ARS | Publication request: Salmonella and E. coli O157:H7 contamination on hides and carcasses of cull cattle presented for slaughter in the U.S.: an evaluation of prevalence and bacterial loads by immunomagnetic separation and direct plating methods

Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 11, 2008
Publication Date: October 1, 2008
Citation: Harhay, D.M., Guerini, M.N., Arthur, T.M., Bosilevac, J.M., Kalchayanand, N., Shackelford, S.D., Wheeler, T.L., Koohmaraie, M. Salmonella and Escherichia coli O157:H7 contamination on hides and carcasses of cull cattle presented for slaughter in the United States: an evaluation of prevalence and bacterial loads by immunomagnetic separation and direct plating methods. 2008. Applied and Environmental Microbiology 74(20):6289-6297.

Interpretive Summary: Salmonella and E. coli O157:H7 are foodborne pathogens that are of great concern to beef producers and consumers alike. Cattle are noted as frequent reservoirs of these pathogens, and ground beef has been implicated as the mode of transmission in multiple foodborne outbreaks. In this study, we examined the prevalence and load of Salmonella and E. coli O157:H7 on the hides and carcasses of cull cattle at slaughter. Samples were collected during the summer, fall, winter, and spring seasons in four geographically distant regions of the United States. Pathogen prevalence on hides and carcasses was not found to be significantly affected by sample season. However, significant differences were observed between plants with respect to incoming pathogen load and the ability to mitigate hide to carcass transfer. In spite of these differences, antimicrobial interventions employed at all four plants significantly reduced contamination between pre-evisceration and post-intervention carcasses. These data represent the most comprehensive characterization of pathogen prevalence and levels in U.S. cull cow processing plants to date.

Technical Abstract: Hide and carcass hygiene of cull cattle at slaughter, in four geographically distant regions of the United States was examined from July 2005 to April 2006 by measuring the aerobic plate count (APC), and the prevalence and load of Salmonella and E. coli O157:H7. The geometric mean Log10 APC colony forming unit (CFU)/100 cm2 levels on hides, pre-evisceration and post-intervention carcasses ranged from 6.17 to 8.19, 4.24 to 6.47 and 1.46 to 1.96, respectively, and were highest in the summer (P < 0.0001). Average prevalence of Salmonella on hides, pre-evisceration and post-intervention carcasses was 89.6% (95% confidence interval [CI] 85.1 to 94.0) and 50.2% (95% CI 40.9 to 59.5) and 0.8% (95% CI 0.18 to 1.42), respectively. Prevalence of E. coli O157:H7 was 46.9% (95% CI 37.3 to 56.6) and 16.7% (95% CI 9.8 to 23.6) on hides and pre-evisceration carcasses, respectively. Examination of the concomitant incidence of Salmonella and E. coli O157:H7 showed that on average, 33.3% (95% CI 15.9 to 69.8) of cattle hides and 4.1% (95% CI 0.98 to 17.3) of pre-evisceration carcass samples were contaminated with both pathogens. Pathogen prevalence on hides and carcasses was not significantly affected by season, however, significant differences were observed between plants with respect to incoming pathogen load and the ability to mitigate hide to carcass transfer. In spite of these differences, multiple hurdle interventions employed at all four plants significantly reduced carcass contamination (P < 0.001).