Description of sp. nov., an emergent fish pathogen, and assessment of virulence using a tiger barb () infection model.

A recently described emergent disease of ornamental fish has been associated with an species positive for the surface protective antigen () C gene. Whole genome sequencing was performed on five isolates from diseased ornamental fish. In addition, these isolates were compared to and other -positive species isolated from terrestrial and marine mammals, birds and fish using multi-locus sequence analysis (MLSA). The genomes of fish pathogenic isolates were genetically distinct from , sharing 86.61-86.94 % average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) values of 31.6-32.2 %, but 99.01-99.11 % ANI and 90.8-91.9 % dDDH values with the uncharacterized -positive sp. strain 2 isolated from swine. The findings indicate the -positive fish and swine isolates are conspecific and represent a previously unrecognized taxon. While phylogenies inferred from MLSA sequences confirm this conclusion, slight genetic differences between the fish isolates and swine strain 2 were indicated. Bath immersion challenge trials were conducted using tiger barbs () exposed by immersion to 10 c.f.u. ml of three fish pathogenic species, and three and two isolates as a model of infection. Thirty days post-challenge, cumulative mean percentage survival was 37 % for the , 100 % for the and 13 % for the isolates, revealing differences in virulence among the various genotypes in fish. Genetic findings and observed differences in virulence demonstrate the fish pathogenic isolates represent a novel species, for which the name sp. nov. is proposed. The type strain is 15TAL0474 (=NRRL B-65533=ATCC-TSD-175=DSM 110099).