Saltelli Global Sensitivity Analysis and Simulation Modelling to Identify Intervention Strategies to Reduce the Prevalence of Escherichia coli O157 Contaminated Beef Carcasses
OBJECTIVES The main objective of this study was to determine the impact of transport and lairage on the isolation rate and the number of Escherichia coli O157 on cattle. MATERIALS Ninety animals, divided into three groups (A, B, and C) of 30 animals each, were used in this study. Individual animals were tagged, and samples were collected from the hides and feces of each at a feedlot and again after slaughter. The carcass of each animal was also sampled. Samples were also collected from the feedlot pens, the sides and floors of the transport trucks, and abattoir holding pens. The isolation rate and the number of E. coli O157 were estimated using a combination of immunomagnetic separation and the Most Probable Number technique. RESULTS Cattle hides were more likely to be contaminated with E. coli O157 at the feedlot (31%) than at the abattoir (4%). E. coli O157 was detected in 18% and 12% of cattle feces collected at the feedlot and after slaughter, respectively. E. coli O157 was isolated from truck floors (26%), truck sides (11%), abattoir pen rails (47%), and pen floors (42%). The mean count of E. coli O157 in positive feces was log(10) 1.17 and 2.37 MPN/g at the feedlot and slaughter, respectively. A 3 log(10) increase in the number of E. coli O157 was observed between the feedlot (2.66 MPN/g) and slaughter (5.66 MPN/g) in the feces of one animal in group B. E. coli O157 was isolated from the hide and carcass of this animal. CONCLUSIONS Transport and lairage did not lead to an increase in the number or isolation rate of E. coli O157 from cattle. APPLICATIONS Intervention strategies for reducing E. coli O157 contamination of cattle carcasses should target mechanisms that limit the impact of animals shedding a high number throughout production and processing.