Biological Hazard – Antibiotic resistance, Colistin, MCR-2, plasmid, E. coli: (Animal, Human) European continent, Belgium
ANTIBIOTIC RESISTANCE – BELGIUM: COLISTIN, MCR-2, PLASMID-MEDIATED, E. COLI, PIGLETS, CALVES
Published Date: 2016-07-09 18:10:24
Subject: PRO/AH/EDR> Antibiotic resistance – Belgium: colistin, MCR-2, plasmid, E. coli, pigs, calves
Archive Number: 20160709.4335297
Date: Thursday, 7 Jul 2016
Source: Center for Infectious Disease Research & Policy (CIDRAP) [edited]
A team of researchers in Belgium is reporting the discovery of a new gene distinct from _mcr-1_ that can confer colistin resistance in _Escherichia coli_ samples taken from cows and pigs.
The authors of the report, published today [7 Jul 2016] in the journal Eurosurveillance , said the gene, which they are calling _mcr-2_, was detected on plasmids from 3 of 10 colistin-resistant _E. coli_ isolates taken from calves and piglets in Belgium.
Those isolates had been randomly selected from 92 bovine and porcine colistin-resistant _E. coli_ isolates that did not show the presence of the _mcr-2_ gene, which was 1st identified in _E. coli_ samples in China in late 2015 and has now been detected in 30 countries.
The _mcr-2_ gene has raised alarms among public health officials because it enables bacteria to disable colistin, a last-resort antibiotic that is used to treat highly resistant bacteria. In addition, because the genes are carried on plasmids, which are highly mobile pieces of DNA, they can be easily copied and transferred between different strains of bacteria and, therefore, have the potential to spread rapidly in both animals and humans.
In May , US health officials announced that the _mcr-1_ gene had been detected in the urine of a 49-year-old Pennsylvania woman with _E. coli_. The gene has also been found in _Klebsiella pneumoniae_ and carbapenem-resistant Enterobacteriaceae samples. Last week, researchers in Portugal reported on the detection of _mcr-1_ genes in _Salmonella_ isolates.
Now it appears that there is another gene capable of conferring colistin resistance. The authors of the study said a phylogenic analysis of _mcr-2_ provided strong evidence that the gene is distinct from _mcr-1_, and that it might have originated from _Moraxella catarrhalis_, an exclusively human pathogen that is a common cause of ear infections in infants. Their experiments also indicated that the _mcr-2_ gene may be able to spread more rapidly than _mcr-1_.
“They showed that this has a higher transfer frequency, so this thing has the potential to disseminate more quickly than _mcr-1_,” Lance Price, PhD, director of the Antibiotic Resistance Action Center at George Washington University, told the medical news service Stat.
The authors are calling for immediate inclusion of _mcr-2_ in ongoing molecular epidemiologic surveillance of colistin-resistant pathogens in the food supply and in humans.
[1. Xavier BB, Lammens C, Ruhal R, et al. 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: http://dx.doi.org/10.2807/1560-7917.ES.2016.21.27.30280. http://www.eurosurveillance.org/ViewArticle.aspx?ArticleId=22525report>.]
[Byline: Chris Dall]
ProMED-mail Rapporteur Mary Marshall
[Colistin is a polycationic antibiotic that binds to the anionic lipopolysaccharide in the outer cell membrane of Gram-negative bacteria, displacing magnesium and calcium, which normally stabilize the LPS molecule; this leads to disruption of the outer cell membrane and bacterial death. The drug also binds to and neutralizes the toxicity of the lipid A portion of lipopolysaccharide in circulation.
The mechanism of resistance to colistin frequently involves modification of lipid A in the bacterial cell wall, achieved, for example by the addition of phosphoethanolamine to lipid A, which reduces the affinity of colistin for its site of action. The _mcr-1_ gene encodes a phosphoethanolamine transferase that catalyses the addition of phosphoethanolamine to lipid A. The _mcr-2_ gene has 76.7% nucleotide identity to _mcr-1_ and encodes a similar gene product. Both _mcr-1_ and _mcr-2_ genes are borne on plasmids, which enabled resistance to readily spread to other bacteria of the same or different species.
The following is the abstract from reference 1 above:
“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 1617 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.”
For additional discussions of bacterial resistance to colistin, see my moderator comments in prior ProMED-mail posts on this subject. – Mod.ML
A HealthMap/ProMED-mail map can be accessed at: http://healthmap.org/promed/p/99.]
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