Protective effects of chicken egg yolk immunoglobulins (IgY) against experimental Aeromonas hydrophila infection in blunt snout bream (Megalobrama amblycephala)

The emergence of multi antibiotic resistance by the pathogens and toxic impacts on host metabolism has opened new perspectives to rational novel vaccine techniques. Outbreaks of Aeromonas hydrophila in aquaculture caused high mortality throughout the world and resulted in the extensive economic loss in the aquaculture industry. In this study, we report the efficacy of anti-A. hydrophila IgY antibodies by passive vaccination and its prophylactic or therapeutic effects against A. hydrophila in blunt snout bream. Inactivated A. hydrophila immunized hens produced effective IgY antibodies that were stable at temperatures less than 60 °C or the pH value was >4. The specific IgY can be bound directly to A. hydrophila that efficiently agglutinated and inhibited the bacterial growth in a dose-dependent manner. The specific IgY had significantly enhanced the phagocytosis activity of macrophages and resulted in rapid bacterial clearance. Anti-A. hydrophila IgY antibodies significantly increased macrophage mediated respiratory burst, including nitric oxide and superoxide anion production and subsequently killed the pathogen. Histopathological studies of intestine and spleen from vaccinated blunt-snout bream challenged with A. hydrophila showed the structural integrity of the organs was maintained intact from the bacterial injury. In addition, the prophylactic and therapeutic immunization, protected the blunt snout bream and the survival is approximately about 60% and 50%, respectively. These data suggest that specific IgY has the potential for protecting blunt snout bream against A. hydrophila infection and show promise for the future development of harmless vaccines.