Characterization of a pathogenic Vibrio harveyi strain from diseased Epinephelus coioides and evaluation of different methods to control its infection

Abstract

Vibrio harveyi is a common opportunistic pathogen that leads to vibriosis when it infects animals. In previous study, several V. harveyi strains with high virulence have been isolated from diseased fish or shrimp. In this study, we have characterized a V. harveyi strain NS131652 which is one of the pathogenic strains and evaluated applicable methods for controlling its infection in aquaculture. The LD50 of NS131652 was 3.9 × 103 CFU/g according to our experiments. The antibiotic susceptibility assay showed that NS131652 was susceptible to 7 antibiotics (40 in total), but none of them was suitable for aquaculture application. Interestingly, we found that a low salinity could reduce the amount of strain NS131652 in reared water and the mortality of groupers significantly. The ERIC-PCR and phylogenetic analysis showed that NS131652 had a close relationship with a non-toxic V. harveyi strain WC13DH51. Using the non-toxic V. harveyi strain WC13DH51 as a live-attenuated bacteria vaccine, the groupers gained a relative percent survival (RPS) of 100% when the amount of stain NS131652 was equal to or less than 104 CFU/mL in water. In conclusion, we have evaluated three methods in control the pathogenic V. harveyi strain NS131652 in grouper reared environment and found out that low salinity and a live-attenuated vaccine would be the best ways to avoid the vibriosis caused by V. harveyi strain NS131652.