Different antigen ratio in bivalent vaccine can affect immunological activation and protection against Aeromonas salmonicida and Vibrio anguillarum in Atlantic salmon

Identification and characterization of Vibrio anguillarum (GA strain) isolated from Obscure Pufferfish Takifugu obscurus

OBJECTIVE

Aquaculture has faced significant challenges due to the emergence of various pathogens affecting fish species. One such species, the Obscure Pufferfish Takifugu obscurus, has experienced high mortality rates due to an outbreak of disease on a fishery farm in Shanghai.

METHODS

The pathogen responsible for this outbreak was isolated and identified as Vibrio anguillarum (GA strain) using a combination of morphological, biochemical, and whole-genome single-nucleotide polymorphism-based phylogenetic analyses. Pathogenicity tests confirmed that the GA strain could cause disease in healthy Obscure Pufferfish, inducing overt hemorrhagic symptoms. Histopathological analysis was performed to assess whether tissue damage had occurred. Whole-genome sequencing revealed that the GA strain possessed 235 virulence genes and two drug resistance-related genes: cyclic AMP receptor protein (CRP) and regulator of secondary metabolites A (rsmA). Testing via PCR further confirmed the presence of 10 common virulence genes.

RESULTS

Antibiotic susceptibility testing showed that the GA strain was highly sensitive to antibiotics such as tetracycline, doxycycline, minocycline, and compound sulfamethoxazole and was resistant to cefradine, cefazolin, penicillin, and vancomycin.

CONCLUSIONS

To the best of our knowledge, this is the first study to report V. anguillarum as the pathogen responsible for this disease in Obscure Pufferfish. The isolate exhibited strong virulence and multidrug resistance. The findings lay the foundation for further disease control in Obscure Pufferfish and the investigation of the epidemiological mechanisms of V. anguillarum.

Immuno-protective response of Asian seabass (Lates calcarifer) to inactivated vaccines against Streptococcus iniae and Vibrio harveyi

BACKGROUND

In this study, the protective immunity and immunogenicity of the monovalent and bivalent Streptococcus iniae and Vibrio harveyi vaccine were evaluated in Asian seabass. To analyze immune responses, 1200 Asian seabass with an average weight of 132.6 ± 25.4 g were divided into eight treatments in triplicates (50 fish per tank) as follows: S. iniae immunized by injection (SI), V. harveyi immunized by injection (VI), bivalent S. iniae and V. harveyi (SVI) immunized by injection, S. iniae immunized by immersion (SIM), V. harveyi (VIM) immunized by immersion, bivalent S. iniae and V. harvei (SVIM) immunized by immersion, phosphate-buffered saline (PBS) by injection (PBSI) and control group without vaccine administration (CTRL). Blood and serum samples were taken at the end of the 30th and 60th days. Then the vaccinated groups were challenged with two bacteria (S. iniae) and (V. harveyi) separately and mortality was recorded for 14 days.

RESULTS

This study reveals that there is no significant difference in the hematological parameters on the 30th and 60th days of the experiment in the vaccine-immunized groups compared to the CTRL group (P > 0.05). Meanwhile, there was no significant difference in the amount of serum albumin level, respiratory burst activity, and serum bactericidal activity in the vaccine-immunized groups compared to the CTRL group on the 30th and 60th days of the experiment (P > 0.05). Total protein on the 60th day (in the VI and SVI groups), globulin on the 30th day (in the VI and SVI groups) and the 60th day (in the VI group) compared to the CTRL and PBSI groups had a significant increase (P < 0.05). Complement activity (in the VI and SVI groups) and lysozyme (in the SI and SVI groups) increased significantly compared to the control group (P < 0.05). Serum antibody titer against S. iniae had a significant increase in the SI, VI, SVI and SVIM groups compared to the CTRL and PBSI groups (P < 0.05). Serum antibody titer against V. harveyi had a significant increase in the groups immunized with the vaccine compared to the CTRL and PBSI groups (P < 0.05). A significant increase in the relative percentage survival (RPS) following challenge with S. iniae in the SVI (86.6%), SI (83.3%,) and VI (73.3%) groups were observed compared to the CTRL (43.3%) and PBSI (40%) groups (P < 0.05). Also, a significant increase in the RPS after challenge with V. harveyi in the SVI group, VI 86.6%, SVI 83.3%, VIM 80% and SVIM 76.6% were observed compared to the CTRL (46.6%) and PBSI (50%) groups (P < 0.05).

CONCLUSION

Overall, the results demonstrated that the bivalent vaccine of S. iniae and V. harveywas able to produce significant immunogenicity and RPS in Asian seabass.