Occurrence of Antibiotic Resistance Genes in Green Stormwater Infrastructure

Antibiotic resistance is the phenomenon of bacteria acquiring antibiotic resistance genes (ARGs) that resist the effects of the antibiotics designed to target and kill them. Though ARGs occur naturally, their presence has become widespread in nature due to the overuse of antibiotics in medical and agricultural sectors and it is threatening the core of modern medicine and human health as ARGs are rendering antibiotics less effective against bacterial infections. Recent research aimed at understanding environmental factors that contribute to ARG spread has identified stormwater as a vector ARGs entering the aquatic environment, with greater ARG concentrations in stormwater compared to baseflow conditions. Consequently, while we know that ARGs are in stormwater, we do not know how ARGs are accumulating or moving through stormwater infrastructure, specifically green stormwater infrastructure (GSI), which are designed to mitigate conventional pollutants. The objectives of this study are to: (1) understand if GSI accumulate and/or transmit ARGs into the environment and (2) determine if GSI properties contribute to ARG proliferation in bacterial soil communities. 24 GSI sites in Milwaukee, WI were selected, including 14 bioswales, 7 bioretention cells, and 3 wetlands; a rural, non-engineered reference site was also included. Soil samples from each site were collected and analyzed to measure soil quality. DNA was also extracted from the soil and ARGs were analyzed via metagenomic sequencing. The results indicate that a wide breath of GSI sites were sampled representing diverse soil, site, and catchment characteristics. The number of ARGs in the soil samples ranged from 799 to 3402 with 83% of the GSI systems having a greater number of ARGs than the reference site. GSI characteristics and design features that are influential over the occurrence of ARGs in GSI will be discussed as well as the impact of soil quality properties and microbial communities.