The Passive Immunoprotective Activity Using Egg Yolk IgY Antibodies of Live or Inactivated Aeromonas veronii Against Major Pathogenic Bacteria (A. veronii and A. hydrophila) in Fish.

Egg yolk immunoglobulin Y (IgY) has significant application potential in aquaculture as passive immunotherapy against various bacterial infections owing to its capacity for large-scale and cost-effective production. In this study, IgY antibodies of live or inactivated Aeromonas veronii were generated by laying hens immunization. Subsequently, passive immune protection experiments of the two IgY antibodies were conducted on goldfish (Carassius auratus) infected with A. veronii and Aeromonas hydrophila. The results indicated that both live and inactivated bacteria IgY antibodies provided significant passive protection rates (p < 0.05). Furthermore, ELISA tests demonstrated that the two IgY antibodies, as well as the serum of C. auratus, interacted with A. veronii or A. hydrophila (p < 0.05) in vitro. The bacterial loads in the kidneys of C. auratus immunized with the two IgY antibodies were decreased (p < 0.05), and C. auratus phagocytes had enhanced phagocytic activity. The expression levels of antioxidant factors (SOD, CAT, GSH-Px) and inflammatory factors mRNA (TNF-α, IL-1β, IL-6, IL-8) were down-regulated (p < 0.05). Additionally, histopathological analysis indicated that the renal, splenic, and intestinal tissue structures remained intact, and the immunofluorescence confirmed that apoptosis and DNA damage factors of p53 and γH2A.X reduced (p < 0.05), respectively. Thus, the IgY antibodies of live and inactivated A. veronii exhibit passive immune-protective effects against different pathogenic bacteria in C. auratus. Further, inactivated A. veronii immunization causes less damage to laying hens than that of live bacteria, which aligns more closely with welfare standards for laying hens, and the IgY of inactivated A. veronii is anticipated as a cross-protection against A. veronii and A. hydrophila infections in aquaculture.