Abstract
Egg yolk immunoglobulin Y (IgY) possesses advantages such as low cost, easy availability, simple preparation, high antigen specificity, absence of drug residues, and compliance with animal welfare standards, making it an environmentally friendly and safe alternative to antibiotics. This research utilizes IgY antibody technology to develop a multivalent passive immune vaccine for major pathogenic bacteria in aquaculture. In this study, IgY antibodies against live Shewanella xiamenensis (LSX-IgY) and inactivated S. xiamenensis (ISX-IgY) were prepared by immunizing laying hens, and passive immunization protection experiments were conducted in Carassius auratus infected with S. xiamenensis and Aeromonas hydrophila. The passive immunization protection rates of LSX-IgY and ISX-IgY against S. xiamenensis were 63.64% and 72.73%, respectively, and the passive cross-protection rates against A. hydrophila were 50% and 71.43%, respectively. Further, C. auratus sera could specifically bind to S. xiamenensis or A. hydrophila in vitro, and the phagocytic activity of leukocytes was increased. LSX-IgY and ISX-IgY could reduce the bacterial load in the C. auratus kidneys. Meanwhile, they could significantly reduce the levels of antioxidant factors in serum and inhibit the mRNA expression of inflammation-related factors in the kidneys and spleens. Additionally, histopathology and immunofluorescence analysis showed that both IgY preparations preserved tissue integrity and reduced the expression of apoptosis factor (p53) and DNA damage factor (γH2A.X) of visceral organs, respectively. In summary, LSX-IgY and ISX-IgY can combat various bacterial infections, with no significant difference between the two. Additionally, inactivated bacterial immunization is more aligned with animal welfare standards for laying hens. Therefore, ISX-IgY is expected to serve as a multivalent vaccine against major aquaculture pathogens.