Enumeration of Salmonella and Escherichia coli O157:H7 in ground beef, cattle carcass, hide and faecal samples using direct plating methods

The 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 counts (APC) and the prevalences and loads of Salmonella and Escherichia coliO157:H7. The geometric mean log10 APC CFU/100 cm 2 levels on hides and preevisceration and postintervention 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). The average prevalences of Salmonella on hides and preevisceration and postintervention carcasses were 89.6 % (95 % confidence interval [CI], 85.1 to 94.0), 50.2 % (95 % CI, 40.9 to 59.5), and 0.8 % (95 % CI, 0.18 to 1.42), respectively. The prevalences of E. coli O157:H7 were 46.9 % (95 % CI, 37.3 to 56.6) and 16.7 % (95 % CI, 9.8 to 23.6) on hides and preevisceration 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 hide and 4.1 % (95 % CI, 0.98 to 17.3) of preevisceration carcass samples were contaminated with both pathogens. The pathogen prevalence on hides and carcasses was not significantly affected by the season; however, significant differences were observed between plants with respect to the incoming pathogen load and the ability to mitigate hide-to-carcass transfer. In spite of these differences, postintervention carcass contamination was significantly reduced (P < 0.001), likely as a result o