Toxicity evaluation of recombinant Fim-C Salmonella typhi Protein on ddY Mice for Typhoid Vaccine Development

Abstract Background: Typhoid fever is caused by Salmonella typhi infection, commonly occurs in developing countries from bad sanitation and living conditions. Vaccination against the fever has been developed by means of induction of antibody through introduction of Fim-C, one of the virulence factor proteins on the cell surface of the bacterium. Recently, we have cloned and overexpressed the protein in Escherichia coli . The 31 kDa recombinant Fim-C induced immune response upon introduction to ddY mice at a concentration of 40-60 µg/mL, indicating its potency as an anti-typhoid fever vaccine candidate. Objective: In this study, the safety of the protein was evaluated through abnormal and acute toxicity test in ddY mice, as well as determine its lethal dose (LD50). Methods: Forty of equal number male and female mice were recruited and observed according to the physiology, body weight and temperature, and mortality rate was performed on fourteenth days after immunization. Results: No abnormalities were observed at 25 µg/mL while 60% mortality occurred at 125 µg/mL. The latter observation correlates with our finding that the LD50 of the recombinant Fim-C was 123.5 µg/mL. Conclusion: Our results suggest that the recombinant Fim-C protein is safe for use as anti typhoid fever vaccine.