Identification of polyvalent passive vaccine candidates from egg yolk antibodies (IgY) of important outer membrane proteins of Aeromonas hydrophila in fish

The antibodies of outer membrane proteins (OMPs) of bacteria have application value in polyvalent passive vaccines. IgY antibodies can be obtained in large quantities and economically from egg yolk, and have the potential to be applied in aquaculture. The OMPs (OmpAII, OmpW, P5, and Slp) of Aeromonas hydrophila were expressed and purified, and the corresponding IgY antibodies were prepared. Passive immunization to goldfish (Carassius auratus) indicated that the four IgY antibodies had an effective immune protection rate, could activate the innate immune responses, down-regulated the expression of inflammation-related genes (p < 0.05) to reduce inflammatory reactions, down-regulated the expression of antioxidant-related factors (p < 0.05) to reduce antioxidant reactions, protected the integrity of visceral tissue structure, and reduced apoptosis and DNA damage for kidney cells infected by A. hydrophila and Pseudomonas fluorescens. Moreover, the IgY passive (A. hydrophila) and passive cross-protective (P. fluorescens) abilities of OmpW and Slp were higher than those of OmpAII and P5. Thus, the IgY antibodies of OmpW and Slp can be considered as polyvalent vaccine candidates for passive immunization in aquaculture.