Distribution and retention of antigens of Aeromonas salmonicida in Atlantic salmon (Salmo salar L.) vaccinated with a ΔaroA mutant or formalin-inactivated bacteria in oil-adjuvant

In this study we report the differences in distribution and retention of Aeromonas salmonicida antigens after vaccination with two different vaccines. Parr of Atlantic salmon (Salmo salar) were given intraperitoneal injections of either a commercial, monovalent furunculosis vaccine (Apoject) or live, attenuated A. salmonicida (ΔaroA). Fish were sampled at weeks 2, 4 and 12 post-vaccination and head kidney and spleen were collected. Presence of LPS and 16S rDNA in isolated leukocytes were investigated by immunocytochemistry and polymerase chain reaction (PCR). NA was detected in head kidney and spleen of all ΔaroA vaccinated and most Apoject-vaccinated fish at weeks 2 and 4. At week 12, 16S rDNA was detected in none of the ΔaroA vaccinated fish, but it was detected in head kidney of 75% of Apoject-vaccinated fish. LPS was detected in both vaccination groups at all sampling times, but most frequently in the ΔaroA vaccinated fish (in head kidney 75–83% vs. 50%, in spleen 58–67% vs. 17–25%).