IN-VITRO KILLING OF PASTEURELLA-PISCICIDA BY FISH MACROPHAGES

The capacity of Pasteurella piscicida strains to survive contact with macrophages obtained from rainbow trout Oncorhynchus mykiss, sea bass Dicentrarchus labrax and gilthead sea bream Sparus aurata was evaluate d using an in vitro assay. Both virulent and avirulent isolates were k illed by all the macrophages tested after 3 and 5 h incubation. The in creased production of superoxide anion (O-2(-)) by rainbow trout macro phages infected with P. piscicida coinciding with the highest bacteric idal activity (5 h incubation) suggests that the O-2(-) could be invol ved in the killing of P. piscicida. Bactericidal activity of cell-free generated O-2(-) confirms this hypothesis, although this indicates th at some other microbicidal factors must also contribute to the killing of P. piscicida by fish macrophages.