Chitosan-based nanoparticles encapsulating Nocardia seriolae lysates confer protection against nocardiasis through immersion vaccination in Micropterus salmoides

Development of effective vaccines with convenient administration, including oral immunization or immersion, to control pathogens is important for the sustainability of aquaculture. Nocardia seriolae was found to harm over 40 types of cultured marine and freshwater species, especially in Micropterus salmoides and Channa argus , causing more than 30% mortality. In this study, a novel isolate of N. seriolae (B20200724) growing fast and manifesting comparative virulence with other N. seriolae was identified from diseased M. salmoides . Chitosan-based nanoparticles encapsulating whole-cell lysates of N. seriolae B20200724 with great mucoadhesive features were prepared for evaluation of the protective effect against N. seriolae in M. salmoides . Chitosan-based nanoparticles via immersion vaccination boost the innate immune response, elicit the expression of Th2 cytokines and high-titer antibody responses, ultimately conferring a 45% relative protection rate against N. seriolae infection. These findings provide a novel vaccine candidate and verify a convenient immunization route, which promotes the potential of the vaccine against fish nocardiosis for commercial use.