Performing Department
Population Health & Reproduction
Non Technical Summary
Contamination of produce with E. coli O157:H7 continues to be a public health threat that has led to repeated US outbreaks of foodborne disease over recent years. Considerable pressure has been put on growers to minimize the risk of contaminated leafy greens and other produce to enter distribution chains. Due to the complexity of identifying key sources of E. coli O157:H7 and other serotypes in a field setting, rarely are definitive sources identified following an outbreak. Cattle in proximity to produce fields have long been suspected as a possible contributor to the problem, which has resulted in conflicting land use restrictions between cattle grazing and produce growers. Although cattle do not have access to produce fields, indirect routes of contamination through wildlife species, winter precipitation runoff, or through the air are conceivable. A vaccine targeting E. coli O157:H7 in cattle is available and has shown to significantly reduce fecal shedding of the pathogen in feedlot settings. However, its potential to reduce shedding in rangeland cattle typical of central coastal California where most of our leafy green commodities are grown has not yet been evaluated as a produce food safety intervention. Based on previous research, E. coli O157:H7 shedding in rangeland or pastured cattle is more sporadic, with overall low prevalence interspersed by acute spikes in fecal shedding. Regardless of the cause, the vaccine could be a relatively low-cost, low-intensity intervention to significantly reduce fecal shedding from rangeland cattle in proximity to produce fields. We propose to conduct a vaccine trial at the cow-calf operation managed by UC's Sierra Foothill Research and Extension Center to test the hypothesis that vaccinated herds have reduced prevalence and/or intensity of E. coli O157:H7 fecal shedding, which could potentially lead to reduced environmental loads of this pathogen and thereby improved produce safety.
Animal Health Component
100%
Research Effort Categories
Basic
(N/A)
Applied
100%
Developmental
(N/A)
Goals / Objectives
The main objective of this study is to test the efficacy of the E. coli Bacterial Extract vaccine with SRP technology in reducing E. coli O157:H7 fecal shedding in a cow-calf herd when administered twice before calving.
Project Methods
Cattle from the cow-calf herd at Sierra Foothill Research and Extension Center will be stratified by age and randomized to either treatment (vaccinated) or control (saline placebo) in a 2-arm parallel trial with 1:1 allocation ratio. Fecal samples from a random sample of cows and heifers will be collected at study start from the rectum to calculate baseline shedding prevalence. Pregnant dams will receive either vaccine (labelled dose of the E. coli Bacterial Extract vaccine) or saline placebo at pregnancy diagnosis and at weaning of calves prior to the 2021 calving season. Study personnel will be blinded to treatments. Groups will be kept on separate grazing locations to avoid the vaccine group experiencing exposure from unvaccinated herd mates, and the control group benefitting from herd immunity through vaccinated herd mates. Fresh fecal samples from cows and calves born to trial cows will be collected from the ground once a month for one month after the second dose of the vaccine and three times once a month after all calves have been born and tested for the presence of E. coli O157:H7. The concentration of E. coli O157:H7 will then be determined for positive samples using a Most Probably Number (MPN) assay.