Abstract:
Bacterial pathogens are a great threat to fish production. The intention of this study was to isolate pathogenic Edwardsiella and Yersinia species on fishes, identify the possible risk factors associated to bacterial infection, and determine their antimicrobial sensitivity test from lakes in Haramaya district. The cross-sectional study was conducted to isolate Edwardsiella and Yersinia pathogens from apparently healthy fish reared in Adelle, Haramaya, and Tinike lakes found in Haramaya district in eastern Ethiopia. A total of 225 heart, kidney, and liver tissues were aseptically collected from 75 apparently healthy fish in the species Oreochromis niloticus and Clarias gariepinus. Standard bacteriologic culture and biochemical tests were employed to isolate the target bacteria at the species level. In addition, an antimicrobial susceptibility test of isolated bacteria was conducted by the Kirby-Bauer disc diffusion method. SPSS Statistical Package version 20.0 was employed to analyse the data. Statistical tools such as chi-square, the Fisher test, and descriptive statistics were used to compute the statistical association of variables. Accordingly, the total fish-level prevalence of bacteria was 49.3% and the organ-level prevalence was 20%. The fish level prevalence of E. ictaluri, E. tarda, and Y. ruckeri was detected at 17.3%, 25.3%, and 14.7%, respectively. Based on risk factors such as sex, age, lakes, and fish species, a relatively higher prevalence was found in female, young, Haramaya, and Nile tilapia. Based on organ source, a high prevalence was recorded in the liver (28.0%), followed by the kidney (21.3%) and heart (10.7%). From all examined tissues, Edwardsiella tarda was the dominant isolate (8.9%), followed by Edwardsiella ictaluri (5.8%), and Yersinia ruckeri (5.33%). However, there was no significant difference in both fish and organ levels in the prevalence of bacteria (P<0.05) among the tested variables. All isolates tested were susceptible to at least three (3) of the seven antimicrobials evaluated. High levels of resistance were expressed by all isolates to tetracycline and ampicillin. The multidrug resistance pattern of isolates showed resistance to at least two and a maximum of four antimicrobials. The present study deals with starting point information for the occurrence of three bacterial species, future investigation with a broader antimicrobial susceptibility test, and fish disease management in the study area.
