Will mcr-1 gene cause a new superbug?

E. coli - Photo Janice Haney Carr, CDC
A highly magnified view of E. coli bacteria. – Photo: Janice Haney Carr/CDC

Alarm bells have been sounded after a woman in the U.S. was detected with bacteria resistant to a last-resort antibiotic. The 49-year-old was carrying E. coli bearing a new gene, mcr-1, which is resistant to colistin, the last available antibiotic that works against strains that have acquired protection against all other medication. This is the first reported case of the mcr-1 gene in an E. coli strain found in a person living in America, but it raises worries about how far it may have spread. The results of mcr-1 gene identification were published recently in the journal Antimicrobial Agents and Chemotherapy. Though resistance to colistin have been detected for about 10 years in several countries, the danger of this has been somewhat played down since such resistance was brought about by gene mutations that cannot spread easily between bacteria. But mcr-1 poses a threat of an entirely different order; in this case a small piece of DNA (plasmid) found outside the chromosome carries a gene responsible for antibiotic resistance. Since the gene is found outside the chromosome, it can spread easily between different types of bacteria, as well as between patients. In the case of E. coli, the colistin resistance is not insurmountable, as it is still treatable by other known drugs. But were the gene to spread to bugs treatable by only last-resort antibiotics, we could be facing the dreaded — and indeed, long anticipated — superbug. Thus the discovery of mcr-1 gene in more countries and settings increases the chances of the emergence and spread of resistance against all available antibiotics. It could well lead to an era without effective drugs to treat bacterial infections — the post-antibiotic age, as it were. Though Colistin has been around for more than 50 years, it has not been used widely due to its serious adverse effects. But the increase in carbapenem resistant bacteria resulted in increased use of colistin.

The mcr-1 gene was first identified in China in November last year following which there were similar reports from Europe and Canada. In each case, including the latest one, it is important to investigate if the mcr-1 gene emerged locally or if the patient had acquired it from outside the country as all efforts to contain its spread will depend on this information. The unchecked use of antibiotics in livestock is a major reason for the development of drug resistance. Indeed, given the widespread use of colistin in animals, the connection to the drug-resistant mcr-1 gene appears quite clear. A November 2015 paper in The Lancet noted that a significantly higher proportion of mcr-1 positive samples was found in animals compared with humans, suggesting the mcr-1 gene had emerged in animals before spreading to humans. Besides being administered for veterinary purposes, colistin is used in agriculture as well. The global community needs to urgently address the indiscriminate use of antibiotics in an actionable manner and fast-track research on the next generation of drugs.

UPDATE: July 12, 2016:

A second case of E. coli with mcr-1 gene has been discovered in the U.S. The results of this discovery was published on July 11, 2016 in the journal Antimicrobial Agents and Chemotherapy

Published in The Hindu on May 30, 2016

One thought

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