Accuracy is paramount in pathogen testing, but speed is an important consideration as well. If a supplier has perishable food sitting in a climate-controlled warehouse, the shorter the time to results the better, and 3M claims that MDA delivers molecular level accuracy in real time. The process still requires enrichment time of anywhere between 18 to 24 hours depending on the target pathogen. But once the enriched sample is placed in the instrument, a presumptive positive can be seen in as little as 15 minutes, and a negative result takes 75 minutes.
Life Technologies, providers of a PCR test, is currently developing a technology that improves upon the conventional PCR platform. The company believes its new assay will increase accuracy and shorten time to results. The confirmation test, run after the presumptive positive, adds time to pathogen testing. In the interests of accuracy and consumer safety, it is a good idea to confirm negative results as well. However, some food processing companies skip the confirmation assay if the initial results turn up negative, although this is a risk because a false negative can allow a potentially deadly pathogen to slip into commerce. According to Nir Nimrodi, director of Life Technologies’ food safety division, the technology now under development will allow the confirmation assay to run simultaneously with the initial test, using the same sample, saving time and improving accuracy for testing laboratories.
Both false negatives and false positives of Salmonella and Campylobacter have an impact: False positives have an economic impact and false negatives lead to a health impact and potentially, an economic one as well. In the case of a false positive, pristine meat, dairy, produce, etc. will either be destroyed and thereby become a total loss, or be cooked before sale, which results in a smaller profit margin. False negatives allow dangerous pathogens to be released into commerce, sickening consumers. Many brands cannot recover from the damage that resulting recalls and lawsuits bring about–emphasizing that the importance of precision in pathogen detection cannot be overestimated.
Cowan-Lincoln is a science/technical writer based in New Jersey. She is a frequent Wiley-Blackwell contributor who has been featured in numerous publications. Reach her at mlincoln214@yahoo.com.
Proficiency Testing Process
Pathogen testing is what stands between consumers and potentially deadly outbreaks of foodborne illnesses, so accuracy in the lab is paramount. Proficiency testing is an objective means of testing lab accuracy, or as Christopher Snabes of the American Proficiency Institute puts it, “We…test the labs that test the food.” Unless a lab is ISO17025 certified, in which case annual proficiency testing is mandated, laboratories voluntarily submit to this analysis as part of quality control. American Proficiency Institute sends client labs two samples of food to test, each infected with different bacteria in varying concentrations. The lab tests it for pathogens using any method it choose—culture, ELISA, or PCR—and sends its findings to the Institute to check it against what was added. The Institute then posts its report on the lab’s accuracy on a secure area of its website, accessible only to the client laboratory. Clients log onto their own secure page to find out how this test rates their exactitude.
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