The 3M Molecular Detection Assay 2 – Salmonella follows the single assay protocol of the molecular detection assays for the Listeria, and Listeria monocytogenes tests, enabling batch processing of samples and improving efficiency in the laboratory.
The firm said incorporation of a color-change indicator provides increased confidence during the process.
Compared to first generation tests, assay processing time is 30% faster and instrument run time is one hour.
Running the assay
John David, global business manager with 3M Food Safety, said the set-up and result could be achieved within one day for certain food types, specifically Salmonella in raw ground beef and chicken, which was a great benefit to perishable food producers.
“The sensitivity of the assay for all molecular generations is one to five cfu per portion size. This applies to a range of sample sizes including the standard 25g, and larger sample sizes such as 125g Listeria monocytogenes in RTE meats or 325g Salmonella in ground meats,” he told FoodQualityNews.
“Enrichment time depends on the matrix, for L. mono it is generally 24 hours and for Salmonella it is 18 hours but certain raw ground beef and raw ground chicken takes 10 hours enrichment.
“The back end of the test can essentially detect a single copy of DNA in the reaction tubes. After enrichment, the preparation time is approximately a half-hour and the instrument can be run with positive results in 15 minutes but you need to wait the full run time to see negative results (60-75 minutes).”
David said the color-change indicator is in the lysis solution, the tube has a volume of liquid coloured pink.
“You don’t see other systems with this type of industry process control for lysis steps, the purpose of the lysis step is to break up bacteria to free DNA, which are then amplified in the reagent tubes.
“The color change indicator is the control for the process, it starts pink and when it is heated it turns from pink to yellow. After heating is the cooling step where you let it cool for the three to five minutes at room temperature it takes to revert from yellow to pink.
“It is a visual indicator for the lysis step, you don’t have to rely on setting a timer or standing by; you can check the color and you know it is cool enough to proceed to the next step.”
Single assay protocol significance
David said it had the single assay protocol with the first generation tests.
“We followed the same assay protocol with the next generation tests so they all have the same workflow which is important for customers who batch and process samples and customers who test for more than one pathogen and do the preparation together and run concurrently,” he said.
“With other systems the lysis may be different for Listeria as it is gram positive than Salmonella and E. coli which are gram negative.
“Feedback from a US customer who evaluated the new assay said it frees up 15-20 minutes within the protocol which is huge savings as they look to be operational efficient, every minute counts.
“It is easier to train lab technicians with a single assay protocol as technician turnover can be an issue, new employees are easily trained and it helps in the long run to maintain the level and consistency.
“The more times you handle or touch a process, you can potentially increase the risk of cross contamination and our research demonstrated that touch points are reduced by 37% from the generation one to the generation two system.”
When asked if the nanotechnology aspect scared customers, David said: “Both existing and new customers were presented with the system through events and education seminars and they were never scared, they were interested in what the technology does.
“Basically, the nanotechnology is a small, solid material in the tube which functions to clean-up the sample. The nanotechnology replaces the larger resin beads used in the first generation lysis solution, eliminating the extra capping and mixing steps because it doesn’t settle-out of the tube.”
David added the next target was E.coli O157 and then it will continue to ‘monitor the landscape’ and listen to customers to look at new and emerging targets.