EFFECT OF SERUM FACTORS ON THE SURVIVAL OF RENIBACTERIUM-SALMONINARUMWITHIN RAINBOW-TROUT MACROPHAGES

While the phagocytosis of Renibacterium salmoninarum by rainbow trout macrophages in vitro occurred in the absence of serum factors, opsoniz ed bacteria once phagocytosed survived for a longer period than bacter ia not exposed to serum. Immune sera favoured survival to a greater ex tent than non-immune sera. Although heat-inactivated immune sera reduc ed the extent of bacterial killing, bacterial persistence was enhanced to such an extent when both complement and antibodies were present, t hat opsonized bacteria grew faster within macrophages than extracellul arly. The effect of serum was observed following 16 h, but not 3 h, of prior exposure of the bacteria to serum, suggesting that opsonization per se was not the basis for improved survival, but that the serum in duced an adaptative change in the bacterium.