The Enrichment-Free Confirmation Conundrum
For environmental samples, there are a range of detection methods that can be used with varying degrees of accuracy and time trade offs. Most food processors select a rapid screening test such as an immunoassay or PCR test, which provide them results in 3 days. In the event that a positive is found with one of these methods, many food processors will chose to confirm using culture. The full USDA culture protocol requires 5 days, and includes 2 types of selective enrichment and then 2 days on agar plates.
Why Confirm? Why Not Just Retest?
Best practice would call for both. Running a confirmation test from the same sample will allow you to obtain a strain. This can be used to identify which type of Listeria is present. Strain information is often used as part of investigations. However, most plants will remediate based on a presumed positive and will retest. The retesting will confirm whether your sanitation was effective.
How Does this Work Without Enrichment?
With enrichment-based tests, a large volume of material is generated through the enrichment. Therefore, if confirmation is required, additional samples can be drawn from that volume and processed. In the event of a presumed positive, most remediation processes will include additional sampling in the same area and vectoring to identify the source. However, this is not effective for confirming the first result because, for two sponges taken from the same location, there is only a 69% correlation in results. Therefore, for the purposes of validating the initial result, the ability to run a confirmation process on the same sample bag is critical.
Sample6 DETECT is an enrichment-free process. The small number of cells that were present in a sample interact with the phage in the Sample6 Solution. This produces an enzyme, which we can detect in very low levels with the Sample6 Reader. However, this process destroys the Listeria cells. Therefore, a path for confirmation must be defined before the Sample6 Solution is added.
Here’s how it works:
- Collect a sample.
- Squeeze the sponge to remove as much liquid as possible.
- Remove the liquid from the bag and place in the reserve tube.
- Ship the reserve tube off to your lab.
- This liquid sample is enriched for testing by your lab.
- Following enrichment, the liquid sample can be run through the full culture protocol.
How Do You Capture this Information?
You’ll have to wait about a week for the confirmation results depending on the method you select and your lab. Once you receive your test report, it is important to capture this information in your environmental tracking software.
Sample6 CONTROL was recently enhanced to support this seamlessly. When a single sample has been processed by two methods, it is important to capture this information and differentiate it from separate methods used on separate samples.
Here’s how it works:
- First, a sample is read and the result is input into CONTROL.
- If you chose to confirm, click the Confirm button.
- This allows the user to enter the separate details of test method and result in the same schedule.
- This information is visible in a report or in the test point detail.
With a strong environmental program, your presumed positive test results will be few and far between. However, in the event that you find presumed positive which you need to confirm, Sample6 DETECT and Sample6 CONTROL have the tools to support you.
Together, we can make food safer.