An international team of scientists from Cornell University and the University of Zurich has discovered a new jumping gene that makes bacteria resistant to colistin, a last-resort antibiotic used to treat severe bacterial infections.

Mcr (mobilized colistin-resistance) genes are plasmid-borne genes that confer resistance to colistin, an antibiotic that is used to treat severe infections caused by multidrug-resistant bacteria.

In 2015, a team of researchers from China, the United Kingdom and the United States discovered the first plasmid-mediated colistin resistance gene, mcr-1, in a strain of Escherichia coli.

Since then, seven additional mcr genes — mcr-2 to -8 — have been identified in Escherichia, Salmonella, Moraxella and Klebsiella bacteria.

The new mcr gene, named mcr-9, was found in Salmonella enterica bacteria isolated from a human patient in Washington State.

“Details about mcr-9 in national and international databases enable scientists to develop better prevention and treatment,” said Cornell University’s Professor Martin Wiedmann, senior author of the study.

“This improves our ability to get an early warning.”

“Bacteria isolated from food products can now be tested for mcr-9, and patients can be screened for colistin-resistant bacteria, which possess mcr-9.”

“If you go to a hospital and this gene is floating around, that can be trouble,” he added.

“The gene is moveable. It jumps.”

“In a hospital setting, being able to screen a patient for resistance allows doctors and nurses to isolate the patient and maintain biosecurity.”

The results were published in the journal mBio.

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Laura M. Carroll et al. 2019. Identification of Novel Mobilized Colistin Resistance Gene mcr-9 in a Multidrug-Resistant, Colistin-Susceptible Salmonella enterica Serotype Typhimurium Isolate. mBio 10: e00853-19; doi: 10.1128/mBio.00853-19