Analysis ofSalmonellaand enterococci isolated from rendered animal products

Abstract

The objectives of this study were to determine the current status of bacterial contamination in rendered animal products and to analyze Salmonella and enterococci isolates from the samples. One hundred and fifty samples were provided by various rendering companies across the United States, including the following meal types: feather, meat, meat and bone, meat and bone from poultry, poultry, and blood meals. The average pH of the meals ranged from 6.16 to 7.36, and the moisture content ranged from 1.9% to 11.5%. The total bacterial counts were in the range of 1.7 to 6.68 log10CFU/g, with the highest in blood meal and the lowest in meat meal. Enterococcus species were detected in 81.3% of the samples and accounted for up to 54% of the total bacterial counts in some samples. Both blood meal and feather meal were more contaminated (P < 0.05) with enterococci than other meal types, although all blood meals were from a single company. Salmonella was detected in 8.7% of the samples. Escherichia coli was not detected in any of the samples, but coliforms were detected in four samples. Among enterococci isolates, three were vancomycin resistant. Thirteen serotypes of Salmonella displayed 16 pulsed-field gel electrophoresis patterns. Pulsed-field gel electrophoresis analysis has indicated that Salmonella contamination was not persistent in the plant environment over time. The D-values for the Salmonella isolates at 55, 60, and 65 °C were in the ranges of 9.27–9.99, 2.07–2.28, and 0.35–0.40 min, respectively. These results suggest that the presence of Salmonella in the finished products may be due to postprocessing contamination. This study has also revealed that the rendering industry has microbiologically improved its products since earlier studies were conducted.