Scientists have detected the first plasmid mediated colistin resistance (mcr-1) gene in food and human isolates in England and Wales.

Image: © Freephoto/alwajasm.
Image: © Freephoto/alwajasm.

Veterinary and human health officials expressed concerns last month when The Lancet Infectious Diseases published a report from China describing the discovery of transferable colistin resistance.

The Chinese mcr-1 gene was detected in Escherichia coli from pigs, raw pig and poultry meat and in approximately 1% of E coli and Klebsiella-causing infections in hospital patients in the sampled districts.

Subsequently, Public Health England’s Gastrointestinal Bacteria Reference Unit (GBRU) and Antimicrobial Resistance and Healthcare Associated Infections Reference Unit (AMRHAI) examined the genome sequence data of more than 24,000 Salmonella, E coli, Klebsiella species, Enterobacter species and Campylobacter human and food isolates from the Public Health England (PHE) sequence archive. These isolates are derived from general surveillance systems, submissions to reference services and research projects. More genome data are still being examined.

So far the mcr-1 gene has been detected using a bioinformatics approach in 15 isolates. They have been characterised as follows:

  • Ten genotypically-diverse human Salmonella isolates (eight S typhimurium, one S Paratyphi B var Java and one S virchow), reported through the national surveillance system.
    All reported isolates from 2014-2015 and a proportion of those from 2012-2013, for which sequence information was available, were screened. Of these, two of the S typhimurium cases and the S Java case had a reported travel history (to Asia). Various other resistance genes were detected. Of note, one isolate had a gene for an acquired AmpC enzyme, conferring resistance to third-generation cephalosporins.
  • Two isolates of S Java phage type Colindale detected in a single sample of poultry meat imported from the EU. Various other resistance genes were detected.
  • Three E coli isolates derived from two patients. Various other resistance genes were detected. Of note, all three produced CTX-M-type extended spectrum beta lactamases, conferring resistance to third-generation cephalosporins.
  • At this time, the earliest positive isolate identified is an S typhimurium from 2012.

These findings confirm, although newly discovered, the mcr-1 gene is already present in England and Wales in various bacterial species harboured by the human population.

PHE stated, as colistin is primarily used in the UK to treat multidrug-resistant Gram-negative infections, development of colistin resistance due to interspecies transfer of the mcr-1 gene would further severely limit treatment options, and even result in untreatable infections.

PHE is liaising with Defra, Department of Health, the APHA, Food Standards Agency and Veterinary Medicines Directorate to ensure assessment of risk to public health considers the available evidence and identifies the gaps in knowledge.

It says its current assessment is that public health risk is very low.

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