INTERACTION OF THE FISH PATHOGEN AEROMONAS-HYDROPHILA WITH TILAPIA, OREOCHROMIS-AUREUS (STEINDACHNER), PHAGOCYTES

Interaction of Aeromonas hydrophila and tilapia, Oreochromis aureus (S teindachner), phagocytes was studied in vitro. All virulent and avirul ent strains of A, hydrophila tested could multiply in non-activated an d Freund's complete adjuvant activated phagocytes. Activated phagocyte s increased the uptake of bacteria into cells, and the rates of intrac ellular replication for these bacteria were faster than in non-activat ed phagocytes. Among the A. hydrophila strains examined, virulent stra in PPD 134/91 replicated at the fastest rate inside phagocytic cells a nd produced cytopathic effect in the phagocytes in the shortest incuba tion time. Opsonized avirulent A. hydrophila were sensitive to phagocy te-mediated killing or unable to grow in phagocytes. Serum components and phagocytes may together prevent the growth of avirulent A. hydroph ila in fish. The release of extracellular oxygen radicals during phago cytosis was examined using chemiluminescence assay (CL). Virulent stra ins induced CL responses but avirulent strains did not. This suggests that the virulent strains interacted with the phagocytes somewhat diff erently from the avirulent strains.