Modulation of the immune response to an Aeromonas hydrophila aroA live vaccine in rainbow trout: effect of culture media on the humoral immune response and complement consumption

The Aeromonas hydrophila aroA is an attenuated strain that has been assessed as a live vaccine in rainbow trout, Oncorhynchus mykiss. In this study the effects of different culture media used to grow the strain on its survival after in vitro exposure to rainbow trout serum, and on its immunogenicity in rainbow trout were compared. Four culture media were tested: Luria broth (LB), Luria broth with 0.25% glucose, trypticase soy broth (TSB), and brain-heart infusion broth (BHIB). Bacteria grown in culture media with glucose (TSB, BHIB and LB with 0.25% glucose) showed reduced complement consumption and a lower serum susceptibility. O. mykiss vaccinated with inocula prepared with BHIB- and LB-grown aroA cells resuspended in phosphate-buffered saline (PBS) showed higher and longer-lasting serum agglutinating antibody titres than those vaccinated with TSB-grown bacteria. Thus, a direct relationship between serum resistance and immunogenicity could not be established, but BHIB and LB culture media were the most effective in increasing the immunogenicity of the A. hydrophila aroA vaccine.