Verification of the level of Microbiological Control for the Slaughter and Cooling Processes of Beef Carcass Production at a High-line-Speed Abattoir

Abstract

Methods are described which were used to verify the microbiological adequacy of the processes of production and chilling of carcasses at a high-line-speed abattoir. Ten excision samples (5 by 5 by 0.2 cm) were taken from each of 16 to 20 carcasses for each evaluation of these processes. Twelve monthly evaluations were made for the slaughter of steers, heifers, and cows and additional evaluations for each of the slaughter of cows and the chill process of carcasses. The ranges of the estimated mean log10 most probable number of growth units per square centimeter (LMPN, for 236 carcasses) and Escherichia coli per square centimeter (LEC, for 240 carcasses) enumerated by hydrophobic-grid membrane filter technology for the 12 monthly evaluations of the slaughter floor were 1.11 to 1.62 (LMPN) for single samples and 0.20 to 0.65 (LEC) for pooled samples. Based on a published advisory scale for the slaughter floor the aerobic bacterial counts reflect a cleanliness level of ”excellent” to “good.” For single evaluations of cow carcasses at the end of slaughter and of chilled carcasses the mean LMPN was 1.78 (“good”) and 1.40 respectively. From pooled samples of each of the 236 steer, heifer, and cow carcasses the pathogen E. coli O157:H7 was identified by polymerase chain reaction on one carcass whereas Listeria monocytogenes was identified on 14 carcasses. Verocytoxigenic E. coli (6 isolates) and L. monocytogenes were not isolated from the same carcasses. These low isolation rates dictate a large sample size and therefore these pathogens are excluded from use to routinely verify the workings of hazard analyses and critical control point (HACCP) systems for beef slaughter processes in Alberta. Alternatively the use of aerobic bacterial counts to directly measure cleanliness or of E. coli counts to indirectly measure fecal contamination appears to be more practical than the use of specific pathogen counts for regulatory agencies to verify the workings of quality control programs, including HACCP systems.