Genotyping and antimicrobial resistance genes of Yersinia ruckeri isolates from rainbow trout farms.

In this study, we compared 142 Yersinia ruckeri isolates collected between 2013 and 2016 from 6 different regions in Turkey. A total of 18 different genogroups were found, though most of the isolates clustered into the same genogroup as serotype O1. As immunization of fish with inactivated Y. ruckeri by injection, immersion, or feeding provide minimal protection against Y. ruckeri infection in Turkey, many fish producers use antimicrobials unrestrictedly, resulting in antimicrobial resistance in aquatic pathogens. Accordingly, we investigated resistance to the antimicrobials most commonly used to treat yersiniosis. More than 80% of the Y. ruckeri isolates were susceptible to sulfamethoxazole-trimethoprim (SXT), florfenicol (FFC), and tetracycline, whereas none were susceptible to sulfamethoxazole. The most commonly used antimicrobials (SXT and FFC) can be effectively administered because the resistance levels to these drugs are the lowest among those reported for agents used to control enteric red mouth disease (12.6 and 14.7%, respectively). In conclusion, to the best of our knowledge, this study is the first characterization of the antimicrobial resistance genes floR, sulI, tetC, tetD, and tetE in Y. ruckeri isolates from aquaculture. Additionally, we detected the sulII gene but not the tetA, tetB, tetM, tetS, or sulIII genes.