title: Prevalence and proliferation of antibiotic resistance genes in two municipal wastewater treatment plants.
abstract: The propagation of antibiotic resistance genes (ARGs) is an emerging health concern worldwide. Thus, it is important to understand and mitigate their occurrence in different systems. In this study, 30 ARGs that confer resistance to tetracyclines, sulfonamides, quinolones or macrolides were detected in two activated sludge wastewater treatment plants (WWTPs) in northern China. Bacteria harboring ARGs persisted through all treatment units, and survived disinfection by chlorination in greater percentages than total Bacteria (assessed by 16S rRNA genes). Although the absolute abundances of ARGs were reduced from the raw influent to the effluent by 89.0%-99.8%, considerable ARG levels [(1.0 ± 0.2) × 10(3) to (9.5 ± 1.8) × 10(5) copies/mL)] were found in WWTP effluent samples. ARGs were concentrated in the waste sludge (through settling of bacteria and sludge dewatering) at (1.5 ± 2.3) × 10(9) to (2.2 ± 2.8) × 10(11) copies/g dry weight. Twelve ARGs (tetA, tetB, tetE, tetG, tetH, tetS, tetT, tetX, sul1, sul2, qnrB, ermC) were discharged through the dewatered sludge and plant effluent at higher rates than influent values, indicating overall proliferation of resistant bacteria. Significant antibiotic concentrations (2%-50% of raw influent concentrations) remained throughout all treatment units. This apparently contributed selective pressure for ARG replication since the relative abundance of resistant bacteria (assessed by ARG/16S rRNA gene ratios) was significantly correlated to the corresponding effluent antibiotic concentrations. Similarly, the concentrations of various heavy metals (which induce a similar bacterial resistance mechanism as antibiotics - efflux pumps) were also correlated to the enrichment of some ARGs. Thus, curtailing the release of antibiotics and heavy metals to sewage systems (or enhancing their removal in pre-treatment units) may alleviate their selective pressure and mitigate ARG proliferation in WWTPs.
authors.affiliation: School of Environmental Science and Engineering, Tianjin University, Tianjin 300072, China.
authors.forename: Daqing
authors.initials: D
authors.lastname: Mao
authors.affiliation: College of Environmental Science and Engineering, Ministry of Education Key Laboratory of Pollution Processes and Environmental Criteria, Nankai University, Tianjin 300071, China.
authors.forename: Shuai
authors.initials: S
authors.lastname: Yu
authors.affiliation: GSI Environmental Inc., 2211 Norfolk, Suite 1000, Houston 77098, TX, USA.
authors.forename: Michal
authors.initials: M
authors.lastname: Rysz
authors.affiliation: College of Environmental Science and Engineering, Ministry of Education Key Laboratory of Pollution Processes and Environmental Criteria, Nankai University, Tianjin 300071, China. Electronic address: luoy@nankai.edu.cn.
authors.forename: Yi
authors.initials: Y
authors.lastname: Luo
authors.affiliation: School of Environmental Science and Engineering, Tianjin University, Tianjin 300072, China; College of Environmental Science and Engineering, Ministry of Education Key Laboratory of Pollution Processes and Environmental Criteria, Nankai University, Tianjin 300071, China.
authors.forename: Fengxia
authors.initials: F
authors.lastname: Yang
authors.affiliation: College of Environmental Science and Engineering, Ministry of Education Key Laboratory of Pollution Processes and Environmental Criteria, Nankai University, Tianjin 300071, China.
authors.forename: Fengxiang
authors.initials: F
authors.lastname: Li
authors.affiliation: College of Environmental Science and Engineering, Ministry of Education Key Laboratory of Pollution Processes and Environmental Criteria, Nankai University, Tianjin 300071, China.
authors.forename: Jie
authors.initials: J
authors.lastname: Hou
authors.affiliation: College of Environmental Science and Engineering, Ministry of Education Key Laboratory of Pollution Processes and Environmental Criteria, Nankai University, Tianjin 300071, China.
authors.forename: Quanhua
authors.initials: Q
authors.lastname: Mu
authors.affiliation: Department of Civil and Environmental Engineering, Rice University, MS 519, 6100 Main Street, Houston 77005, TX, USA. Electronic address: alvarez@rice.edu.
authors.forename: P J J
authors.initials: PJ
authors.lastname: Alvarez
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001419:Bacteria / Q000145:classification / Q000187:drug effects / Q000235:genetics*; D002681:China; D004352:Drug Resistance, Microbial / Q000235:genetics*; D005798:Genes, Bacterial / Q000235:genetics*; D012336:RNA, Ribosomal, 16S / Q000235:genetics / Q000378:metabolism; D060888:Real-Time Polymerase Chain Reaction; D017422:Sequence Analysis, DNA; D014865:Waste Disposal, Fluid; D062065:Wastewater / Q000382:microbiology*
chemical_list: D000900:Anti-Bacterial Agents; D012336:RNA, Ribosomal, 16S; D062065:Wastewater
keywords: Antibiotic resistance propagation; Antibiotics removal; Wastewater treatment plant