Consumer advocates say the fast-food industry is moving too slowly to eliminate antibiotics from its beef supplies, a delay they say contributes to the problem of treatment-resistant bacteria in people as well as animals.

The groups — which include the U.S. Public Interest Research Group, Consumer Reports, Center for Food Safety and George Washington University's Milken Institute for Public Health — said in a report on Thursday that overuse of antibiotics in agriculture can result in more "superbugs."

Meat producers routinely give animals that are not ill antibiotics to make them grow faster and prevent disease, the groups said. But the practice can lead to germs becoming resistant to drugs, with some antibiotics losing their effectiveness in treating illnesses in humans.

Get Breaking News Delivered to Your Inbox

"The bottom line is we can't afford to lose life-saving antibiotics to produce slightly cheaper beef," said Matthew Wellington, campaign director at U.S. PIRG Education Fund and an author of the report.

Antibiotic-resistant bacteria infect at least 2 million Americans a year and kill 23,000, according to the U.S. Centers for Disease Control and Prevention, which has called the problem "one of the most urgent threats to the public's health."

Just two major fast-food chains — Chipotle and Panera Bread — source beef raised without the routine use of antibiotics, according to the groups. Wendy's says it sources roughly a third of its beef from producers that have cut the use of one antibiotic by 20%, a small step by the nation's third-largest burger chain, the report found.

McDonald's drew praise for its recent efforts to lessen the fast-food chain's use of antibiotics. The restaurant giant is now measuring antibiotic use in the U.S. and other top beef markets, with plans to set targets for reductions by the end of 2020.

"McDonald's made the big jump, taking a comprehensive approach that other restaurants should follow," said Wellington, who noted that the burger chain helped push the poultry industry away from routinely feeding antibiotics to chickens.