الفهرس 
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Abstract
The misuse of antibacterial therapeutics within the veterinary fields may lead to the emergence and spread of multidrug resistant (MDR) pathogens. This became a worldwide concern thanks to not only its drawbacks on the animal production economy but also the possible transmission of such strains to humans resulting in untreatable diseases. During this study, 40 E. coli isolates, recovered from broiler flocks in Egypt from 2019 to 2021, were serotyped and tested against different antibacterial therapeutic agents. Meanwhile, selected MDR strains were tested for the existence of two quinolone resistance genes, namely qnrA and qepA. OnrA gene is liable for protecting the bacterial DNA gyrase and type IV topoisomerase from quinolones while qepA is chargeable for extruding quinolones from the bacterial cell. Serotyping of the isolates revealed that the isolates belonged to different 18 E. coli serotypes. Out of the 40 isolates, the most common serotypes were O91:K- (9, 22.5%), O78:K80 (5, 12.5%), and O125:K70 (4, 10%). Other detected serotypes were O159:K- (3, 7.5%), O86:K (3, 7.5%). Serotypes O166, O26:K60 and O126 were represented by 2 isolates of every (2, 5%). the remainder of the isolates were serotyped as O103:K-, O128, O142, O144:K90, O155, O158:K-, O27, O28, O55:H7, and O6, one isolate of every (2.5%). Antibiotic resistance conducted against 14 antibacterial drugs revealed that of the 40 isolates, all were resistant to ampicillin and amoxicillin/clavulanic acid (100%). On the other hand, 39 isolates were sensitive for fosfomycin (97.5%), 34 isolates were sensitive for both norfloxacin and levofloxacin (85%) while 29 isolates showed intermediate sensitivity for ciprofloxacin (72.5%). Detection of quinolone resistance genes for selected E. coli isolates recovered during this study were tested by PCR assays to detect the qnrA and qepA. Out of 17 tested isolates, all of them were harboring qnrA gene (100%), while only 5 were positive for the qepA gene (29.4%).