstrating the effectiveness of restricting CIA usage for preventing the emergence of resistance to key drugs amongst commensal organisms in animal production would do much to strengthen international efforts to control antimicrobial resistance (AMR). As Australia has strict controls on antimicrobial use in layer hens, and internationally comparatively low levels of poultry disease due to strict national biosecurity measures, we investigated whether these circumstances have resulted in curtailing development of critical forms of AMR. The work comprised a cross-sectional national survey of 62 commercial layer farms with each assessed for AMR in <jats:italic>Escherichia coli<\/jats:italic> isolates recovered from faeces. Minimum inhibitory concentration analysis using a panel of 13 antimicrobials was performed on 296 isolates, with those exhibiting phenotypic resistance to fluoroquinolones (a CIA) or multi-class drug resistance (MCR) subjected to whole genome sequencing. Overall, 53.0% of isolates were susceptible to all antimicrobials tested, and all isolates were susceptible to cefoxitin, ceftiofur, ceftriaxone, chloramphenicol and colistin. Resistance was observed for amoxicillin-clavulanate (9.1%), ampicillin (16.2%), ciprofloxacin (2.7%), florfenicol (2.4%), gentamicin (1.0%), streptomycin (4.7%), tetracycline (37.8%) and trimethoprim\/sulfamethoxazole (9.5%). MCR was observed in 21 isolates (7.0%), with two isolates exhibiting resistance to four antimicrobial classes. Whole genome sequencing revealed that ciprofloxacin-resistant (fluoroquinolone) isolates were devoid of both known chromosomal mutations in the quinolone resistance determinant regions and plasmid-mediated quinolone resistance genes (<jats:italic>qnr<\/jats:italic>)\u2014other than in one isolate (ST155) which carried the <jats:italic>qnrS<\/jats:italic> gene. Two MCR <jats:italic>E<\/jats:italic>. <jats:italic>coli<\/jats:italic> isolates with ciprofloxacin-resistance were found to be carrying known resistance genes including <jats:italic>aadA1<\/jats:italic>, <jats:italic>dfrA1<\/jats:italic>, <jats:italic>strA<\/jats:italic>, <jats:italic>strB<\/jats:italic>, <jats:italic>sul1<\/jats:italic>, <jats:italic>sul2<\/jats:italic>, <jats:italic>tet(A)<\/jats:italic>, <jats:italic>bla<\/jats:italic><jats:sub>TEM-1B<\/jats:sub>, <jats:italic>qnrS1<\/jats:italic> and <jats:italic>tet(A)<\/jats:italic>. Overall, this study found that <jats:italic>E<\/jats:italic>. <jats:italic>coli<\/jats:italic> from layer hens in Australia have low rates of AMR, likely due to strict control on antimicrobial usage achieved by the sum of regulation and voluntary measures.<\/jats:p>","DOI":"10.1371\/journal.pone.0281848","type":"journal-article","created":{"date-parts":[[2023,7,7]],"date-time":"2023-07-07T17:23:43Z","timestamp":1688750623000},"page":"e0281848","update-policy":"https:\/\/doi.org\/10.1371\/journal.pone.corrections_policy","source":"Crossref","is-referenced-by-count":11,"title":["A national study confirms that Escherichia coli from Australian commercial layer hens remain susceptible to critically important antimicrobials"],"prefix":"10.1371","volume":"18","author":[{"given":"Rebecca","family":"Abraham","sequence":"first","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Hui San","family":"Allison","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Terence","family":"Lee","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-8830-1806","authenticated-orcid":true,"given":"Anthony","family":"Pavic","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Raymond","family":"Chia","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Kylie","family":"Hewson","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Zheng Zhou","family":"Lee","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-7729-0427","authenticated-orcid":true,"given":"David J.","family":"Hampson","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"David","family":"Jordan","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-0950-2317","authenticated-orcid":true,"given":"Sam","family":"Abraham","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"340","published-online":{"date-parts":[[2023,7,7]]},"reference":[{"key":"pone.0281848.ref001","volume-title":"Critically important antimicrobials for human medicine 6th revision 2018","author":"World Health Organization","year":"2019"},{"key":"pone.0281848.ref002","volume-title":"DANMAP 2020\u2014Use of antimicrobial agents and occurrence of antimicrobial resistance in bacteria from food animals, food and humans in Denmark","author":"DANMAP","year":"2020"},{"issue":"8","key":"pone.0281848.ref003","article-title":"High fecal prevalence of mcr-positive Escherichia coli in veal calves at slaughter in France","volume":"11","author":"MM Um","year":"2022","journal-title":"Antibiotics (Basel)"},{"key":"pone.0281848.ref004","unstructured":"U.S. Food & Drug Administration. 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