Comparative efficacy of second- and third-generation fluoroquinolone antibiotics against systemic Escherichia coli infection in broiler chickens in Qalyubia Governorate, Egypt.

Avian pathogenic Escherichia coli (APEC) causes severe colibacillosis in poultry. 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 E. coli 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 mm) compared with enrofloxacin (18.75%, 13 mm), 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%) (P < 0.05). Levofloxacin was further associated with improved hematological and biochemical profiles, reduced oxidative stress markers (MDA, SOD, GSH), and lower bacterial counts in visceral organs (P < 0.05). Collectively, these findings indicate that levofloxacin offers enhanced therapeutic efficacy over enrofloxacin in the treatment of avian colibacillosis under the conditions of this study.