Occurrence of antibiotic resistance genes as emerging contaminants in watersheds of Tama River and Lake Kasumigaura in Japan

Abstract

Antibiotic resistance is one of the important health issues. Since antibiotic resistance genes (ARGs) can transfer to pathogenic bacteria in the circulation of human-animal-ecosystems, they are regarded as emerging contaminants. However, little is known about the prevalence of ARGs in water environment. In our study, we investigated the occurrence of ARGs in two watersheds in Japan. Water samples were collected in Tama River in Tokyo in October 2018. Another sampling was conducted in Lake Kasumigaura in Ibaraki Prefecture in November 2018. Four ARGs (bla TEM encoding extended spectrum β-lactamase, sulI encoding the resistance to sulphonamide, tetA encoding the resistance to tetracycline, ere(A) encoding the resistance to macrolide-lincosamide-streptogramin) and one mobile genetic element (intI1 encoding integron) were determined by quantitative PCR. In Tama River, bla TEM and ere(A) were below quantification limit at the most upstream point before receiving wastewater effluent. However, they jumped up in the order of 106-107 copies/L just after receiving the effluent from wastewater treatment plants. The concentrations of the other ARGs and intI1 also increased due to the impact of wastewater effluent. In Lake Kasumigaura, the sampling point which was close to the discharge point of wastewater effluent and the mouth of Sakura River showed the highest copy numbers of intI1, sul1, and ere(A). All target genes were detected at the farthest point in the lake, suggesting that ARGs were persistent in water environment. In order to maintain sustainable water environment, monitoring of ARGs released from wastewater treatment plant is necessary.