Mark Bittman on food and all things related.

The story of antibiotic-resistant bacteria in farm animals is not a simple one. But here’s the pitch version: Yet another study has reinforced the idea that keeping animals in confinement and feeding them antibiotics prophylactically breeds varieties of bacteria that cause disease in humans, disease that may not readily be treated by antibiotics. Since some of these bacteria can be fatal, that’s a scary combination.

Antibiotic-resistant bacteria are bad enough, but now there are more kinds; they’re better at warding off attack by antibiotics; and they can be transferred to humans by increasingly varied methods. The situation is demonstrably dire.

Two of the examples highlighted in a Food and Drug Administration report are that about 10 percent of all chicken breasts sold at retail are contaminated with a form of salmonella that’s resistant to at least one antibiotic, and nearly half of all chicken that’s sold is contaminated with antibiotic-resistant campylobacter. Some of the antibiotics in question are used to treat sick people but are also used daily in raising livestock. And it seems that these livestock, especially ones raised by contemporary industrial means, are a breeding ground for making these and other bacteria more resistant [1] .



Some of this resistance comes from overuse in humans, but there’s increasing evidence that resistance is being bred in animals that are a) raised in confinement and b) given antibiotics routinely. We want to know, of course, whether these bacteria move from animals to humans. Of particular concern is one called MRSA ST398, or “livestock-associated MRSA.” MRSA [2] is shorthand for Methicillin (a type of antibiotic)-resistant Staphylococcus aureus.

MRSA is serious [3] . Maryn McKenna [4] , a journalist who specializes in these matters and the author of “Superbug,” says that “MRSA is an underappreciated epidemic in the U.S. — over all, that organism causes more than 18,000 deaths and more than 365,000 hospitalizations a year — although we don’t know how much of that epidemic ‘livestock-associated MRSA’ is responsible for.”

The latest study concerning antibiotic resistance was published last week in the journal PLoS One. It looked at livestock workers in North Carolina (the nation’s second biggest hog-producing state, after Iowa), including those in what the study’s authors called “industrial” livestock production and those on farms where the animals were raised without antibiotics and grown on pasture. In this study, the S. aureus bacteria with genetic markers most closely linked to livestock were found in far greater numbers in workers on the industrial farms.

In fact, says Christopher Heaney, corresponding author of the study and assistant professor of environmental health sciences and epidemiology at the Johns Hopkins Bloomberg School of Public Health, “This study shows that these livestock-associated strains are present among workers at industrial livestock operations and that these strains are resistant not just to methicillin, but to multiple antibiotics — including antibiotics that are used to treat human infections.”

Because the study looked at workers and not animals on the same farms, there are gaps to fill in, as Heaney freely admits. “But everyone in our study had direct or indirect contact with livestock,” he says, “and one might expect to find similar prevalence of an opportunistic pathogen like S. aureus that is linked with livestock in both groups.

“But we didn’t see that: we saw both a higher prevalence of drug resistance — for tetracycline and multidrug resistance — in the industrial compared to the antibiotic-free group and, in the industrial group only, we saw drug-resistant strains with multiple genetic characteristics linked to livestock.

“That’s remarkable; we never expected to see something so clear at the outset of the study.”

A reasonable person could assume that these drug-resistant staph bacteria are coming from animals, since you generally don’t find them in the non-livestock-working population in the United States.

This is another dot in a sketch that’s becoming clearer. There’s evidence of MRSA moving from pigs to humans in Iowa — where pioneering research has been done by Tara Smith at the University of Iowa — and in Europe, where Jan Kluytmans, an epidemiologist at VU University Medical Center Amsterdam, has found that “approximately 40 percent of all new persons with MRSA carry the livestock-associated strain, and most are related to contact with animals. Our data on MRSA are convincing that livestock is now a huge reservoir of MRSA for humans.”

The F.D.A., which is under court order to do something about the routine use of antibiotics, has come up with a lame voluntary reduction scheme — “Guidance 213,” it’s called — acting as if it will save its real regulatory muscle for after this scheme flops. (Which it will — flop, that is.) Worse, despite repeated promises that the voluntary guidelines were imminent, they haven’t issued even those. And now, “Guidance 213 is currently in the clearance process, but we cannot predict a timeline on its release,” an agency spokeswoman wrote me in an e-mail. Period.

That’s simply insulting. Of course, almost no one is pushing the F.D.A. to do its job. There are a handful of people in Congress; certainly some well-meaning NGOs like Pew Charitable Trusts, Natural Resources Defense Council and others; and dedicated individuals like the lawyer Bill Marler. Against them are arrayed not only Big Pharma — which is providing four times as many antibiotics to animals as it is to humans — but industrial ag, which cares only about raising animals “efficiently” and profitably.

At whose cost? Well, the answer to that question, at least, is pretty simple.

1. Bacteria can share resistance genes with other bacteria, even in humans, even with those that have never been exposed to antibiotics or seen the inside of a farm animal.

2. I said this was not simple: There are some broad categories of MRSAs: community-associated, hospital-acquired (the best-known) and livestock-associated. Each of the first two comprises dozens — or more — different strains. At the moment, ST (sequence type) 398 is the most common livestock-associated MRSA, but there are others. And there is also MDRSA — for Multi-Drug Resistant staph aureus — which is ultimately even scarier, because the drug resistance has spread to other important antibiotics. (Like, “Oh, we can’t use methicillin? Let’s use tetracycline. Oh, that doesn’t work either?” Meanwhile the patient is getting sicker and sicker.) It gets more complex but no less awful.

3. This (PDF) long anecdote is quite horrifying and the opposite of reassuring. Be prepared.

4. Here’s her blog on Wired about this subject.