Repeated Oral Vaccination of Cattle with Shiga Toxin-Negative Escherichia coli O157:H7 Reduces Carriage of Wild-Type E. coli O157:H7 after Challenge.

Subcutaneous vaccination of cattle for enterohemorrhagic O157:H7 reduces the magnitude and duration of fecal shedding, but the often-required, repeated cattle restraint can increase costs, deterring adoption by producers. In contrast, live oral vaccines may be repeatedly administered in feed, without animal restraint. We investigated whether oral immunization with live -negative LEE O157:H7 reduced rectoanal junction (RAJ) colonization by wild-type (WT) O157:H7 strains after challenge. Two groups of cattle were orally dosed twice weekly for 6 weeks with 3 × 10 CFU of a pool of three -negative LEE O157:H7 strains (vaccine group) or three -negative LEE non-O157:H7 strains (control group). Three weeks following the final oral dose, animals in both groups were orally challenged with a cocktail of four LEE O157:H7 WT strains. Subsequently, WT strains at the RAJ were enumerated weekly for 4 weeks. Serum antibodies against type III secretion protein (TTSP), the translocated intimin receptor (Tir), and EspA were determined by enzyme-linked immunosorbent assay (ELISA) at day 0 (preimmunization), day 61 (postimmunization, prechallenge), and day 89 (postchallenge). Vaccine group cattle had lower numbers of WT strains at the RAJ than control group cattle on postchallenge days 3 and 7 (0.05). Also, vaccine group cattle shed WT strains for a shorter duration than control group cattle. All cattle seroconverted to TTSP, Tir, and EspA, either following immunization (vaccine group) or following challenge (control group). Increased antibody titers against Tir and TTSP postimmunization were associated with decreased numbers of WT O157:H7 organisms at the RAJ. The bacterium O157:H7 causes foodborne disease in humans that can lead to bloody diarrhea, kidney failure, vascular damage, and death. Healthy cattle are the main source of this human pathogen. Reducing O157:H7 in cattle will reduce human disease. Using a randomized comparison, a bovine vaccine to reduce carriage of the human pathogen was tested. A detoxified O157:H7 strain, missing genes that cause disease, was fed to cattle as an oral vaccine to reduce carriage of pathogenic O157:H7. After vaccination, the cattle were challenged with disease-causing O157:H7. The vaccinated cattle had decreased O157:H7 during the first 7 days postchallenge and shed the bacteria for a shorter duration than the nonvaccinated control cattle. The results support optimization of the approach to cattle vaccination that would reduce human disease.