Efficacy of inactivated Aeromonas hydrophila vaccine with a new biodegradable material adjuvant in Carassius auratus gibelio by immersion immunization

Castor oil polyethylene glycol monoester glucoside (CPMG) is a kind of biodegradable and artificial material. Formalin-inactivated Aeromonas hydrophila bacteria with or without CPMG, CPMG + anisodamine mixture were administered on days 1 and 7 to Carassius auratus gibelio through immersion. Spleens were sampled on days 2, 4, 7, 11, 14 and 21 post-second vaccination, and the expression quantities of IgM, IL-1β, C3, C-lectin and lysozyme mRNAs in spleen were detected through the real-time fluorescence quantitative PCR (RT-PCR). Formalin-inactivated A. hydrophila vaccine with CPMG + anisodamine mixture was immersion administered just once, then, specific antibodies were detected and the fish were challenged intraperitoneally with lethal A. hydrophila at different time post-vaccination. The results of vaccination twice showed that fish immunized with inactivated A. hydrophila vaccine and CPMG exhibited enhanced expression of genes that are involved in both innate and adaptive immune responses (IgM, IL-1β, C3, C-lectin and lysozyme) compared to no adjuvant control or saline control. The relative percent survival (RPS) was found to be 70.6% on day 30 post-vaccination, while immunization with the antigen alone followed by an experimental challenge gave an RPS of 56.0%, moreover, the CPMG + anisodamine coupled vaccine showed an RPS of 88.2%.The results of vaccination just once showed that the CPMG + anisodamine coupled vaccine could augment the production of specific serum antibodies, which reached the highest level 6 weeks post-vaccination. The resulting RPS calculated was 54.6%, 44.0% and 12.5% on days 30, 60, 120 post-vaccination, respectively. These results indicate that formalin-inactivated A. hydrophila vaccine with CPMG immersion administered to gibel carps can significantly promote the gene expression of IgM, IL-1β, C3, C-lectin and lysozyme in spleen and enhance specific immune responses against A. hydrophila infection.