TonB-Dependent Receptor Protein Displayed on Spores of Bacillus subtilis Stimulates Protective Immune Responses against Acinetobacter baumannii

The emergence of antibiotic-resistant Acinetobacter baumannii strains with limited treatment options has become a significant global health concern. Efforts to develop vaccines against the bacteria have centred on several potential protein targets, including the TonB-dependent receptors (TBDRs). In the present study, TBDRs from A. baumannii were displayed on the surface of Bacillus subtilis spores. The immunogenicity of the recombinant spores was evaluated in orally vaccinated mice. None of the immunized mice demonstrated signs of illness and were observed to be healthy throughout the study. Sera and the intestinal secretions from the recombinant spores-treated mice demonstrated mucosal and humoral antibody responses to the vaccine antigen. In addition, bactericidal activities of the sera against A. baumannii clinical isolates were demonstrated. These observations suggest that the B. subtilis spore-displayed TBDRs should be further explored as much-needed potential oral vaccine candidates against A. baumannii.