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Purdue Scientist Develops Fast, Smart E. coli Test

Somebody may need to send a memo to J. Patrick Boyle at the American Meat Institute.   That rapid analytical test for non-O157: H7 Shiga toxin-producing E. coli (STEC) that AMI said just a couple of weeks ago was not available may now be available.

A food science researcher at Purdue University has come up with an infrared spectroscopy that can detect and differentiate between E coli strains and do it faster than existing methods.

Lisa Mauer, associate professor of food science at Purdue, says the new method can differentiate between different E. coli strains, including O157:H7 and the non-O157 varieties that can also make people sick.

Such a test makes it more likely that the U.S. Department of Agriculture’s Food Safety & Inspection Service will classify six other E. coli strains in addition to O157:H7 as “adulterants”. These STECs include 026, 045, 0111, 0121, 0145, and 0103.

Only E. coli O157:H7 is currently defined as an “adulterant” in food.  While the other six strains are more rare, they kill 30 people a year and infect about 37,000.

“A faster test method enables a faster distribution chain to get fresher product to consumers and/or faster response to an outbreak or suspected case of product contamination,” Mauer told Food Safety News.

In a letter to Secretary of Agriculture Tom Vilsack, the Meat Institute’s Boyle threw several roadblocks in front of making the non-O157 E. coli strains adulterants, but the main one was testing.

“At the present time, no relevant, validated, FSIS-accepted, rapid analytical test for non-O157:H7 STECs is commercially available,” Boyle wrote.   “It is important to acknowledge that due to the limited time perishable beef products can be held and the logistics of holding products for several days pending cultural confirmation that non-O157:H7 STECs are present, a viable, rapid screening test is needed to make product dispositions. 

“Therefore, an accurate, validated, rapid analytical test must be available to the industry to effectively implement any regulatory program that would make it illegal to enter product containing non-O157:H7 STECs into commerce.”

But Mauer’s test can detect E coli strains in about an hour using “Fourier transform infrared spectroscopy,” a big improvement over the 48 hours required for conventional plating technology with its need to culture cells in a laboratory.

“Even with all the other bacteria present in ground beef, we could still detect E. coli and recognize different strains,” she said.   Her findings, based on work funded by USDA’s Agricultural Research Service and the Purdue Center for Food Safety Engineering, were published the August issue of the Journal of Food Science.

Mauer demonstrated two methods for separating bacteria from ground beef for testing.  An antibody-capture method, which binds bacteria to antibodies attached to magnetic beads, gave results in about four hours.  A filtration method achieved results in about an hour.

Infrared spectroscopy could detect as little as 1 E. coli cell if the bacteria were cultured for six hours.  Conventional plating techniques used for E. coli require culturing cells for 48 hours.

Mauer said E. coli has a specific infrared spectrum that can be read with a Fourier transform infrared spectrometer.  Infrared light is passed over the sample.  The spectrometer reads the spectrum created by the combination of energy that has been absorbed and energy that has been reflected back.

“Energy is only absorbed by certain components of the sample,” she said.  “If that component or bacteria isn’t there, the energy is reflected back.”

Mauer’s method can also differentiate between living and dead E. coli cells, which is something current testing cannot do.

“If the cells are dead, they are not harmful,” she said.  “But the presence of that dead population could tell you something about the quality of the product.”

About 70,000 Americans annually fall victim to E. coli O157:H7.  They suffer from stomach cramps, diarrhea, and vomiting, and sometimes develop life-threatening complications like hemolytic uremic syndrome, or HUS.

The Purdue University researcher previously used the technology to detect melamine in food.   “FR-IR spectroscopy has many potential applications for food safety,” she told Food Safety News.

FSIS has not yet acted on a petition asking for non-O157 E. coli strains to be classified as adulterants.  Food safety attorney William Marler filed the petition on behalf of victims of non-O157 E. coli strains.

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