Dirt Tells Resistance Tales

Despite measures aimed at curbing antibiotic resistance, a study in Europe suggests that resistance might still be on the rise in the environment (Environ. Sci. Technol., DOI: 10.1021/es901221x). The work provides data spanning nearly 70 years, and it complements public health data from patients.

For years, studies have shown that antibiotic resistance is up at hospitals, apparently due to clinical use of antibiotics. But antibiotics are also used in agriculture to increase productivity and prevent disease in livestock. In theory, excessive use of antibiotics could expand reservoirs of resistance in soil microbes. Antibiotic resistance genes naturally exist in soil and sewage microbes, but no long-term studies have been performed to gauge how resistance might have changed since the 1940s, when antibiotic mass production kicked in.

Now, environmental engineer David W. Graham of Newcastle University, in England; molecular ecologist Charles W. Knapp, now at the University of Strathclyde, in Scotland; and colleagues have found a way to delve into that past. “We thought that by extracting DNA from soil archives, we might be able to learn something about the longer term history,” he says. In collaboration with TAGA, a soil archive maintained by research institute Alterra at Wageningen University, in the Netherlands, the team quantified antibiotic resistance genes for five sets of soil samples from across the Netherlands, with one set dating back to 1940.

For every drug class the team examined, levels of resistance genes have significantly increased since 1940. In particular, genes that confer resistance to tetra­cycline antibiotics have spiked in recent decades, becoming 15 times more abundant than in the 1970s.

The work suggests that resistance research should be broadened to include environmental reservoirs so that resistance can be more efficiently mitigated in the future, Graham says. This study was relatively local, he notes, but “we suspect similar patterns also are occurring in soils from other locations around the world.”

“In retrospect, we should have anticipated the environmental outcome that this study documents,” says Shahriar Mobashery, who studies antibiotic resistance at the University of Notre Dame.