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November 30, 2012

Sources of E. coli are not always what they seem

by Taking Stock Contributor
ecoli_river

By Sandra Avant / USDA ARS Public Affairs

Agricultural Research Service (ARS) scientists have identified sources of Escherichia coli bacteria that could help restore the reputation of local livestock. Studies by ARS microbiologist Mark Ibekwe suggest that in some parts of California, pathogens in local waterways are more often carried there via runoff from urban areas, not from animal production facilities. 

ARS is the chief intramural scientific research agency of the U.S. Department of Agriculture (USDA), and this work supports the USDA priority of ensuring food safety.

Even though most strains of E. coli are non-pathogenic, the bacterium is monitored by public health officials as an indicator of water quality.  Cows are often seen as the culprits when E. coli is found in local lakes, rivers and other bodies of water.

Ibekwe, who works at the ARS U.S. Salinity Laboratory in Riverside, Calif., and his colleagues collected 450 water and sediment samples from 20 sites throughout California’s middle Santa Ana River Watershed. The collection sites included urban areas, livestock feeding areas, parks, National Forest lands, and three wastewater treatment plants.

Then the scientists extracted E. coli bacteria from each sample and identified 600 different isolates of E. coli in their samples, many of which could be placed into six clonal populations. They found the greatest variety of different types of E. coli in runoff discharged from areas dominated by urban development or human activities.

Ibekwe also tested all the E. coli isolates for resistance to various antibiotics. He found that from 88 to 95 percent of the isolates were resistant to rifampicin, and that around 75 percent were resistant to tetracycline. Tetracycline resistance was by far the most common type of resistance observed in E. coli isolates collected near wastewater treatment plants.

The scientists also found that 24 percent of E. coli collected in sediment samples associated with urban runoff—a total of 144 isolates—showed resistance to as many as seven antibiotics. Results from this work were published in PLOS ONE.

Read more about this work in the November/December 2012 issue of Agricultural Research magazine.

SCIENTIFIC CONTACT: Mark Ibekwe, ARS Contaminant Fate and Transport Research Unit, , Riverside, Calif., phone (951) 369-4828, mark.ibekwe@ars.usda.gov.

FOR FURTHER READING:

E. coli can survive in streambed sediments for months http://www.ars.usda.gov/is/pr/2011/110701.htm

Studies focus on feed ingredient’s effects on levels of E. coli O157:H7 in cattle
http://www.ars.usda.gov/is/pr/2011/110519.htm

E. coli an unlikely contaminant of plant vascular systems http://www.ars.usda.gov/is/pr/2011/110401.htm

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