A new study claims that not only does half the meat sold in groceries harbor a nasty little bacteria called Staphylococcus aureus, but a full quarter of the beef, chicken, pork and turkey carries a drug-resistant strain of the bug.

The study, published in the journal Clinical Infectious Diseases, checked out 80 brands of meat from 26 grocery stores in five U.S. cities — L.A., Chicago, Ft. Lauderdale, Flagstaff and Washington, D.C. — and found that 47% of the meats tested positive for S. aureus, which can cause skin infections, pneumonia, sepsis or endocarditis. And 52%percent of those positive tests were for a strain of the bacteria that is resistant to at least three types of antibiotics.

“For the first time, we know how much of our meat and poultry is contaminated with antibiotic-resistant Staph, and it is substantial,” said the senior author of the study. “The fact that drug-resistant S. aureus was so prevalent, and likely came from the food animals themselves, is troubling, and demands attention to how antibiotics are used in food-animal production today.”

The bacteria can be killed in most cases by just cooking the meat, but that won’t prevent it from infecting people and surfaces touched by the meat before it is cooked.

Since the bacteria was found in the meat instead of on its outer surface, the researchers believe the infection likely results from “densely-stocked industrial farms, where food animals are steadily fed low doses of antibiotics… ideal breeding grounds for drug-resistant bacteria that move from animals to humans.”

Study: 25% of meat has drug-resistant bacteria [Chicago Breaking News]