The assay allows food companies to detect environmental Listeria spp. in less than 8 hours – saving more than two days on traditional detection methods and allowing problems to be swiftly identified, ultimately helping companies avoid product recalls and processing line shutdowns.
Food manufacturers have a legal and moral obligation to ensure that their products are free from food-borne pathogens, such as Salmonella and Listeria monocytogenes. To do this, they will have a number of steps in place, including: hazard-analysis critical control points (HACCP), overnight factory cleaning between production runs; building and equipment maintenance; environmental monitoring.
Listeria spp., which are widespread in the environment, pose a particular problem for hygiene teams in food factories. Where Listeria are found, there is a good chance that the pathogenic species, L. monocytogenes, might also be present. Environmental monitoring of the food processing environment is therefore vital – particularly where food comes into direct contact with machinery such as meat slicers and hoppers.
Reverse-transcriptase PCR is a two-step process, in which the first reaction generates complementary DNA (cDNA) from the rRNA template, and the second reaction amplifies the cDNA by the standard PCR reaction. The high numbers of RNA fragments present at the start of the PCR reaction lead to dramatically improved sensitivity compared to other detection methods.
With the new BAX System 8-hour Listeria Assay, results from environmental samples can be available the same day they are taken. If the result is positive, there is only a limited amount of production to be concerned about, meaning the problem can likely be identified and resolved before the next shift begins. This speed is of particular value to manufacturers of short shelf-life, ready-to-eat products including chilled meals, cooked meats, smoked fish, bagged salads and dairy products.
This reverse-transcriptase PCR assay allows for detection of Listeria at concentrations as low as 10 CFU/ml. Samples do not require the normal enrichment period which can range from one to several days. Listeria cells are simply resuscitated by incubation in a specific collection buffer for just four hours. Then, following a short reverse transcriptase step which gives a ‘jump-start’ to the PCR replication process, samples are loaded into the BAX System cycler/detector for processing. Results are automatically interpreted by the systems’ user-friendly software and displayed on screen using positive (red) or negative (green) icons.
In validation studies, the performance of the BAX System 8-hour Listeria Assay was superior to the reference USDA FSIS culture method in the detection of Listeria from stainless steel surfaces.
Using a panel of 58 Listeria strains, across the seven species of Listeria, and 52 non-Listeria strains, the assay demonstrated 100 percent inclusivity and exclusivity. The BAX® System 8-hour Listeria Assay has been approved and certified by the AOAC Research Institute (AOAC RI Performance Tested Method number 030801).
Oxoid (part of Thermo Fisher Scientific Inc)
