Much of the ground turkey tested in a study released Tuesday by Consumer Reports — including meat from Minnesota-based turkey giants Cargill and Hormel — came back positive for pathogens that were resistant to antibiotics, a hot-button issue in public health circles.

Antibiotic drugs have long been used by livestock industries to keep animals healthy, but also to speed up growth, a controversial practice. Some scientists have grown concerned that antibiotic-resistant strains of bad bacteria can be transferred from animals to humans through the food supply.

The result is that some illnesses — for instance, those caused by the foodborne pathogen salmonella — might become more virulent in humans and thus more difficult to treat with antibiotics. Such a scenario developed in 2011 during a nationwide salmonella outbreak linked to ground turkey produced at a Cargill plant in Arkansas.

"We have a growing public health crisis with antibiotics becoming less effective in treating human disease," said Urvashi Rangan, director of food safety and sustainability at Consumer Reports, a prominent consumer watchdog organization. "On farms, you are creating huge reservoirs of resistant bacteria."

In an article posted on its website Tuesday, the U.S. Food and Drug Administration said it considers antibiotic-resistant bacteria "a major public health threat."

The agency is writing new guidelines to limit antibiotic use in the livestock industry. Still, a top FDA scientist said in the online article that "for most patients, antibiotics still work well."

Plus, thorough cooking kills harmful bacteria in meat.

Consumer Reports purchased 257 samples of raw ground turkey products from major food retailers, testing them for five bacteria, four of which can be directly associated with food poisoning in humans. Ninety percent of the turkey harbored at least one of the bacteria.

And more than half of those bacteria samples were resistant to three or more classes of antibiotics, Rangan said.

However, the study found that bacteria found in ground turkey products that were labeled "organic" or "raised with no antibiotics" were much less likely to be antibiotic-resistant.

In a statement, the Washington-based National Turkey Federation accused Consumer Reports of putting out "sensationalized and misleading findings," saying the industry has "spent millions of dollars to control pathogens on its products."

Minnesota is the nation's leading state for turkey production, and Minnetonka-based Cargill and Austin-based Hormel Foods are leading national turkey processors. Included in the Consumer Reports report was turkey that originated at Cargill's plants in Arkansas and Virginia and Hormel's operations in Barron, Wis. and Faribault, Minn.

In a statement, Hormel said its Jennie-O Turkey Store business follows "strict food safety and quality requirements." Veterinarians prescribe only medication dosages "to properly treat, control and prevent illness in animals."

Cargill, in a response to Consumer Reports, said "safe food is fundamental to our business," and that the company has invested more than $1 billion in North American meat safety efforts over the past decade.

In August 2011, Cargill recalled 36 million pounds of ground turkey — the largest U.S. poultry recall ever — after the spread of an antibiotic-resistant strain of Salmonella Heidelberg was linked to its product. Nationwide, 136 people were sickened in the outbreak, and one California woman died.

"To this day, we don't know the origin of the outbreak of illnesses," Cargill said in its response to Consumer Reports. The inability to find the cause "speaks to the random and naturally occurring attributes of bacteria such as Salmonella, in all of its 2,400+ variant strains."

Cargill says it has taken steps to improve safety at the Arkansas plant and has seen significant reductions in the prevalence of salmonella in its supply chain.

Eight ground turkey samples in Consumer Reports' tests contained salmonella resistant to at least three antibiotic classes, including one sample that originated at Cargill's Arkansas plant. However, the overall incidence of salmonella found by Consumer Reports in plants run by Cargill, Hormel and the rest of the industry was relatively low.

Government studies have typically found that 12 percent of samples from turkey plants contain salmonella, compared to only 5 percent of the samples tested by Consumer Reports.