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What's Surprising About the Discovery of MCR1_NJ?


The MCR1_NJ gene has been found to be both colistin- and carbapenem-resistant. Barry Kreiswirth, PhD, founding director, Public Health Research Institute Tuberculosis Center, professor of medicine at Rutgers University, discusses his team’s findings on MCR1_NJ and bacterial drug resistance. In addition to the discovery of the gene MCR1_NJ, other researchers have identified another colistin-resistance gene dubbed mcr-2. Dr. Kreiswirth notes that with the addition of carbapenem resistance, MCR1_NJ gives bacteria the ability to be resistant to two last-line treatments. This emphasizes the need for surveillance for MCR1_NJ and other known resistance genes.

 Interview Transcript (slightly modified for readability)

“What we’ve learned is that the mcr-1 gene that we found in our strain has also been found in other strains throughout the United States, mostly associated with animal reservoirs. We know that pig isolates of Enterobacteriaceae E. coli and Klebsiella, as well as isolates coming from bovine, have the mcr-1 gene. The surprise wasn’t that we found it in a human, the surprise was that we found it in association with a second resistance gene, which was the carbapenem-resistant [gene]; that’s the new finding.

It’s not surprising that mcr-1 is associated with animal isolates because, again, we’ve learned now that they use colistin in animal feed lots, so it’s probably logical that that’s where the reservoir is going to be. In fact, just to extend the problem, there was a recent report [from] Belgium that actually identified a second gene, mcr-2, which is now raising concern that we need to start looking for both mcr-1 and mcr-2. If there’s mcr-1 and mcr-2 out there, the logical assumption is that there may be other resistance genes that we haven’t been able to identify yet.

This just [emphasizes] that we need to do active surveillance. I think the most important finding of our study and the most important take home message is that the fact that we found an isolate [with] both carbapenem-resistant and colistin-resistant [genes] from 2014, means that these strains are probably out there and the only way that we’re actually going to understand the extent of this problem is that hospital labs, as well as commercial labs, probably need to do surveillance, looking for colistin-resistant genes and really try and get an understanding of the extent of this problem.”
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