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

Abstract

Subcutaneous vaccination of cattle for enterohemorrhagic Escherichia coli O157:H7 reduces the magnitude and duration of fecal shedding, but the oftenrequired, 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 stx-negative LEE+ E. coli O157:H7 reduced rectoanal junction (RAJ) colonization by wild-type (WT) E. coli O157:H7 strains after challenge. Two groups of cattle were orally dosed twice weekly for 6 weeks with 3x109 CFU of a pool of three stx-negative LEE+ E. coli O157:H7 strains (vaccine group) or three stx-negative LEE- non-O157:H7 E. coli strains (control group). Three weeks following the final oral dose, animals in both groups were orally challenged with a cocktail of four stx- LEE+ E. coli 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 (P ≤ 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 E. coli O157:H7 organisms at the RAJ.