Purpose: This field study was conducted to determine the concordance of the Roka Bioscience Atlas Listeria Detection Assay (LDA) with a validated USDA-FSIS MLG protocol for L. monocytogenes using environmental sponge samples collected from two meat processing facilities.
Methods: Duplicate sponge samples were collected mid-shift from 101 environmental sites in the two facilities. One whole sponge was subjected to enrichment and detection via the LDA Protocol while the other was enriched and cultured according to the USDA-FSIS MLG Protocol 8.09 with modifications. Concordance between the two methods is reported as the percentage of total samples with identical outcomes. For discrepant LDA detection and MLG culture results, an aliquot of LDA enrichment was subjected to MLG culture procedures to assess agreement between the detection result and presence of viable listeriae in the enrichment.
Results: Concordance between the two methods was high (94.1%) with 11.9% and 82.2% of samples having LDA(+)/MLG(+) or LDA(-)/MLG(-) outcomes, respectively. Discrepancies arose in 6.0% of samples with 5.0% reported as LDA(-)/MLG(+), and 1.0% as LDA(+)/MLG(-). Culturing the LDA enrichment for LDA(-)/MLG(+) samples yielded no growth on plates, revealing that these LDA detection results were accurate given the absence of viable listeriae. Culturing the LDA enrichment of the lone LDA(+)/MLG(-) sample also yielded no growth though the LDA detection yielded a second positive result when repeated for verification.
Significance: The high concordance between the two methods demonstrates that detection via the LDA protocol is comparable to the USDA-FSIS MLG protocol for L. monocytogenes. Discrepancies that arose can likely be attributed to inconsistencies in sampling or enrichment.