Characterization of Antibiotic Resistant Genes in Two Unique City Sewer Systems

Abstract

Sewer systems are known as point sources for the release of antibiotic resistance into the environment. Antibiotic resistance genes (ARGs) provide bacteria the ability to fight antibiotics and are viewed as emerging contaminants in environmental waterways. To minimize the spread of ARGs to the environment, this study assessed the prevalence of ARGs in upstream sewer systems that feed into wastewater treatment plants (WWTPs) so that source control strategies can be developed to mitigate the spread of antibiotic resistance. Wastewaters were examined from two unique city sewer systems containing three source types: hospital, residential, and industrial. Twenty-nine ARGs, 3 integron-intergrases, and 4 metal resistance genes were quantified using conventional and microfluidic polymerase chain reactions. Bacterial community compositions were characterized using high-throughput 16S rRNA amplicon sequencing. We found the levels of ARGs and bacterial community compositions to be dependent on the source of wastewater, the city, and the season. The abundance of ARGs in hospital wastewater were relatively constant and associated with clinically relevant antibiotics. ARG abundance in residential wastewater showed seasonal variations with high levels in winter associated with outpatient antibiotics. High levels of integron-integrase genes, a proxy for horizontal gene transfer and anthropogenic impacts, were also observed in residential wastewaters. Based on these findings we suggest satellite treatment of ARGs at hospital and residential sources to reduce their loading to WWTPs and their inevitable release to the environment.