Skip to Main Content

A wide variety of E. coli bacteria in China have developed resistance to a key antibiotic of last resort, a new study has revealed, a worrying development in the rise of so-called superbugs.

A second study released Friday, like the first published in the journal Lancet Infectious Diseases, found the superbug is still uncommon in Chinese hospitals — though not as rare as experts might like.

The drug resistance gene known as mcr-1 — which has the capacity to move from one bacterium to another — was found in about 1 percent of E. coli bacteria and 1 percent of a bacteria known as Klebsiella pneumoniae, that can cause pneumonia, bloodstream infections, and wound infections.


Although that incidence was described as rare, it wasn’t especially reassuring to Lance Price, director of the Antibiotic Resistance Action Center at George Washington University.

“One percent doesn’t sound huge, but for something that we didn’t know about a little more than a year ago and that is clearly a recently evolved [drug resistance] element, it’s pretty substantial,” said Price, who was not involved in the study.


The mcr-1 gene gives bacteria the ability to withstand treatment with a drug called colistin. It’s an old antibiotic that wasn’t used much for years because it has unpleasant side effects; other newer drugs were simply better. But with resistance to better drugs on the rise, colistin has taken on increasing importance in medicine.

The superbugs are growing in number and strength. Hyacinth Empinado/STAT

In many places it is reserved for human use — and even then, only when absolutely needed. But China has been using it in agriculture, to speed growth of animals raised for meat.

In November 2015 scientists reported finding this gene in China, raising alarms around the world. Within a short span of time, researchers elsewhere revealed they had looked for and found the gene in their stored bacteria collections.

An alarming feature of mcr-1 is that the gene moves easily from bug to bug and also from a family like E. coli to others, like Klebsiella pneumoniae.

The authors of the new paper reporting the incidence of the gene in hospital infections are from Sir Run Run Shaw Hospital, College of Medicine, Zhejiang University, in Hangzhou.

Professor Timothy Walsh of the University of Cardiff was one of the discoverers of mcr-1 and is also an author of the paper that tracked the gene’s spread among E. coli bacteria.

“I think the takeaway message is that mcr-1 is very, very widely spread among many different types of E. coli and therefore is kind of pervasive, really, throughout Chinese communities,” Walsh told STAT.

And that picture could be about to get a lot worse.

China has agreed to ban use of colistin for growth promotion purposes. That policy comes into effect on April 1, Walsh said. But it also plans to license the drug for human use there.

China is making that move, Walsh said, because it realizes it is morally unacceptable to use the drug in animal feed. But there’s another reason: It needs colistin to deal with the rapid spread of other superbugs in China.

In particular, China has a “massive” problem with what are known as CREs — carbapenem-resistant Enterobacteriaceae, bacteria of the gut that are not susceptible to an important family of antibiotics called carbapenems.

The fear is that bacteria that can fend off carbapenems will also acquire the ability to evade colistin — producing untreatable superbugs with the power to turn back the clock on modern medicine. Medical procedures that are currently standards of care — hip replacements, for instance — could become too dangerous to perform.

“At this stage we can conclude that the doomsday scenario of convergence of carbapenem resistance and colistin resistance (via mcr-1) has not yet occurred to any great extent in China,” a commentary published with the studies said.

But the authors — professor David Paterson, of Australia’s University of Queensland, and associate professor David van Duin, of the University of North Carolina — noted that Walsh’s study found people who had previously taken antibiotics were more likely to carry E. coli with the mcr-1 gene. That suggests, they wrote, “that the intersection between carbapenem resistance and the presence of this colistin resistance mechanism may yet be seen in the future.”

Price uses an analogy of sparks, fuel, and fire. Agricultural use of colistin in China has allowed a lot of bacteria to develop resistance to it. Those are the sparks. “Now we’ve generated all these sparks if we start to use that drug in hospitals then that’s the fuel to set the fire,” he said.