DEVELOPMENT OF NEW STRATEGY FOR PREVENTING AND CONTROLLING ENTERIC SEPTICEMIA OF CATFISH

Edwardsiella ictaluri is the causative agent of enteric septicemia of catfish (ESC) and one of the most important pathogens affecting the catfish industry in the United States. The current preventive strategies to control ESC have limitations, and catfish operations continue to suffer significant losses because of ESC. Therefore, it is necessary to develop a safe and effective management tool to control ESC outbreaks. Our long-term goal is to support the US aquaculture industry by identifying potential intervention strategies to reduce catfish mortality associated with bacterial infections. The objective of this study is to assess the safety and efficacy of newly constructed mutants, evaluate their potential as live attenuated vaccine candidates, and investigate the effectiveness of β-glucan as a vaccine adjuvant. We will achieve our objective through the following two specific aims:Specific Aim 1. Evaluate the virulence of constructed mutants and identify the critical mutations responsible for virulence attenuation. In this aim, we will characterize the safety and efficacy of novel E. ictaluri mutants in catfish fingerlings and fry. We will evaluate for the first time the effectiveness of β-glucan as a vaccine adjuvant to improve the efficacy of our vaccine candidate and induce effective immunity. This aim will identify novel virulence factors in E. ictaluri and lay the foundation for the development of attenuated vaccine candidates to prevent ESC.Specific Aim 2. Assess the ability of the attenuated mutants to stimulate protective immunity against E. ictaluri. In this aim, we will evaluate the effects of the safest and most efficacious vaccine candidates on phagocytic cells, B cell-specific gene expression, and IgM titers. The potential candidate vaccine strains are expected to boost the immune responses of catfish such that they are better able to resist ESC infection.