IVD Technology Magazine
IVDT Article Index

Originally published September, 1998

IVD Technology News

Safer foods through IVD testing

Detecting diseases in humans is important, but perhaps just as important is the task of detecting disease-causing bacteria in foods—preferably before they ever reach the supermarket shelves. Recent outbreaks of food-related gastrointestinal and renal disease have suggested a need for better methods and procedures for food testing. Several diagnostic manufacturers have taken up that challenge and are now applying state-of-the-art technology to improve the way food is inspected.

Most food assays currently in use employ some form of chromatography or lateral-flow technology, similar to that of an ordinary home pregnancy test. The difficulty with such assays arises not in performance of the actual tests, but in the steps required to prepare a sample to be tested.

The most time-consuming part of such tests is the process of enriching a sample for bacteria. Sensitivity levels of current tests require samples to be cultured in a broth medium until enough bacteria have grown to be assayed—a process that can take several hours. All together, such a bacterial assay can take anywhere from 8 to 18 hours to complete—longer than the normal work shift—meaning that discovery of any contamination problems has to be handed off to the next shift.

Igen International, Inc. (Gaithersburg, MD), has teamed with researchers of the Agricultural Research Service (ARS) at the United States Department of Agriculture (USDA) to produce a new, faster test for E. coli 0157—the strain responsible for the 1993 "Jack in the Box" outbreak in the Pacific Northwest. Field evaluations of the test began in July. If successful, the test could soon be in use by major food and beverage manufacturers.

Igen's new test for E. coli 0157 uses the company's Origen electrochemiluminesence technology. Photo courtesy Igen International

The new test promises to increase sensitivity by 10–100% over current methods and to shorten assay time to about 8 hours. Developed in conjunction with ARS's C. Gerald Crawford, Mark Rasmussen, and Thomas Casey, the test uses Igen's patented Origen electrochemiluminescence technology. Crawford explains that the test obviates the need for a long culture-enrichment step by separating E. coli 0157 with a specific monoclonal antibody conjugated to a magnetic bead. A secondary antibody labeled with the metal ruthenium catalyzes a chemical reaction that emits the light used for detection.

When asked about false positives due to antibody cross-reactivity, Crawford says, "I haven't seen it happen yet, but we are also developing a polymerase chain reaction—based confirmatory test that will be used in conjunction with the Origen test." This second test adds about 2 hours to the total process, but "we're aiming to get both tests done within 8 hours," adds Crawford.

While Igen's E. coli test is being evaluated at a large commercial meat supplier, other tests are also in the works. In collaboration with the Centers for Disease Control and Prevention, Igen plans to begin field testing of a similar system to detect cryptosporidium parasite. Cryptosporidium infection causes gastrointestinal disorders and can be life threatening in the young or immunocompromised. Most outbreaks originate from contaminated water supplies, but many animals, including cattle, can appear healthy and still harbor the parasite.

Other IVD food safety tests already on the market include the product line of Vicam LP (Watertown, MA). The company's tests for salmonella and listeria use antibody-coated, magnetic beads to isolate bacteria from a sample. After the laboratorian has isolated the bacteria, the beads are plated onto conventional agar medium and colony formation is scored visually. Completion of the tests takes about 24 hours.

Vicam offers rapid test kits for mycotoxins. Photo courtesy Vicam

By contrast, Vicam's line of mycotoxin testing kits is quite expedient. After grinding a sample and extracting it by filtration, performing the actual test takes less than 10 minutes. Vicam's mycotoxin test again uses beads and monoclonal antibodies. Because of the small size of mycotoxins, however, separation is performed by using an ordinary affinity column rather than magnetism. Fluorescent developer is added to the eluate and the results can be read on a conventional fluorimeter.

Mycotoxins are produced by many types of molds and fungi and some are classified as Group I carcinogens. Mycotoxin tests available from Vicam include aflatoxin, fumonisin, and ochratoxin.

Prototype of a fluorescent spectroscope for contamination detection, developed by Jacob Petrich (Iowa State University) and USDA researchers Mark Rasmussen and Thomas Casey. Photo courtesy Iowa State University

New IVD tests may help detect contaminated food, but the unsavory truth is that many of the bacteria found in meat originate from the animal's own feces. With USDA's food safety and inspection service now enforcing a zero-tolerance standard for fecal contamination, researchers have developed a new tool to fight this problem. Working with ARS researchers, Jacob W. Petrich, a professor of chemistry at Iowa State University, has built a fluorescent spectroscope to spot unseen feces on meat. The handheld device is used like an airport metal detector. Capable of detecting contamination in seconds, the new monitor could replace the standard practice of visual inspection. Patents for the technology are pending and commercial partnerships are being explored.—Gary Woo