Isolation and identification of Vibrio rotiferianus from diseased half-smooth tongue sole (Cynoglossus semilaevis Günther)

Four strains dominant bacteria associated with skin ulcers were isolated from half-smooth tongue sole, Cynoglossus semilaevis. Bacterial strain BV1 was proved to be a pathogen by muscle injection with bacteria suspension, the LD₅₀ was 1.5×10⁵ cfu/mL. The morphological, physiological and biochemical characteristics were examined, the 16S rRNA and gyrB gene were partially sequenced and compared with sequences deposited in genebank, and the molecular phylogenetic trees were constructed. The sequenced 16S rRNA gene of strain BV1 (GenBank accession No. JN391272) is 1379bp in length, the sequenced gyrB gene of strain BV1 (GenBank accession No. JN 168882) is 1130bp in length, and gyrB gene exhibited high similarity in 99% with the gyrB gene of Vibrio rotiferianus from GenBank database. The results of physiological and biochemical tests and molecular identification suggested that the pathogen was V. rotiferianus. Detection of the activity of extracellular products (ECP) and hemolysin showed that the strain BV1 could produced amylase, lipase, urease, lecithinase, and with β-haemolysis in containing 4% defibrinated rabbit blood of TSA plates, but no proteinase, gelatinase. Drug resistance of the pathogen to 17 antimicrobial agents were detected, the results showed that the strain was sensitive to streptomycin, tetracycline and so on.