## 4 Conclusions  
As colistin is the last alternative to treat MDR infections, the prevalence of MCR-1 has become a critical challenge for treating and controlling infectious diseases. It is important to highlight the surveillance of polymyxin residues in aquatic environments because of the generation and spread potential of MCR-1. In the present study, an efficient and selective HPLC-UV method based on imprinted material for the determination of polymyxins from environmental water was developed. MIP synthesized by precipitation polymerization had higher affinity to target compounds than its corresponding NIP, confirming the presence of specific binding sites. Compared with a traditional C\({}_{18}\) cartridge, the MIP cartridge could remove much more matrix interferences and reduce baseline noises significantly, allowing to obtain low LOD using HPLC-UV detector. This method could be applied to detect trace amounts of polymyxins in water, which will benefit the control of microbiological risk associated with the consumption of polymyxins. Moreover, in order to prevent polymyxins from being released into the aquatic environment and reduce the occurrence and dissemination of MCR-1, more measures need to be enforced including decreasing the usage of polymyxins in veterinary medicine as well as performing strict wastewater treatment processes.  
**Supplementary Materials:** The following are available online at [[http://www.mdpi.com/2073-4360/12/1/131/s1](http://www.mdpi.com/2073-4360/12/1/131/s1)]([http://www.mdpi.com/2073-4360/12/1/131/s1](http://www.mdpi.com/2073-4360/12/1/131/s1)), Figure S1: IR spectra of MIPs and NIPs, Figure S2: The thermogravimetric analysis of MIPs and NIPs, Figure S3: Effect of loading volume on the recoveries of colistin A (CSA), colistin B (CSB) and polymyxin B (PMB) obtained after SPE onto (A) MIP and (B) NIP cartridges, Figure S4: HPLC chromatograms obtained after MISPE of target  
Figure 6: HPLC chromatograms of non-spiked river water extracted with (**a**) C\({}_{18}\) cartridge and (**b**) MIP cartridge, (**c**) spiked river water at 10 \(\upmu\)g L\({}^{-1}\) concentration level extracted with MIP cartridge and (**d**) the corresponding standard solution. Peak identifications: 1, colistin B; 2, colistin A; 3 polymyxin B.  
analytes from lake and spring water: (a) non-spiked water, (b) spiked water at 10 ug L\({}^{-1}\) concentration level and (c) mixed standard solution. Peak identifications: 1, colistin B; 2, colistin A; 3 polymyxin B.  
**Author Contributions:** Formal analysis, X.S. and A.M.-E.; Funding acquisition, L.H.; Investigation, X.S.; Methodology, X.S. and E.T.; Project administration, E.T.; Software, X.S.; Supervision, A.M.-E. and L.H.; Writing--original draft, X.S. and E.T.; Writing--review & editing, A.M.-E. and L.H. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research was funded by the National Science Foundation of China (31572562), the Key Program of Guangzhou Science and Technology Plan (201804020019) and International Joint Doctoral Program Project of College of Veterinary Medicine (SCAU).  
**Acknowledgments:** The authors are grateful to the assistance from [PERSON].  
**Conflicts of Interest:** The other co-authors declare that they have no conflict of interest.