Ground beef from conventionally raised cattle is more contaminated and contains a heavier concentration of antibiotic-resistant bacteria than samples from antibiotic-free and organic or grass-fed animals, a new study shows.

A report published Monday by Consumer Reports is one of the first of its kind to compare ground beef from the two sources. It found that nearly 20 percent of the beef from cows that finish their lives in crowded feedlots were tainted with superbugs compared with less than 10 percent of the group largely raised on pastures. Conventional samples also had much higher levels of E. coli, an indication of fecal contamination.

“This is really one of the more significant studies showing the difference in prevalence rates based on those production practices,” said Urvashi Rangan, head of food safety at Consumer Reports.

Consumer Reports tested 300 packages or nearly 500 pounds of ground beef that was purchased last October from big box stores and groceries specializing in sustainable products in 26 cities across the country, including Seattle, San Francisco and Los Angeles on the West Coast. The samples included a variety of labels, leanness, packaging and countries of origin. Just over 60 percent of the ground beef was from conventionally produced cattle and the rest came from cows raised without antibiotics that were either organic, grass-fed or both.

At what point can consumers have E. coli levels on labels? These are just catch-phrases.

The samples were tested for five common pathogens associated with beef: E. coli, salmonella, enterococcus, Clostridium perfringens and Staphylococcus aureus.

The North American Meat Institute said, in response to the study’s findings, that the research in fact “confirms strong safety of ground beef,” noting that the results did not report findings of highly pathogenic E. coli or Salmonella.

“A review of Consumer Reports’ new study on the safety of ground beef in the U.S. confirms that pathogenic bacteria is rarely found in meat,” the organization said in a release. “The bacteria identified in the Consumer Reports testing are types that rarely cause foodborne illness. Bacteria such as Staphylococcus aureus, Enterococcus and generic E. coli are commonly found in the environment and are not considered pathogenic bacteria.

“The real headline here is the bacteria that Consumer Reports doesn’t report finding in their testing — Shiga toxin-producing E. coli and Salmonella — which are the foodborne bacteria of greatest public health concern in beef,” said North American Meat Institute Vice President of Scientific Affairs Betsy Booren, in NAMI’s statement.

The National Cattlemen’s Beef Association likewise saw a different picture.

“I have relied on Consumer Reports when purchasing cars and electronics but unfortunately this report will not help consumers when purchasing safe ground beef,” said Mandy Carr Johnson, senior executive director, Science and Product Solutions, for NCBA. “The bacteria found in the Consumer Reports tests are not the type of bacteria commonly associated with foodborne illness in ground beef.”

Said NCBA’s Carr: “The only helpful takeaway from the report for consumers is that all ground beef should be cooked to and internal temperature of 160 degrees Fahrenheit and confirmed with an instant-read meat thermometer, as recommended by the U.S. Department of Agriculture.”

Just cook it doesn’t cut it, and doesn’t deal with cross-contamination. Lower loads.