Axel Ellerhorst

Repeat after me: Antibiotic-free.

On the heels of news from the U.S. Food and Drug Administration that sales of antibiotics for livestock rose 23 percent in recent years, the agriculture industry is bracing for regulators to set what are expected to be much stricter regulations for their usage by the end of 2016.

At the same time, major food companies like McDonald’s and Subway are pledging to stop serving meat raised with antibiotics, applying additional pressure for the industry to turn away from a practice that many scientists believe presents a major health risk.

Specifically, a growing number of researchers has linked the excessive use of antibiotics in livestock with fueling drug resistance in humans, putting the population at risk of falling victim to “superbug” bacterial mutations. Some have warned increased resistance means humanity is nearing a "post-antibiotic era."

Alarm around antibiotic use in livestock, however, is nothing new -- even if it’s taken several decades for the issue to go mainstream.

In 1976, Dr. Stuart Levy, a physician and director of Tuft University’s Center for Adaptation Genetics and Drug Resistance, published the results of his and his colleagues’ study to determine what impact the addition of antibiotics to the feed of a farm’s chickens would have on both the chickens themselves, but also in the farm workers who were in contact with them.

The results, published in the New England Journal of Medicine, “shocked people,” Levy recently told The Huffington Post. The chickens, just a week after being given feed supplemented with tetracycline, developed tetracycline-resistant bacteria, as did the farm workers who were caring for them.

As Levy explained, these results did not square with the prevailing beliefs about bacteria and resistance at the time.

“It was a revelation and the company sponsoring the study thought we did something to change the results,” Levy said. “In those days, the thought was that animals had their own bacteria and people had their own, so you would never get a mix.”

Levy’s findings were not a surprise to him, however.

“It made sense that if you use tetracycline [in the feed], you’ll get the tetracycline-resistant bacteria,” he continued. “I remember arguing with people about this. You had to fight a battle to get this across in the ‘70s or ‘80s. There was so much misconception.”

Today, 40 years later, there is more agreement on the subject and consumers are catching on, pushing the industry and its regulators to change.

But the regular “sub-therapeutic” doses of antibiotics for livestock is so common, there is still a long way to go before the practice would be fully eliminated. About 32 million pounds of antibiotics intended for farm animals are sold every year and some 80 percent of the antibiotics sold in the U.S. are estimated to be used on livestock, rather than by humans, though meat industry groups have disputed that figure.

For its part, the meat industry maintains that its use of antibiotics in livestock is necessary to help the animals stay healthy and to keep the price of meat low.

"Animal antibiotics make our food supply safer and people healthier," a statement on the industry group Animal Health Institute's website reads. "Antibiotics are a critical tool to prevent, control and treat disease in animals. In doing so, they also reduce the chance of bacterial transmission from animals to humans."

Still, even as the meat industry isn't solely to blame for the broader problem of antibiotic resistance, Levy believes the ever-growing body of evidence of what's at stake should not be ignored.

"You can’t shy away from the fact that the most important risk factor of antibiotic usage in animals, people or agriculture is the emergence of resistance," Levy added.

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