Development of chicken egg yolk antibodies (IgY) aginst aeromonas hydrophila and Its effect on disease control In farmed fishes

Abstract

Aeromonas hydrophila, the causative agent of Motile Aeromonas Septicemia (MAS), has emerged as a major threat to aquaculture because of high fish mortality, economic losses, and the increasing prevalence of antimicrobial resistance resulting from excessive antibiotic use. The present study aimed to develop, characterize, and evaluate chicken egg yolk immunoglobulin Y (IgY) antibodies against A. hydrophila and to investigate their prophylactic and therapeutic potential for controlling bacterial infections in cultured fish. Specific IgY antibodies were produced by immunizing White Leghorn hens with formaldehyde-inactivated A. hydrophila. The antibodies were extracted from egg yolks using polyethylene glycol (PEG) and ammonium sulphate precipitation and purified by DEAE cellulose ion-exchange chromatography. SDS-PAGE analysis revealed a distinct protein band at approximately 180 kDa, confirming the purity and structural integrity of IgY. The average IgY yield was 11.88 mg/mL, of which 26% was antigen-specific. Indirect ELISA demonstrated a high antibody titre of 1:10,000, indicating successful production of highly specific antibodies against A. hydrophila. The biological activity of purified IgY was evaluated through a series of in vitro assays. IgY effectively inhibited the growth of A. hydrophila and exhibited cross-reactivity with Aeromonas caviae. In combination with ciprofloxacin and chloramphenicol, IgY showed synergistic activity, with Fractional Inhibitory Concentration Index (FICI) values below 0.5, suggesting enhanced antibacterial efficacy and reduced antibiotic dependence. The antibodies retained substantial antigen-binding activity over a wide pH range (3-10), remained stable at temperatures up to 70°C, and maintained functional activity under different molar concentrations and in the presence of ethanol, methanol, and isopropanol. The protective efficacy of IgY was further assessed through in vivo challenge studies using grass carp (Ctenopharyngodon idella) experimentally infected with A. hydrophila. Following determination of the pathogen LC₅₀, IgY-coated feed was evaluated under pathogen-neutralization, therapeutic, and prophylactic treatment regimes. Oral administration of IgY significantly improved fish survival, with survival rates of 70%, 60%, and 80% in the neutralization, therapeutic, and prophylactic groups, respectively. Histopathological examination revealed markedly reduced tissue damage, inflammatory cell infiltration, necrosis, and epithelial degeneration in IgY-treated fish. The use of IgY-coated feed offers a practical strategy to enhance fish survival, reduce antibiotic usage, and promote sustainable aquaculture production.