The University of Georgia’s J. Vaun McArthur, a senior research ecologist with the Savannah River Ecology Laboratory and Odum School of Ecology, believes environmental contaminants may play a greater role in the rise in antibiotic-resistant bacteria than previously thought.
To test his hypothesis, McArthur turned to the streams on the U.S. Department of Energy’s Savannah River Site, located East of the Savannah River near Aiken, South Carolina. The 310-square mile site was constructed in the 1950s for the production of materials used in nuclear weapons, and has been closed since that time to public access.
“The site was constructed and closed to the public before antibiotics were used in medical practices and agriculture,” said McArthur, according to Science News Online. “The streams have not had inputs from waste-water, so we know the observed patterns are from something other than antibiotics.”
Five antibiotics were tested against 427 strains of Escherichia coli from 11 locations in nine streams covering the property that included both sediment and water samples. The sites chosen included a range of watersheds, from areas of minimally disturbed water to areas where the water was highly impacted. Metal contamination at the chosen sites varied from little to high levels.
Lab Manager reports that high levels of antibiotic resistance were found in eight of the 11 water samples. Interestingly, the highest levels of antibiotic resistance in both water and sediment were found in the northern section of Upper Three Runs Creek, where the stream system enters the site, and in two tributaries located in the industrial area, U4 and U8.
Upper Three Runs Creek flows through residential, agricultural and industrial areas before reaching the Savannah River Site, so McArthur concludes the bacteria in the stream have been exposed to antibiotics. The bacteria in the U4 and U8 sites have no known input from antibiotics, says McArthur, and he attributes the high level of antibiotic resistance to “legacy waste.”
Legacy waste is defined as wastes containing radium, or radioactive material, and are usually the by-products of nuclear power generation and other applications of nuclear fission or nuclear technology, such as research and medicine.
A second series of screenings using 23 antibiotics was done on the U4 and U8 sites, along with the U10 site, a small stream little impacted from industry. “More than 95 percent of the bacteria samples from these streams were resistant to 10 or more of the 23 antibiotics,” McArthur said. This included two “front-line” antibiotics, gatifloxacin and ciprofloxacin, both widely used to treat everything from pink-eye to urinary tract infections.
“These streams have no source of antibiotic input, thus, the only explanation for the high level of antibiotic resistance is the environmental contaminants in these streams—the metals, including cadmium and mercury,” McArthur said. While it is possible that the streams could have been contaminated by animal contact, it doesn’t explain the reason that only streams with a history of industrial input had antibiotic-resistant bacteria.
McArthur is concerned about this discovery because the streams drain into the Savannah River. The river shares two common characteristics of many rivers that lie in close proximity to residential areas in the U.S. It receives industrially contaminated water-prone to antibiotic resistance. “The findings of this study may very well explain why resistant bacteria are so widely distributed,” McArthur said.
The study, “Patterns of Multi-Antibiotic-Resistant Escherichia Coli from Streams with No History of Antimicrobial Inputs,” was published in the journal Environmental Microbiology on November 3, 2015.
