Tracking Fecal Pathogens in Troubled Waters

When asked about her professional interest in feces, Dr. Alexandria Graves lets out a hearty laugh and recalls the time a man checking out her research poster at a microbiology conference told her she really knew her, ahem, stuff. But the impact of her work to track the source of pathogens like E.coli and Enterococcus that wind up in North Carolina’s waterways is no laughing matter to Graves, an assistant professor in the Department of Soil Science. “If I can help people,” she says, “that pleases me as much as the science involved in my work.”

Antibiotic resistance and genetic markers can be used to determine the source of fecal bacteria.

The science of Graves’ work involves using antibiotic resistance and genetic markers to determine the source of fecal bacteria. By collecting fecal samples from livestock and wildlife near a contaminated site and from residential septic systems in the area, Graves and her graduate students can build a database against which an unknown sample can be compared. Human fecal bacteria would show the most resistance to a range of antibiotics, while that of wildlife like birds or deer would show the least. Pinpointing the source of the contamination not only facilitates an environmental cleanup, she says, but also ensures that regulations address problems adequately.

In one project, for example, Graves’ team tested streams near Sampson County hog farms, as well as the soil and groundwater beneath fields where effluent from a waste lagoon was sprayed. The varied nature of the contamination found in the area led them to conclude that wildlife was the primary culprit. Birds landing in the waste lagoon would spread bacteria, Graves says, adding that turtle tracks have also been seen between lagoons and streams near the study site. “The swine industry bears the brunt of criticism for pollution in eastern North Carolina, but some of it is undeserved,” she says. “Regulators need to distinguish between what farmers can and cannot control.”

Pinpointing the source of contamination not only facilitates an environmental cleanup, but also ensures that regulations address problems adequately.

Graves recently finished a two-year study of the North River in Carteret County, which has been closed to shellfishing because of high bacterial counts. Her team used a fluorometer to test the water for optical brighteners—chemicals added to detergents to make clothes brighter—and traced the contamination to septic systems in a nearby community. “There are many low-lying areas in North Carolina where tidal activity can infiltrate septic system drain fields and then carry away bacteria,” she says. Communities have previously used such findings to obtain federal funding for wastewater treatment systems. The thought of cleansing a river and possibly helping a low-income community get proper wastewater treatment elicits only a smile—no laughs—from Graves.


To determine the source of contamination, Dr. Alexandria Graves tests fecal bacteria against a database she and her students created after collecting samples of feces from wildlife and septic systems.