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 <i>Aeromonas veronii</i> were generated by laying hens immunization. Subsequently, passive immune protection experiments of the two IgY antibodies were conducted on goldfish (<i>Carassius auratus</i>) infected with <i>A. veronii</i> and <i>Aeromonas hydrophila</i>. The results indicated that both live and inactivated bacteria IgY antibodies provided significant passive protection rates (<i>p</i> < 0.05). Furthermore, ELISA tests demonstrated that the two IgY antibodies, as well as the serum of <i>C. auratus</i>, interacted with <i>A. veronii</i> or <i>A. hydrophila</i> (<i>p</i> < 0.05) in vitro. The bacterial loads in the kidneys of <i>C. auratus</i> immunized with the two IgY antibodies were decreased (<i>p</i> < 0.05), and <i>C. auratus</i> 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 (<i>p</i> < 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 (<i>p</i> < 0.05), respectively. Thus, the IgY antibodies of live and inactivated <i>A. veronii</i> exhibit passive immune-protective effects against different pathogenic bacteria in <i>C. auratus</i>. Further, inactivated <i>A. veronii</i> 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 <i>A</i>. <i>veronii</i> is anticipated as a cross-protection against <i>A. veronii</i> and <i>A. hydrophila</i> infections in aquaculture.