One of the greatest medical discoveries of the 20th century happened by accident.

In 1928 scientist Alexander Fleming found mold growing in one of his petri dishes—then noticed that the bacteria all around it had been destroyed. That bacteria-killing mold was the first form of penicillin—and we as a society embarked on a brave new world in medicine. Suddenly, deadly diseases such as tuberculosis, scarlet fever, bacterial meningitis, and diphtheria could be cured with a pill. Surgery for heart disease and organ transplants, as well as chemotherapy, could succeed because those miracle drugs wiped out the infections that arose after treatment.

But less than 100 years after that breakthrough, antibiotics are losing their lifesaving effectiveness. Their overuse has allowed bacteria to evolve so that they are almost impervious to the drugs. That has led to the rise of “superbugs”—which include methicillin-resistant staphylococcus aureus (MRSA) and bacteria resistant to three or more types of antibiotics. And as the number of superbugs increases, the development of new antibiotics to kill them has lagged. At least 2 million Americans fall victim to antibiotic-resistant infections every year; 23,000 die. “The antibiotics we’ve relied on for decades are becoming less effective—and we risk turning back the clock to a time where simple infections killed people,” says Tom Frieden, M.D., M.P.H., director of the Centers for Disease Control and Prevention.

Over this past year, Consumer Reports has investigated the dangers of antibiotic overuse in hospitals and doctors’ offices. But nowhere are the drugs more inappropriately employed than in the meat and poultry industries. About 80 percent of the antibiotics sold in the U.S. are given to animals raised for food—including hogs, cattle, chickens, and turkeys. The most recent data from the Food and Drug Administration show that more than 32 million pounds of antibiotics were sold for use in food animals in the U.S. in 2013—up 17 percent from just four years earlier.

Recently, several meat and poultry producers, such as Tyson, and restaurant chains, like McDonald’s and Subway, have pledged to reduce the production or sale of meat or poultry from animals raised with antibiotics. “But whether such measures will end up significantly reducing antibiotic use remains to be seen,” says Gail Hansen, D.V.M., who has more than 25 years of experience in veterinary public health and infectious disease.

“In the last few years we’ve witnessed some of the bacteria most commonly found in food—germs such as salmonella and campylobacter—become increasingly resistant to some important antibiotics,” says Robert Tauxe, M.D., M.P.H., deputy director of the CDC’s Division of Foodborne, Waterborne, and Environmental Diseases. Those resistant strains can cause infections that are “more severe, longer lasting, and harder to treat,” Tauxe says. In fact, our calculations using data from the CDC show that about 20 percent of people sickened by an antibiotic-resistant bug don’t pick it up in the hospital or from another person—they get it from their food.