The Verdict Is in: Antibiotics in Animal Feed Create Superbugs

A new study answers the question that has been pitting scientists against agribusiness for years.
(LadyDragonflyCC/Creative Commons)
Feb 22, 2012
Megan Bedard is a sucker for sustainable agriculture and a good farmers market, she likes writing about food almost as much as eating it.

Researchers may have finally put to rest a question that has routinely plagued agribusiness advocates: do antibiotics in livestock feed propagate antibiotic-resistent germs that put human health at risk? The answer: a definitive yes.

A study published Tuesday in the journal mBio (and reported on NPR) demonstrates how an antibiotic-susceptible staph germ was passed from humans to pigs, then back again. Before making the leap back into humans, the staph germ became resistant to antibiotics tetracycline and methicillan.

That's problematic, because human bacteria that develop immunity to antibiotics pass their immunity to future generations, rendering current treatments for bacteria ineffective. 

According to the Union of Concerned Scientists, antiobiotic-resistant illness "causes tens of thousands of premature deaths in the United States annually and drives up medical costs."

To reach their conclusion, the study's 20 authors conducted whole-genome analysis on a staph strain called CC398 and 88 other variations that are similar to C398, also known as methicillian-resistant Staphylococcus aureus (MRSA). NPR reports that the MRSA strain "emerged within the past decade in pigs and has since spread widely in cattle and poultry as well as pigs."

Through the analysis, the authors were able to trace the lineage of the bug to its antibiotic-susceptible human "ancestors," removing any doubt that the bacteria "jumped back into humans with close exposure to livestock."

Agribusiness relies on antibiotics to boost animal growth and keep animals from getting sick in overcrowded, unsanitary factory farms. Though the European Union has abandoned the practice—treating animals only after they're sick—the U.S. Food and Drug Administration (FDA) recently opted to allow use of penicilin and tetracyclines to continue unabated

In fact, antibiotic use is actually on the rise, up 6.7 percent from 2009-2010, according to FDA data released in November of 2011.

If consumers can be comforted by the fact that cooking food well eliminates most staph, they might still be unsettled by the fact that the MRSA was detected in 6 percent of 395 pork samples in a recent study.

Worse, eating meat labeled "raised without antibiotics" won't necessarily improve chances of avoiding the staph bacteria. Tara Smith, lead author of the study that revealed the bacteria's prevalence, told that, unlike meat marked "organic," products with the "raised without antibiotics" label "are not routinely verified by an independent third party." She also noted that conventionally produced pork can be processed at the same plants, allowing contamination to occur.

Fiercly defensive of its practices, the American Meat Institute insists that human use of antibiotics—and not animal use—is responsible for antibiotic resistence among humans.

Trouble is, pointing the finger of blame doesn't put a stop to the problem. Lance Price of the Translational Genomics Research Institute—and one of the 20 authors of the most recent study—tells NPR that the new bug is spreading beyond people in direct contact with livestock.

Price explains that previously, MRSA was always traced back to livestock exposure. But scientists are now seeing cases of resistant strains that they can't trace back, suggesting that the strain is passing from human to human. If that's true, a major health crisis could be in store.

In June of 2010, the FDA released a policy report saying that livestock should only receive antibiotics to treat illness, not as an automatic additive to their feed. Experts scoffed at the FDA's announcement, predicting it would take ages to implement. Nearly two years later, it seems they were on the mark, and Price fears a troublesome road ahead.

"We're seeing this one coming," Price tells NPR. "The question is, how often will this occur in the future if we don't start controlling antibiotic use?"

Read the full story on NPR.

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