Use of the RapidChek® Listeria F.A.S.T. Test System to Detect Low Levels of Listeria Species in Composite Environmental Sponge Samples

Introduction: Numerous listeriosis outbreaks have linked the food processing environment as a source of Listeria monocytogenes contamination of food. The USDA FSIS has recently published guidelines that require meat and poultry processors to test for the presence of Listeria monocytogenes or indicator organisms such as Listeria spp. in the food processing environment. Sample compositing is under consideration as a means to save food producers labor and cost while maintaining robust test performance.

Purpose: The aim of the study is to evaluate the performance of the RapidChek^® Listeria F.A.S.T. test system compared to the USDA-FSIS method (MLG8.09) for the detection of low levels of various Listeria spp. in composite environmental sponge samples.

Methods: Three strains of Listeria (L. monocytogenes ATCC 13932, L. innocua ATCC 33090 and L. seeligeri ATCC 51334) were used to spike sponges. Seventy-five composite sponge samples (5 sponges per sample) were analyzed by both methods. For each strain, 20 spiked samples (1 CFU per sample) and 5 non-spiked samples were tested. The test system composite samples were enriched in 300 ml media while USDA samples were enriched according to MLG 8.09 in 500 ml UVM and transferred to Fraser broth. All samples were confirmed for the presence of Listeria spp. through biochemical methods.

Results: The test system reported forty-five confirmed positive results while the MLG method reported forty-three. The 24h test system demonstrated equivalent performance as compared to the MLG method (overall χ²= 0.24) resulting in 106% overall accuracy, 100% average sensitivity and 100% average specificity. 

Significance: The test system detected low levels of Listeria spp. with less media volume and in a shorter timeframe (24h). This should enable food producers to quickly and efficiently identify Listeria spp. in a potentially-contaminated environment, with reduced time and labor inputs while maintaining test method performance.