Abstract:

In recent years, species in the Chryseobacterium genus have emerged as opportunistic fish pathogens that can cause death in fish in many countries. In the last decade, C. aahli, C. oncorhynchi, C. chaponense, and C. piscico-la have been reported to cause systemic infections in fish. In the present study, Chryseobacterium sp. C-204 was iso-lated from 1g weight rainbow trout showing clinical signs such as abnormal swimming, dorsal skin ulceration, darkening in color, and bilateral exophthalmos. The detailed phenotypic characteristics of the C-204 were characterized by API 20NE, and the BIOLOG GEN III system includes 106 phenotypes. Antimicrobial susceptibility of the C-204 was also determined by the broth microdilution method against five antimicrobial agents commonly used in the Aquaculture. Sequence-based identification was done using 16S rRNA genome sequencing. The genome structure of the C-204 was revealed by using next-generation genome sequencing with reading a total of 24195304 bases and assembled in 4012452 base. Genome-based species delineation of C-204 was done 100 different housekeeping gene regions and 50 the closest Chryseobacterium species with Automated Multi-Locus Species Tree (autoMLST, https://automlst.ziemertlab.com). Antimicrobial resistance genes (AMR) and virulence genes in the C-204 genome were iden-tified using the Virulence Factor Database (VFDB) NCBI-reference antimicrobial resistance genes database. The 16S rRNA sequence of C-204 isolate had similarities with the C. aquaticum (99.65%) and C. greenlandense (98.95%) in GenBank. In parallel 19 biochemical tests, C-204 isolate can be differentiated from the closest type strains by nitrate reduction and inability to produce acid from glucose. With regard to antimicrobial susceptibility, the C-204 isolate can grow even at high antimicrobial concentrations determined for Flavobacteriaceae. According to genome-based species delineation, the C-204 isolate was identified as Chryseobacterium aquaticum subsp greenlandense. 13 virulence and eight AMR genes were detected in the genome of the C-204 isolate. Conclusively, the detailed phenotypic characteris-tic includes 106 biochemical test and genome structure of C-204 isolate by whole genome sequencing were deter-mined.

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