Development of a recombinant adenovirus-vectored vaccine against Pseudomonas plecoglossicida in large yellow croaker (Larimichthys crocea).

Abstract

Pseudomonas plecoglossicida is a Gram-negative bacterial pathogen of visceral granuloma disease (VGD) in large yellow croaker (LYC, Larimichthys crocea), which causes major economic losses to modern LYC farming industry. In this study, a safe and effective recombinant adenovirus-vectored vaccine containing the coding regions of OprF and OprI genes of P. plecoglossicida was developed. After the LYC was administrated with the vaccine via the immersion route, the expression levels of OprF and OprI genes of P. plecoglossicida and the representative immune-related genes were examined to investigate the correlation of immune responses and the expressions of pathogen genes. Meanwhile, the specific antibody levels in the serum of vaccinated LYC and the protection efficacy of the vaccine against P. plecoglossicida were evaluated. The expression levels of OprF and OprI genes of P. plecoglossicida and all immune-related genes were significantly upregulated in the vaccinated LYC. This finding suggests that elevated immune responses may be induced by the high expression levels of two target genes. In addition, high levels of specific IgM against P. plecoglossicida were induced in the serum of vaccinated LYC, unlike in the control fish. The recombinant adenovirus-vectored vaccine displayed a high protection rate against P. plecoglossicida, with a relative percentage survival of 79.07 %. Altogether, our results demonstrate that the adenovirus-vectored vaccine can provide effective immune protection against P. plecoglossicida infection for LYC, and the replication-defective adenovirus can be developed as a qualified vector for fish vaccines. This study provides new insights into the development of adenovirus-vectored vaccines and control of the spread of VGD caused by P. plecoglossicida in LYC.