Superbug resistant to last-resort antibiotics now found on multiple continents

Epidemiologists — people who track diseases — use an expression: Seek and ye shall find. It’s a reminder that sometimes when you see a phenomenon, it may not be entirely new. It may be that you’ve only just noticed it.

Well, the world seems to be having a major seek-and-ye-shall-find moment right now with a worrisome new superbug.

This week alone reports have emerged that the mcr-1 gene, which confers resistance to an important antibiotic of last-resort, has been found in bacteria previously collected in the Netherlands, Laos, Algeria, Thailand, and France. There is reason to believe it may also be circulating in Bolivia, Peru, Tunisia, Portugal, Malaysia, and possibly Vietnam and Cambodia.

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The journal that has published many of these findings, the Lancet Infectious Diseases, indicated on its Twitter feed Friday that it has more mcr-1 reports in its hopper: “There will be another wave of reports soon.”

This is in addition to Denmark and Britain. Scientists in those two countries reported finding the bacterial resistance gene earlier this month. All these findings have come to light in the month — one single month — since Chinese scientists made the first-ever report of mcr-1.

This week, the Lancet Infectious Diseases published five more reports of work done by researchers in a number of countries who searched their databases for mcr-1. A group from the Netherlands identified the gene in E. coli found in stool samples collected from six travelers who had been on three different continents: South America (Bolivia, Peru), Africa (Tunisia), and Asia (Thailand, Laos, Vietnam, and Cambodia.)

The travelers took part in a study in which stool samples were collected before and after foreign travel, providing a nice reminder that an antibiotic-resistant gene such as mcr-1 can journey the world over in the stomachs of healthy people while no one is the wiser, said Lance Price, director of the Antibiotic Resistance Action Center at George Washington University.

Price said he hopes the rapid discovery of the gene across such a large expanse will serve as a wake-up call.

Mcr-1 is a gene that gives bacteria that carry it resistance to a drug called colistin, the last antibiotic that can cure highly resistant infections. From a human point of view, that’s a very bad skill for bacteria to have.

But it gets worse: This gene is carried on a plasmid, a mobile piece of DNA that that can be swapped from one bacterium to another within a family like E. coli, but also to other bacterial families as well.

This gene can get around. And it clearly has been.

After Chinese researchers reported the first discovery of mcr-1 on Nov. 18, researchers with access to databases containing the genetic sequences of E. coli, Salmonella, and other bacteria scrambled to search those collected codes for evidence of mcr-1. The hope, of course, was that this bug was contained to China.

Not even close, it turns out. Two weeks later Danish researchers reported finding the gene in samples taken from one hospital patient and five commercial meat products. The earliest evidence of it in Denmark was from 2012.

“I had really sincerely hoped not to see it,” Frank Aarestrup, head of the genomic epidemiology group at Denmark’s National Food Institute, told STAT the day he and his colleagues reported their finding.

The poultry meat in Denmark that turned up mcr-1 containing E. coli had been imported from Germany, which adds to the evidence that this gene is hopscotching around the globe.

Colistin is actually not a great antibiotic — it can be toxic to the kidneys. In fact, for decades, it was rarely used. Other, newer antibiotics were easier to take, so doctors in the main stopped using colistin, which is probably why it still works.

As the newer, better drugs have fallen prey to resistance, colistin has gained a new place of prestige in modern medicine. The World Health Organization actually declared it critically important for human medicine in 2012.

But China has been using the drug in agriculture, which is what likely led to the development of mcr-1, experts believe.

Price said the emergence of mcr-1 and the evidence of its wide spread is proof the time has come to draw some firm boundaries between the antibiotics that should be reserved for human use and those that can be used to treat infections in animals.

Feeding antibiotics to pigs, cows, and other food animals as growth promoters, or to prevent the diseases that arise as a result of industrialized production practices, simply shouldn’t be allowed, he said.

These developments come in a week when Congress upped spending on antibiotic resistance, increasing the pot being shared by a number of federal agencies by $303 million — a 64 percent bump.

One might be tempted to see that as a sign that the US government is seized of the threat antibiotic resistance poses to modern medicine. But Price noted that none of that extra money was allocated to the Department of Agriculture, even though the agricultural sector uses many times more antibiotics than human medicine does.

He thinks it is a sign of continued resistance to the need to limit agricultural use of antibiotics. “They do not want clear lines drawn,” Price said.

This story was updated to include discussion of colistin’s agricultural use.

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