The Transfer and Transport of Antibiotic Resistance in Heavy-Metal Contaminated StreamsEPA Grant Number: FP916326
Title: The Transfer and Transport of Antibiotic Resistance in Heavy-Metal Contaminated Streams
Investigators: Wright, Meredith S.
Institution: University of Georgia
EPA Project Officer: Michaud, Jayne
Project Period: January 1, 2004 through December 31, 2006
Project Amount: $104,644
RFA: STAR Graduate Fellowships (2004) RFA Text | Recipients Lists
Research Category: Academic Fellowships , Aquatic Ecosystems , Fellowship - Aquatic Ecology and Ecosystems
One aspect challenging public health efforts to minimize the spread of antibiotic resistance (AR) is the prevalence of resistant bacteria in the environment. Anthropogenic-derived sources of selection typically are implicated as mechanisms for increasing AR in the environment, whether it is through the release of antibiotics or resistant bacteria from confined animal feeding operations, hospital waste, or sewage treatment facilities. An increasing number of studies have documented an additional potential mechanism for AR bacteria through co- or cross-resistance to heavy metals. Preliminary studies conducted at the Savannah River Ecology Laboratory demonstrate that bacteria isolated from heavy-metal contaminated streams have a higher frequency of AR compared to reference streams, despite no significant source of anthropogenic-derived antibiotics or sewage inputs at these sites. Therefore, it appears likely that heavy metal contamination may directly select for metal-tolerant (MT) bacteria while indirectly selecting for antibiotic resistant bacteria. The objective of this research is to investigate what mechanisms are involved in the development and transmission of antibiotic resistance in streams with heavy metal contamination.
In addressing the central question of how AR is transferred and transported in heavy-metal contaminated streams, two scales must be considered. The first is the molecular scale at which genes are transferred between bacterial genomes. Predicted factors influencing the gene transfer rate include the degree of selective pressure (e.g., metal availability), aspects influencing bacterial abundance and activity, such as carbon and nutrient availability and temperature, and factors that influence the extent of cell contact and bacterial competency. The second scale is the watershed scale at which genes are transported through the stream network. Transport routes for bacteria in stream networks include aerial dispersal, groundwater connectivity, surface water flow, or transport via other organisms such as invertebrates or fish. Only the latter two transport routes will be considered in this study. Factors influencing bacterial transport are predicted to be those contributing to bacterial dislodgement from microhabitats (e.g., physical scouring due to stream flow, disruption of habitat due to invertebrate activities) and the degree of selective pressure favoring the establishment of the bacteria or gene.
The goal of this project is to unite the two scales of gene transfer and transport by: (1) analyzing AR and MT patterns in stream microhabitats to identify important sites of gene transfer and transport; (2) examining how physical and chemical stream attributes correlate with these patterns to predict how AR and MT will be transferred and transported under different stream conditions; and (3) manipulating these attributes for a direct assessment of their effects on gene transfer and transport rates. The approach I will take is a combined observational and experimental study involving reference and heavy-metal contaminated sites. I will transplant invertebrates and biofilm from reference to contaminated sites and examine subsequent changes in their microbial communities and manipulate biotic and abiotic factors using a series of microcosms that test gene transfer mechanisms. Results are expected to demonstrate that heavy metal contamination is another mechanism for maintaining antibiotic resistance in the environment and to generate information regarding the frequency of gene transfer events in the environment under varying degrees of selective pressure.