(AP) -- The Food and Drug Administration called on drug companies Wednesday to help limit the use of antibiotics given to farm animals, a decades-old practice that scientists say has contributed to a surge in dangerous, drug-resistant bacteria.

Antibiotics are mixed with animal feed to help livestock, pigs and chickens put on weight and stay healthy in crowded barns. Scientists have warned that this routine use leads to the growth of antibiotic-resistant germs that can be passed to humans.

The FDA has struggled for decades with how to tackle the problem because the powerful agriculture industry says the drugs are needed to keep animals healthy.

Under the new FDA guidelines, the agency recommends antibiotics be used only when needed to keep animals healthy. The agency also wants to require a veterinarian to prescribe the drugs. They can currently be purchased over-the-counter by farmers.

The draft recommendations by the FDA are not binding, and the agency is asking for drug manufacturers' cooperation to put the limits in place. Drug companies would need to adjust the labeling of their antibiotics to remove so-called production uses of the drugs. Production uses include increased weight gain and accelerated growth, which helps farmer save money by reducing feed costs.

But the voluntary approach was met with skepticism by some public health advocates, who said they do not trust the drug industry to voluntarily restrict its own products.

"This is not an issue where trust should be the measure. This is an issue where the measure is whether or not the FDA has fulfilled its authority of protecting public health," said Richard Wood, Chair of the Keep Antibiotics Working coalition, in a statement.

FDA officials said that a formal ban would have required individual hearings for each drug, which could take decades.

"The process we would have to go through is a formal hearing process, product-by-product that that is extremely cumbersome," said Mike Taylor, FDA Commissioner for foods. "There's no point in going through those legalistic proceedings when companies are willing to make this shift voluntarily."

Taylor said the FDA has worked closely with drugmakers, and expects them to support the measures.

The debate over antibiotics has long pitted the benefits for producing safe, low-cost meat against the risk of contributing to dangerous antibiotic-resistant bacteria that can infect humans. In its posting Wednesday, the FDA said the benefits for meat production do not warrant overuse of the drugs.

"FDA believes that using medically important antimicrobial drugs to increase production in food-producing animals is not a judicious use," the agency states.

The waning effectiveness of antibiotics has been a global health concern for several decades, attracting the attention of the World Health Organization, the Institute of Medicine and other health groups. As bacteria have grown more resistant, new and more deadly forms of malaria, staph and other infections that were once easily treatable have emerged across the globe.

Experts say overuse of antibiotics in both animals and among humans has contributed to the problem.

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