{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,9,30]],"date-time":"2026-09-30T06:50:33Z","timestamp":1790751033362,"version":"4.1.0"},"reference-count":48,"publisher":"American Society for Microbiology","issue":"1","license":[{"start":{"date-parts":[[2024,1,11]],"date-time":"2024-01-11T00:00:00Z","timestamp":1704931200000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/doi.org\/10.1128\/AuthorWarrantyLicense.v1"},{"start":{"date-parts":[[2024,1,11]],"date-time":"2024-01-11T00:00:00Z","timestamp":1704931200000},"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":["Microbiol Spectr"],"published-print":{"date-parts":[[2024,1,11]]},"abstract":"<jats:title>ABSTRACT<\/jats:title>\n          <jats:p>\n            Azithromycin, a 15-membered ring macrolide, is among the recommended antimicrobials for treating invasive salmonellosis in humans. It is not approved for use in veterinary medicine. We analyzed the U.S. National Antimicrobial Resistance Monitoring System (NARMS) culture collections (~40,700) between 2011 and 2021 from food animals at slaughter and processing and retail meats, and identified 31 azithromycin-resistant\n            <jats:italic>Salmonella<\/jats:italic>\n            spp. with the first occurrence in 2015. These isolates belonged to 12\n            <jats:italic>Salmonella<\/jats:italic>\n            serovars and possessed one or more macrolide resistance determinants:\n            <jats:italic>erm<\/jats:italic>\n            (42),\n            <jats:italic>mef<\/jats:italic>\n            (C),\n            <jats:italic>mph<\/jats:italic>\n            (A),\n            <jats:italic>mph<\/jats:italic>\n            (E),\n            <jats:italic>mph<\/jats:italic>\n            (G), and\n            <jats:italic>msr<\/jats:italic>\n            (E) or a point mutation (\n            <jats:italic>acrB<\/jats:italic>\n            _R717L), of which\n            <jats:italic>mph<\/jats:italic>\n            (A) was dominant (61.3%). Compared with azithromycin-susceptible controls, these determinants accounted for up to 256-fold MIC increases against azithromycin with MIC\n            <jats:sub>50<\/jats:sub>\n            and MIC\n            <jats:sub>90<\/jats:sub>\n            increased by 32- and 8-fold, respectively. We report the first detection of an\n            <jats:italic>mph<\/jats:italic>\n            (G)-\n            <jats:italic>mef<\/jats:italic>\n            (C)-\n            <jats:italic>mph<\/jats:italic>\n            (E)-\n            <jats:italic>msr<\/jats:italic>\n            (E)-containing\n            <jats:italic>Salmonella<\/jats:italic>\n            Agona isolate with very high-level azithromycin resistance (1,024 \u00b5g\/mL) and the first detection of\n            <jats:italic>acrB<\/jats:italic>\n            _R717L accounting for azithromycin resistance in nontyphoidal\n            <jats:italic>Salmonella<\/jats:italic>\n            serovars in the United States. Plasmids of diverse replicon types were identified, with 86.2% carrying multidrug resistance including azithromycin and ceftriaxone, or decreased susceptibility to ciprofloxacin. This report also highlights an emerging\n            <jats:italic>mph<\/jats:italic>\n            (A)-containing (on an IncR plasmid)\n            <jats:italic>Salmonella<\/jats:italic>\n            Newport clone of cattle\/beef origin with high-level azithromycin resistance (128 \u00b5g\/mL) and decreased susceptibility to ciprofloxacin (0.25 \u00b5g\/mL). Further work is needed to better understand the drivers of emerging azithromycin resistance in nontyphoidal\n            <jats:italic>Salmonella<\/jats:italic>\n            associated with food animal sources.\n          <\/jats:p>\n          <jats:sec>\n            <jats:title>IMPORTANCE<\/jats:title>\n            <jats:p>\n              Macrolides of different ring sizes are critically important antimicrobials for human medicine and veterinary medicine, though the widely used 15-membered ring azithromycin in humans is not approved for use in veterinary medicine. We document here the emergence of azithromycin-resistant\n              <jats:italic>Salmonella<\/jats:italic>\n              among the NARMS culture collections between 2011 and 2021 in food animals and retail meats, some with co-resistance to ceftriaxone or decreased susceptibility to ciprofloxacin. We