Design and Production of Engineered Sta Toxin as a Vaccine Candidate Against Enterotoxigenic Escherichia coli

Introduction: Enterotoxigenic E. coli (ETEC) is one of the major causes of watery diarrhea outbreaks in children under five years of age and passengers in developing countries. The pathogenicity of ETEC is due to the secretion of Colonization factors (Cfs) and two enterotoxins including heat-labile (Lt) and heat-stable (St). Although diarrhea is considered as one of the causes of mortality in developing countries, no approved vaccine is available for the disease caused by ETEC. Accordingly, the objective of the present study was to design a vaccine candidate containing Sta toxin which accounts for 30-75% of ETEC species. Materials and Methods: A chimeric construct consisting of two Sta toxoid connected together by two linkers was designed. After expression and purification by Ni-NTA column, western blotting was performed to confirm the protein. The 2Sta protein was administered to BALB/c mice via injection and the serum and fecal antibodies titer was evaluated by the ELISA test. Results: The recombinant 2Sta protein was expressed in an insoluble form (inclusion body) and the 20 kDa band was observed on the SDS-PAGE 12%. The results of the ELISA test suggested that IgG and IgA antibodies had enhanced compared to the control group. Conclusions: The Sta protein which was produced in most ETEC species can be induced in the immune system and raised the serum and fecal antibodies. Using this candidate subunit vaccine could actually protect bacterial infection.