{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,3,8]],"date-time":"2026-03-08T11:24:07Z","timestamp":1772969047162,"version":"3.50.1"},"reference-count":48,"publisher":"American Society for Microbiology","issue":"20","license":[{"start":{"date-parts":[[2011,10,15]],"date-time":"2011-10-15T00:00:00Z","timestamp":1318636800000},"content-version":"tdm","delay-in-days":0,"URL":"https:\/\/journals.asm.org\/non-commercial-tdm-license"}],"content-domain":{"domain":["journals.asm.org"],"crossmark-restriction":true},"short-container-title":["Appl Environ Microbiol"],"published-print":{"date-parts":[[2011,10,15]]},"abstract":"<jats:title>ABSTRACT<\/jats:title>\n          <jats:p>\n            Eleven multidrug-resistant\n            <jats:named-content content-type=\"genus-species\">Escherichia coli<\/jats:named-content>\n            isolates (comprising 6 porcine and 5 bovine field isolates) displaying fluoroquinolone (FQ) resistance were selected from a collection obtained from the University Veterinary Hospital (Dublin, Ireland). MICs of nalidixic acid and ciprofloxacin were determined by Etest. All showed MICs of nalidixic acid of &gt;256 \u03bcg\/ml and MICs of ciprofloxacin ranging from 4 to &gt;32 \u03bcg\/ml. DNA sequencing was used to identify mutations within the quinolone resistance-determining regions of target genes, and quantitative real-time PCR (qRT-PCR) was used to evaluate the expression of the major porin, OmpF, and component genes of the AcrAB-TolC efflux pump and its associated regulatory loci. Decreased MIC values to nalidixic acid and\/or ciprofloxacin were observed in the presence of the efflux pump inhibitor phenylalanine-arginine-\u03b2-naphthylamide (PA\u03b2N) in some but not all isolates. Several mutations were identified in genes coding for quinolone target enzymes (3 to 5 mutations per strain). All isolates harbored GyrA amino acid substitutions at positions 83 and 87. Novel GyrA (Asp87 \u2192 Ala), ParC (Ser80 \u2192 Trp), and ParE (Glu460 \u2192 Val) substitutions were observed. The efflux activity of these isolates was evaluated using a semiautomated ethidium bromide (EB) uptake assay. Compared to wild-type\n            <jats:named-content content-type=\"genus-species\">E. coli<\/jats:named-content>\n            K-12 AG100, isolates accumulated less EB, and in the presence of PA\u03b2N the accumulation of EB increased. Upregulation of the\n            <jats:italic>acrB<\/jats:italic>\n            gene, encoding the pump component of the AcrAB-TolC efflux pump, was observed in 5 of 11 isolates, while 10 isolates showed decreased expression of OmpF. This study identified multiple mechanisms that likely contribute to resistance to quinolone-based drugs in the field isolates studied.\n          <\/jats:p>","DOI":"10.1128\/aem.00600-11","type":"journal-article","created":{"date-parts":[[2011,8,20]],"date-time":"2011-08-20T02:29:42Z","timestamp":1313807382000},"page":"7113-7120","update-policy":"https:\/\/doi.org\/10.1128\/asmj-crossmark-policy-page","source":"Crossref","is-referenced-by-count":63,"title":["Mechanisms of Fluoroquinolone Resistance in Escherichia coli Isolates from Food-Producing Animals"],"prefix":"10.1128","volume":"77","author":[{"given":"Maria","family":"Karczmarczyk","sequence":"first","affiliation":[{"name":"UCD Centre for Food Safety &amp; Centre for Food-borne Zoonomics, UCD Veterinary Sciences Centre, School of Public Health, Physiotherapy &amp; Population Science, University College Dublin, Belfield, Dublin 4, Ireland"}]},{"given":"Marta","family":"Martins","sequence":"additional","affiliation":[{"name":"UCD Centre for Food Safety &amp; Centre for Food-borne Zoonomics, UCD Veterinary Sciences Centre, School of Public Health, Physiotherapy &amp; Population Science, University College Dublin, Belfield, Dublin 4, Ireland"},{"name":"Unit of Mycobacteriology and UPMM, Instituto de Higiene e Medicina Tropical, Universidade Nova de Lisboa (IHMT\/UNL), Rua da Junqueira, 100, 1349-008 Lisbon, Portugal"}]},{"given":"Teresa","family":"Quinn","sequence":"additional","affiliation":[{"name":"UCD Centre for Food Safety &amp; Centre for Food-borne Zoonomics, UCD Veterinary Sciences Centre, School of Public Health, Physiotherapy &amp; Population Science, University College Dublin, Belfield, Dublin 4, Ireland"}]},{"given":"Nola","family":"Leonard","sequence":"additional","affiliation":[{"name":"UCD Veterinary Sciences Centre, University College Dublin, Belfield, Dublin 4, Ireland"}]},{"given":"S\u00e9amus","family":"Fanning","sequence":"additional","affiliation":[{"name":"UCD Centre for Food Safety &amp; Centre for Food-borne Zoonomics, UCD Veterinary Sciences Centre, School of Public Health, Physiotherapy &amp; Population Science, University College Dublin, Belfield, Dublin 4, Ireland"}]}],"member":"235","reference":[{"key":"e_1_3_2_2_2","doi-asserted-by":"publisher","DOI":"10.1099\/jmm.0.45908-0"},{"key":"e_1_3_2_3_2","doi-asserted-by":"publisher","DOI":"10.1128\/AAC.41.10.2067"},{"key":"e_1_3_2_4_2","doi-asserted-by":"publisher","DOI":"10.1038\/90429"},{"key":"e_1_3_2_5_2","doi-asserted-by":"publisher","DOI":"10.1002\/9780470920541.ch2"},{"key":"e_1_3_2_6_2","doi-asserted-by":"publisher","DOI":"10.1128\/AAC.45.7.1994-2000.2001"},{"key":"e_1_3_2_7_2","doi-asserted-by":"publisher","DOI":"10.1074\/jbc.M405512200"},{"key":"e_1_3_2_8_2","doi-asserted-by":"publisher","DOI":"10.1128\/jb.175.4.1026-1031.1993"},{"key":"e_1_3_2_9_2","unstructured":"Clinical Laboratory Standards Institute. 2008. 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