Purpose: This study evaluated the MDS Listeria for its ability to detect Listeria spp. in environmental samples from seafood processing plants.
Methods: Duplicate environmental sponge samples were collected from 222 different sites within three seafood processing plants in Southern Thailand. Each duplicate set of sponges was screened for Listeria spp. following two methods: (1) MDS method after 26 h and 48 h of enrichment; (2) FDA-BAM method with minor modifications. Additionally, cultures of three Listeria spp. (L. monocytogenes, L. innocua, and L. ivanovii) were separately spiked onto plastic and stainless steel surfaces at a low level (1-5 CFU). Sponge samples (n=36) from these surfaces were analyzed following the MDS method.
Results: Detection of Listeria spp. by the two methods did not differ significantly (P < 0.05). Among 222 samples, 11 and 13 samples were positive for Listeria spp. by the MDS and FDA-BAM method, respectively. Five samples tested positive by the MDS only and seven samples tested positive by the FDA-BAM only. The MDS was able to detect as low as 4 CFU of Listeria spp. in sponge samples. Overall, the sensitivity of the MDS was 87.0% (95% CI: 77.4-96.6%), specificity was 97.6% (95% CI: 95.5-99.7%), accuracy was 95.3%, and the positive predictive value was 89.4% (95% CI: 80.5-98.2%).
Significance: The MSD Listeria provides rapid and reliable detection and monitoring of Listeria spp. that may be a source of product cross-contamination in seafood plant environments.