Potential use of chitosan nanoparticles for oral delivery of DNA vaccine in black seabream Acanthopagrus schlegelii Bleeker to protect from Vibrio parahaemolyticus.

To develop an effective and easy-to-administer vaccine against vibriosis of fish, the chitosan nanoparticles-loaded DNA vaccine against Vibrio parahaemolyticus was studied. A DNA vaccine was constructed using the outer membrane protein K (ompK) gene of V. parahaemolyticus strain (OS4) and pEGFP-N2 , a eukaryotic expression vector, and the construct was named pEGFP-N2 -OMPK (pDNA). The pDNA was encapsulated in chitosan particles (chitosan/pDNA). The effective diameter, mean diameter and polydispersity of the particles were 284.4 nm, 218.9 nm and 0.160, respectively. Scanning electron microscopy showed that the particles are dispersed as individual nanoparticles with spherical shape of around 200 nm and are homogeneously distributed. Encapsulation efficiency and loading percentage of nanoparticles were 91.5% and 2.08%, respectively. Reverse transcription-polymerase chain reaction (RT-PCR) showed that RNA-containing information of the ompK gene existed in mid-intestine, liver, kidney and muscle 3 weeks after oral administration in black seabream Acanthopagrus schlegelii Bleeker. Expression of the reporter gene, green fluorescent protein (GFP), was observed in the above-mentioned tissues by fluorescence microscopy. Expression of the ompK gene within 3 weeks evoked an immune response. Black seabream was protected from V. parahaemolyticus (OS4), with 72.3% relative percentage survival (RPS) 3 weeks post-vaccination with chitosan/pDNA. The direct agglutination test indicated that oral administration with chitosan/pDNA induced an antibody immune response in fish against V. parahaemolyticus (OS4). Data obtained, here and in other related studies, suggest that chitosan nanoparticles are promising carriers for an oral pDNA vaccine.