Association of colistin residues and manure treatment with the abundance of mcr-1 gene in swine feedlots

• Published in: Environment international 2019-06, Vol.127, p.361-370
• Main Authors: Xia, Xi, Wang, Zheng, Fu, Yulin, Du, Xiang-dang, Gao, Binwen, Zhou, Yuqing, He, Junjia, Wang, Yang, Shen, Jianzhong, Jiang, Haiyang, Wu, Yongning
• Format: Article
• Language: English
• Subjects: Bacterial community; Colistin; mcr-1 gene; Swine feedlot; Wastewater treat process
• ISSN: 0160-4120; 1873-6750
• DOI: 10.1016/j.envint.2019.03.061

The extensive use of colistin in swine production may have contributed to the recent emergence of corresponding mobile resistance gene mcr-1. The use of colistin as a feed additive was banned in China in April 2017. To examine the occurrence of colistin and dissemination of mcr-1 in swine feedlots before and after the colistin ban and effects of different manure treatments. Environmental samples were collected from swine feedlots before (December 2016) and after (December 2017) the colistin ban. Colistin concentrations were determined by ultra-high performance liquid chromatography coupled to tandem mass spectrometry. The prevalence of mcr-1 were determined by quantitative PCR analysis, while bacterial community composition was investigated by 16S rRNA sequencing. In 2016, colistin was detected in feed and fresh manure samples at 67 mg/kg and 17 mg/kg, respectively, but was absent from all samples in 2017. In 2016, the relative abundance of mcr-1 in fresh manure was lower than that in solid samples after natural drying, while a higher relative abundance was detected in fresh manure samples compared with biogas slurry samples. A strong correlation between colistin concentration and relative abundance of mcr-1 was observed in fresh manure. The samples collected in 2017 showed a lower relative abundance of mcr-1 compared with those collected in 2016. Bacterial community analysis showed that the abundance of Enterobacteriaceae, which act as a vehicle and reservoir of mcr-1, increased with natural dying but decreased with anaerobic digestion. The presence of colistin exerts direct selection pressure for the accumulation of mcr-1 in manure, while the ban on colistin likely halted the dissemination of mcr-1 on pig farms. Anaerobic digestion is an effective waste treatment process for removing mcr-1, which might be mainly driven by the shift in bacterial community structure. •The presence of colistin exerts direct selection pressure for the accumulation of mcr-1 in swine feedlots.•The ban on the use of colistin as an animal feed additive helped decrease the prevalence of mcr-1 in pig farm environments.•Anaerobic digestion is an effective waste treatment process for removing mcr-1.