CHARACTERIZATION AND PATHOLOGICAL STUDY OF A. HYDROPHILA IN WALKING CATFISH (CLARIAS GARIEPINUS)
SRI LESTARI ANGKA
SRI LESTARI ANGKA
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Abstract
In this study, 18 strains of Aeromonas hydrophila had been isolated
from healthy and diseased fish and three other known strains of U14, TF7
and ATCC7966 were used for comparison. They were identified using LD50
determination, haemolytic activity, DNA-DNA hybridization and analysis of
their proteins by SDS electrophoresis. Their pathogenicity was studied in
fingerlings and adult walking catfish, Clarias gariepinus using three
different preparations of unwashed, washed or washed but sonicated
bacteria. The pathological effects of the virulent strain were also studied in
immunized fish or fish injected with immunostimulant, complete Freund's
adjuvant (CFA).
The results of this study indicated that the virulence of each isolated
Aeromonas hydrophila was different from one another, even though they
had the same biochemical characteristics. No specific characters could be
solely attributed to their virulence. Both virulent or avirulent strains were
able, in vitro, to lyse red blood cells not only from fish but also from some
terrestrial animals including man. They could grow in vitro at 37°C. This
suggests that Aeromonas hydrophila isolated from fish could possibly cause
zoonotic disease to other warm-blooded animals.
The results also showed that extracellular products (ECPs) of the
bacteria might play an important role in causing the disease that led to the
death of fingerlings and adult catfish.
The injection of the unwashed and sonicated bacteria caused the
total counts of the thrombocytes and monocytes in the blood to be higher
than those in the control fish or in fish injected with washed bacterial cells.
It is therefore concluded that the marked increase of thrombocytes and
monocytes in the blood could be due to the counter reactions of the fish
body towards the severe lesion and the haemorrhage caused by exotoxins
and endotoxins of the bacteria. On the other hand, blood lymphocytes and
granulocytes were lower than those of the control fish. The reasons of their
reduction were discussed.
This study also showed that fish immunized with low dose of virulent
strain of the bacteria with or without CFA or treated with CFA alone
exhibited no clinical signs of the disease that appeared in the bacteria-
injected control fish. This indicates that there is a possibility of preventing
the ulcerative disease caused by A. hydrophila via immunization or treated
with immunostimulants.
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Date
1998
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