Use of shotgun immunoproteomics for the development of protein vaccines against Edwardsiella piscicida

Edwardsiella piscicida is an important emerging pathogen in various cultured fish species. This study aimed to identify immunogenic E. piscicida proteins and evaluate these antigens as protein vaccines for use in aquaculture. Shotgun immunoproteomics using anti-E. piscicida serum from rainbow trout (Oncorhynchus mykiss) and channel catfish (Ictalurus punctatus) (♀) × blue catfish (Ictalurus furcatus) (♂) hybrids inoculated with formalin-killed whole-bacteria preparations identified 36 candidate immunogenic E. piscicida proteins. The chaparonin GroEL, the glycine 2TM zipper domain-containing protein (GlyZip), and coproporphyrinogen-III oxidase (COPIII) were used to orally (PO) and intra-coelomically (IC) immunize Chinook salmon (Oncorhynchus tshawytscha). Fish IC vaccinated with either GlyZip or COPIII demonstrated a slight, but non-significant, improvement in survival post-challenge with E. piscicida S11-285. Surprisingly, fish IC or PO vaccinated with GroEL displayed an anti-protective effect (RPS = -184 % and RPS = -76 %, respectively) against subsequent challenge. All IC vaccinated fish generated a strong specific antibody response against the immunizing protein, and sham vaccinated fish challenged with E. piscicida S11-285 generated a significantly higher specific antibody response to the GroEL and GlyZip proteins than negative control fish, suggesting that shotgun immunoproteomics was effective for detection of immunogenic bacterial proteins that can stimulate humoral immune responses in the host fish.