PCR a Simple Solution for a More Sustainable Lab

We see it all around us—households, schools, and businesses trying to be more “green.” Whether it is by recycling, buying a hybrid car, or eating locally grown food, people are trying to do their part. Food safety laboratories are no different. Sustainability is important and can be measured. Small changes can make a difference in the amount of waste that is generated, the time required to run tests, the space needed to house them, and most importantly, the amount of money that it all costs. Savings in all of these areas can make a huge difference when it comes to product testing.

An in-depth evaluation of sustainability and cost analysis was performed by a service laboratory that runs, on average, 25,000 Salmonella and 20,000 Listeria monocytogenes tests per year. The lab found that it was able to decrease waste by 97% per year, spend significantly less money, and test samples for pathogens as much as a full day faster by using Bio-Rad Laboratories’ iQ-Check real-time polymerase chain reaction (PCR) method instead of its current automated enzyme-linked immunosorbent assay-based test method. What follows is a portrait of how much money and time this lab saved by switching its rapid food pathogen detection system.

The Techniques

The ELISA method depends on an antibody interaction with a specific antigen expressed by the target organism. This detection can often be complicated by similar competing organisms in food producing similar antigens, resulting in a cross-reaction. Conversely, polymerase chain reaction is based on amplification of the DNA of target pathogens. In the case of real-time PCR, specificity is increased by the use of probes and primers designed to target highly conserved regions of the target genome. The iQ-Check kits use a patented probe technology for increased sensitivity and specificity.

The ELISA method depends on an antibody interaction with a specific antigen expressed by the target organism; polymerase chainreaction is based on amplification of the DNA of target pathogens.

A key difference between ELISA and PCR tests is detection limit. Typically, an ELISA-based method will have a limit of 104-106 CFU/ml, whereas a PCR method can detect in the range of 103 CFU/ml. This difference in detection limit usually means that a longer enrichment time is required for an ELISA method. In order to combat overgrowth of competing non-target bacteria in a food sample, a secondary selective enrichment is typically required in an ELISA method to give the target bacteria a chance to grow. Selective enrichment is not required for the PCR method because of the selectivity of the probes and primers used in the assay.

Quit Wasting Away

Because sustainability is often characterized in terms of waste, an in-depth look at just how much waste each of these techniques generates was considered. Over the course of a year, this service lab calculated that its ELISA use would require two tons of tubes for transfers, resulting in 166 waste containers. In addition to the tubes, 45,000 strips and tips generated around 0.6 tons, equivalent to 150 waste containers. In total, the amount of waste this lab generated in a year was equal to 311 containers.

After evaluating the real-time PCR method, which utilized the high throughput sample prep system, the lab found that it generated significantly less waste, mainly due to the fact that 94 samples can be processed at one time in a deep well microplate format. In a year, this lab calculated it would use 450 extraction plates, weighing 121 pounds in total, as well as 450 PCR plates that weigh 123 pounds. This added up to seven waste containers per year—304 fewer waste containers than ELISA. When calculating the cost of disposing of these waste containers, the lab figured savings of $10,300 per year, solely in waste management (Figure 1).

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