Date Approved

2026

Degree Type

Open Access Thesis

Degree Name

Master of Science (MS)

Department or School

Biology

Committee Member

Maitreyee Mukherjee, Ph.D.

Committee Member

Kristin Judd, Ph.D.

Committee Member

Maria Goodrich, M.S.

Abstract

Antibiotic resistance is a growing global public health concern that extends beyond clinical settings and into natural freshwater environments, where resistant bacteria and antibiotic resistance genes (ARGs) can persist and disseminate through watersheds. Despite growing recognition of freshwater systems as environmental reservoirs of resistance, no published studies have examined antibiotic resistance within the Huron River watershed in Southeast Michigan. Water samples were collected monthly from May through October 2025 at 10 sites along the Huron River. E. coli and Enterococcus isolates were evaluated for resistance to eight antibiotics using the Kirby-Bauer disk diffusion method, and environmental DNA was analyzed by qPCR for five ARGs including sul1, ermB, tetW, intI1, and dfrA1. Antimicrobial resistance and multidrug resistance were detected in both organisms across all sites and sampling months, with erythromycin and cephalothin showing the highest resistance in E. coli and ciprofloxacin and erythromycin most prominent in Enterococcus. All five ARGs were detected throughout the sampling period, with intI1 consistently showing the highest abundance across all months. This was followed by sul1 and tetW which both had corresponding peaks in phenotypic resistances . Significant differences in resistance levels across sampling months were detected for tested antibiotics and all five ARG targets. These findings provide the first baseline characterization of antibiotic resistance within the Huron River watershed and demonstrate that the river harbors a persistent and diverse environmental resistome shaped by multiple anthropogenic inputs, with implications for water quality management and public health monitoring in the region.

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