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Field Studies Begin on New, Improved Tests to Identify Major Bacterial Food Pathogens

By Linda McGraw
February 4, 1999

WASHINGTON, Feb. 4--A U.S. Department of Agriculture scientist who has developed faster and more reliable tests to identify major bacterial food pathogens is now using these tests in large-scale field studies to show that they’ll work on live animals.

Irene V. Wesley, a microbiologist with USDA’s Agricultural Research Service in Ames, Iowa, developed several tests to identify bacteria that may cause human illness. These tests use a gene multiplying technique called polymerase chain reaction (PCR) to recognize the pathogens in animal, human and food samples in less than eight hours. Current culturing techniques can take up to two weeks.

Every year, 6.5 to 33 million people in the United States come down with foodborne illnesses. The estimated medical costs and productivity losses from these illnesses range from $6 to $34 billion.

“Added to the tragic human toll, the food industry loses money and product reputation through embargoes, recalls, and voluntary destruction of products,” says Floyd P. Horn, ARS administrator. “Expanding research to identify major bacterial pathogens is an important element of President Clinton’s National Food Safety Initiative--a commitment to improving food safety all the way from the farm to the table.”

Wesley is based at the ARS National Animal Disease Center in Ames, Iowa. ARS is USDA’s chief scientific research agency. The USDA carries out the President’s food safety initiative along with the Food and Drug Administration, Centers for Disease Control and Prevention, and the U.S. Environmental Protection Agency.

Campylobacter is a normal inhabitant of livestock and poultry, but in humans it may cause disease. C. jejuni is one of the most frequent causes of bacterial food poisoning. Each year, four million C. jejuni infections occur in humans in the United States, according to the CDC. This adds up to four times more illness from Campylobacter than from Salmonella.

C. coli--another type of Campylobacter--is often found in pigs but rarely causes human illness in the United States. C. coli is so closely related to C. jejuni that it takes highly specific tests to differentiate between them. Wesley’s PCR test is one of the newest ways to distinguish between them. She and colleagues are currently using the PCR test to detect Campylobacter, especially C. coli in pigs.

In a current project, funded by USDA’s Food Safety and Inspection Service, researchers with ARS, Iowa State University, and North Carolina State University are tracking the spread of Campylobacter and other bacteria in pigs from the nursery stage to slaughter. The study, which includes eight farms and two slaughterhouses, compares two different ways of raising hogs in Iowa and North Carolina. Results of the study will be used to determine which farm management practices reduce foodborne pathogens.

Another PCR test stands ready to check for the presence of Listeria monocytogenes. Listeria has been found in a range of food products--dairy, liquid whole eggs, red meat, poultry, seafood, and vegetables. Identifying L. monocytogenes quickly is critical to ensure that our nation has the safest food supply.

A more in-depth article on the research appears in the February issue of Agricultural Research, ARS’ monthly magazine. The article is also on the World Wide Web at:


Scientific contact: Irene V. Wesley, ARS National Animal Disease Center, Ames, Iowa, phone (515) 663-7200, fax (515) 663-7458, e-mail