A New Phage-based Immunoassay for Detection of Listeria in Food and Environmental Samples

Introduction: A new immunoassay, the VIDAS®UP Listeria (LPT) for detection of Listeriaspecies in food and environmental surfaces was developed. This assay incorporates phage proteins to increase the sensitivity and specificity compared to traditional immunoassays.

Purpose: The study was undertaken to validate the LPT method as part of the AOAC RI approval process.

Methods: In the new method, food samples are enriched in LPT broth (26-30 h for food, 22-30 h for swabs) then 0.5 ml is transferred to the VIDAS strip, heat treated for 5 minutes and cooled before performing the assay (62 min). Five meat products (hot dogs, pepperoni, deli ham, chicken nuggets and liver pate) and 4 surfaces (plastic, stainless, ceramic and concrete) were included in the study. For each matrix, twenty samples inoculated at a low level (target 0.2-2 CFU) and 5 uninoculated samples were tested using the LPT assay and the USDA reference method.

Results: The LPT method gave comparable results to the USDA method using an unpaired Chi-square test at the 5% level. Results were available within 28 h for food samples and 24 h for environmental swabs.

Significance: The LPT test is simple to perform and allows next-day detection of Listeria species in food products or manufacturing environments.