also provide insights into the underlying genetic mechanisms and genomic contexts, including the first report of a novel combination of azithromycin resistance determinants and the characterization of multidrug-resistant plasmids. Further, we highlight the emergence of a multidrug-resistant\n              <jats:italic>Salmonella<\/jats:italic>\n              Newport clone in food animals (mainly cattle) with both azithromycin resistance and decreased susceptibility to ciprofloxacin. These findings contribute to a better understating of azithromycin resistance mechanisms in\n              <jats:italic>Salmonella<\/jats:italic>\n              and warrant further investigations on the drivers behind the emergence of resistant clones.\n            <\/jats:p>\n          <\/jats:sec>","DOI":"10.1128\/spectrum.03485-23","type":"journal-article","created":{"date-parts":[[2023,11,22]],"date-time":"2023-11-22T14:05:47Z","timestamp":1700661947000},"update-policy":"https:\/\/doi.org\/10.1128\/asmj-crossmark-policy-page","source":"Crossref","is-referenced-by-count":16,"title":["Genomic analysis of azithromycin-resistant\n            <i>Salmonella<\/i>\n            from food animals at slaughter and processing, and retail meats, 2011\u20132021, United States"],"prefix":"10.1128","volume":"12","author":[{"ORCID":"https:\/\/orcid.org\/0000-0001-7995-7427","authenticated-orcid":false,"given":"Beilei","family":"Ge","sequence":"first","affiliation":[{"name":"Center for Veterinary Medicine, U.S. Food and Drug Administration , Laurel, Maryland, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Sampa","family":"Mukherjee","sequence":"additional","affiliation":[{"name":"Center for Veterinary Medicine, U.S. Food and Drug Administration , Laurel, Maryland, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Cong","family":"Li","sequence":"additional","affiliation":[{"name":"Center for Veterinary Medicine, U.S. Food and Drug Administration , Laurel, Maryland, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Lucas B.","family":"Harrison","sequence":"additional","affiliation":[{"name":"Center for Veterinary Medicine, U.S. Food and Drug Administration , Laurel, Maryland, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Chih-Hao","family":"Hsu","sequence":"additional","affiliation":[{"name":"Center for Veterinary Medicine, U.S. Food and Drug Administration , Laurel, Maryland, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Thu-Thuy","family":"Tran","sequence":"additional","affiliation":[{"name":"Center for Veterinary Medicine, U.S. Food and Drug Administration , Laurel, Maryland, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Jean M.","family":"Whichard","sequence":"additional","affiliation":[{"name":"Division of Foodborne, Waterborne, and Environmental Diseases, Centers for Disease Control and Prevention , Atlanta, Georgia, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Uday","family":"Dessai","sequence":"additional","affiliation":[{"name":"Food Safety and Inspection Service, U.S. Department of Agriculture , Washington, DC, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Ruby","family":"Singh","sequence":"additional","affiliation":[{"name":"Center for Veterinary Medicine, U.S. Food and Drug Administration , Rockville, Maryland, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Jeffrey M.","family":"Gilbert","sequence":"additional","affiliation":[{"name":"Center for Veterinary Medicine, U.S. Food and Drug Administration , Rockville, Maryland, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Errol A.","family":"Strain","sequence":"additional","affiliation":[{"name":"Center for Veterinary Medicine, U.S. Food and Drug Administration , Laurel, Maryland, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Patrick F.","family":"McDermott","sequence":"additional","affiliation":[{"name":"Center for Veterinary Medicine, U.S. Food and Drug Administration , Laurel, Maryland, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-2587-1684","authenticated-orcid":false,"given":"Shaohua","family":"Zhao","sequence":"additional","affiliation":[{"name":"Center for Veterinary Medicine, U.S. Food and Drug Administration , Laurel, Maryland, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"235","reference":[{"key":"e_1_3_3_2_2","unstructured":"WHO . 2018. 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