Validation of the Use of Composite Sampling for Listeria monocytogenes in Ready-to-Eat Meat and Poultry Products

This study determined what were the most reliable methods for detection of Listeria spp. and Listeria monocytogenes in RTE products and if RTE meat products could be composited into analytical units greater than 25g as a means of reducing the labor and cost.

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Objectives

To determine reliable methods (USDA (Revisions 1 and 2), ELISA, and PCR) for detection of Listeria spp. and Listeria monocytogenes in RTE products and environmental swabs and if RTE meat products can be composited into analytical units greater than 25g (125g and 375g) as a means of reducing the labor and cost.

Conclusions

Of 226 inoculated 25-gram samples analyzed by the USDA Rev-1 method, 124 were positive for L. monocytogenes. At the 125-gram sample size, 112 samples were positive, a result not significantly different (p=0.12) than the result observed at the 25-gram size. However, the number of positives at the 375-gram sample size, 95, was significantly different (p<0.01) than the number of positives at the 25-gram size. For the USDA Rev-2 method, 128 of 226 were positive at the 25-gram test size. At the 125 and 375 gram sample sizes, 115 and 103 were positive, respectively. The result at the 125-gram size was equal to the result at 25-gram (p=0.09), but the 375-gram result was not equivalent to the 25-gram result (p<0.01).

Tests conducted at the 3 sample sizes using the PCR method showed that the 25-gram results were equivalent to the 125- gram results (p=0.039) and not equivalent to the results for the 375-gram sample size (p=0.05). For the ELISA method, neither the result for the 125-gram sample size (p<0.01) nor the 375-gram samples size (p<0.01) sample size was equivalent to the 25-gram results.

Deliverable

The study generated data to support the use of sample compositing up to a total of 125 grams of RTE meat or poultry using the USDA and PCR methods for detection of L. monocytogenes. Compositing a total of 375 grams is not recommended for these methods. Compositing is not recommended for the ELISA method.