{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,4,10]],"date-time":"2026-04-10T00:47:57Z","timestamp":1775782077234,"version":"3.50.1"},"reference-count":69,"publisher":"Frontiers Media SA","license":[{"start":{"date-parts":[[2022,11,25]],"date-time":"2022-11-25T00:00:00Z","timestamp":1669334400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":["frontiersin.org"],"crossmark-restriction":true},"short-container-title":["Front. Vet. Sci."],"abstract":"<jats:p>The third- or fourth-generation cephalosporins (3GC or 4 GC) are classified as \u201ccritically important antimicrobials for human medicine\u201d by WHO, but resistance to these drugs is increasing rapidly in avian pathogenic <jats:italic>E. coli<\/jats:italic> (APEC). This study investigated the distribution and genetic characteristics of 3GC- or 4 GC-resistant APEC isolates from five major integrated broiler operations in Korea. The prevalence of 3GC- or 4GC-resistant APEC isolates in 1-week-old broilers was the highest in farms of operation C (53.3%); however, the highest prevalence of these isolates in 4-week-old broilers was the highest on the farms of operation A (60.0%), followed by operations E (50.0%) and C (35.7%). All 49 3GC- or 4GC-resistant APEC isolates had at least one \u03b2-lactamase-encoding gene. The most common \u03b2-lactamase-encoding genes was extended-spectrum \u03b2-lactamase gene, <jats:italic>bla<\/jats:italic><jats:sub>CTX\u2212M\u221215<\/jats:sub>, detected in 24 isolates (49.0%), followed by <jats:italic>bla<\/jats:italic><jats:sub>TEM\u22121<\/jats:sub> (32.7%). Sixteen isolates (32.7%) harbored class 1 integrons, and four isolates (8.2%) showed different gene cassette-arrangements. However, only 1 of 26 isolates harboring class 2 integrons carried a gene cassette. Furthermore, both CRISPR 1 and 2 arrays were detected in most isolates (36 isolates; 73.5%), followed by CRISPR 2 (18.4%) and CRISPR 1 (4.1%). Interestingly, CRISPR 2 was significantly more prevalent in multidrug resistant (MDR)-APEC isolates than in non-MDR APEC isolates, whereas CRISPR 3 and 4 were significantly more prevalent in non-MDR APEC isolates (each 11.1%; <jats:italic>p<\/jats:italic> &amp;lt; 0.05). None of the protospacers of CRISPR arrays were directly associated with antimicrobial resistance. Our findings indicate that the distribution and characteristics of 3GC or 4GC-resistant APEC isolates differed among the integrated broiler operations; moreover, improved management protocols are needed to control the horizontal transmission of 3GC or 4GC-resistant APEC isolates.<\/jats:p>","DOI":"10.3389\/fvets.2022.1055320","type":"journal-article","created":{"date-parts":[[2022,11,25]],"date-time":"2022-11-25T07:36:57Z","timestamp":1669361817000},"update-policy":"https:\/\/doi.org\/10.3389\/crossmark-policy","source":"Crossref","is-referenced-by-count":4,"title":["Genetic characterization of third- or fourth-generation cephalosporin-resistant avian pathogenic Escherichia coli isolated from broilers"],"prefix":"10.3389","volume":"9","author":[{"given":"Hyo 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