A newly developed oral infection mouse model of shigellosis for immunogenicity and protective efficacy studies of a candidate vaccine

<i>Shigella</i> infection poses a significant public health challenge in the developing world. However, lack of a widely available mouse model that replicates human shigellosis creates a major bottleneck to better understanding of disease pathogenesis and development of newer drugs and vaccines. BALB/c mice pre-treated with streptomycin and iron (FeCl₃) plus desferrioxamine intraperitoneally followed by oral infection with virulent <i>Shigella flexneri 2a</i> resulted in diarrhea, loss of body weight, bacterial colonization and progressive colitis characterized by disruption of epithelial lining, loss of crypt architecture with goblet cell depletion, increased polymorphonuclear infiltration into the mucosa, submucosal swelling (edema), and raised proinflammatory cytokines and chemokines in the large intestine. To evaluate the usefulness of the model for vaccine efficacy studies, mice were immunized intranasally with a recombinant protein vaccine containing <i>Shigella</i> invasion protein invasion plasmid antigen B (IpaB). Vaccinated mice conferred protection against <i>Shigella</i>, indicating that the model is suitable for testing of vaccine candidates. To protect both <i>Shigella</i> and <i>Salmonella</i>, a chimeric recombinant vaccine (rIpaB-T2544) was developed by fusing IpaB with <i>Salmonella</i> outer membrane protein T2544. Vaccinated mice developed antigen-specific serum IgG and IgA antibodies and a balanced Th1/Th2 response and were protected against oral challenge with <i>Shigella</i> (<i>S. flexneri 2a</i>, <i>Shigella dysenteriae</i>, and <i>Shigella sonnei</i>) using our present mouse model and <i>Salmonella</i> (<i>Salmonella</i> Typhi and Paratyphi) using an iron overload mouse model. We describe here the development of an oral S<i>higella</i> infection model in wild-type mouse. This model was successfully used to demonstrate the immunogenicity and protective efficacy of a candidate protein subunit vaccine against <i>Shigella</i>.