Vaccination of Pregnant Dams with Intimin _O157 Protects Suckling Piglets from Escherichia coli O157:H7 Infection

Abstract

Cattle are important reservoirs of enterohemorrhagic Escherichia coli (EHEC) O157:H7 that cause disease in humans. Both dairy and beef cattle are asymptomatically and sporadically infected with EHEC. Our long-term goal is to develop an effective vaccine to prevent cattle from becoming infected and transmitting EHEC O157:H7 to humans. We used passive immunization of neonatal piglets (as a surrogate model) to determine if antibodies against EHEC O157 adhesin (intimin O157 ) inhibit EHEC colonization. Pregnant swine (dams) with serum anti-intimin titers of <100 were vaccinated twice with purified intimin O157 or shamvaccinated with sterile buffer. Intimin O157 -specific antibody titers in colostrum and serum of dams were increased after parenteral vaccination with intimin O157 . Neonatal piglets were allowed to suckle vaccinated or sham-vaccinated dams for up to 8 h before they were inoculated with 10 6 CFU of a Shiga toxin-negative (for humane reasons) strain of EHEC O157:H7. Piglets were necropsied at 2 to 10 days after inoculation, and intestinal samples were collected for determination of bacteriological counts and histopathological analysis. Piglets that ingested colostrum containing intimin O157 -specific antibodies from vaccinated dams, but not those nursing sham-vaccinated dams, were protected from EHEC O157:H7 colonization and intestinal damage. These results establish intimin O157 as a viable candidate for an EHEC O157:H7 antitransmission vaccine.Enterohemorrhagic Escherichia coli (EHEC) O157:H7 is a common cause of bloody diarrhea and the most common cause of hemolytic-uremic syndrome in humans in the United States (1). EHEC strains can be foodborne pathogens, and cattle are important reservoirs of EHEC O157:H7 strains. All EHEC strains produce cytotoxins called Shiga toxins (Stx1 and Stx2), previously called Shiga-like toxins (SLT-1 and SLT-2) or verotoxins (VT1 and VT2). Many EHEC strains, including EHEC O157:H7, can attach intimately to host cell membranes and efface microvilli and cytoplasm in a pattern referred to as an attaching-and-effacing (A/E) lesion (18). EHEC intimin is an outer membrane protein adhesin encoded by the eae gene of EHEC (16) that is required for intestinal colonization and for A/E activity of EHEC O157:H7 in piglets (6,8,9,19) and neonatal calves (6). Antibodies against intimin O157 significantly reduce the adherence of E. coli O157:H7 strains, as well as certain related strains, to HEp-2 cells (11). Based on this observation, we hypothesize that a vaccine that contains intimin O157 may induce an immune response in cattle that will prevent or decrease the level of intestinal colonization by E. coli O157:H7. We speculate that the resultant diminution in fecal shedding of EHEC O157:H7 by these animals could, in turn, lead to a decrease in the transmission of EHEC O157:H7 and other A/E E. coli strains to humans.In the study reported here, we tested the concept that antiintimin antibodies can protect animals from colonization with EHEC O157:H7. For that purpose, we selected neonata...

Strain-Dependent Cellular Immune Responses in Cattle following Escherichia coli O157:H7 Colonization

“…It is reasonable to hypothesize that antibodies directed against the structural components of the T3SS, such as EspA/B/D, or against adhesion factors, such as intimin and its cognate receptor Tir, may block bacterial binding. In support of this hypothesis, vaccination of sows with intimin has been shown to reduce the level of EHEC O157:H7 colonization of suckling piglets (24), presumably through antibody-mediated blocking of bacterial binding. In addition, bovine colostrum has been shown to reduce T3SS-mediated hemolysis in vitro (25), and passive transfer of EspB, intimin, and neutralizing antibodies against Stx2 to calves has been demonstrated following maternal vaccination (26).…”

Isolation of Recombinant Antibodies against EspA and Intimin of Escherichia coli O157:H7

“…The results here demonstrate that the residues within EHEC intimin188 did not elicit a strong immune response when the larger fragment intimin313 was used as an immunogen. Other studies have shown that polyclonal antibodies raised against EHEC intimin282 can decrease the adherence of bacteria to HEp-2 cells (6,11). Taken together, these results suggest that antibodies capable of inhibiting bacterium-host cell interaction may well have specificities to the immunoglobulin-like domain 2 of intimin.…”

OMV-based vaccine formulations against Shiga toxin producingEscherichia colistrains are both protective in mice and immunogenic in calves

“…19–21 Extensive research has been conducted on such vaccine candidates, in both murine and bovine models. These models include formulations based on recombinant expression of virulence factors, 22–26 culture supernatants from virulent strains grown under conditions promoting virulence factor secretion, 27 , 28 subunits or components directly extracted from STEC strains, 29–31 and heterologous expression of STEC virulence factors in both attenuated and unrelated bacteria. 32 Due to the complex mechanism responsible for colonization, it is not surprising that protection has only been observed for multi-antigenic formulations.…”