In Consumer Reports new tests of ground beef, 18 percent of the beef samples from conventionally-raised cows contained dangerous superbugs resistant to three or more classes of antibiotics used to treat illness in humans compared with just 9 percent of beef from samples that were sustainably produced.

Consumer Reports’ investigation comes as food poisonings are striking an estimated 48 million people in the U.S. each year with beef being a top cause of outbreaks.

Compounding the issue, Americans often prefer their beef on the rare side.

The grinding process used to produce ground beef can distribute bacteria throughout the meat and if it’s not cooked properly through to the center, the potential for getting sick increases.

Consumer Reports purchased 300 packages – 458 pounds – of conventionally and sustainably produced ground beef from grocery, big-box, and natural food stores in 26 cities across the country.

The samples were tested for five common types of bacteria associated with beef—Clostridium perfringens, E. coli (including O157 and six other toxin-producing strains), Enterococcus, Salmonella, and Staphylococcus aureus.

The testing, which is among the largest conducted to date, found bacteria on all of the beef samples.

However, ground beef from cows raised more sustainably was significantly less likely to have two potentially harmful bacteria (S. aureus and E.coli) than those from cows raised conventionally.

The sustainably-produced beef came from cows that were raised without antibiotics and in some cases were either organic, grass-fed, or both.

Beef from grass-fed and organic cows have access to pasture, are fed a grass-based diet, and are treated more humanely.

Conventional cows can live on feedlots, be regularly fed antibiotics, as well as animal waste and other by-products.

“Better ways of producing beef from farm to fork have real impact on the health and safety of our food and the animals themselves,” said Urvashi Rangan, Ph.D., executive director of the Center for Food Safety and Sustainability at Consumer Reports. “Farming animals without antibiotics is the first step toward a more sustainable system. Grassfed animals and good welfare practices produce fewer public health risks.”