DuPont E.coli detection system gains USDA approval

By Joe Whitworth

- Last updated on GMT

DuPont Qualicon BAX System Real-Time PCR STEC Suite
DuPont Qualicon has received a letter of no objection from the USDA for a device used to detect non-O157 Shiga toxin-producing E.coli, in the same month that the regulatory authority began enforcing testing on imported beef manufacturing trimmings for strains other than E.coli O157:H7.

The letter from the US Department of Agriculture (USDA) Food Safety and Inspection Service (FSIS) said it approved the DuPont Qualicon BAX STEC suite testing kit and recognized the challenges faced in conducting robust validation studies for STEC detection methodologies.

The FSIS reviewed the data provided through a DuPont submission and compared it to the current USDA MLG 5B.01 method for the detection of Shiga toxin-producing strains of E.coli (STEC).

They determined that “there is a basis for DuPont Qualicon’s claim that the tests are comparable​” with respect to recovery at low inoculum levels, specificity and sensitivity.

The USDA FSIS began enforcement testing this month after an announcement in September 2011 that it considered the six non-O157 STEC as adulterants in non-intact raw beef.

STEC strains

The DuPont Qualicon BAX STEC suite is used for detection and identification of STEC strains (E.coli O26, O45, O103, O111, O121 and O145) in beef trim and ground beef.

The BAX System Real-Time PCR STEC Suite is the umbrella term for three assays, STEC screening for stx and eae, STEC panel one for E.coli O26, O111, O121 and STEC panel two for E.coli O45, O103, O145.

Barbara Robleto, communications manager at DuPont Nutrition and Health, told said the letter of no objection meant beef processors know it is an FSIS-acceptable method for detecting STEC.

The BAX System STEC screening assay detects virulence genes stx and eae to clear negative samples quickly and cost-effectively.

“Panel assays determine if positive screening samples contain one of the top six serogroups of non-O157 Shiga toxin-producing E.coli,” ​she said.

“The BAX System is a molecular method that uses the power of PCR to amplify genetic fragments of the targeted organism in enriched samples, providing highly accurate positive or negative results for STEC in less than an hour of processing.

“All of the STEC assays in this suite, along with the BAX System Real-Time PCR assay for E.coli O157:H7, can be run together from the same prepared sample for efficiency and flexibility.”

Clearance within an hour

The BAX System STEC suite allows negative samples to be cleared within an hour, followed by panel tests for positive samples that detect and identify which of the six serogroups may be present.

Detection is achieved using Scorpion probes, which fluoresce when incorporated into Polymerase Chain Reaction (PCR) products.

The BAX system amplifies specific fragments of bacterial DNA before evaluating the data to determine a positive or negative result, which is displayed on screen as a grid of colour-cued icons.

Robleto added: “We were the first company to apply polymerase chain reaction (PCR) technology to commercial food testing with the BAX System, which delivered a dramatic increase in speed over traditional methods—and led the food industry into a new era of fast, easy-to-use molecular testing with highly accurate results.

“As a result, in October 2011 we were able to commercialize the BAX System STEC suite, months ahead of the enforcement date​.”

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