Preparation Of Specific Egg Yolk Immunoglobulin(IgY) Against Fish Bacterial Septicemia-causing Aeromolla Hydrophila And Evaluation Of Its Properties

Aeromonas hydrophila is the most prevalent pathogen that causes Fish Systemic Bacterial Septicemia, which has limited the development of Chinese aquiculture seriously. IgY, which is refer to Egg yolk Immunoglobulins, are enriched in poultry egg yolk and always represent powerful bacteriostasis activity. IgY is characterized by its stable chemical property, non-inducing drug-resistant strains, and long distance for animal phylogenetic. The application of the IgY on the treatment of bacterial infectious disease has been reported.The objective of this study was to produce egg yolk immunoglobulin (IgY) against septicemia-causing A. hydrophila and evaluate its activity.Laying hens were immunized with formalin-killed A. hydrophila. IgY was purified from the water-soluble fraction by a combination of several purification techniques including salt precipitations and ultrafiltration. The purity of the IgY finally purified was 89.3% and the yield was 40.54 mg/egg. The highest titer of specific IgY determined by indirect enzyme-linked immunosorbent assay (ELISA) was 1:12800. IgY content (in WSF) measured by competitive ELISA was 9.47 mg/rnL. The inhibiting activity was dose-dependent and the growth of A. hydrophila was inhibited completely by specific IgY at the concentration of 75 mg/ml.In viral neutralization experiment by intramuscular injection, specific IgY against A. hydrophila could inhibit A. hydrophila to some extent.The mortality decreased apparently (40%).The effects of protection and treatment by IgY powder against A. hydrophila in the experiment ainimals were evaluated. In oral administration experiment, The effects of protection by IgY used before challenge and the effects of protection by IgY used after challenge were evaluated, those pre-fed a diet containing 5% IgY power of inactivated A. hydrophila showed mortalities of 50%, while those fed a diet containing 0.5% IgY power showed poor effect of treatment at mortalities of 80%. In immersion administration experiment, the effects of protection by IgY used before challenge and the effects of protection by IgY used after challenge were evaluated, the high concention (400mg/mL) pre-immersion group showed a mortality of 30%, and the mortality of treatment group by low concention immersion was 80%. In injection administration experiment, the effects of protection by IgY used before challenge and the effects of protection by IgY used after challenge were evaluated, the high concention (4mg/fish) pre-injected group showed a mortality of 50%, and the mortality of treatment group by low concention injection was 80%.These results have significantly differences compared to the positive control group which showed a mortality of 100%(P<0.05). The results suggested that passive and active immunization of specific IgY antibodies through oral administration, immersion and injection were effective to infected fish against A. hydrophila.In conclusion, the specific IgY preparation in this study can provide a novel approach to the prevention and treatment of A. hydrophila infection, which will have a industrial prospect.