Provide immunity protection against Acinetobacter baumannii by exposed loops of BauA and Omp34 in a murine model
Provide immunity protection against Acinetobacter baumannii by exposed loops of BauA and Omp34 in a murine model
Zahra Akbari,1Iraj Rasooli,2,*Anthony B. Schryvers,3
1. 1 Department of Biology, Shahed University, Tehran-Iran 2. Molecular Microbiology Research Center and Department of Biology, Shahed University, Tehran-Iran 3. Department of Microbiology, Immunology and Infectious Diseases, Cumming School of Medicine, University of Calgary, Canada
Introduction: Acinetobacter baumannii causes a wide range of infections due to its persistence and ability to survive and adapt in the hospital environment. Due to the resistance of this bacterium to various drugs and its prevalence, basic strategies are needed for the prevention and treatment of related diseases. Omp34 is one of several pathogens of Acinetobacter baumannii that its important role in the pathogenesis and survival of this bacterium has been proven. According to studies and understanding the important role of protein BauA (Baumannii Acinetobactin Utilization), which is produced under iron deficiency conditions and is required for the transfer of acinetobactin (iron-containing siderophore) to bacterial cells, makes it necessary to use BauA and Omp34 to make vaccines.
Methods: By examining the BauA and Omp34 immunogenic regions, the loops with the highest bioinformatics immunogenicity scores were selected. Using a new hybrid antigen method in which superficial epitopes of the TbpA receptor protein from Neisseria meningitidis are displayed on the C-lobe of a TbpB surface lipoprotein called Loopless C Lobe or LCL. After designing specific primers from the desired genes and regions and gene amplification, for replication, the amplified fragment was treated with a vector in the desired enzymatic digestion reaction. Then, using ligase enzyme, the digested fragment was SOE-PCRed into the LCL at the designated position, and the resulting fragment was inserted into the expression vector. The recombinant proteins were expressed and purified using a Ni-NTA column. After the immunization of the laboratory animal, the production of antibodies against the recombinant proteins was assessed by indirect ELISA. The animal challenge was performed in active and passive immune groups and the survival of the challenged control and immunized mice were evaluated. The microbial load on lung, spleen, and liver organs was counted.
Results: The hybrid antigens produced in the cytoplasm of E. coli were expressed as soluble antigens. The antigens were used to immunize mice, followed by challenge trials with A. baumannii clinical isolate (ABI022). Mice immunized with the combination of BauA7 loop (BauAL7P3) and Omp34 loop 3 (Omp34 L3P1) provided a 71.43% survival rate against A. baumannii infection. Each single protein group showed 42.86% protectivity on the basis of survival rate. A significant reduction in microbial load was evident in the lungs, livers, and spleens of the immunized groups.
Conclusion: The results show that immunization with the immunogenic loops causes a strong protective reaction in the mouse model. The findings support the use of multiple antibodies to induce wider reactive antibody responses against heterogeneous strains of Acinetobacter baumannii.