Remember pink slime -- that Dayglo-bright mash of ground up meat scraps and cow connective tissues larded with industrial strength ammonia that was being served up in school lunch programs in the United States last year?

More ominously, there was mad cow disease, which has killed scores of people in Britain and elsewhere. Bird-flue outbreaks originating in poultry farms in China and Southeast Asia have also led to periodic scares. And did I mention salmonella?

But these food-related scourges pale in comparison with another threat, which was the subject of a report released last Monday by the U.S. Centers for Disease Control : the spread of antibiotic resistant bacteria. In its first estimate of the scope of the problem, the CDC says that 23,000 people -- and possibly many more than that -- die in the U.S. each year from infection by microorganisms that can no longer be controlled by our current array of antibiotics.

We've known for a long time that our chronic overuse of antibiotics is helping to create these dangerous new strains of bacteria. Public health officials worry that doctors are routinely overprescribing powerful broad-spectrum antibiotics for everything from stomach aches to common colds. The CDC report says that 50 percent of all the antibiotics prescribed for people are not actually necessary.

But antibiotics are not just overused in medical care; we're also feeding them indiscriminately to cows, pigs and chickens. Fully 80 percent of the antibiotics sold in the U.S. are administered to farm animals in their water and feed. The use of these drugs in agriculture is not properly regulated, according to Keeve Nachman, the director of the Center for a Livable Future at Johns Hopkins University.

Nachman told me that we don't know exactly what antibiotics are being used in meat production, or how large the doses that are administered are. Even more critically, we don't know how much of these antibiotics remains in the meat that we eat. Eating meat, even with low doses of antibiotics, he warns, may lead to the spread of antibiotic resistant bacteria in our own guts, if the meat is mishandled or undercooked.

There is also ample evidence that the overuse of antibiotics has created resistant bacteria in the external environment. Studies have shown them in water downstream from livestock farms, as well as in the air and soil near facilities where antibiotics are used. Nachman himself published a study in JAMA Internal Medicine that shows that people living near swine production sites are more likely to be infected with the superbug MRSA (Methicillin-Resistant Staphylococcus aureus).

In light of these risks, the CDC report says pointblank: "The use of antibiotics for growth is not necessary, and the practice should be phased out."

Most antibiotics currently used on farms are not for the treatment of sick animals, or even the prevention of disease, but to promote the growth and weight of livestock. Until recently scientists didn't know how antibiotics stimulated growth. However, a study published in Nature last year helped to clear up this mystery.

New York University researchers found that antibiotics have a big impact on what is called the microbiome, the teeming ecosystem of billions of diverse bacteria that live within the gut. Not only do they kill off many valuable microorganisms, but they also apparently alter the ability of some gut bacteria to metabolize carbohydrates. With the result that mice that the scientists fed antibiotics fattened up , just as as livestock do.

So if animals typically put on weight when they take antibiotics, what about humans? A study published in the Journal of Obesity found a strong correlation between exposure to antibiotics in childhood and later obesity . But that may not be the worst of it. Evidence is also mounting that low microbial diversity in the gut is associated with a whole range of inflammatory illnesses including heart disease, type 2 diabetes and cancer.

With all of these dangers deriving from our overuse of antibiotics, Keeve Nachman argues that the time has come to get serious about regulating them. He says: "The FDA has proposed a voluntary program in which the pharmaceutical companies are asked to give up their drug approvals for purposes of growth promotion and to relist them for purposes of disease prevention."

But Nachman calls this "essentially a shell game" which will change how the drugs are labelled, but not the way they are actually used in animals.

To solve the problem, he says, we'll have to ban antibiotics except in actual cases of illness. Farmers should be required to get a prescription from a veterinarian, much as you and I need a prescription from their physician before we can use the drugs.

There are already several European countries that have banned the indiscriminate use of antibiotics in meat production. But so far neither Congress nor regulators in the U.S. have been willing to stand up to the livestock lobby and protect the public's health.

An earlier version of this story appeared in the Guardian .