High Prevalence of Colistin-Resistant Escherichia coli with Chromosomally Carried mcr-1 in Healthy Residents in Vietnam.

The wide distribution of colistin-resistant bacteria in developing countries has become a common phenomenon. To understand the mechanisms underlying their distribution, we studied the mcr genetic background of colistin-resistant Escherichia coli isolates from the fecal microbiota of healthy human residents from a community in Vietnam with a high prevalence of colistin-resistant E. coli with mcr Fifty-seven colistin-resistant isolates were obtained from 98 residents; one isolate was collected from each individual and analyzed for mcr We found that 36.8% of the isolates carried chromosomal mcr-1 Further, 63.2% and 1.8% of the isolates carried mcr-1 on the plasmid and the plasmid/chromosome, respectively. Whole-genome sequencing of genetically unrelated isolates showed that the majority (6 of 7) of the isolates had the chromosomal mcr-1 in a complete ancestral mcr-1 transposon Tn6330, ISApl1-mcr-1-PAP2-ISApl1, which was inserted at various positions on the chromosomes. In addition, the majority (87.5%) of Tn6330 of mcr-1-carrying plasmids (n = 8) lacked both upstream and downstream ISApl1 transposons. The results obtained in this study indicate that plasmid-to-chromosomal transfer of mcr-1 may have occurred recently in the fecal microbiota of the residents. Additionally, Tn6330 on the chromosome may lose ISApl1 from the transposon during multiplication to gain a more stable mcr-1 state on the chromosome. Stabilization of resistance by the chromosomal incorporation of mcr-1 would be an additional challenge in combating the dissemination of resistant bacteria.IMPORTANCE Elucidation of the mechanism of the wide dissemination of colistin-resistant bacteria in communities of developing countries is an urgent public health issue. In this study, we investigated the genetic background of the colistin resistance gene mcr in E. coli isolates from the fecal microbiota of healthy human residents living in a community in Vietnam with a high prevalence of colistin-resistant E. coli Our study revealed for the first time, a surprisingly high percentage (36.8%) of colistin-resistant E. coli carrying chromosomal mcr-1, the emergence of which may have occurred recently, in the fecal microbiota of the community residents. The mcr-1 transposon on the chromosome may develop into a more stable genotype by the loss of insertion sequences (ISs). Our results are valuable in understanding the mechanism underlying the increasing prevalence of colistin-resistant bacteria within a community.

Yamaguchi T ，Kawahara R ，Hamamoto K ，Hirai I ，Khong DT ，Nguyen TN ，Tran HT ，Motooka D ，Nakamura S ，Yamamoto Y ... -  《mSphere》

Characterization of Genetic Elements Carrying mcr-1 Gene in Escherichia coli from the Community and Hospital Settings in Vietnam.

Vu Thi Ngoc B ，Le Viet T ，Nguyen Thi Tuyet M ，Nguyen Thi Hong T ，Nguyen Thi Ngoc D ，Le Van D ，Chu Thi L ，Tran Huy H ，Penders J ，Wertheim H ，van Doorn HR ... -  《Microbiology Spectrum》

Comparative genome analysis of colistin-resistant Escherichia coli harboring mcr isolated from rural community residents in Ecuador and Vietnam.

Thanh Hoang HT ，Yamamoto M ，Calvopina M ，Bastidas-Caldes C ，Khong DT ，Nguyen TN ，Kawahara R ，Yamaguchi T ，Yamamoto Y ... -  《PLoS One》

Genetic basis of chromosomally-encoded mcr-1 gene.

Compared with plasmid-borne mcr-1, the occurrence of chromosomally-encoded mcr-1 is rare although it has been reported in several cases. This study aimed to investigate the genetic features of chromosomally-encoded mcr-1 among Escherichia coli strains as well as the potential genetic basis governing mobilisation of mcr-1 in bacterial chromosomes. The genome sequences of 16 E. coli strains containing a chromosomal mcr-1 gene were obtained and analysed. Phylogenetic and whole-genome sequencing (WGS) analysis demonstrated that mcr-1 was associated with four major types of genetic arrangements, namely ISApl1-mcr1-orf, Tn6330, complex Tn6330 and ΔTn6330 in chromosomes of genetically unrelated E. coli strains. The mcr-1-carrying mobile elements were shown to insert into the AT-rich region, which was also the case for ISApl1. Analysis of complete E. coli genome sequences showed that there were multiple copies of ISApl1 present in E. coli chromosomes that also carried mcr-1, whilst all mcr-1-negative chromosomes were absent of any copy of ISApl1, suggesting the strong association of ISApl1 and mcr-1. Insertion of ISApl1 into E. coli chromosomes may be a prerequisite for the insertion of mcr-1-carrying mobile elements. Insertion of mcr-1 into E. coli chromosomes would enable it to become intrinsically resistant, which is expected to become more prevalent. Policy on the prudent use of colistin both in veterinary and clinical settings should be imposed globally to further prevent dissemination of mcr-1 in E. coli and other bacterial pathogens.

Li R ，Yu H ，Xie M ，Chen K ，Dong N ，Lin D ，Chan EW ，Chen S ... -  《-》

Prevalence and Genomic Characteristics of mcr-Positive Escherichia coli Strains Isolated from Humans, Pigs, and Foods in China.

Lu X ，Zhang P ，Du P ，Zhang X ，Wang J ，Yang Y ，Sun H ，Wang Z ，Cui S ，Li R ，Bai L ... -  《Microbiology Spectrum》