Egg-yolk antibodies raised to VacJ passively immunize mice against Acinetobacter baumannii pneumonia in a neutropenic murine model

There is no effective antibiotic against emerging highly resistant Acinetobacter baumannii strains, and there is a need for alternative treatment options. Egg-yolk antibodies (IgYs) are the avian equivalent of mammalian IgG that could confer passive protection against various infections. VacJ is a virulence factor of the pathogen in the lungs. In addition, previous studies have shown that immunization of mice with this antigen resulted in decreased bacterial burden in the lung. Hence, it could be a suitable antigen to achieve protective IgYs. In the current study, the recombinant VacJ was expressed, purified, and administered to laying White Leghorn hens followed by IgY extraction from egg yolks. Indirect ELISA showed maximum IgY titers against VacJ raised two weeks following the last immunization. The immunoprotective effects of IgYs were investigated in neutropenic mice. The mice received intranasal IgYs one hour before the nasal instillation of the 10 ×LD50 with a clinical isolate of A. baumannii. A significant reduction in bacterial population loaded in the lungs and spleen was noted. A 100% survival was recorded in the group receiving anti-VacJ antibodies. The results indicate that VacJ is a good immunogen for the production of anti-A. baumannii IgY.