Abstract

Rainbow trout (Oncorhynchus mykiss, Walbaum) production has shown rapid development in the last 30 years in Turkey, and the total production volume reached 100,000 tons in 2016, making Turkey the largest rainbow trout producer among the European countries.¹ Sustainable fishery management depends on rearing the fish in appropriate conditions and improving successful preventive health care.² The intensive production of rainbow trout has resulted in increased health problems and economic losses related to bacterial diseases. Flavobacterial diseases in fish are caused by multiple bacterial species within the family Flavobacteriaceae and are responsible for devastating losses in wild and farmed fish stocks around the world. During the last ten years alone, numerous novel Flavobacterium spp., including F. oncorhynchi, F. branchiicola, F. succinicans, F. pectinovorum, and F. spartani were described and recovered from systemically infected fishes exhibiting clinical disease signs.³ The widespread therapeutic use of antimicrobial agents has the potential to increase the frequency of antimicrobial-resistant aquatic bacteria. The aquatic environment can serve both as a natural reservoir of antibiotic resistance genes and to spread bacteria and antimicrobial resistance genes to the environment.⁴ In this study, our hypothesis and aim are to investigate the presence of antimicrobial resistance genes in possible novel Flavobacterium species and the determination of whether antimicrobial resistance genes found in isolates create a risk to the aquatic ecosystem.

Eight possible novel Flavobacterium isolates were recovered from farmed rainbow trout and brook trout exhibiting clinical signs, such as darkening of body color, exophthalmos, enlarged spleen, and focal necrosis of the liver. Isolates were identified with 16S rRNA sequence analysis.⁵ Antimicrobial susceptibilities among the strains were determined using a minimum inhibitory concentration method against licensed antimicrobials in Turkey, and the frequency of antimicrobial resistance genes was investigated by PCR.⁶

According to sequence analysis of our isolates’ results in Genbank and Ez Taxon-e database; F. collinsii 97,05%, F. oncorhynchi 97,82%, F. pectinovorum 97,31%, F. terrigena 98,11%, F. tiangeerense 98,3%, F. xueshanense 97,22%, F. frigoris 97,62% and F. crassostreae 97,26% were identified. The rates of reduced susceptibility phenotypically were determined for enrofloxacin (62,5%), florfenicol (87,5%), amoxicillin (100%), and sulfametoksazol/trimethoprim (87,5%). Also, we found that of the eight isolates, one isolate harbored both floR and qnrS, one isolate harbored sul2, and one isolate harbored both tetE and QnrS.

In conclusion, this study is the first report on the presence of possible novel Flavobacterium species recovered from farmed trout in Turkey. In our next study, we will do polyphasic identification and naming of possible novel Flavobacterium species by phylogenetic analysis and whole-genome sequencing, morphological, physiological, biochemical, and chemotaxonomic characterization. Additionally, these isolates showed high rates of antimicrobial resistance phenotypically and genotypically, underlining the importance of the aquatic environment as a reservoir for the dissemination of potentially possible Flavobacterium spp. and horizontal gene transfer between other waterborne bacterial species.

Acknowledgments

This research was supported by The Research Fund of the Erciyes University. Project Number: TCD-2019-9733.

*Presenting author
+Student presenter

Literature Cited

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