Development of a Salmonella-based oral vaccine to control intestinal colonization of Shiga-toxin-producing Escherichia coli (STEC) in animals

Abstract

Shiga-toxin-producing Escherichia coli (STEC) is an important food-borne pathogen that causes hemorrhagic colitis and hemolytic uremic syndrome (HUS) in humans. Since no vaccines are available and antibiotic treatment is not recommended because promotes the appearance of HUS symptoms, the control of STEC intestinal colonization in cows, which is an important environmental reservoir, is crucial to control this zoonosis. Here, we evaluated the adaptation of an attenuated strain of Salmonella enterica serovar Typhimurium (ΔaroA mutant) as a vaccine platform for preventing STEC intestinal colonization that was studied in a mouse model. A chimeric antigen formed by the combination of the STEC peptides EspA36-192, Intimin653-935, Tir 258-361, and H7 flagellin352-374 (EITH7) was constructed and fused to the β-lactamase signal sequence (bla SS) that drives the secretion of the chimeric antigen to the bacterial periplasmic space. Oral administration of ΔaroA-ST(EITH7) in a regime of three doses of immunization elicited both mucosal and humoral immune responses that protect mice against a STEC oral experimental infection. Remarkably, serum antibodies not only were able to bind the chimeric antigen EITH7 but also to block actin pedestal formation triggered by the type three secretion system (T3SS) in Enteropathogenic Escherichia coli (EPEC). Furthermore, a single-dose protocol was evaluated, and mice were orally immunized with ΔaroA-ST(EITH7). Interestingly, although with this protocol of immunization only fecal α-EITH7 IgA antibodies were induced and no α-EITH7 in sera were detected, mice were able to efficiently control an oral experimental infection with 1010 STEC (strain Escherichia coli O157:H7), suggesting that mucosal immune response was necessary and sufficient to control STEC intestinal colonization.