Abstract
A large-scale clinical vaccine trial of commercially fed cattle was conducted to test the efficacy of a two-dose regimen of a vaccine product against type III secreted proteins of enterohemorrhagic Escherichia coli O157:H7 on the probability to detect the same organism from terminal rectal mucosa (TRM) as a measure of gut colonization. Vaccine was administered to all cattle within treated pens at arrival processing and at reimplant processing. At harvest, TRM was collected from a sample of cattle from within vaccinated and nonvaccinated pens. The TRM were collected by scraping the mucosa of the terminal rectum 3–5 cm proximal to the rectoanal juncture. E. coli O157:H7 was isolated and identified from TRM using standard culture methods involving selective enrichment, immunomagnetic separation, and PCR confirmation. The probability to detect E. coli O157:H7 from TRM was modeled using a generalized linear mixed model with a logit link function and accounting for random effects of pen within feedlot. Seven hundred eighteen cattle were tested from within 21 pens of cattle (11 vaccinated and 10 not vaccinated) representing 3683 cattle. E. coli O157:H7 was cultured from 68 of 718 (9.5%) TRM samples. Eleven of 382 (2.9%) vaccinated cattle and 57 of 336 (17.0%) nonvaccinated cattle were TRM culture positive. From the multilevel logistic model, vaccinated cattle were 92% less likely to be colonized with E. coli O157:H7 than nonvaccinated cattle (odds ratio [OR] = 0.07, p = 0.0008). Additional explanatory variables were region of the state (OR = 7.4, p = 0.04), and pens with fewer cattle (OR = 0.22, p = 0.05). We concluded that the two-dose vaccine regimen effectively reduced the probability for E. coli O157:H7 colonization of the terminal rectum of commercially fed cattle at harvest.