Assessment of Mouse Ileal loop Protection against Clinically Isolated Vibrio cholerae Outer Membrane Vesicles as a Vaccine Candidate

Cholera, a life-threatening disease caused by the Gram-negative bacterium Vibrio cholera, remains a concern in developing countries. The present study investigated the immunogenicity and protective immunity of outer membrane vesicles (OMVs) and combination of OMV and killed whole cells (WC) of a local strain isolated from the last outbreak in Iran in addition to reference and local strains of V. cholerae El Tor O1 in comparison to Dukoral vaccine in mice model. The protein content, morphology, and size of extracted OMVs were evaluated by electrophoresis and microscopic analyses, respectively. The serum titers of total immunoglobulin G (IgG), IgG1, IgG2a, and immunoglobulin A (IgA) in addition to secretory IgA and total IgG in different mice groups were determined by enzyme-linked immunosorbent assay (ELISA). In addition, fluid accumulation (FA) assay regarding the resistance to live strain of V. cholerae in ligated ileal loops was carried out to determine immunogenicity by OMV or combination of OMV and WC in comparison to that reported for Dukoral vaccine. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of purified OMVs indicated protein profiles within the range of 34-52 kDa. Furthermore, transmission electron microscopy demonstrated the spherical shaped vesicles of 50-200 nm. The results of ELISA showed significant titers of systemic and mucosal immune anti-OMV IgGs in immunized BALB/c mice with different vaccine regimens. Additionally, a notable increase in the FA ratio was demonstrated in this study. The obtained results of the present study revealed that the WC-OMV combination of local strain can induce a high level of antibody response indicating more protection than OMV or WC separately. Moreover, it can be considered an effective immunogen against V. cholerae.