Intragastric immunization of mice with enterohemorrhagic Escherichia coli O157:H7 bacterial ghosts reduces mortality and shedding and induces a Th2-type dominated mixed immune response

A bacterial ghost (BG)-based vaccine was developed against enterohemorrhagic Escherichia coli O157:H7 infection. The aim of this study was to evaluate the protective effect of E. coli O157:H7 BGs in a mouse model and to reveal the mechanism of the immune response. Booster immunization provided a higher protection rate (84%) than single-dose immunization (56%). Intragastric immunization of E. coli O157:H7 BGs induced both humoral and cellular immune responses. The proliferative response of CD4(+) T cells was mediated by the antigen-presenting cells. The humoral immune response dominated the immune response, while the cellular immune response developed later. Inflammatory reaction was balanced by the mixed Th1/Th2 immune response. The immune sera anti-adhesion effect was confirmed by the inhibition effect, which could inhibit >90% of the adhesion of E. coli O157:H7 to Hep-2 target cells in vitro. Antibody titer specific for intimin, a molecule important for adhesion of E. coli O157:H7 to target cells, correlated with specific immunoglobulin A or G antibody titer. Therefore, it might be feasible to clinically test BG vaccines in the future.