Effects of a siderophore receptor and porin proteins-based vaccination on fecal shedding of Escherichia coli O157:H7 in experimentally inoculated cattle.

ABSTRACT

The efficacy of a vaccine containing outer membrane siderophore receptor and porin (SRP) proteins for reducing fecal prevalence and shedding of Escherichia coli O157H7 was evaluated in cattle inoculated with E. coli O157H7. Thirty calves were randomly assigned to one of two groups, and on days 1 and 21 these calves were given subcutaneous injections of either a placebo (control) or the vaccine. Blood was collected weekly to monitor the serum anti-SRP antibody titers. Two weeks after the second vaccination, calves were orally inoculated with a mixture of five strains of nalidixic acid-resistant (NalR) E. coli O157H7. Fecal samples and rectoanal mucosal swabs were collected daily for the first 5 days and then three times each week for the following 4 weeks to determine the presence and enumerate the fecal concentration of NalR E. coli O157H7. At necropsy on day 35, gut contents and tissue swabs were collected to determine the presence and concentration of NalR E. coli O157H7. Vaccinated cattle had significantly higher anti-SRP antibody titers than did control cattle, with a significant treatment x week interaction (P < 0.01). Vaccination of cattle with the SRP protein tended to decrease fecal concentration (1.9 versus 1.6 log CFU/g) of NalR E. coli O157H7 (P = 0.10). The number of calves that were fecal culture positive for E. coli O157H7 was lower (P = 0.05) in the vaccinated group than in the control group. The E. coli O157H7 SRP vaccine tended to reduce fecal prevalence and concentration of E. coli O157H7 in cattle orally inoculated with NalR E. coli 0157H7 and may be a useful prehavest intervention strategy. Future research must be conducted on natural prevalence in feedlot operations to further evaluate the efficacy of this novel vaccine.