Rationale

The dramatic decline in the effectiveness of antibiotics during the last decade provides a striking example of bacterial evolution in action. Many genes conferring antibiotic resistance are located on mobile genetic elements (e.g., plasmids, transposons, and integrons), some of which are easily exchanged among phylogenetically distant bacteria. Many of these mobile genetic elements encode resistance to multiple antibiotics, heavy metals, and other toxic compounds. It is, therefore, likely that selective pressure by one such compound indirectly selects for the whole set of resistances. Indeed, our preliminary studies indicate that the frequency of antibiotic resistance is significantly elevated in heavy metal-contaminated environments, including stream sediments, benthic fish, and organic foam. Because the number and total area of the earth's habitats contaminated with heavy metals far exceeds that contaminated with antibiotics, metal-contaminated sites may provide a critical, globally-dispersed environment for the creation, maintenance, and transfer of antibiotic resistance among bacteria.

Approach

We are initiating an extensive study encompassing both manipulative microcosm experiments to establish cause-effect relationships as well as fieldwork in metal-contaminated and pristine freshwater environments to detect correlative associations in situ. The introduction of cutting-edge culture-independent methodology is essential for a comprehensive examination of the abundance, selective mechanisms, and transfer routes of antibiotic resistance determinants in the environment. Quantitative PCR will be used to determine the ratio of specific resistance genes to bacterial DNA, and flow-cytometric cell viability analyses to determine the fraction and identity of cells resistant to the action of antibiotics and heavy metals. These analyses will be complemented with traditional plating techniques. We believe that this work provides a critical bridge between the knowledge of microbial ecology and evolution and research focusing on public health concerns over the rapid proliferation of antibiotic resistance.

Research Team

J Vaun McArthur, Senior Scientist, SREL

Travis C. Glenn, Assistant Research Scientist, SREL

Charles H. Jagoe, Associate Research Scientist, SREL

Ramunas Stepanauskas, Postdoctoral Researcher, SREL

R. Cary Tuckfield, Statistical Consulting Section Leader, Westinghouse Savannah River Company

Stuart Thompson,Assistant Professor, Medical College of Georgia

Angela Lindell, Research Technician, SREL

Cathy King, Research Technician, SREL