Efficacy of an Escherichia coli O157:H7 SRP Vaccine in Orally Challenged Goats and Strain Persistence Over Time.

ABSTRACT

Small ruminants have been implicated in outbreaks of Escherichia coli O157H7 at livestock exhibitions throughout the United States. Additionally, goat meat or milk may serve as a reservoir for foodborne transmission of the organism. These associations highlight the public health importance of an effective strategy to reduce E. coli O157H7 shedding in goats. We examined the efficacy of the SRP® vaccine in goats orally challenged with E. coli O157H7. Mixed-breed goats (n = 14) were randomly allocated into vaccinated and unvaccinated treatments (n = 7 per treatment). Goats were housed with a vaccinated and unvaccinated animal in each pen. Feces were collected for 3 weeks, then at necropsy, gastrointestinal contents were collected to determine the concentration of E. coli O157H7. Three isolates per positive sample were saved and evaluated by pulsed-field gel electrophoresis (PFGE) to assess strain persistence over time. The mean concentration of E. coli O157H7 in the feces of goats was numerically reduced in the vaccinated treatment; however, it was not statistically significant. In addition, the total number of days goats were fecal positive for E. coli O157H7 were not different between vaccinated and unvaccinated treatments. Pulsotypes of isolates revealed that goats initially shed two of the four challenge strains of E. coli O157H7, after which there was a distinct shift to two different strains. Further work is needed to evaluate cost-effective intervention strategies that reliably reduce E. coli O157H7 shedding in goats, particularly those that may reduce the risk of transmission at public events, including petting zoos and fairs.