TOXICITY OF CRUDE EXTRACELLULAR PRODUCTS OF AEROMONAS-HYDROPHILA IN TILAPIA, TILAPIA-NILOTICA

Extracellular products (ECP) secreted from Aeromonas hydrophila with h aemolytic and proteolytic activity were studied with respect to temper ature and time of incubation as well as the lethal toxicity on tilapia , Tilapia nilotica. The highest production of the haemolysin product w as achieved when Aer. hydrophila was grown at 35 degrees C for 30 h. T ilapia erythrocyte was found to be more susceptible than sheep erythro cyte for determining the haemolytic activity. The haemolytic activity against tilapia erythrocyte was completely inactivated after heating t he ECP at 60 degrees C for 10 min or 55 degrees C for 15 min. The prot eolytic activity was maximized when the bacterium was grown at 30 degr ees C for 36 h. Complete inactivation of the protease enzyme was perfo rmed after heating the ECP at 80 degrees C for 10 min or 70 degrees C for 15 min. Aeromonas hydrophila was found to produce haemolytic and p roteolytic exotoxin lethal to tilapia (LD50 2.1 x 10(4) cell/fish), as well as heat stable unknown virulent factors that were responsible fo r 20% mortality. The lethality of ECP was decreased by heating and com pletely inactivated by boiling at 100 degrees C for 10 min.