Journal of Environmental Biology

Sewage treatment plant serves as a hot-spot reservoir of

integrons and gene cassettes

Liping Ma, Xu-Xiang Zhang*, Fuzheng Zhao, Bing Wu, Shupei Cheng and LiuyanYang

State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University,
Nanjing, 210 046, China.

*Corresponding Author email : zhangxx@nju.edu.cn

Publication Data

Paper received:

8 June 2012

Revised received:

20 October 2012

Accepted:

18 December 2012

Abstract

This study investigated the occurrence and abundance of class 1 integrons and related antibiotic resistance genes (ARGs) in a sewage treatment plant (STP) of China. Totally, 189 bacterial strains were isolated from influent, activated sludge and effluent, and 40 isolates contained the integons with a complete structure. The intI1-carrying isolates were found to harbor two types of gene cassettes: dfr17-aadA5 and aadA2, conferring resistances to trimethoprim and streptomycin, which were further confirmed by antimicrobial susceptibility analysis. Many other gene cassettes were carried on integron, including qnrVC1, catB-8-blaoxa-10-aadA1-aac(6'), aadB-aacA29b, aadA2, aac(6')-1b, aadA6 and aadA12, which were detected using DNA cloning. Quantitative real time PCR showed that over 99% of the integrons was eliminated in activated sludge process, but average copy number of integrons in given bacterial cells was increased by 56% in treated sewage. Besides integrons, other mobile gene elements (MGEs) were present in the STP with high abundance. MGEs and the associated ARGs may be wide-spread in STPs, which constitute a potential hot spot for selection of antibiotic resistant bacteria and horizontal transfer of ARGs.

Key words

Class 1 integron, Antibiotic resistance gene, Gene cassette, Mobile gene element, Sewage treatment plant, Bacterial strains

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