Role of Point Sources on the Dissemination of Antibiotic Resistance in the Environment

Abstract

Point sources such as wastewater treatment plants (WWTPs), terrestrial agriculture, and aquaculture, release antibiotic residues, antibiotic resistant bacteria (ARB), and antibiotic resistance genes (ARG) into the aquatic ecosystem. However, increases of ARB and ARG in the natural environment associated with specific point sources have not been widely quantified. The goals of this dissertation were to improve study designs for measuring environmental ARB and ARG, and the methodology to attribute environmental findings to specific point sources. Two systematic reviews were conducted to analyze the evidence for increases of ARB and ARG in the natural environment associated with point sources. Both reviews highlighted the lack of quantitative causal research, and the need for improved study design, control of biases, and analytical tools to provide effect measures. Recommendations drawn from these systematic reviews informed two longitudinal studies assessing the role of freshwater trout farms and WWTPs on environmental ARG abundance in a watershed in Chile. Sediment samples from river sites located at different distances upstream and downstream from each point source were analyzed. Also, wild birds trapped around one of the WWTPs were evaluated for their role as disseminators of ARG. A microfluidic qPCR approach was used to quantify an array of ARG, and statistical analyses were conducted to evaluate the effect of the point sources on ARG abundance in the surrounding natural environment. Results showed a statistically significant increase of ARG at downstream sites compared to upstream sites, indicating that these sources were contributing to releases of ARG into the surrounding environment. However, the biological significance remains unclear and deserves further examination. Migratory birds presented a statistically significantly higher ARG abundance compared to non-migratory species. Even though wild birds are recognized as playing a part in the dissemination of ARB globally, results from this study can’t be overstated. The long-term goal of this research would include the development of a watershed-based monitoring system to evaluate all point sources that contribute to increases and dissemination of ARB and ARG. A better understanding of dissemination pathways would allow targeting management strategies to mitigate the risk to public health, animal health, and ecosystem health.