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New Test Detects All Known Shiga Toxins

Most Escherichia coli bacteria living inside the intestines of humans and other animals are harmless and important to our health. But some types of E. coli can make us sick. These types, or strains, of E. coli produce a toxin called “Shiga toxin,” which can cause diarrhea and disease. The name for these bacteria is “Shiga toxin-producing E. coli,”or STEC.

STEC bacteria are responsible for more than 265,000 illnesses and 3,600 hospitalizations each year in the United States, according to the Centers for Disease Control and Prevention. About 8 percent of patients hospitalized from these infections develop hemolytic uremic syndrome, which is life threatening.

The most common STEC strain, E. coli O157:H7, is often the cause of the foodborne outbreaks that make news. But many other kinds of E. coli can cause disease. Several commercial tests are available for detecting these bacteria, but none of the tests can recognize all STEC.

At the Agricultural Research Service’s (ARS) Western Regional Research Center (WRRC) in Albany, California, however, scientists have developed a highly sensitive test that can detect all known STEC strains. The test, which is an ELISA (enzyme-linked immunosorbent assay), uses novel antibodies developed by molecular biologist Xiaohua He and her team in WRRC’s Foodborne Toxin Detection and Prevention Research Unit.

“We develop affordable methods to detect and help prevent STEC in food such as fresh produce, meat, and dairy products,” He says. “This new assay can be used to rapidly detect new and emerging serotypes and to screen food early on for contamination.”

The new antibody-based assay identifies all known subtypes of Shiga toxins produced by STEC and has been tested in various studies by He, research leader Luisa Cheng, biologist Larry Stanker, and former ARS postdoctoral research associate Craig Skinner.

Antibodies used in current commercial tests recognize only a subset of Shiga toxins, but not all of them, He explains. The new assay, which uses both monoclonal and polyclonal antibodies, can recognize both Shiga toxin 1 and Shiga toxin 2 and all of their known subtypes.

The research involves many collaborators, including scientists Pina Fratamico and Andrew Gehring at ARS’s Eastern Regional Research Center in Wyndmoor, Pennsylvania.

“Because the antibodies we made have strong affinity for native [naturally occurring] Shiga toxins, the tests developed using these antibodies are very sensitive,” Cheng says. “Therefore, we are also able to detect the toxin in blood.” In one study, the newly developed antibodies were able to clear toxins from the blood of mice, protecting them from illness. “So our antibodies can potentially be adapted as therapeutics for human diseases caused by Shiga toxins,” Cheng adds.

ARS holds patents for these novel antibodies, which have been licensed to Abraxis LLC, TechLab, Inc., and List Biological Laboratories, Inc.—By Sandra Avant, ARS Office of Communications.

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Key Facts

  • Some E. coli bacteria make a toxin called Shiga toxin.
  • Shiga toxins cause more than 265,000 U.S. illnesses each year.
  • ARS scientists developed a test that identifies all known Shiga toxins.
  • The research may lead to treatments for foodborne illness.

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