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It's a kitchen credo that you should wash your hands and utensils thoroughly, especially after they've touched raw meat or poultry, which may contain a host of bacteria — salmonella, listeria, E. coli — that can make you sick. Now add a new pathogen to the list.

Researchers were surprised to find that nearly half of samples of beef, pork and poultry tested from popular grocery stores were contaminated with Staphylococcus aureus, a bacteria that the U.S. Department of Agriculture (USDA) doesn't even monitor in the food source, because it's not known as a common food-borne pathogen. And of the bacteria found, nearly all were strains that were resistant to more than one antibiotic. (More on TIME.com: Top 10 Most Dangerous Foods)

Staph is the same bug that caused headlines several years ago, when hospitals and communities started reporting a particularly virulent strain, methicillin-resistant staphylococcus aureus, or MRSA, that sickened children and led to tens of thousands of deaths. The bacteria dies when heated, but until contaminated meat is cooked, it can pose a health hazard in kitchens.

Lance Price, a professor at the Translational Genomics Research Institute, which conducted the staph study, decided to focus on this bacteria because recent reports showed that people working on farms had picked up staph infections directly from affected animals. If the bacteria had colonized the animals, Price wondered, what about their meat when they were slaughtered?

"Now we now that when the average consumer purchases meat, he has a one-in-four chance of bringing a multidrug-resistant strain of staph into the kitchen," he says. "Bacteria in meat and poultry is something we deal with every day. We try to minimize it, but it's a normal part of slaughtering animals. But the fact that we have multidrug-resistant strains of staph is not normal." (More on TIME.com: Mind Reading: Can We Protect Ourselves from the 'Superbug' MRSA?)

The results of the study, he says, reflect the dangers of the overuse of antibiotics in agriculture. "The multidrug-resistant strains are the direct result of antibiotic use in food animal production, (even if) they aren't used to treat infection but instead to make the animals grow faster, make their feed more efficient and to prevent diseases from spreading in the crowded unsanitary conditions in which the animals are raised."

By analyzing the strains of staph picked up in the samples, Price and his team were able to show a diversity of strains that could come only from infected animals, including chicken, turkey, cattle and pigs — but not from human contamination, which originates from fewer strains of the bug. (More on TIME.com: Bug Cuisine)

The study is the first to show such widespread colonization of our favorite meats with staph, and, says Price, should give government regulators reason to consider adding staph to the list of potentially dangerous food-borne pathogens. The Food and Drug Administration and the USDA are already conducting a pilot survey of how commonly staph bacteria occur in the meat supply, and if their results mirror those of the current report, then staph could join E. coli and salmonella as potential food-borne hazards.

It's not clear how much illness the contaminated food causes each year, but annually 12 million people visit the emergency room with potential staph infections.

The findings are a warning that those numbers will only rise, thanks to meat-production methods that aren't entirely healthy, says Price. In particular, overuse of antibiotics will only make the problem worse. "The most effective way to reduce antibiotic resistance in the food supply is to stop using it in food production to boost yields," he says, "and only use it to treat sick animals." (More on TIME.com: Are Hot Dogs Better For You Than Roasted Chicken?)

Until then, remember to clean knives, countertops, cutting boards and even faucets that might have come into contact with staph from meat. Handling contaminated tools could be enough to cause nausea or diarrhea, and in people who are particularly vulnerable to bacterial infections, it could even lead to more serious issues such as toxic shock or a form of sepsis.

• Alice Park