The role of specific antiserum of catfish, Clarias gariepinus, as a defence against Aeromonas hydrophila

Catfish (Clarias gariepinus) were vaccinated against a virulent (PPD 134/91) and an avirulent strain (L37) of formalin-inactivated Aeromonas hydrophila. The specific antiserum against the avirulent strain, in. vitro, showed a significant inhibition in the growth of the avirulent strain as compared to that treated with control serum. In contrast, no significant difference was found in the growth rate of the virulent strain (PPD 134/91) which was treated with either the specific antiserum or control serum. The specific antibodies against PPD 134/91 showed an increased opsonizing effect. However, opsonization did not enhance the bactericidal activity of phagocytic cells against the virulent strain. The specific antiserum did not show any opsonizing effect on the serologically different virulent strain (PPD 122/91). The specific antiserum against PPD 134/91 could inhibit, in vitro, the invasive ability of the same virulent strain of A. hydrophila to epithelial cells. However, no significant protection was encountered in naive fish when they were intramuscularly injected with the virulent strain of A. hydrophila pretreated with the specific antiserum. Hence, the present in vitro findings suggest that the specific antiserum in the mucus might play an important role in fish disease resistance by preventing serologically similar virulent strains of A. hydrophila from attaching and penetrating into the integument at the initial stage of infection. (C) 1996 Academic Press Limited