Ah. Khalil et Eh. Mansour, TOXICITY OF CRUDE EXTRACELLULAR PRODUCTS OF AEROMONAS-HYDROPHILA IN TILAPIA, TILAPIA-NILOTICA, Letters in applied microbiology, 25(4), 1997, pp. 269-273
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.