Purpose: To perform a preliminary evaluation of LPT assay to detect low levels of Listeria(0-5 CFU/ sample) in artificially contaminated food and environmental surface samples with comparison to reference method.
Methods: Twenty-five gram samples (ham, turkey sausage, salmon and spinach) of each food matrix were diluted (1:10) in proprietary LPT broth and incubated at 30 °C for 26-30 h. Two types of environmental samples including sponges from ceramic tiles, and cotton swabs from stainless steel, plastic and rubber surfaces were also enriched in LPT broth at 30 °C for 22-30 h. All enriched samples (n=20) were analyzed using LPT assay and simultaneously confirmed on selective media. The reference method (FDA-BAM or USDA-MLG) was performed in parallel for all samples.
Results: The results of LPT assay and reference method for any tested foods were not found statistically significantly different. Matrix-wise results (positives for LPT/reference) were 19/19 for ham; 5/5 for sausage; 11/9 for salmon; and 5/5 for spinach. For environmental samples phage-based assay either performed statistically better or equivalent to the reference method. The results for environmental samples were 14/9 for sponges from ceramic tiles, and 6/5 for swabs from rubber, 15/14 from plastic and 15/4 from stainless steel surface.
Significance: The evaluations of LPT assay provided satisfactory results for the detection of Listeria in artificially contaminated food and environmental surface samples and uninoculated controls. This automated assay could provide an easy to use solution for the detection of low levels of Listeria in a sensitive and rapid manner.