Phenotypic, molecular detection, and antibiogram analysis of Pseudomonas species from Oreochromis niloticus.L 1758 (Nile Tilapia) from aquaculture pond, Ethiopia.

Abstract

BACKGROUND: Pseudomonas species, including P. aeruginosa, P. putida, and P. fluorescens, are zoonotic bacterial pathogens responsible for significant disease and mortality in both farmed and wild fish worldwide. In Ethiopia, these bacteria have been identified in Sebeta fish ponds and Rift Valley lakes, yet there is limited data on their molecular and phenotypic characteristics in local aquaculture systems. To address this gap, a cross-sectional study was conducted from November 2022 to May 2023 in selected aquaculture ponds in Ethiopia. RESULTS: A total of 637 samples were aseptically collected from the muscle, liver, spleen, and kidney of fish using purposive sampling. Pseudomonas base agar selective medium morphological characteristic and biochemical tests were used to isolate and identify pseudomonas species. Pseudomonas species were isolated from 81 samples, representing 12.7% of the total. Among these isolates, 85.6% displayed virulence traits, including β- hemolysis on 5% sheep blood agar. Additionally, 75 isolates (92.59%) was confirmed using conventional PCR with Pseudomonas-specific primers. Of the PCR-positive samples, 8 (10.66%) were identified as P. aeruginosa, 28 (37.63%) as P. putida, and 39 (52%) as P. fluorescens from Nile Tilapia (O. niloticus). Antibiotic susceptibility testing on ten representative isolates revealed that all strains were sensitive to Ciprofloxacin, Gentamicin, and Ceftriaxone but resistant to Amoxicillin and Penicillin. CONCLUSIONS: The findings indicate that Pseudomonas species carrying virulence genes, exhibiting β- hemolytic activity, and showing resistance to commonly used antibiotics in both human and veterinary medicine are present in aquaculture. The detection of this pathogen in 75 fish samples raises concerns about potential outbreaks and zoonotic transmission. Therefore, further research on the molecular epidemiology of the disease is necessary to understand inter-host transmission and antibiotic resistance patterns.