Antibiotic susceptibility and resistance genes of Escherichia coli isolates from diseased rainbow trouts (Oncorhynchus mykiss)

It was aimed to isolate Escherichia coli from infected trouts in different farms, and to investigate antibiotic susceptibility profiles and antibiotic resistance genes of these isolates. Identification processes were carried out according to ISO 6887–3:2017 and ISO 16654:2001 guidelines. Antimicrobial susceptibility was tested according to the Clinical and Laboratory Standards Institute (CLSI) guidelines. Extended–spectrum beta–lactamase (ESBL) resistant strains were investigated by the Modified Double Disc Synergy Test (MDDST) method. The specific regions of 15 genes were analyzed by the real–time PCR system. As a result, 24 isolations were performed from different tissues belonging to eight out of 108 diseased trouts. The highest phenotypical resistance status was found against penicillins (ampicillin 100%, amoxicillin 91.67%) and first–generation cephalosporins (cefazolin 100%). Phenotypic resistance rates of amoxicillin–clavulanate, nalidixic acid, and erythromycin were 83,33%, tetracycline was 75%, ceftazidime, ceftriaxone, cefotaxime, cefepime, and ciprofloxacin were 66,67%, trimethoprim‐sulfamethoxazole was 50%, and chloramphenicol and gentamycin were 33.33%. Phenotypical resistances for amikacin and imipenem were detected at the level of 16.67%. In addition, ESBL production was detected phenotypically in 12 (50%) out of 24 E. coli isolates. The highest antimicrobial resistance gene rate was 58.33% for tetA. Gene regions of sull, ermB, ermF, qnrB, suIll, qnrS, and tetB were detected at 50%, 50%, 50%, 33.33%, 25%, 16.67%, and 16.67% respectively. None of the isolates included the gene region of the qnrA, qnrC, qnrD, and qepA. ESBL–producing genes, blaTEM, blaCTX, and blaSHV were detected at 33.33%, 33.33%, and 16.67% respectively. In conclusion, E. coli contamination of the water can cause infections among fish and increase the agent’s antimicrobial resistance. Resistant strains of E. coli cannot only cause financial damage to create yield loss but also can threaten human health by causing infections throughout the food chain.