Proliferation of Multidrug-Resistant New Delhi Metallo-β-lactamase Genes in Municipal Wastewater Treatment Plants in Northern China Yi Luo, † Fengxia Yang, †,‡ Jacques Mathieu, § Daqing Mao,* ,‡ Qing Wang, † and P. J. J. Alvarez* ,§ † College of Environmental Science and Engineering, Ministry of Education Key Laboratory of Pollution Processes and Environmental Criteria, Nankai University, Tianjin 300071, China ‡ School of Environmental Science and Engineering, Tianjin University, Tianjin 300072, China § Department of Civil and Environmental Engineering, Rice University, MS 519, 6100 Main Street, Houston, Texas 77005, United States * S Supporting Information ABSTRACT: The New Delhi metallo-β-lactamase (NDM-1) increases bacterial resistance to a broad range of antibiotics, and bacteria that produce it can cause infections that are very difficult to treat, thus posing great risks to human health. This paper addresses the occurrence of NDM-1 genes through different processes in wastewater treatment plants (WWTPs). NDM-1 genes prevailed through several treatment units (including disinfection by chlorination) in two WWTPs in northern China. Significant NDM-1 gene levels were present in the effluent discharged from both WWTPs (from 1316 ± 232 to 1431 ± 247 copies/ mL, representing from 4.4 to 93.2%, respectively, of influent levels). NDM-1 genes were present at much higher concentrations in dewatered waste sludge that is applied to soils [(4.06 ± 0.98) × 10 7 to (6.21 ± 2.23) × 10 7 copies/g of dry weight], raising the possibility of propagation to indigenous bacteria. This concern was validated by a conjugation experiment with Haihe River sediment not harboring NDM-1 genes at detectable levels, where an NDM-1-positive Achromobacter sp. isolated from a WWTP transferred the NDM-1 gene to an indigenous Comamonas sp. The discharge of NDM- 1 genes in the effluent and dewatered waste sludge from WWTPs (even at rates higher than influent values) underscores the need to better understand and mitigate their proliferation and propagation from WWTPs. ■ INTRODUCTION Multidrug-resistant bacteria (MRB) pose an imminent threat to global health. 1,2 The emergence of MRB is commonly acknowledged to be due to the widespread, indiscriminate, and increasing use of antibiotics, of which β-lactam antibiotics are among the most commonly prescribed. Bacterial genes encoding β-lactamases, which hydrolyze β-lactam rings and disrupt the antibiotic properties of the molecules, are continuously being identi fied as major determinants of multidrug resistance. In particular, the metallo-β-lactamases (MBL) are the most troubling because of their zinc-catalyzed mechanism of hydrolysis, and bacteria that produce them can cause infections that are very difficult to treat. 3 In 2009, a broad-spectrum antibiotic-resistant strain of Klebsiella pneumonia was isolated from a Swedish patient previously hospitalized in India. 4 The antibiotic resistance determinant was identified as a novel MBL and designated the New Delhi metallo-β-lactamase (NDM-1). To date, cases of multidrug-resistant bacteria (mostly enterobacteria) harboring the encoding gene, bla NDM‑1 , have been found on every continent except Antarctica. The widespread proliferation of bla NDM‑1 is particularly concerning because it endows its host with resistance to all β-lactam antibiotics except aztreonam. Furthermore, bla NDM‑1 is plasmid-borne and can propagate rapidly. In some cases, bla NDM‑1 -positive isolates have been found to be resistant to all antibiotics, including tigecycline and colistin to which these isolates are normally susceptible. 5,6 NDM-1 genes are appearing more frequently in nonclinical samples and were recently detected in Acinetobacter lwof f ii isolated from chicken in eastern China 7 and in seepage and tap water samples from New Delhi. 8 Most recently, the NDM-1 gene was detected in hospital sewage; 9 however, there are few or no data regarding propagation of the NDM-1 gene and its fate in the environment. This is the first report of the occurrence, persistence, and fate of NDM-1 genes through different processes in wastewater treatment plants (WWTPs). Conjugation experiments with an NDM-1-positive Achromobacter sp. isolated from a WWTP and indigenous bacteria in Haihe River sediment were also conducted to address the potential propagation of NDM-1 genes in environments receiving WWTP discharges. Knowl- Received: November 14, 2013 Revised: December 3, 2013 Accepted: December 4, 2013 Published: December 4, 2013 Letter pubs.acs.org/journal/estlcu © 2013 American Chemical Society 26 dx.doi.org/10.1021/ez400152e | Environ. Sci. Technol. Lett. 2014, 1, 26-30