Superbugs for dummies: Explaining the battle between bacteria and antibiotics

The discovery of an alarming new superbug in the US has set off a flood of media coverage warning of dire days ahead.

The term “nightmare scenario” is often applied to unwelcome developments in the battle between bacteria and antibiotics, and news that mcr-1 has been found in the United States is no exception.

The very real fear is that invincible bacteria — bugs that can’t be killed by any existing drugs — will widely render antibiotics ineffective.

Are we there yet? No. That said, there’s increasingly ample reason to be concerned and to take action.

Let’s explore why. We’ll start with some basics.

What is mcr-1?

It’s a gene that can make bacteria resistant to colistin, an antibiotic that is important because it can treat infections caused by bacteria that are resistant to most other drugs.

What makes experts so nervous about mcr-1 is that it is contained in plasmids, which are mobile pieces of DNA. It’s not locked into the genetic structure of bacteria.

Because it’s in plasmids, mcr-1 can move from one bacterium to another within a family like E. coli. But it can also jump to other families of bacteria and make them resistant to antibiotics as well.

You can think of it like a Lego piece that can be added to a bunch of different structures, making them all stronger and harder to knock down.

I think I heard about this superbug last year. Why the fuss now?

Congratulations, you’ve been paying attention. Mcr-1 was first described last November by researchers who found it in China.

Laboratories around the world instantly started looking for it in stored bacterial samples taken from people who had been sick, animals, and commercial meat products.

Then Bing! Bing! Bing! — the global map started to light up. Mcr-1 has been found in many European countries, parts of Asia, North Africa, South America, and North America, including Canada.

On Thursday, US health and agriculture authorities announced mcr-1 has been found twice in recent weeks in the United States, the first such findings here.

A woman in Pennsylvania who was tested for a urinary tract infection had E. coli in her urine that contained the gene. It was also found in the intestine of a pig that had been screened as part of a Department of Agriculture program looking for it in animals.

The Centers for Disease Control and Prevention sees this as very unwelcome news. But experts aren’t really surprised. Mcr-1 is on the move.

So is this the start of the end of antibiotics?

That’s taking this too far. At this point, it’s unclear what impact mcr-1 will have on people, experts said.

Some superbugs that have cropped in the past — for example, VRSA or vancomycin-resistant Staphylococcus aureus — really haven’t triggered the serious problems they were expected to cause. (There’s no guarantee, though, that VRSA won’t cause problems in the future.)

Other superbugs are already plaguing patients in major ways.

“I think the story is still waiting to be told about exactly how this is spreading and how common it is around the world and how likely it is to be a threat in the long run to people,” said Dr. Alexander Kallen, who leads the CDC’s Antimicrobial Resistance and Emerging Pathogens Team.

“But it certainly has that potential.”

With new forms of antibiotic resistance, the safest approach is to assume the worst.

What is the worst?

The scenario experts are currently worried about involves mcr-1 hooking up with another kind of mobile resistance factor, known as CRE. That’s short for carbapenem-resistant Enterobacteriaceae — bacteria that are resistant to a very good family of antibiotics known as carbapenems.

CRE + mcr-1 = all sorts of bad news. Bacteria with these two weapons might be impossible to treat.

“If it becomes connected with CRE on a regular basis, that’s the grimmest scenario,” said Gerry Wright, director of the Michael DeGroote Institute for Infectious Diseases Research at MacMaster University in Hamilton, Ontario.

And Lance Price, who is director of the Antibiotic Resistance Action Center at George Washington University, noted that both mcr-1 and CRE are very promiscuous. They swap into new bacteria easily.

What does the grimmest scenario mean for medicine? Are these bugs going to start killing people left, right, and center?

Healthy people who stay healthy won’t be keeling over in the streets.

“It’s not the zombie apocalypse, where one day everybody is fine and the next day, everyone’s infected. That’s not how this works,” Wright said.

But everyone gets sick at a point and that’s when the picture changes. The many miracles of modern medicine are harder to take for granted when difficult-to-treat or untreatable bacteria are floating around.

“These bugs, they get into our hospitals, they get hard to get rid of and our most vulnerable patients are at risk,’’ Wright said. “It makes you rethink whether or not you get your new hip, it makes you rethink whether or not you’re going to have cancer chemotherapy, whether or not you’re going to get that heart valve replaced.”

So what really is the significance of this finding?

It’s more evidence that the bugs are winning. And that the way we use antibiotics is helping them win.

We use them when we don’t need them, killing off vulnerable bacteria in our systems and encouraging the proliferation of bugs that can evade the drugs. Doctors give broad spectrum antibiotics — ones that attack a range of bacteria — when more targeted versions would work. We feed them to animals, as growth promoters and to fend off infections that would eat into profits.

“This is just another example of this slow progression that we’ve seen over the last years of the potential for increasing resistance,” said Kallen.

“For the individual patient level, this may not be a huge issue, unless you are unfortunate enough to get a pan-resistant strain. But for the overall nation, here’s just another [step] in this steady progression of increasing resistance.”

Is the world taking this seriously enough?

Any expert you ask will say much, much more needs to be done. That starts with making clear to people that antibiotics don’t cure viral infections like colds or the flu, and they should not pressure doctors for prescriptions in these circumstances.

That said, the issue is on the global radar in a way it may not have been previously. Kallen, who has been working on antibiotic resistance for 20 years, said there is more interest in and money for the fight than he can ever remember.

But Price thinks there still needs to be a major shift in mindset. “We need to see this as a global challenge,” he said. “We need to put this in the same category as biodefense.’’

“We need global agreements that say, ‘Hey, feeding antibiotics to animals to make them grow faster or to prevent diseases that are occurring because of the way we’re raising them is unacceptable.’”

“We need to value these drugs for what they are.’’