Nasim Arshadi - Department of Biology, Faculty of Basic Sciences, Shahed University, Tehran, Iran
Seyed Latif Mousavi Gargari - Department of Biology, Faculty of Basic Sciences, Shahed University, Tehran, Iran
Jafar Amani - Applied Microbiology Research Center, Systems Biology and Poisonings Institute, Baqiyatallah University of Medical Sciences, Tehran, Iran
Shahram Nazarian - Department of Biology, Imam Hussein University, Tehran, Iran

Objective(s): Vaccination using inactivated bacteria is one of the most effective ways to protect against EHEC infection. Escherichia coli O۱۵۷:H۷ infections are mainly influenced by Shiga toxins (Stx) and attaching/effacing factors. Among various factors, Stx۲B is gaining much attention as a vaccine candidate. Formulating an inactivated bacteria with a suitable adjuvant increases vaccine efficacy and antibody production and can lead to a lasting immune response and protection against O۱۵۷:H۷. Materials and Methods: To assess vaccine efficacy, in this study, we have considered heat and formalin-inactivated bacteria along with chitosan-coated Stx۲B/ Stx۲B in a mouse model. Ionotropic gelation via tripolyphosphate anions was used to coat Stx۲B on chitosan. Subcutaneous injection or oral gavage was used to immunize mice, which were then challenged with E. coli O۱۵۷:H۷. Results: Immunity and protection against E. coli  O۱۵۷:H۷ were achieved by all forms of the vaccine. Inactivated E. coli  O۱۵۷:H۷ formulated with chitosan-coated Stx۲B effectively evoked humoral and mucosal immune responses. However, minimum shedding appeared with the mice groups orally immunized with formalin-inactivated bacteria sublimated with chitosan-coated Stx۲B and heat-inactivated bacteria plus Stx۲B in subcutaneous immunization.Conclusion: Administration of inactivated whole-cell and toxin was synergistic and increased the protection capacity with both parenteral and oral immunization routes.

Chitosan, Escherichia coli O۱۵۷:H۷, Inactivated vaccine, Oral vaccine, Shiga toxin