Development of intimin-enriched outer membrane vesicles (OMVs) as a vaccine to control intestinal carriage of Enterohemorrhagic Escherichia coli

Enterohemorrhagic Escherichia coli (EHEC) are foodborne pathogens causing severe human infections including hemorrhagic colitis and hemolytic uremic syndrome, particularly in children. Ruminants are the main reservoir of EHEC which colonize their intestinal tract through a mechanism involving the bacterial adhesin intimin. Vaccination of cattle has shown efficacy in reducing EHEC O157:H7 shedding in feces. However, most of these vaccines rely on purified proteins and/or adjuvants, making them expensive and not used by breeders. This study introduced the development of a new type of vaccine based on Outer Membrane Vesicles (OMVs) carrying the C-terminal domain of intimin (Int280). A vaccine which combines OMVs carrying luminal Int280 and OMVs displaying surface-exposed Int280 was produced using two addressing systems based on PelB peptide signal and Lpp-OmpA hybrid protein, respectively. Dot blot experiments on OMVs combined with FAS assay with bacteria confirmed the correct localization of the fusion proteins and the functionality of Lpp-OmpA-Int280, respectively. As a proof of concept, the efficiency of the mixed vaccine was tested in a mouse model using the pathogen Citrobacter rodentium which shares a similar intimin-based adhesion mechanism with EHEC. Intraperitoneal vaccination of mice, at two-week intervals with 1 μg of the mixture of OMV-Int280, elicited a strong anti-intimin IgG response. Interestingly, we observed a shortened C. rodentium fecal shedding duration in immunized mice compared to the control unvaccinated group, with significant reduction of C. rodentium colonization from day 14 (q < 0.0001) to day 18 (q = 0.0068). This OMV-Int280 vaccine therefore represents a promising candidate for the control of EHEC intestinal carriage and fecal shedding in ruminants.