Bacteria Has Been Found With Resistance To A "Last Resort" Antibiotic

The new gene was found in the plasmids of E. coli, and have the potential to spread between bacterial species. Kateryna kon/Shutterstock
Josh Davis 19 Nov 2015, 13:25

Researchers have identified a gene that gives bacteria resistance to the last line of antibiotic defense, a class of drugs called polymyxins. Despite being discovered around 60 years ago, the drugs maintained their effectiveness as they were seldom used due to concerns about their toxicity. But in recent years, with antibiotic resistance becoming more and more of a global concern, they have been called upon precisely because of this lack of use; bacteria had not yet had a chance to become resistant, until now.

While this is not the first time such a mutation to protect against polymyxins has been identified in bacteria, this time around the gene has been found on what are known as plasmids. These are tiny pieces of DNA that bacteria are able to share not just with other members of their own species, but with bacteria that are completely unrelated. This means that the polymyxin resistance has the opportunity to spread to all types of bacteria.  

The gene in question is called mcr-1, and was first identified in Escherichia coli bacteria living in pigs in China. The researchers think that the gene is probably widespread within the Enterobacteriaceae family in which E. coli resides, and found in both domestic animals and humans. The research, published in The Lancet, found that 21 percent of the domestic animals they tested harbored E. coli containing the mcr-1 gene, as well as 15 percent of raw meat sampled, and 1 percent of hospital patients with infections.

“These are extremely worrying results,” explained Professor Jian-Hua Liu, who co-authored the study, to The Guardian. “Our results reveal the emergence of the first polymyxin resistance gene that is readily passed between common bacteria such as Escherichia coli and Klebsiella pneumoniae, suggesting that the progression from extensive drug resistance to pandrug resistance is inevitable.”

They warn that this gene has the potential to spread rapidly worldwide, and that if bacteria picked up this resistance in combination with resistance to other drugs, it could usher in the post-antibiotic era. Known as the “antibiotic apocalypse,” it could see infections that were once routine and easy to cure become deadly and untreatable, taking medicine back to the “dark ages.” This could be of particular concern for cancer treatments and surgeries that rely on antibiotics. 

With reports already coming in that the mcr-1 gene might be present in Laos and Malaysia, the threat posed by this new resistance is very real and very serious. Experts are calling on a ban of using the same antibiotics for both humans and animals, and while we are not yet in the post-antibiotic era, doctors should tread very carefully indeed. 

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