RapidChek Listeria monocytogenes is backed for use on environmental surfaces and ready-to-eat foods including hot dogs, frozen breaded chicken and cooked shrimp, cured ham and ice cream.
Romer Labs said it took several months and a lot of lab work to compete all required testing before AOAC approved the test as part of its Performance Tested Methods program.
Results on lateral flow test
The single-step enrichment takes 44 or 20 hours of additional enrichment after a positive Listeria spp. result from the RapidChek Listeria NextDay system.
After enrichment, strips indicate the presence of L. monocytogenes in 10 minutes without any further sample manipulation steps.
Stefan Widmann, product manager for pathogens, said interpreting results is simple.
“There is a test line and a control line integrated into the RapidChek Listeria monocytogenes lateral flow strip,” he told FoodQualityNews.
“If only the control line appears, it indicates a negative result. If the test line also appears, it indicates a positive result. The control line is built into the lateral flow strip so you can confirm that the test worked correctly. Both lines are in an easy-to-spot red colour.
“The test was developed for all food producers, while the focus lies on testing RTE foods and samples from the processing environment. It offers significant advantages for the food producer to use RapidChek Listeria monocytogenes as a verification test in addition to our 24-hour RapidChek Listeria NextDay system as the same enrichment media is used.”
Single-step enrichment media can be stored in liquid form, after autoclaving, at room temperatures for four weeks.
Test kits use selective enrichment media coupled to a lateral flow immunochemical device with a proprietary antibody mix. Kits can be stored at room temperature and have a shelf life of up to 18 months.
From one to hundreds of samples at once, strips can be read between 10 and 20 minutes after development.
Frequency and demand for testing
Widmann said frequency of testing depends on many different factors and should be decided by a risk-based approach.
“For high-risk foodstuff and process environments, testing should be conducted on a daily basis,” he said.
“There are currently only two pathogens, which, according to various national regulations, must be completely absent in foodstuffs: L. monocytogenes and Salmonella spp. The foods in which each is present and poses a danger to human health overlap only slightly.
“This means that there are not a lot of foodstuffs regularly tested for both pathogens. This reduces the advantage of a multiplex assay tremendously, not to mention the disadvantage of using the same enrichment media for both pathogens.
“These are very different microorganisms, one gram positive and the other gram negative, and they have starkly divergent requirements in their enrichment media. That’s why we view multiplexing with scepticism in this field of application.”
The USDA’S Food and Safety Inspection Service (FSIS) maintains a ‘zero-tolerance’ policy for the pathogen in RTE meat and poultry products.
L. monocytogenes is able to survive and thrive in cool, damp conditions where other bacteria cannot.
Romer Labs said an aggressive and verifiable sanitation program is necessary to avoid cross-contamination of processing equipment in production plants.
Kurt Brunner, Romer Labs R&D director, said: “Food producers can leverage the same media they prepare for RapidChek Listeria NextDay to test for L. monocytogenes; if the first test is positive, the same media can be used to deliver results for L. monocytogenes just one day later.”
He added the two tools form a system for on-site Listeria detection to help food producers discover and control presence of the pathogen in production facilities.