Immunoprotective characterization of egg yolk immunoglobulin raised to loop 3 of outer membrane protein 34 (Omp34) in a murine model against Acinetobacter baumannii

Acinetobacter baumannii is one of the most notorious nosocomial pathogens with high mortality rates. Recently, egg yolk antibody (IgY), has been considered as a promising biomolecule against pneumonia caused by this bacterium. Loop 3 of outer membrane protein 34 (Omp34) was predicted as a highly exposed immunogenic peptide. However, its immunogenicity remains to be experimentally elucidated. In the current study, a construct composed of 5 copies of loop3 of Omp34 labeled as Omp34L3X5 was designed. This construct as well as the recombinant Omp34 were expressed, purified, and injected into laying hens to raise specific antibodies. The specific IgYs were extracted from hyperimmune egg yolks. The Omp34L3X5 and whole cells (WC) of A. baumannii served as antigens in indirect ELISA to assess the purified IgYs reactivity. These antibodies were administered to neutropenic mice 1 h before the challenge with 10 × LD 50 of a clinical isolate of A. baumannii. The specific IgYs recognized recombinant Omp34 (P < 0.0001) as well as WC of A. baumannii (P < 0.05). The survival rate of mice that received anti- Omp34L3X5 or anti-Omp34 IgYs was 83.33 % and 100 % respectively. All control mice died within 24 h while mice that received non-specific IgYs died within 72 h. After 24 h, bacterial load in the lung of mice received non-specific IgYs, anti-Omp34L3X5 or anti-Omp34 IgYs were 2.03 × 10 8, 2.2 × 10 8, and 1.93 × 10 8 CFU/organ respectively. Bacterial load in the spleen of mice received non-specific IgYs, anti-Omp34L3X5 or anti-Omp34 IgYs were 1.03 × 10 8, 7.8 × 10 7, and 6.3 × 10 7 CFU/organ respectively. Bacterial load in lung and spleen of control mice were 3.03 × 10 9 and 1.45 × 10 8 CFU/organ respectively.