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Transmission of mcr-1-Producing Multidrug-resistant Enterobacteriaceae in Public Transportation in Guangzhou, China.

Objectives
mcr-1-mediated colistin resistance in bacteria is concerning, as colistin is used in treating multidrug-resistant bacterial infections. And mcr-1-producing bacteria have been identified in multiple sources. Up to 248 million people use public transportation daily in China, however; public transportation hasn't been studied as a potential source of community-based transmission of mcr-1. Herein we investigated mcr-1-producing isolates from public transportation and explored the genomic characteristics of them.


Methods
Surface samples were collected from public transportation in Guangzhou, China, from October 2016 to April 2017. Polymerase chain reaction was performed to detect mcr-1 gene, plasmid replicon type and phylogenetic group. Minimum inhibitory concentrations (MICs) were determined by microdilution method. S1-nuclease digestion and pulsed-field gel electrophoresis (S1-PFGE) and Southern blotting were performed with mcr-1-harboring plasmids. Whole-genome sequencing was performed with mcr-1-producing isolates.


Results
Of the 737 samples with bacterial growth, 26 isolates were positive for mcr-1, including 23 Escherichia coli and 3 Klebsiella pneumoniae isolates. The E. coli isolates belonged to phylogroups A and B1. Most mcr-1-producing isolates were resistant to ampicillin (25), cefotaxime (21), fosfomycin (16), and gentamicin (15). S1-PFGE, Southern blotting and replicon typing showed that mcr-1 was mainly located on ~33.3 kb to ~220 kb IncX4, IncI2 and IncHI2 plasmids in E. coli, while located on ~33.3 kb untyped plasmid in K. pneumoniae. Several sequence types (ST), including ST2253, ST101, ST10 complex and ST37, were revealed. Between 53 and 66 (mean = 61.8) resistance genes were identified among mcr-1-producing isolates.


Conclusions
Public transportation may serve as a source of mcr-1-producing bacteria.