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Edwardsiella trada (E. tarda) and Aeromonas hydrophila (A. hydrophila) were cultured in brain heart infusion agar plate at 37 ·c for 18 hrs. respectively. The bact erial cells were harvested and washed with phosphate buffered saline (PBS-). Then the concentration was adjusted to 4-5x 1010 CFU/ml. after bacterial suspension was inactivat-ed with 0.3 % Formalin. An equal volume of the suspensions of E. tarda and A. hydrop-hila were combined. Finally. 10 % volume of the Aluminum hydroxide gel (33 mg/ml) was added as adjuvant.
As for the safety test of the combined bacterin. the administrations of 0.5 ml each to 10 mice subcutaneously and 1.0 ml each to 10 eels intramascularly were made. No side reaction was observed. In the potency test the mice were challenged with E. tarda. A. hydrophila and its combination, the protection indexes of 101 .94 (87.1), 10192 (83.1) and 102·06 (114.8), respectively, were obtained.
Forty eight percent (17/35) of the eels showed positive agglutination titer against E. tarda. when 1.0 ml each was inoculated IM. The titer ranged from 1 : 80 to 1 : 320, with a maximum of 1 : 1,280. The figue for A. Hydrophila 51.4 % (18/35). But the titer ranged rather low. in between 1 : 20 and 1 : 40, with a maximum of l : 80. It indicated that the combination bacterin has practical values for the control of both Edwardsiellosis and Red fin disease of eel.
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