Isolation an Antimicrobial Susceptibility Profile of Edwardsiella Species and Escherichia coli O157:H7 From Fish and Their Handling Environment in Lake Abaya and Gilgel Gibe-3 Dam, Southern Ethiopia

Edwardsiella species are reassigned under the family Hafniaceae following phylogenomic revisions of the order Enterobacterales, a primary pathogenic strain of fish, while Escherichia coli are members of the Enterobacteriaceae family that are frequently reported as contaminants with rare causes of illness in fish but severely affect other mammals. A cross-sectional study was conducted from April to November 2022 with the objectives of estimating the prevalence of Edwardsiella tarda, Edwardsiella ictaluri, and E. coli O157:H7 in fish and determining the antimicrobial susceptibility pattern of the isolates. A total of 768 tissue samples comprising intestine, liver, and kidney were collected from 256 apparently healthy fish. Bacterial isolation was performed using selective and differential culture media, including MacConkey agar, xylose lysine deoxycholate (XLD) agar, Edwardsiella isolation medium, eosin methylene blue (EMB) agar, and sorbitol MacConkey agar. Further identification was performed using biochemical tests and latex agglutination assays, particularly for the targeted strain of E. coli. The disk diffusion test was employed to determine the susceptibility pattern of isolates against seven standard antimicrobial disks. The findings were presented using descriptive statistics, while the association of categorical variables with the occurrence of bacterial species was computed using chi-square and logistic regression analysis. The overall prevalence of E. tarda, E. ictaluri, and E. coli O157:H7 among fish was 8.6%, 4.7%, and 14.1%, respectively, and among organs (intestine, liver, and kidney) was 4.01%, 1.95%, and 5.34%, respectively. The maturity of fish and lake showed a significant association (p < 0.05) with the occurrence of E. tarda. Resistance to tetracycline was noted in all of the isolates. The results of this study concluded that the intestines of fish harbor E. tarda, E. ictaluri, as primary inhabitant pathogens, and E. coli O157:H7, which may be a transient microorganism mostly associated with fault handling practice.