Occurrence and antibiotic susceptibility of edwardsiella tarda isolated from fish obtained at selected selling points around Kampala

Abstract

Edwardsiella tarda is one of the serious threats affecting aquaculture globally. The pathogenic bacteria also possess zoonotic potential however, there has been a lack of information over the past decade on its occurrence and antibiotic susceptibility in fish sold on Uganda market. Fish is considered a reservoir for the transmission of Edwardsiella tarda to humans. This study was done to determine the prevalence and antibiotic susceptibility patterns of Edwardsiella tarda isolated from fish sold around Kampala. A total of 117 fish samples were randomly collected from three different markets around Kampala (Kalerwe, Bwaise and Wandegeya) between June and September, 2022. Samples were enriched in Tryptone Soya Broth (TSB) and isolation of Edwardsiella tarda was done on Xylose Lysine Deoxycholate agar. Basing on colony morphology and conventional biochemical tests, of the 117 samples, 20(17.1%) contained E. tarda isolates i.e. 8(40.0%) from Kalerwe, 8(40.0%) from Bwaise and 4(20.0%) from Wandegeya. In this study, antibiotic susceptibility patterns of E. tarda against six antibiotics commonly used in fish farming was investigated by disc diffusion. The study revealed low antibiotic resistance (16.7%) of the E. tarda isolates with 100% sensitivity to Gentamycin, Trimethoprim-sulfamethoxazole, Chloramphenicol and Tetracycline. Intermediate sensitivity was observed in Ciprofloxacin by 40% of the isolates and penicillin resistance was by all the isolates (100%). The resistance indicated the potential misuse of antibiotics possibly in treatment of fish diseases as well as sub therapeutic levels in fish feeds as growth promoters and waterbodies drug residues. Despite its low occurrence, presence of E. tarda isolates in fish sold on market indicates its potential to affect fish and human health. The antibiotic resistance implied a potential Antimicrobial Resistance (AMR) burden in case of an outbreak. This could possibly cause complication of antibiotic therapy in humans when such bacterial spill over into the human population hence suggesting the necessity of implementing interventions to reduce its prevalence in farmed fish and as well that on market for human consumption.