Characterization of two strains of Vibrio sp. from cultured sea urchin, Strongylocentrotus intermedius, in China

Spotting disease is common in cultured sea urchin (Strongylocentrotus intermedius) from China, and outbreaks are most frequent in summer when seawater temperatures exceed 20 °C. In this study, we used 16S rRNA and housekeeping gene sequence alignments to characterize two strains of Vibrio sp. from diseased sea urchins in a North China farm in September 2017. The strains included a new strain of Vibrio owensii (named HD-1) and a new Vibrio species (named HD-2). Phylogenetic analysis indicated that HD-1 and HD-2 are located in different evolutionary clades and exhibited a high degree of divergence. Transmission electron microscopy showed morphological differences between HD-1 and HD-2. Laboratory-based challenge tests showed that sea urchins infected with either HD-1 or HD-2 exhibited pathological symptoms of spotting disease in a dosage- and temperature-dependent manner. The virulence of HD-1 was greater than that of HD-2. Antimicrobial susceptibility tests demonstrated that both HD-1 and HD-2 are sensitive to ciprofloxacin and florfenicol. HD-1 is specifically sensitive to neomycin, and HD-2 is specifically sensitive to cephalexin.