When a community finds that water it relies on for drinking or recreation contains E. coli (Escherichia coli), a bacterium found in the feces of warm-blooded animals that indicates fecal contamination, residents and officials naturally want to find the cause and fix it -- quickly. But several testing methods using E. coli to identify the sources of fecal contamination were less accurate in field application than previously reported, according to a recent U.S. Geological Survey (USGS) report published in the journal Environmental Science and Technology.

The USGS-led study, done in cooperation with state and local government agencies and several universities and affiliated consultants, was among the first to test the accuracy of microbial source tracking methods against samples of known origin, called "challenge isolates." Scientists compared the accuracy of several source tracking tools in classifying E. coli strains to various sources (humans, dogs, geese, deer, horses, pigs, cows, and chickens).

When researchers sent E. coli challenge isolates (the sources of which were unknown to those conducting the tests) for testing, many isolates either remained unclassified or were classified to incorrect sources. In all, fewer than 30 percent of challenge isolates were classified to the correct source-animal species by any method.

"When people are faced with contaminated drinking water, they want a rapid response and remediation," said Don Stoeckel, USGS technical lead for the project. "This could involve repairing sewers, modifying agricultural practices, or other efforts that are costly. The ability to trace back to the source is crucial in making sure the response actually fixes the problem."

Within the last five years, state governments have begun using microbial source tracking methods with E. coli bacteria to help manage bacteria loads to streams. Various commercial firms offer source tracking services to clients around t
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6-Dec-2004

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