The non-specific immunostimulation and adjuvant effects of Vibrio anguillarum bacterin, M-glucan, chitin and Freund's complete adjuvant against Pasteurella piscicida infection in yellowtail

Abstract

The non-specific immunostimulation and adjuvant effects of Vibrio anguillarum bacterin (VAB), M-glucan, chitin and Freund's complete adjuvant (FCA) against pasteurellosis were examined in yellowtail, Seriola quinqueradiata. Control fish were injected intraperitoneally with 0.1 ml of sterile phosphate buffered saline (PBS). Experimental fish were injected similarly with either vaccine (lipopolysaccharide-mixed chloroform-killed Pasteurellapiscicida, LPS-CKC), an immunostimulant or mixture of the vaccine and an immunostimulant. All fish were subsequently challenged by the same but live P. piscicida strain using an immersion method at 15, 25, 35 and 45 days post-inoculation. Immunostimulants alone were found to slightly increase the protection against Pasteurella infection, but the effects were not statistically significant. The most effective adjuvant was FCA, however the enhanced protection was not statistically different from that of fish inoculated with LPS-CKC alone. However, the relative percent survival (RPS) of fish vaccinated with M-glucan, chitin or Vibrio bacterin as adjuvant was lower than that of fish vaccinated with only LPS-CKC bacterin alone. Thus, M-glucan, chitin and Vibrio bacterin had no positive adjuvant effects on the P. piscicida vaccine.