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Here’s Why Doctors Are So Worried About the New Superbug

A much-feared superbug gene has been found for the first time in the United States, and it has health officials very worried.

The gene, called mcr-1, was found in a woman from Pennsylvania who had a bad infection last month. In her case, it was an E. coli bacteria. But scientists say this particular gene can turn up in any bacteria, including strains that are already hard to treat, and that's what's scare. Here are a few things to know about mcr-1:

It spreads badness

Mcr-1 is found on a little piece of DNA called a plasmid, which bacteria can pass very easily from one to another. Plasmids can even be passed between species — a kind of interspecies bacterial sex. Patrick McGann at the Walter Reed Army Institute of Research outside Washington, D.C. likens it to a truck. "We refer to them as promiscuous plasmids," McGann said. "This truck comes up and it picks up a load and moves it to another loading dock." In this case the load is a gene that gives bacteria the ability to survive treatment with an important antibiotic. Bacteria are already able to mutate at a blinding rate, but plasmids provide an extra shortcut to mutation.

Staff at Walter Reed Army Institute of Research test the concerning new bacteria carrying the mcr-1 antibiotic resistance gene Walter Reed Army Institute of Research

There's already bad stuff out there

On its own, the mcr-1 gene would not be worrying. It protects bacteria against an antibiotic called colistin, which isn't used much because it damages the kidneys and has to be injected. But colistin is often the only antibiotic that will work against a type of superbug called CRE, for carbapenem-resistant Enterobacteriaceae. That's why it's called an antibiotic of last resort. So if a CRE superbug gets hold of mcr-1, whoever is infected with that superbug would have no treatment options. These are all very contagious bacteria, and while the most vulnerable people are the very sick patients in hospitals, anyone could catch one during surgery or even out in public. Methicillin resistant Staphylococcus aureas or MRSA, for example, has been found on gym equipment.

If they found it, there's more

Mcr-1 was first spotted in China, and now reports have popped up from all over the world. It's being found in a range of bacteria. So just last month, McGann and his colleagues were asked to start looking for it, too. They found it in the very first sample they tested. "What seems likely is they have been there for years but nobody had tested for it," McGann said. "A lot of experts had suspected that it was in the United States because all these other countries were finding it," agreed Dr. David Hyun, an expert on antibiotic-resistant microbes at the Pew Charitable Trusts.

This one was extra nasty

E. coli is usually a harmless bacteria, found all though the human digestive tract. This sample had been sent to McGann's lab at Walter Reed because it was clearly a superbug of some sort, and the local hospital couldn't figure out what it was. It turns out it was an extended-spectrum beta-lactamase (ESBL)-producing E.coli. "They are quite nasty," McGann said. "Usually the only options for treating them is a carbapenem." Luckily, this particular germ could be killed by carbapenems, one of a number of classes of antibiotics and the patient who had it has recovered. But besides the mcr-1 gene that gave it resistance to colistin, it also had resistance to other classes of antibiotics, including the fluoroquinolones such as ciprofloxacin. "So the truck has been loaded with a total of eight antibiotic resistance genes," McGann said. "It's quite scary."

These things are killing people and there aren't new weapons

Public health experts have been screaming about antibiotic resistance for years. More than two million people in the U.S. are infected by drug-resistant germs each year, and 23,000 die of their infections, according to the Centers for Disease Control and Prevention. What the CDC fears is a return to the "pre-antibiotic era," when people died by the millions from infections such as pneumonia or strep throat, from infected cuts and scrapes and after childbirth.

Bacteria develop resistance to drugs quickly. By the time the first antibiotic, penicillin, was introduced in 1943, staphylococcus germs had developed resistance. It only took nine years for a strain of tetracycline-resistant Shigella to evolve after that drug hit the market in 1950. MRSA turned up two years after methicillin's development in 1960.

The last new antibiotic to be introduced was ceftaroline, in the cephalosporin class, in 2010. It took just a year for the first staph germ to emerge that resisted its effects. "Every currently available antibiotic is a derivative of a class discovered between the early 1900s and 1984," Pew's Antibiotic Resistance Project says on its website. Drug companies are reluctant to work on developing new antibiotics because they are not very profitable. President Barack Obama has made fighting antibiotic resistance a priority for his administration, but development of new drugs and tests takes years.