Isolation and identification of Pseudomonas fluoeroscens and evaluation of its antimicrobial sensitivity from fish in Lake Haramaya, East Hararghe Zone, Oromia Regional State, Ethiopia

Abstract

Abstract Pseudomonas fluorescens ( P. fluorescens ) is an opportunistic Gram-negative bacterium associated with disease in freshwater and marine fish, resulting in economic losses to aquaculture. This study aimed to isolate and identify P. fluorescens from wild Nile tilapia ( Oreochromis niloticus ) and African catfish ( Clarias gariepinus ) collected from Lake Haramaya, Ethiopia, and to evaluate the antimicrobial susceptibility profile of the isolates. A cross-sectional study was conducted from December 2022 to May 2023. A total of 50 fish (32 Nile tilapia and 18 African catfish) were sampled, and 250 swab specimens were collected from the skin, gills, intestine, liver, and kidney. Isolation and identification were performed using conventional cultural, morphological, and biochemical methods. Antimicrobial susceptibility testing was conducted on 10 representative presumptive isolates using the Kirby–Bauer disk diffusion method according to Clinical and Laboratory Standards Institute (CLSI) guidelines. Presumptive P. fluorescens was detected in 21 of 50 (42.0%) wild fish examined. A total of 27 presumptive isolates were recovered from the sampled organs based on their cultural, morphological, and biochemical characteristics. The highest isolate-level occurrence was observed in the skin (20%), followed by the intestine (14%), gills (12%), liver (6%), and kidney (2%). Bacterial occurrence differed significantly among organs ( P < 0.05), whereas no significant association was observed with fish species or sex ( P > 0.05). Among the 10 representative isolates tested, all were resistant to tetracycline and ciprofloxacin, whereas 90% and 70% were susceptible to kanamycin and gentamicin, respectively. These findings provide preliminary evidence of the occurrence of presumptive P. fluorescens and antimicrobial-resistant isolates in wild fish from Lake Haramaya. Molecular confirmation of species identity and comprehensive antimicrobial susceptibility testing using a larger number of isolates are needed, as identification was based solely on phenotypic methods and antimicrobial susceptibility testing was limited to 10 representative isolates. The findings establish baseline information for future surveillance of P. fluorescens and antimicrobial resistance in Ethiopian freshwater ecosystems within a One Health framework.