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Life Tech's Listeria Spp. Detection Kit Receives AOAC Approval

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Life Technologies' MicroSEQ real-time PCR-based Listeria spp. detection kit has been validated by the Association of Analytical Communities Research Institute, company officials said this week.

MicroSEQ Listeria spp. is the fourth MicroSEQ food pathogen detection kit sold by Life Tech's Applied Biosystems business to receive AOAC certification. Previously validated kits include MicroSEQ Listeria monocytogenes, MicroSEQ Salmonella spp., and MicroSEQ E. coli O157:H7.

MicroSEQ detection kits use TaqMan-based real-time PCR in a lyophilized format and are optimized for use with the Applied Biosystems 7500 Fast Real-Time PCR system.

Together, the four kits "address more than 90 percent of the food pathogen testing market worldwide," a Life Tech spokesperson said. Life Tech sells all four kits as part of its MicroSEQ Pathogen Detection Solution, which combines sample preparation kits, lyophilized pathogen detection assays, instrumentation, and data-analysis software.

"Listeria is one of the four biggest pathogens that any food producers would want to go after, and is one of the trickiest ones, because you really need to test not only the food, but also the environment in which the food is being kept," Nir Nimrodi, general manager of food safety and animal health at Life Tech, told PCR Insider.

The Listeria spp. kit can detect "dozens" of other Listeria strains, Nimrodi said, including Listeria monocytogenes, which is perhaps the most dangerous strain in terms of human health.

"If you're only using MicroSEQ Listeria [monocytogenes], you are safe saying that you don't have L. monocytogenes if your sample tested negative," Nimrodi said. "However, the recommended method is to do Listeria spp., and then … if you have a positive sample, you can dig deeper and test for [L. monocytogenes]. Ideally you would want both."

There are scores of other commercial tests for Listeria available, some of them PCR-based, including tests from DuPont Qualicon, Bio-Rad, and Norgen Biotek.

All of these tests provide results faster than the gold standard of microbiological culture, which can take several days. Nimrodi said that Life Tech claims a time to result of 28 hours for MicroSEQ Listeria spp.

"This is not necessarily faster than other PCR methods; however, it is more sensitive because of the combination of our sample prep and the actual chemistry, TaqMan chemistry, which is unique to us," Nimrodi said.

"The biggest chunk of time here is actual sample enrichment," he added. "Once the sample is enriched, it takes minutes to run it on the 7500 Fast. You could settle for a shorter enrichment time, but that may impair your sensitivity."

Nimrodi said that MicroSEQ Listeria spp. has a sensitivity of about one to three colony-forming units per 25 g of solid sample or 25 mL of liquid sample.

AOAC is an analytical method and laboratory quality assurance organization, and its validation is crucial for companies wishing to sell commercial products such as MicroSEQ detection kits. "You don't have to get [AOAC] approval," Nimrodi explained, "but as a customer you want to make sure that the product has been validated and basically meets certain analytical criteria.

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