In vitro immunopathogenesis of Edwardsiella tarda in catla Catla catla (Hamilton)

Immunopathogenesis of Edwardsiella tarda in Catla (Catla catla) was evaluated by in vitro interaction of catla head kidney (HK) phagocytes with the bacterium. Interactions of E. tarda with catla HK phagocytes were studied by light microscopy as well as by phagocytosis, intracellular replication, superoxide anion and nitric oxide production assays. Both opsonised and non-opsonized bacteria could adhere to, survive and replicate within phagocytes. Furthermore, there was no significant alteration in superoxide anion production by phagocytes when infected with E. tarda, indicating that they were able to avoid and/or resist reactive oxygen species mediated killing by the phagocytes. Enhancement of nitric oxide production indicated its possible involvement as inflammation mediator to facilitate pathogenesis. The results suggest the fact that E. tarda strain has the ability to resist phagocyte mediated killing, thereby proliferating within the host and causing infection.