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Description

Antimicrobial resistance is an emerging public health crisis, leading to 23,000 deaths annually in the United States. Resistance to antimicrobials is conferred by acquisition of antibiotic resistance genes (ARG) via horizontal gene transfer, a process that can occur in a variety of settings including healthcare, agriculture, and the environment. Urban rivers are especially vulnerable to promoting the selection and spread of antimicrobial resistance because they are heavily influenced by human activity, including pollution from high nutrient loads, heavy metals, industrial discharge, and sewage. The aim of this study is to quantify the levels of ARG in the lower Merrimack River, which provides drinking water to approximately 500,000 people in southern New Hampshire and northeastern Massachusetts. Water samples were collected at 15 sites along the Merrimack River, between Manchester, NH and Newburyport, MA, throughout the summers of 2024 and 2025. Additional samples were collected in association with combined sewage overflow events. To assay for the presence of antibiotic-resistant bacteria, total DNA was isolated from water microorganisms captured by filtration, and ARG were quantified using quantitative PCR. ARG assays include molecular markers of beta-lactam resistance (bla-TEM), sulfonamide resistance (sul2), and tetracycline resistance (tetA), as well as mobile genetic elements associated with ARG transfer. Our data show that concentrations of bla-TEM are highest relative to sul2 and tetA, and concentrations of all ARGs examined peak in areas downstream of combined sewage outfalls. We are currently analyzing trends in ARG levels to see how they correlate with other water quality parameters.

Publication Date

4-30-2026

Keywords

antibiotic resistance, combined sewage outfalls

Examining Antibiotic Resistance in the Merrimack River

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