What Does “Human Antibiotics” Mean?

Because, like Honey Badger, bacteria just don’t give a shit what they’re called.

Recently, Tyson Food, the largest U.S. poultry producer, announced they’re changing their antibiotic use policies (boldface mine):

Tyson Foods, Inc. (NYSE: TSN) said today it is striving to eliminate the use of human antibiotics from its U.S. broiler* chicken flocks by the end of September 2017. The company will report annually on its progress, beginning with its fiscal 2015 Sustainability Report. Tyson Foods has already stopped using all antibiotics in its 35 broiler hatcheries, requires a veterinary prescription for antibiotics used on broiler farms and has reduced human antibiotics used to treat broiler chickens by more than 80 percent since 2011.

“Antibiotic resistant infections are a global health concern,” said Donnie Smith, president and CEO of Tyson Foods. “We’re confident our meat and poultry products are safe**, but want to do our part to responsibly reduce human antibiotics on the farm so these medicines can continue working when they’re needed to treat illness.”

It’s worth noting Tyson provide themselves an out:

“One of our core values is to serve as responsible stewards of animals – we will not let sick animals suffer,” Smith said. “We believe it’s our responsibility to help drive action towards sustainable solutions to this challenge by working with our chicken, turkey, beef and pork supply chains.”

Mind you, I think sick animals should be treated, but this sounds like a back door to widespread preventative use. As you might imagine, Scary Disease Woman (aka ‘Maryn McKenna’) has some thoughts on the matter:

Here’s the “human-use” complexity: Many of the antibiotics used in agriculture are functionally identical to the ones used in human medicine. That causes concern because, if the use of those antibiotics provokes the development of bacteria that are resistant, and those bacteria then cross to humans and cause infections, the drugs that would normally be used to cure them won’t work.

“Human-use” or “significant in human medicine” is shorthand for those drugs: veterinary antibiotics that are essentially the same as ones used in human medicine. (They are also the target of the long-standing Preservation of Antibiotics for Medical Treatment Act, or PAMTA, introduced in Congress five times now by Rep. Louise Slaughter, D-N.Y., who is also a microbiologist.)

There’s a more serious problem here (actually two, sorta), and it’s not the use of ‘human antibiotics’–that is, those antibiotics used in the clinic. It’s the closely related veterinary-only antibiotics that are the problem. When resistance evolves to the veterinary antibiotics, it can also evolve resistance to other related ‘human antibiotics.’ One example is avoparcin. After many countries in Europe were allowed to use avoparcin in agriculture, resistance to vancomycin in enterococci (gut bacteria that can cause disease–like many disease-causing organisms), also known as VRE, not only evolved, but very rapidly rose to around ten percent of all clinical isolates* (uncharacteristically, the U.S. had the brains to not do this). Another example is the veterinary antibiotic cefquinome, resistance to which confers resistance to ceftiofur and many other cephalosporin antibiotics (basically, drugs that start with cef- or ceph-, along with the ‘-cillins’).

Also, even when the ‘non-human’ antibiotics aren’t defeated by the same genetic mechanism, these resistances be genetically linked: acquiring a resistance gene that protects against antibiotic X also results in gaining a different resistance gene that protects against antibiotic Y (for the cognoscenti, I’m referring to plasmids and other transposable elements).

So while Tyson Foods’ move sounds good, the devil–and the possibility of the evolution of resistance–will be in the details.

*This wasn’t a ‘dose-dependent’ phenomenon; it most likely transferred once or a few times to a common clinical isolate and then took off.

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