Interaction between rainbow trout macrophages and Renibacterium salmoninarum in vitro.
The ability of several strains of R. salmoninarum to resist killing by rainbow trout macrophages for different periods of time was evaluated. Both virulent and avirulent strains survived and possibly multiplied within the phagocytic cells for 3-4 days, but thereafter a decrease in the number of viable bacteria occurred. The superoxide anion response of macrophages to stimulation by phorbol myristate acetate (PMA) was greatly reduced by the presence of R. salmoninarum. However, even though the macrophages were unable to kill R. salmoninarum before day 5 post-infection, the ability of these infected macrophages to kill Aeromonas salmonicida was still present, although impaired. The results suggest that mechanisms other than the superoxide anion-mediated bactericidal system are important in killing R. salmoninarum.