AOAC extends DuPont assay validation with single-stage enrichment media

By Joseph James Whitworth contact

- Last updated on GMT

DuPont BAX System
DuPont BAX System

Related tags: Listeria monocytogenes, Validation, Bax system

DuPont’s BAX System for Listeria has had its validation extended to include a proprietary enrichment media, speeding up time to result.

The AOAC Research Institute (AOAC-RI) granted a method extension for the BAX system real-time PCR assays with single-stage enrichment in FoodChek Actero Listeria media.

The AOAC-RI method allows a single-stage, 20-26 hour enrichment (sample-dependent) in FoodChek Actero Listeria Enrichment Media, followed by real-time processing with the BAX System.

Extension includes detection of Listeria species and L. monocytogenes and has been tested in frankfurters, shrimp, smoked salmon, spinach and queso fresco, on stainless steel, plastic and sealed concrete surfaces.

For some matrixes results can be known within 22 hours.

The news follows approval as a Performance Tested Method (PTM) by AOAC earlier this year for DuPont’s system for Listeria monocytogenes.

Certification included a combined testing method from environmental samples involving a 20-hour, single-stage enrichment in FoodChek’s Actero media followed by processing with the BAX System.

Listeria: A slow growing pathogen

Morgan Wallace, DuPont Nutrition & Health senior microbiologist and validations leader for Diagnostics, said Listeria is a slow-growing pathogen, so any steps that allow for faster detection are important to help provide cost-saving benefits to customers.

“The main benefit of reducing the enrichment time can be found in the cost-savings of either releasing cleared product to the market faster, or acting on positive results earlier to control a potential contamination," ​he said. 

“The shorter time to result helps lessen the risk of shipped product reaching the market before results are available and significantly reduces the hold time required for products kept until test results are confirmed.”

The BAX System real-time PCR assays for Listeria were previously validated by AOAC-RI using standard reference method media and proprietary, single-stage 24 LEB Complete.

Enrichments in standard reference method media were validated with incubation times between 38-48 hours.

Those in 24 LEB Complete were validated with times from 24-48 hours.

Reducing enrichment time

Wallace said each sample type was validated with the shortest enrichment time that ensured accurate, reliable results.

“For example, environmental samples can be reliably enriched in Actero Listeria Enrichment Media for testing with the BAX System method after 20 hours, while most food samples require a minimum of 22 hours.

“All validated samples types can be reliably enriched with the validated method by 26 hours.”

The biggest advantage of the combined testing method is removing the need for a secondary enrichment protocol, said Wallace.

“Our goal in validating a variety of enrichment methods and sample types with each BAX System assay is to provide customers with the flexibility they need to adopt the BAX System method that most efficiently reduces their time to result," ​he said. 

“As such, customers can choose if or when they would like to adopt the use of these BAX System assays with enrichment in FoodChek Actero media to best suit their needs.”

Environmental samples, such as stainless steel and concrete, can return results in 22 hours – including 20 hours of enrichment in FoodChek Actero Listeria Enrichment Media, followed by 45 minutes of basic sample preparation and 75 minutes of automated processing in the BAX System Q7 instrument. 

William J. Hogan, FoodChek chairman, president and CEO, said Actero Listeria Enrichment media allows laboratories to use about 33% less media per sample than other methods. 

“This not only results in less waste disposal during the testing process, but also helps improve the financial bottom line for food companies and commercial testing laboratories alike.”​ 

Related topics: Food Safety & Quality

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