ARS Scientists Devise New Test for E. coli O157 in Water

By Sharon Durham
March 6, 2002

Agricultural Research Service scientists have developed a rapid, easy-to-use testto detect and count E. coli O157:H7 bacteria in natural and constructed bodies of water. ARS microbiologists Dan Shelton and Jeff Karns in the Animal Waste Pathogen Laboratory, Beltsville, Md., developed the test, which uses magnetic beads to detect the pathogen.

The magnetic beads are coated with anti-E. coli monoclonal antibodies that bind to the bacteria, making it possible to count the bacteria. Current testing methods are designed only to detect the bacteria, but not to measure how many are present. The number of E. coli bacteria present is crucial information since the levels that cause infection can vary from person to person, depending on the person’s health status. Also, the new method makes it possible to detect E. coli in water samples in a day or less, compared with traditional testing that can take up to four days to complete.

Usually spread in contaminated food, E. coli is sometimes waterborne. In 1998, an E. coli outbreak occurred at an Atlanta, Ga., water park, causing the hospitalization of several children. E. coli can cause diarrhea, hemorrhagic colitis and hemolytic uremic syndrome (HUS). HUS can result in destruction of red blood cells, damage to the lining of blood vessel walls and, in severe cases, kidney failure.

Investigations are under way to assure no other bacteria cross-react with the magnetic beads. However, if this test proves to be accurate and selective, it should allow for detection of E. coli in a variety of liquid samples, such as swimming pools and other recreational water.

ARS is the U.S. Department of Agriculture’s chief scientific research agency.