Isolation and characterization of Vagococcus carniphilus from diseased crucian carp

The bacterial genus Vagococcus has been described to include eight recognized species: Vagococcus fluvialis, Vagococcus fessus, Vagococcus salmoninarum, Vagococcus lutrae, Vagococcus elongates, Vagococcus penaei, Vagococcus acidifermentans and Vagococcus carniphilus. In this study, V. carniphilus was isolated from the myocardium, liver, spleen and kidney tissues of diseased crucian carps. After isolation, biochemical, 16S rDNA gene sequence and phylogenetic analysis was performed. Next, the phenotypic and genomic characteristics were analysed using different biochemical tests and antibiotic susceptibility testing. The bacterial isolate was gram-positive. The biochemical testing results indicated that a positive reaction occurred in the tubes containing glycerol, galactose, mannitol, sucrose sorbitol and d-ribose, and a negative reaction with α-galactosidase, β-galactosidase and hydrogen sulphide. A DNA product (∼1500 base pairs) was amplified from 16S rDNA. BLAST analysis revealed that V. carniphilus from crucian carps was highly similar to V. carniphilus isolated from other sources and showed the highest similarity (95%) with reference strains. Additionally, pathological analysis revealed that infected crucian carp tissues (myocardium, liver, spleen and kidney) and mouse tissues (myocardium, lung, liver, spleen and kidney) were severely damaged. In summary, we isolated V. carniphilus from diseased crucian carp, and this isolate induced pathological changes in crucian carp and mice.