PCR-based detection system ferrets out pathogens

Kraft Foods, USDA swear by DuPont Qualicon's BAX System

By Mark A. DeSorbo

Wilmington, DE-It will do 200; it has sensitive radar detectors; and it is remarkably efficient.

And with a $39,000 price tag, the PC-equipped BAX System from DuPont Qualicon (Wilmington, DE) sounds more like a sports car than a genetics-based screening method that quickly and accurately detects target bacteria in raw ingredients, finished food products and environmental samples.

Peter M. Mrozinski, a director of research and development for DuPont Qualicon, says the BAX System, through polymerase chain reaction (PCR), provides “yes-no” answers without the need for expert interpretation.

“Normally, it would take three to five days to grow a culture to detect E. coli, Listeria, and Salmonella,” he says. “With the BAX System, tiny tubes are filled with samples enriched with dehydrated PCR tablets that highlight DNA specific to the bacteria you are looking for. Within a matter of hours, it will amplify the DNA so that the bacteria can be positively identified.”

The system, he explains, allows food technologists to load samples and walk away.

The BAX System from DuPont Qualicon allows food technologists to simply load samples and walk away. Elec tronic re sults indicate if patho gens in foods are detected.
Click here to enlarge image

First, enriched samples are put in lysis tubes. The tubes are then heated to release DNA. The end-user(s) then follow(s) screen prompts to set up a rack file. PCR tablets are then hydrated with lysate and the rack of tubes is then placed in the machine.

Over the next three hours, the BAX System then goes to work, automatically amplifying and detecting patho gens in up to 96 sample batches. A plus sign encircled in red indicates the target was detected, while a minus symbol outlined in green means no target was detected.

“A typical food processing company will run 200 tests a day,” Mrozinski says, adding that some of the largest food companies, including Kraft Foods Inc. (Rye Brook, NY), use the BAX System.

Kraft isn't the only heavy hitter to adopt DuPont's BAX System. Earlier this year, the U.S. Department of Agriculture's (USDA) Food Safety and Inspection Service (FSIS) announced that it, too, would used the system to screen meat and poultry samples for Listeria monocytogenes.

After an evaluation, the FSIS determined that the BAX System was as sensitive as the current method in detecting listeria monocytogenes, the Fraser broth method. With BAX, however, fewer samples were falsely screened as positive. Data also showed that the system reduced the reporting time for negative samples by one day when compared to the current method, the USDA reports.

“This is a good example of how FSIS is using new technology to improve efficiency, says Bill Hudnall, acting FSIS administrator. “FSIS can reduce the time it takes to notify mean and poultry producers of a negative result, and fewer false positives will help reduce agency resources used to confirm positive screen tests.”

The BAX system was evaluated at the FSIS Microbial Outbreaks and Special Projects Branch (MOSPB) laboratory in Athens, GA, to determine whether it would be beneficial to the agency. FSIS laboratories employ rigorous evaluations to determine the validity and reliability of BAX, according to the USDA.

After the special projects branch's evaluation, the Eastern field service laboratory in Athens screened approximately 830 random samples for listeria using both the BAX and the Fraser broth method. Each sample was put through the Fraser broth screening analysis, and a portion of the enrichment broth was used to conduct the BAX. The official confirmation analysis method was used to confirm the results of both types of screen tests.

According to the USDA, FSIS will implement the BAX System to screen meat and poultry samples for listeria in the agency's three field service laboratories, located in Athens, GA, St. Louis, MO and Alameda, CA, as well as in the MOSPB laboratory.

FSIS is also planning to evaluate the BAX System to screen samples for E. coli O157:H7 and salmonella.


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