A recent study by Agricultural Research Service scientist Mark Ibekwe suggests that runoff from urban areas in some parts of California may be more to blame for E. coli than confined animal production facilities, according to a news release.
Most strains of E. coli don't cause disease, but they're monitored as an indicator species by public health officials.
Cows often are blamed for the E. coli found in waterways.
Ibekwe, who's based in Riverside, Calif., and colleagues collected 450 water and sediment samples from 20 sites in the Santa Ana River watershed.
The sites included urban ares, livestock feeding areas, national forest lands and three wastewater treatment plants.
From the samples, they identified more than 600 different isolates of E. coli.
They found the greatest variety in runoff from areas dominated by urban development or human activities.
Ibekwe also tested the organisms for antibiotic resistance.
He found that 88 percent to 95 percent of the isolates were resistant to rifampicin, and about 75 percent were resistant to tetracycline.
The scientists also found that 24 percent of the E. coli samples from urban runoff—144 isolates—showed resistance to as many as seven antibiotics.