Within-host heterogeneity and flexibility of mcr-1 transmission in chicken gut.

To characterize the colistin-resistant bacterial population in the gut and assess diversity of mcr-1 transmission within a single individual. Large numbers of isolates (>100 colonies/chicken cecum sample) were collected from nine randomly selected mcr-1-positive chickens in China and used for comprehensive microbiological, molecular and comparative genomics analyses. Of 1273 colonies, 968 were mcr-1 positive (962 Escherichia coli, two Escherichia fergusonii, two Klebsiella pneumoniae and two Klebsiella quasipneumoniae). One to six colistin-resistant species and three to 10 E. coli pulsed-field gel electrophoresis (PFGE) clusters could be identified from each sample. Whole-genome sequencing (WGS) analysis of the representative E. coli strains revealed three to nine sequence types observed in a single chicken host. The mcr-1 genes are located in either chromosomes or plasmids of different types, including IncI2 (n=30), IncHI2 (n=14), IncX4 (n=4), p0111(n=2) and IncHI1(n=1). Strikingly, in single cecum samples, one to five Inc type plasmids harbouring mcr-1 could be identified. Great diversity was also observed for the same IncI2 plasmid within a single chicken host. In addition, up to eight genetic contexts of the mcr-1 gene occurred within a single chicken. There is extensive heterogeneity and flexibility of mcr-1 transmission in chicken gut due to bacterial species differences, distant clonal relatedness of isolates, many types and variations of mcr-positive plasmids, and the flexible genetic context of the mcr-1 gene. These compelling findings indicate that the gut is a 'melting pot' for active horizontal transfer of the mcr-1 gene.

Li XP ，Sun RY ，Song JQ ，Fang LX ，Zhang RM ，Lian XL ，Liao XP ，Liu YH ，Lin J ，Sun J ... -  《-》

Detection of mcr-1 Plasmids in Enterobacteriaceae Isolates From Human Specimens: Comparison With Those in Escherichia coli Isolates From Livestock in Korea.

The emerging mobile colistin resistance gene, mcr-1, is an ongoing worldwide concern and an evaluation of clinical isolates harboring this gene is required in Korea. We investigated mcr-1-possessing Enterobacteriaceae among Enterobacteriaceae strains isolated in Korea, and compared the genetic details of the plasmids with those in Escherichia coli isolates from livestock. Among 9,396 Enterobacteriaceae clinical isolates collected between 2010 and 2015, 1,347 (14.3%) strains were resistant to colistin and those were screened for mcr-1 by PCR. Colistin minimum inhibitory concentrations (MICs) were determined by microdilution, and conjugal transfer of the mcr-1-harboring plasmids was assessed by direct mating. Whole genomes of three mcr-1-positive Enterobacteriaceae clinical isolates and 11 livestock-origin mcr-1-positive E. coli isolates were sequenced. Two E. coli and one Enterobacter aerogenes clinical isolates carried carried IncI2 plasmids harboring mcr-1, which conferred colistin resistance (E. coli MIC, 4 mg/L; E. aerogenes MIC, 32 mg/L). The strains possessed the complete conjugal machinery except for E. aerogenes harboring a truncated prepilin peptidase. The E. coli plasmid transferred more efficiently to E. coli than to Klebsiella pneumoniae or Enterobacter cloacae recipients. Among the three bacterial hosts, the colistin MIC was the highest for E. coli owing to the higher mcr-1-plasmid copy number and mcr-1 expression levels. Ten mcr-1-positive chicken-origin E. coli strains also possessed mcr-1-harboring IncI2 plasmids closely related to that in the clinical E. aerogenes isolate, and the remaining one porcine-origin E. coli possessed an mcr-1-harboring IncX4 plasmid. mcr-1-harboring IncI2 plasmids were identified in clinical Enterobacteriaceae isolates. These plasmids were closely associated with those in chicken-origin E. coli strains in Korea, supporting the concept of mcr-1 dissemination between humans and livestock.

Yoon EJ ，Hong JS ，Yang JW ，Lee KJ ，Lee H ，Jeong SH ... -  《-》

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

Shen C ，Feng S ，Chen H ，Dai M ，Paterson DL ，Zheng X ，Wu X ，Zhong LL ，Liu Y ，Xia Y ，Ma R ，Huang X ，Tian GB ... -  《-》

Colistin Resistance Gene mcr-1 and Its Variant in Escherichia coli Isolates from Chickens in China.

The mcr-1 gene was detected in 5.11% (58/1136) of Escherichia coli isolates of chicken origin from 13 provinces in China. A novel mcr-1 variant, named mcr-1.3, encoding an Ile-to-Val functional variant of MCR-1 was identified in a sequence type 155 (ST155) strain. An mcr-1.3-containing IncI2 plasmid, pHeN867 (60,757 bp), was identified. The transfer of pHeN867 led to a 32-fold increase in the MIC of colistin in the recipient, exhibiting an effect on colistin resistance that was similar to that of mcr-1.

Yang YQ ，Li YX ，Song T ，Yang YX ，Jiang W ，Zhang AY ，Guo XY ，Liu BH ，Wang YX ，Lei CW ，Xiang R ，Wang HN ... -  《-》

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》