J Vet Sci.  2021 Sep;22(5):e68. 10.4142/jvs.2021.22.e68.

Colistin resistance and plasmidmediated mcr genes in Escherichia coli and Salmonella isolated from pigs, pig carcass and pork in Thailand, Lao PDR and Cambodia border provinces

  • 1Research Unit in Microbial Food Safety and Antimicrobial Resistance, Department of Veterinary Public Health, Faculty of Veterinary Science, Chulalongkorn University, Bangkok, Thailand
  • 2Department of Microbiology and Immunology, College of Veterinary Medicine, Cornell University, Ithaca, New York, United States
  • 3Department of Farm Resources and Production Medicine, Faculty of Veterinary Medicine Kasetsart University, Kamphangsaen Nakornpathom, Thailand
  • 4Department of Veterinary Public Health, Faculty of Veterinary Medicine, Khon Kaen University, Khon Kaen, Thailand


Colistin and carbapenem-resistant bacteria have emerged and become a serious public health concern, but their epidemiological data is still limited.
This study examined colistin and carbapenem resistance in Escherichia coli and Salmonella from pigs, pig carcasses, and pork in Thailand, Lao PDR, and Cambodia border provinces.
The phenotypic and genotypic resistance to colistin and meropenem was determined in E. coli and Salmonella obtained from pigs, pig carcasses, and pork (n = 1,619). A conjugative experiment was performed in all isolates carrying the mcr gene (s) (n = 68). The plasmid replicon type was determined in the isolates carrying a conjugative plasmid with mcr by PCR-based replicon typing (n = 7). The genetic relatedness of mcr-positive Salmonella (n = 11) was investigated by multi-locus sequence typing.
Colistin resistance was more common in E. coli (8%) than Salmonella (1%). The highest resistance rate was found in E. coli (17.8%) and Salmonella (1.7%) from Cambodia. Colistin-resistance genes, mcr-1, mcr-3, and mcr-5, were identified, of which mcr-1 and mcr-3 were predominant in E. coli (5.8%) and Salmonella (1.7%), respectively. The mcr-5 gene was observed in E. coli from pork in Cambodia. Two colistin-susceptible pig isolates from Thailand carried both mcr-1 and mcr-3. Seven E. coli and Salmonella isolates contained mcr-1 or mcr-3 associated with the IncF and IncI plasmids. The mcr -positive Salmonella from Thailand and Cambodia were categorized into two clusters with 94%–97% similarity. None of these clusters was meropenem resistant.
Colistin-resistant E. coli and Salmonella were distributed in pigs, pig carcasses, and pork in the border areas. Undivided-One Health collaboration is needed to address the issue.


Drug resistance; swine; Thailand; Laos; Cambodia
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