Immunization with a combination of Bap and Oma۸۷ protectsmice against Acinetobacter baumannii infection in a murine model

Background and Aim : In recent years, persistent outbreaks in hospital environments caused bymultidrug-resistant strains have been making a health crisis worldwide. It is important that newapproaches are developed to prevent or treat the infections caused by multi-drug-resistant strains.Immunological strategies such as active and passive immunization approaches could be considerednew vital options. A surface protein commonly known as biofilm associate protein (Bap) has beenidentified in a bloodstream isolate of A. baumannii. Bap A. baumannii is involved in intercellularadhesion within the mature biofilm. Bap-related proteins are present on the bacterial surface andconfer upon bacteria the capacity to form a biofilm, show a high molecular weight, contain a coredomain of tandem repeats, and play a relevant role in bacterial infectious processes. Oma۸۷ orBamA (β-barrel assembly machinery) has been introduced as an immunogenic outer membrane β-barrel assembly protein via reverse vaccinology by in silico analysis. The easy acquisition ofresistance to antimicrobial agents in this organism leads to the failure of the therapeutic regimens.However, the protectivity of A. baumannii Oma۸۷ is not well known. Some physicochemicalproperties were assessed via in silico analyses. The current research undertakes a study on theimmunogenicity of recombinant Oma۸۷ and Bap in a murine model.Methods : The recombinant proteins were purified and then administered to mice. The titer of IgGantibodies was measured by the indirect ELISA method. We monitored the survival rate inneutropenic mice for ۵ days. The intraperitoneal challenge was done with A. baumannii ۱۹۶۰۶ inimmunized mice and the number of bacteria counted in the spleen, liver, and lungS of the controland test mice groups.Results : IgG level was significantly increased at ۱:۱۲۸,۰۰۰ dilution in immune mice sera. A hightiter of a specific antibody was achieved against rOma۸۷ even after the first injection. A substantialdifference was observed between bacterial counts in the organs of test and control mice afterintraperitoneal challenge with A. baumannii ۱۹۶۰۶.Conclusion : Based on these results, Oma۸۷ and Bap could be considered a promising vaccinecandidate against A. baumannii.