Immunity stimulation by oral administration of encapsulated autologous vaccine against lactococcus garvieae in sea bream and sea bass

Project summary

Lactococcus garvieae is an important emerging pathogen in global freshwater and marine fish farming, also involved in terrestrial animal and human emerging infections. Recently, outbreaks of septicemic disease due to L. garvieae haves been reported also in farmed European sea bass in Italy and Spain. These species of fish are the first non-salmonid species to be farmed in Europe and an important species in Mediterranean basin. The control of this disease is based on antimicrobial therapy and vaccination, but several studies reported a high incidence of multiple resistance on this bacterium. The use of autologous vaccine based on isolated is a strategy to reduce losses in animal productions during outbreaks but the administration of the vaccine is by intraperitoneal injection or immersion, with stress for animals and time consuming.

The first objective of the project will be the characterization of virulence gene’ patterns of L. garvieae isolated during outbreaks by WGS and serologically. In addition, studies on pathogenicity of the strains will be conducted on fish and mouse. The characterized strains will be used for production of vaccine. A further objective will be the study of immunity stimulation after oral administration of the vaccine produced with characterized bacterium in zebrafish, sea bass and sea bream. The gut-associated lymphoid tissue (GALT) stimulation of the fish will be verified using double transgenic zebrafish line, characterized by green fluorescent macrophages and red fluorescent neutrophils.

The investigation of the presence of circulating specific antibody against immunization antigens will be performed by ELISA assay, while the expression of relevant immune-related genes by qPCR at different endpoints in sea bass and sea bream. This study could improve the production of vaccine to use in European marine aquaculture to limits antibiotic use and economic losses in case of outbreaks and to understand the pathogenicity and the virulence gene’ pattern of this microorganism.