It looks like superbugs have finally built resistance to our 'drug of last resort'

Colistin also allows this kind of thing to go on. Picture: Getty Images

It was all but inevitable, but the emergence of a “truly pan-drug resistant bacteria” in the US has researchers deeply concerned.

MCR-1 is a gene found in some bacteria which is resistant to the drug colistin.

Colistin has been around since the 1950s, but not widely used, as it can cause kidney damage. Because it hasn’t been widely used – in humans – it has retained its antibiotic properties better than any other drug.

For that reason, it is known as the human “drug of last resort”.

Where colistin has been used widely is in China. It’s added to animal food because it helps them put muscle mass on quickly and protects against health risks associated with mass farming. Because it’s unpopular for human use, it’s also cheap.

Eight of the top producers of colistin for animals are based in China.

It was Chinese researchers who first noted a strain of colistin-resistant E. coli in 2013, and at the end of last year, they released a report showing the resistance was spreading.

From several years of testing samples of retail meat and from patients in two hospitals, they found the MCR-1 gene present in 15% of raw chicken and pork, 21% of slaughterhouse pigs… and 1% of 1322 samples from hospital patients.

The authors also noted that as colistin resistance looked like it was transmissable, the spread of Enterobacteriaceae (the family that includes E. coli and salmonella) “from extensive drug resistance to pan-drug resistance is inevitable and will ultimately become global”.

Why the concern?

MCR-1, the gene resistant to colistin, is contained on a small piece of DNA called a plasmid.

While they are part of a bacteria’s DNA, plasmids are not part of a bacteria’s chromosome. They can detach themselves from one bacterium and hop to another at any time.

By doing this, plasmids have been known to help spread resistance to antibiotics around the world.

Now a plasmid containing the MCR-1 gene has found its way to the US and not just in an animal, in a human.

US Department of Defense researchers yesterday reported that a 49-year-old woman sought medical care at a military-associated clinic in Pennsylvania last month for a urinary tract infection.

She was instead found to be carrying a strain of E. coli, which in turn was found to carry 15 different antibiotic-resistant genes grouped on two “mobile elements”. On one of those elements was the gene MCR-1.

And while reports of the MCR-1 gene in humans in Europe surfaced earlier this year, what concerns researchers most now is that the use of colistin in the US is relatively low, and the person carrying the strain hadn’t been overseas for many months.

It looks like it’s a home-grown case, most likely picked up in food.

There will be no cure

The discovery, according to the US Department of Defense authors, “heralds the emergence of truly pan-drug resistant bacteria”, and prompted a rapid response from Pennsylvania governor Tom Wolf who said it was imperative to stop it “from becoming a widespread problem with potentially serious consequences”.

It also comes barely a week after a recent review, which predicted superbugs will kill 10 million people a year by 2050, identified inaction against colistin-resistant bacteria as a major concern.

The review urged governments around the world to implement healthcare programs aimed at reducing the demand for antibiotics, both from humans and those used in agriculture.

Doctors, according to Britain’s Treasury secretary Jim O’Neill, need to “stop treating antibiotics like sweets”.

That prompted Britain’s chancellor to call on finance ministers from around the world at September’s G20 meeting – in China – to agree on a common approach to fighting the threat of antibiotics-resistant bacteria.

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