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.