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This study compared the efficacy of the third-generation fluoroquinolone levofloxacin and the second-generation enrofloxacin against APEC. In vitro, 155 samples (livers, hearts, and lungs) from broiler farms in Qalyubia, Egypt, yielded 43\n                    <jats:italic>E. coli<\/jats:italic>\n                    isolates, of which 16 formed strong biofilms. Antibacterial sensitivity testing revealed that levofloxacin achieved a higher susceptibility rate (43.75%) and larger inhibition zones (26\u00a0mm) compared with enrofloxacin (18.75%, 13\u00a0mm), indicating superior antibacterial activity. In vivo, 150 broiler chicks were experimentally infected with APEC O2 and allocated to five groups: negative control, positive control, levofloxacin-treated, enrofloxacin-treated, and enrofloxacin-colistin combination. Levofloxacin treatment resulted in significantly higher cumulative body weight gain and lower mortality (2460.37, 3.33%), compared with enrofloxacin (2126.09, 6.67%) (\n                    <jats:italic>P<\/jats:italic>\n                    \u2009&lt;\u20090.05). Levofloxacin was further associated with improved hematological and biochemical profiles, reduced oxidative stress markers (MDA, SOD, GSH), and lower bacterial counts in visceral organs (\n                    <jats:italic>P<\/jats:italic>\n                    \u2009&lt;\u20090.05). Collectively, these findings indicate that levofloxacin offers enhanced therapeutic efficacy over enrofloxacin in the treatment of avian colibacillosis under the conditions of this study.\n                  <\/jats:p>","DOI":"10.1038\/s41598-026-59593-6","type":"journal-article","created":{"date-parts":[[2026,7,1]],"date-time":"2026-07-01T14:42:36Z","timestamp":1782916956000},"update-policy":"https:\/\/doi.org\/10.1007\/springer_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Comparative efficacy of second- and third-generation fluoroquinolone antibiotics against systemic Escherichia coli infection in broiler chickens in Qalyubia Governorate, Egypt"],"prefix":"10.1038","volume":"16","author":[{"given":"Ali M.","family":"Asy","sequence":"first","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Amany O.","family":"Selim","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Dalia M.","family":"Azab","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Eman A.","family":"Abozeid","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Mona A.","family":"Abd-Elrehim","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Marionette Z.","family":"Nassif","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Gehan","family":"El-Saied","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"297","published-online":{"date-parts":[[2026,7,1]]},"reference":[{"key":"59593_CR1","doi-asserted-by":"publisher","first-page":"1088","DOI":"10.1016\/j.psj.2019.10.047","volume":"99","author":"YB Kim","year":"2020","unstructured":"Kim, Y. 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