Isolation and characterization of Vibrio metschnikovii causing infection in farmed Portunus trituberculatus in China

In August 2008, a massive epizootic occurred among Portunus trituberculatus reared together with Palaemon carincauda Holthuis and Sinonovacula constricta in the seawater pond of Ningang farm, Rudong district, Jiangsu province, China. The disease occurred in crabs from juveniles to adults, and the mortality rate reached 30–40%. The diseased crabs exhibited lethargy, hepatopancreas turgidity, and elevated levels of turbid hemolymph. A gram-negative, rod-shaped bacterium (designated as strain LGS-1) was isolated from the ascitic fluid of the diseased and moribund crabs and was confirmed as the causative agent by our infectivity study. We conducted morphological and biochemical characterization of LGS-1, and sequenced the 16S rRNA gene, which led us to identify the bacterium as Vibrio metschnikovii. Drug sensitivity tests showed that this pathogenic bacterium is sensitive to florfenicol, orfloxacin, and SXT, but completely resistant to antibacterial drugs like gentamicin, erythrocin, and acheomycin. This is the first report on Vibrio metschnikovii as a virulent pathogen for Portunus trituberculatus.