Background and purpose: Different genera of enterobacteriaceae have important roles in gastrointestinal diseases such as diarrhea. Among these, Enterotoxigenic E. coli (ETEC), enterohemorrhagic E. coli (EHEC), and Shigella are three main bacteria which are transmitted via contaminated food and water. Vaccination is a good strategy to combat these pathogens. In the present study, a chimeric antigen, containing the main antigens of these three bacteria was designed, expressed in E. coli host, and tested for protection against EHEC strain.
Materials and methods: Specific primers were designed to fuse these antigens. The properties of the chimeric antigen, including physical and chemical properties, secondary and tertiary structures, and B cell and T cell epitopes were obtained via in silico analysis. After the fusion of the genes, the resulting recombinant pET28a(+) vector was transferred into the competent E. coli cells. Expression was induced and the protein was purified. Then, the animals were immunized through subcutaneous administration of the antigen. Finally, the immunized animals were challenged by live E. coli O157:H7 cells.
Results: In silico analysis showed that the chimeric antigen had appropriate physical and chemical properties which could be expressed in various expression systems.  In addition, the antigen has potent B- and T-cell epitopes. Experimental results showed that the antigen has efficiently provoked the mice's humoral immune system. Challenging the immunized mice by live bacterial cells showed that the chimeric antigen was able to protect the mice against E. coli O157:H7 strain.
Conclusion: Both in silico analysis and experimental results showed that the chimeric antigen has appropriate properties which can be considered as a proper candidate vaccine against the three bacteria mentioned.