Complex dissemination of the diversified mcr-1 -harbouring plasmids in Escherichia coli of different sequence types

// Qingjing Wang 1,* , Zhencui Li 1,* , Jingxia Lin 1 , Xiuna Wang 1,3 , Xianbo Deng 2 and Youjun Feng 1 1 Department of Medical Microbiology and Parasitology, Zhejiang University School of Medicine, Hangzhou, Zhejiang, China 2 College of Veterinary Medicine, South China Agricultural University, Guangzhou, Guangdong, China 3 Fujian Agriculture and Forestry University, Fuzhou, Fujian, China * The authors have contributed equally to this work Correspondence to: Youjun Feng, email: // Xianbo Deng, email: // Keywords : MCR-1, diversity, sequence type (ST), Immunology and Microbiology Section, Immune response, Immunity Received : August 23, 2016 Accepted : October 07, 2016 Published : October 12, 2016 Abstract The emergence of the mobilized colistin resistance gene, representing a novel mechanism for bacterial drug resistance, challenges the last resort against the severe infections by Gram-negative bacteria with multi-drug resistances. Very recently, we showed the diversity in the mcr-1 -carrying plasmid reservoirs from the gut microbiota. Here, we reported that a similar but more complex scenario is present in the healthy swine populations, Southern China, 2016. Amongst the 1026 pieces of Escherichia coli isolates from 3 different pig farms, 302 E. coli isolates were determined to be positive for the mcr-1 gene (30%, 302/1026). Multi-locus sequence typing assigned no less than 11 kinds of sequence types including one novel Sequence Type to these mcr-1 -positive strains. PCR analyses combined with the direct DNA sequencing revealed unexpected complexity of the mcr-1 -harbouring plasmids whose backbones are at least grouped into 6 types four of which are new. Transcriptional analyses showed that the mcr-1 promoter of different origins exhibits similar activity. It seems likely that complex dissemination of the diversified mcr-1 -bearing plasmids occurs amongst the various ST E. coli inhabiting the healthy swine populations, in Southern China.