Characterization and antibiogram of bacterial isolates from diseased farmed Nile tilapia in Beheira governorate, Egypt.

Abstract

UNLABELLED: This study aimed to isolate, identify, and describe the bacteria isolated from mortality events occurred among pond-farmed Nile tilapia in different farms at Edku, Beheira province, Egypt, with special emphasis on their antimicrobial resistance profile. Specimens were collected from six private farms that experienced mortality outbreaks that occurred throughout the year between August 2023 and 2024. Clinical and postmortem examinations uncovered characteristic signs of bacterial septicemia. Forty-three bacterial isolates were recovered from the examined moribund and recently dead specimens. Based on the genetic data and evolutionary relationships derived from the 16S ribosomal RNA gene, six different isolates were resolved as(46.5%),(11.6%),(14%),(9.3%),(11.6%), and(7%). The antibiogram results revealed varying susceptibility patterns among the isolates.showed intermediate susceptibility to ciprofloxacin, whilewas only moderately sensitive to oxytetracycline. Of particular concern,was found to be resistant to all tested antimicrobials. However,displayed sensitivity to ciprofloxacin, making it a potential drug of choice for treating diseased tilapia; this isolate was also moderately susceptible to oxytetracycline, erythromycin, and kanamycin. Finally,exhibited intermediate susceptibility only to amoxycillin/clavulanic acid, oxytetracycline, and ciprofloxacin. Our findings clearly demonstrate that careless antibiotic administration in fish farming drives the emergence of antimicrobial resistance. Therefore, proactive planning is necessary, encompassing comprehensive surveillance, and the establishment of strict control and prevention measures to curb bacterial spread and safeguard productivity in Tilapia aquaculture. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12917-025-05227-4.