Thursday, July 07, 2016

Eurosurveillance: Identification Of A Novel Colistin-Resistant MRC-2 Gene In E Coli - Belgium, 2016


Six years ago the world woke up to the existence of an emerging antibiotic resistance gene dubbed New Delhi metallo-ß-lactamase-1, or NDM-1 (see  NDM-1: A New Acronym To Memorize) which conveyed resistance to Carbapenums - drugs of last resort for treating difficult bacterial infections, including Escherichia coli (E. coli) and Klebsiella pneumoniae.
Of particular concern, this NDM enzyme was carried by a plasmid – a snippet of portable DNA  - that can be easily transferred to other types of bacteria (see Study: Adaptation Of Plasmids To New Bacterial Species).

Since then, scattered variants of NDM-1 have begun to emerge around the globe, including  NDM-2, NDM-4, NDM-5, NDM-7 and NDM-9.  

Last November, in MCR-1: The Return Of The Plasmids,
we looked at the discovery of another resistance gene in China - dubbed mcr-1 - that conveys resistance to Colistin - essentially the last ditch drug available to treat many infections. 

 Since then we've followed that story closely, including:

ECDC Rapid Risk Assessment On MCR-1
CDC HAN: Alerting Healthcare Facilities Of 1st MCR-1 Gene Detection In US Patient
EID Journal: Possible Transmission Of MCR-1 Harboring E. coli Between Companion Animals & Humans

Given the rapid genetic diversification of the NDM resistance gene, I suppose we shouldn't be too surprised by this, but today the ECDC Journal Eurosurveillance reports on the first detection of a variant MCR gene, which they have dubbed mcr-2

Follow the link to read the full report, after which I'll have a bit more. 

Eurosurveillance, Volume 21, Issue 27, 07 July 2016
Rapid communication

Identification of a novel plasmid-mediated colistin-resistance gene, mcr-2, in Escherichia coli, Belgium, June 2016

BB Xavier 1 2 3 , C Lammens 1 2 3 , R Ruhal 1 2 3 , S Kumar-Singh 1 3 4 , P Butaye 5 6 7 , H Goossens 1 2 3 , S Malhotra-Kumar 1 2 3

Correspondence: Surbhi Malhotra-Kumar (

Citation style for this article: Xavier BB, Lammens C, Ruhal R, Kumar-Singh S, Butaye P, Goossens H, Malhotra-Kumar S. Identification of a novel plasmid-mediated colistin-resistance gene, mcr-2, in Escherichia coli, Belgium, June 2016. Euro Surveill. 2016;21(27):pii=30280. DOI:
Received:27 June 2016; Accepted:07 July 2016

We identified a novel plasmid-mediated colistin-resistance gene in porcine and bovine colistin-resistant Escherichia coli that did not contain mcr-1. The gene, termed mcr-2, a 1,617 bp phosphoethanolamine transferase harboured on an IncX4 plasmid, has 76.7% nucleotide identity to mcr-1. Prevalence of mcr-2 in porcine colistin-resistant E. coli (11/53) in Belgium was higher than that of mcr-1 (7/53). These data call for an immediate introduction of mcr-2 screening in ongoing molecular epidemiological surveillance of colistin-resistant Gram-negative pathogens.

(Continue . . . )

Bacteria that carry the mcr-1 or mcr-2 genes aren't necessarily untreatable, since they may still be susceptible to other antibiotics, including Carbapenums. 

But last March The Lancet's Emergence of the mcr-1 colistin resistance gene in carbapenem-resistant Enterobacteriaceae, reported on two K pneumoniae isolates from China that carried both the mcr-1 gene and the gene for NDM-5 (Carbapenem-resistance), providing it near pan-drug resistance.

While still exceedingly rare, this is the kind of nightmare resistance combination that could someday propel us into a post-antibiotic era, one where even minor infections are no longer treatable.

Making the expansion of mcr-1 and NDM-1 very much much a public health concern. 

For more on the implications of growing antibiotic resistance, you may wish to revisit:

Chan: World Faces A `Post-Antibiotic Era’

Maryn McKenna’s TED Talk - What do we do when antibiotics don’t work any more?


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