| description |
Background: The aim of this work was to characterize three colistin resistant bacteria isolated from pigs on a farm in Great Britain. Methods: Antimicrobial susceptibility testing was performed by a broth microdilution method. Whole genome sequencing was used to detect antimicrobial resistance (AMR) and virulence genes. The mcr-1 harbouring plasmid was characterised and conjugations performed. Selected transconjugants were plasmid-profiled and their susceptibility to different antibiotics tested. Findings: Two Escherichia coli and 1 Salmonella Typhimurium var. Copenhagen with phenotypic colistin resistance were shown to be multidrug resistant (MDR), with 1 E. coli (E4) and Salmonella (S3) carrying the mcr-1 gene; all 3 isolates also harboured chromosomal mutations for colistin resistance. The pS3 mcr-1 plasmid was highly similar to pHNSHP45, reported in China, but the pE4 mcr-1 plasmid was distinct with only the ISApII and mcr-1 genes in common. This indicated both plasmid and IS-element mediated dissemination of mcr-1 had occurred. Frequency of mcr-1 plasmid transfer to recipient Enterobacteriaceae from S3 was low, lying between 10-7 to 10-9 colony forming units per recipient colony forming unit, by conjugation; we were unable to demonstrate mcr-1 plasmid transfer from E4 under the conditions tested. Plasmid profiling indicated transfer of multiple plasmids from S3 at conjugation resulting in MDR transconjugants. |