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DuPont’s assay for Listeria backed by AOAC

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By Joe Whitworth+

Last updated on 28-Aug-2014 at 08:54 GMT

DuPont BAX System Real-Time PCR Assay for Genus Listeria
DuPont BAX System Real-Time PCR Assay for Genus Listeria

DuPont’s BAX System Real-Time PCR Assay for Listeria has been certified by the AOAC Research Institute as a Performance Tested Method (PTM).

The AOAC Research Institute validated the BAX System as equivalent to the reference culture method for detecting Listeria species, but with much faster time to results. 

The assay for Genus Listeria can be used as a method for detecting the pathogen in a variety of products.

DuPont launched the BAX System Real-Time PCR Assay for Listeria monocytogenes earlier this month.

Validates against robust criteria

Morgan Wallace, research microbiologist and validations leader, DuPont Nutrition and Health, said certification is valued among customers because it demonstrates that a test has been validated against a set of stringent, standardized criteria.

“The AOAC process requires testing of a method at its limit of detection (where equally-treated samples may return a positive or negative result using the test and/or reference method) to ensure that it performs consistently and reliably even at its “breaking point”,” he told

“In many cases, a customer will not even consider adopting a test method until it has received certification from AOAC or an equivalent ISO-based certifying organization, so these approvals can be critical to the success of a new product.”

As a next-generation test it combines shorter, simpler sample preparation and faster real-time processing, without sacrificing accuracy or reliability, said the firm.

Wallace said reducing time to result is a priority in assay development, and it regularly evaluates new enrichment media options, sample preparation technologies and other time-reducing techniques internally and through partnerships with other experts.

The assay has been validated on frankfurters, cooked shrimp, spinach, queso fresco and environmental surfaces using reference method media as well as proprietary media for a shorter, single-stage enrichment.

Food matrix extension

Wallace said it is continuously evaluating new food types for testing through the Validations team, Product Support Laboratory, and collaborations with end users in industry, academia and government.

“Some of these food types may be submitted to AOAC for validation as a Matrix Extension based on the needs of the market, while other evaluations may be done for specific customers to help them reliably analyse a specific product.”

Validating the assay using both reference method media and proprietary media allows our customers to select an approved enrichment method that best suits their needs, said Wallace.

“For example, proprietary 24 LEB Complete provides a faster time to result for customers who need to release products quickly without sacrificing accuracy, while reference method media can be used for products with longer shelf life and low holding costs,” he said.

BAX System assays for detecting E. coli O157:H7, non-O157 STEC, Campylobacter and other pathogens are already PTM-certified.

AOAC International has awarded Official Method of Analysis (OMA) status to the BAX System method for detecting for Salmonella and Listeria monocytogenes.

The assay can be run with real-time PCR assays for L. monocytogenes and Salmonella, allowing customers to receive results for all three targets in a little over an hour.

The automated system uses technology including PCR assays with tableted reagents and media, to detect Salmonella, Listeria species, Listeria monocytogenes, E. coli O157:H7 and STEC, Campylobacter, Staphylococcus aureus, Vibrio and yeast and mold. 

Some have been certified by AOAC and AFNOR and/or approved by government agencies in the Americas, Asia and Europe.  

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