Woman in Nevada dies of infection resistant to all 26 American antibiotics

The woman was isolated so that her superbug would not infect other patients in the hospital. And subsequent samples from other patients near her in the hospital have not turned it up. If this superbug is somehow gone from the hospital and gone from the U.S., that would be great news. But even if so, other pan-resistant superbugs are likely to emerge.

Here’s why: The most worrisome kind of colistin resistance is caused by a single gene called mcr-1. The bacteria that killed this woman did not have mcr-1; it’s still unclear how they became resistant. Other cases of colistin resistance have emerged before though. What makes mcr-1 special is that sits on a loop of free-floating DNA called a plasmid, which bacteria of different species can pass back and forth. And there are many plasmids out there with genes that confer resistance to this or that class of antibiotics.

Where might bacteria go to hang out and swap plasmids? Well your gut is a big bag of bacteria. One day, you might pick up some bacteria with a plasmid carrying resistance of colistin. Years later, you might pick up some bacteria with a plasmid carrying resistance to carbapenems. And so. They start swapping plasmids. All this time you are healthy, and these bacteria just lurk in your gut, not causing much trouble. Then you get sick, your immune system is down, and you take antibiotics for an infection. The antibiotics kill everything but the resistant bacteria, which have by now collected all the resistance genes and no competition. That’s how you get a pan-resistant infection.