Attenuated Listeria monocytogenes protecting zebrafish (Danio rerio) against Vibrio species challenge.

Live attenuated bacteria is a promising candidate vector for the delivery of vaccines in clinic trials. In the field of aquaculture industry, live vector vaccine also could provide long-term and effective protection against fish bacterial diseases. In our previous work, we demonstrated attenuated Listeria monocytogenes (Lm) had the potential to be an aquaculture vaccine vector in cellular level and zebrafish model. To further investigate the potential application of attenuated Lm in aquaculture vaccines, the outer membrane protein K (OmpK) from Vibrio parahaemolyticus (V. parahaemolyticus), as a conservative protective antigen, was fused to a new antigen-delivery system, and introduced into double-gene attenuated Lm strain (EGDe-ΔactA/inlB, Lmdd) to get live-vector vaccine strain Lmdd-OmpK. The strain Lmdd-OmpK showed the stable secrete efficacy of OmpK and was tested the cross-protective immunity against Vibrio species. After intraperitoneal administration in zebrafish, Lmdd and Lmdd-OmpK strain both improved the survival rates of zebrafish infected by V. parahaemolyticus, Vibrio alginolyticus (V. alginolyticus) and Vibrio anguillarum (V. anguillarum), respectively. In summary, attenuated Lm is able to protect zebrafish against Vibrio species challenge, illustrating its potential value for further aquaculture vaccines development.