DuPont pathogenic E.coli test adopted by USDA-FSIS
From today (1 October) FSIS microbiologists can use BAX System real-time assays to monitor regulated foods for pathogenic E. coli after it was added to the FSIS Microbiology Laboratory Guidebook (MLG) of Test Methods.
The MLG already specifies the BAX System method for Salmonella and Listeria monocytogenes.
USDA FSIS evaluates methods of interest for its micro labs and publishes the ones they select for use in the MLG, explained Barbara Robleto, communications manager at DuPont Nutrition & Health.
Depending on sample size, enrichment of beef trim and raw beef can take from eight to 24 hours for large volumes. Sample prep takes about 35 minutes, and PCR processing for these E. coli assays takes about an hour.
BAX adoption
The BAX System was first adopted by USDA FSIS in 2002 for detecting Listeria monocytogenes in ready-to-eat meat and poultry, Robleto told FoodQualityNews.com.
In 2003 they adopted the BAX System for detecting Salmonella in both ready-to-eat and raw meat and in 2005 they took up the BAX System for detecting E. coli O157:H7 in raw beef and beef trim.
DuPont collaborated with the USDA Agricultural Research Service (ARS) to develop a molecular method for detecting six pathogenic E. coli that had been newly declared adulterants in beef trim.
The resulting BAX System STEC suite, which uses real-time PCR technology, was introduced late 2011.
Prior to that, DuPont had introduced a next-generation version of the E. coli O157:H7 assay that also uses real-time PCR. Because the sample preparation and cycling programs are the same, microbiologists can run all the tests at the same time from a single lysate.
After evaluation, the USDA FSIS replaced the previous E. coli O157:H7 method with the real-time version, and added the STEC method to the MLG.
Automated system
The automated system uses PCR assays, tableted reagents and optimized media to detect Salmonella, Listeria species, Listeria monocytogenes, E. coli O157:H7 and STEC, Campylobacter, Staphylococcus aureus, Vibrio, and yeast and mold.
“For each assay, all necessary PCR reaction reagents are combined into a BAX System tablet, which is hydrated with an aliquot of prepared sample,” said Robleto.
“This eliminates multiple liquid transfers and effectively reduces potential for errors caused by operator technique. These proprietary tablets also allow for efficient processing of up to 96 tests in a single batch.”
Robleto said the device works by loading samples, running the program and reading the results on screen.
The program uses PCR to amplify genetic sequences unique to the targeted bacteria, so if the target is present, the fluorescent signal increases with amplification, if it isn’t, no amplification takes place.
“Our technology team is constantly working on novel and enhanced science-based solutions to make microbial testing faster and more convenient, without sacrificing accuracy,” she said.
“One example is this STEC suite of assays, which was pro-actively developed in collaboration with USDA ARS and introduced as a faster, easier, molecular method for detecting newly designated adulterants.”
