Our Most Potent Antibiotics No Longer Work

A drug called colostin used to be our last line of defense. But researchers have found bacteria in China that's colistin-resistant, and they're certain it will spread.

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Nov 24 2015, 3:10pm

An agar plate with bacteria spread over the surface. The little discs contain antibiotics (like ceftazidime 'CAZ' and cefoxitin 'FOX'). This shows how the bacteria grows straight over the top. The number refers to the concentration of antibiotic in the disc. Photo by Dr. Patrick Harris

Last week researchers announced that they'd found strains of bacteria that are resistant to the planet's most potent antibiotic, colistin. Not only that, but the gene for this resistance is easily shared between different strains. So it's really just a matter of time before this resistance goes global.

The road to this discovery started in 2011. The Chinese Ministry of Science and Technology funded a group of researchers to test meat samples around the southern Chinese city of Guangzhou. Much of the country's meat is produced here in high-intensity factory farms, where farmers stave off infection by feeding the animals human-grade antibiotics. This might insure investments for farmers, but it also encourages bacteria to develop ways of coping with our best antibiotics.

That's not to say China is to blame. Antibiotics have been used in animal agriculture everywhere for a long time and especially in the US. It's just that we're paying for it now.

To unpack this complex issue we spoke to Dr. Patrick Harris. He's an infectious disease physician and microbiologist with the University of Queensland, and he co-wrote a paper on what it means to have our last antibiotic curtailed—both now, and very soon.

VICE: Hi Patrick, are we doomed?
Dr. Patrick Harris: Well I think this is a bit like climate change. We're not there yet, but we will be. See we've always had a few things in the cupboard that we can turn to when needed. These are known as carbapenems—which are a branch of broad-spectrum penicillin drugs for our sickest patients—but since the early 2000s we've seen more and more resistance to these drugs.

And that was when we traditionally used colistin?
That's right. In those circumstances, when nothing else works, we've got colistin. It's a really old, crappy antibiotic in many ways because it's so toxic. It was developed in the 1950s and abandoned because it was too toxic, but it's still around and we can get it when we need it. Colistin usually wipes out most gram-negative infections, but what's new is this gene that makes bacteria resistant to it, called MCR-1.

Now, I understand this resistance is transmissible between bacteria. How does that work?
It works because the MCR-1 gene has latched itself onto a plasmid. A plasmid is mobile packet of DNA. It's like a little tool kit that can carry all kind of resistance genes. Bugs are very clever. They can have a very primitive type of sex and share these genes via plasmids. So if you have drug resistant E. coli sitting in your gut with one of these plasmids, they can pass the plasmid on to all the other different strains of bacteria in your gut. And that's how this resistance spreads very, very quickly.

Let's say that resistance to colistin goes global. What does that future look like?
Well keep in mind that people won't transmit these bugs by shaking hands. The worry is that it'll just take medicine back in time. Before penicillin, if you got a blood infection you had an 80 percent chance of dying. After penicillin, that dropped to 10 percent. Now, at the moment when patients get infected with these bugs, they've got a 50/50 chance of dying, and that's with colistin available. So if you take colistin out of the equation, then we'll go back to pre-penicillin figures of 80 percent mortality. That would mean you could forget about all sorts of modern surgery. We couldn't do transplants or orthopedic surgery or all sorts of things we take for granted. We'd suddenly have very limited options.

It's completely indefensible to be feeding food animals antibiotics for humans.

I'm finding this very depressing.
I don't think it's the end of the world just yet. Instead I'm saying that it's completely indefensible to be feeding food animals antibiotics for humans.

Yes, let's talk about how we got to this point.
Well, it was known even in the 1950s that if you feed animals antibiotics they grow faster. No one really knows why this is. The other thing is that in intensive factory farming animals are much more susceptible to infection so antibiotics are used in the feed as a kind of prophylactic measure. The thinking is that we should just give animals the most powerful antibiotics we've got all the time. That's logical if you're growing chickens, but no one's been thinking about the downstream effects.

Are we still feeding colistin to food animals, even now?
Absolutely. In the US it's something like 60 to 70 percent of all antibiotics are used in agriculture. And of course the agricultural lobby is very powerful. The Iowa pig industry produces billions of bacon rashes every year. If you ask them to stop using antibiotics, they're very reluctant. You might be asking to change how we practice industrial farming.

So why aren't we lobbying against this in the same way we're tackling climate change?
I'll be honest. As an infectious diseases doctor, we've been banging on about this for 20 years. It's just been very difficult to capture the public's imagination.

Are you pissed off about that?
It's not that people don't listen. I just think a lot of people don't understand. It's very technical and a lot of people don't even know the difference between bacteria, a virus, or a parasite. It's hard to capture imaginations when people don't understand the problem.

So is there a moral to the story?
This a wake-up call. It's not the apocalypse, but it is indefensible to be using critical antibiotics as growth promotion in animals. That's just not a logical or ethical thing to do.

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