Immunogenic potential of inactivated Aeromonas hydrophila encapsulated in nanochitosane/sodium alginate microspheres for oral vaccination of rainbow trout (Oncorhynchus mykiss)

Abstract

Due to the antigenic degradation and instability, the use of oral vaccines in fish has several limitations. The immunogenic potential of chitosan in several fish species has been reported. The current study aimed to prepare and characterize an inactivated A. hydrophila vaccine encapsulated in nanochitosane/sodium alginate microspheres for oral vaccination of rainbow trout (Oncorhynchus mykiss). Chitosan nanoparticles were synthesized and characterized using scanning electron microscopy, zeta potential and DLS analyses. Inactivated A. hydrophila bacteria and nanochitosan were encapsulated in alginate microcarriers. Five vaccination trials including (a) whole cells+nanochitosan (WC+NCS), (b) WC+alginate, (c) NCS+alginate, (d) WC+NCS+Alg and (e) control were conducted. Haematologic and immunologic analyses in vaccinated and control fish were investigated on the days 25 and 40 post-vaccination. Then, the efficacy of the vaccines was investigated by experimental infection assay. The highest IgM level, lysozyme activity, ACH50 and intracellular respiratory burst activity were observed among the fish vaccinated with NCS+WC encapsulated in sodium alginate, which was significantly higher than other treatments. Major haematological parameters were not significantly different among different groups except for the WBC count which was higher in the NCS+WC+Alg group. After the experimental challenge of treated fish with pathogenic A. hydrophila, the highest mortality was observed among control (90%) and NCS+Alg (70%) treated fish while the WC+NCS+Alg vaccine caused only 50% of mortality, which was significantly lower than other treatment groups. This study introduced the WC+NCS encapsulated in alginate as a promising oral vaccine to be used against Motile Aeromonas Septicemia in rainbow trout.