For all the worry over the growing threat of superbugs resistant to drugs and the role of antibiotic use in animals, there's surprisingly little information about what goes into our food when we eat out.

Walk down the meat aisle at any grocery store and you'll see packages labeled with information about antibiotic use, but when it comes to restaurants it's often impossible to differentiate between those that use meat treated with antibiotics and those that ban it.

In what is believed to be the first report of its kind, a group of environmental and consumer advocacy organizations has graded 25 of the largest fast-food and fast-casual chains in the United States on their use of antibiotics and their transparency about it.

The researchers surveyed the companies and reviewed their public statements to create scorecards for each restaurant chain.

Only two companies -- Chipotle and Panera -- got top marks.

All but five of 25 U.S. restaurant chains received "F" grades for their antibiotic policies, according to a report by several public interest groups. (Reuters)

"From double bacon cheeseburgers to chicken nuggets, most meat served by America’s top chain restaurants comes from animals raised in industrial-scale facilities where they are routinely fed antibiotics," researchers Kari Hamerschlag of Friends of the Earth, Sasha Stashwick of Natural Resources Defense Council, and their collaborators wrote.

They explained that when livestock producers regularly give antibiotics to their animals, bacteria can become resistant to it and even spread to humans. "The worsening epidemic of resistance means that antibiotics may not work when we need them most: when our kids contract a staph infection (MRSA), or our parents get a life-threatening pneumonia," they said.

Chipotle built its brand on the idea that it stands for the "ethically conscious" consumer and has had a hard line against using meat from animals treated with antibiotics. In 2013, the company's "Scarecrow" video that took stabs at everything from antibiotic use and genetically modified foods to animal cruelty treated went viral with millions of views. (The company's policy does allow for limited emergency purchases of meat treated with antibiotics, but the company says locations inform consumers through prominent signs which meats are impacted.)

Panera, which nearly a decade ago stopped using chicken meat from animals treated with antibiotics, was applauded by the researchers for expanding its commitment to ham, bacon and other types of meat over the years.

Chick-fil-A, Dunkin' Donuts and McDonald's were in the middle of the pack. Chick-fil-A announced it would stop using meat from chickens treated with antibiotics in 2014 but has said the policy will take time to implement.

Dunkin' Donuts has also announced a no-antibiotics policy covering all meats but has not announced a timeline for implementing it. McDonald's has said it will no longer use meat from chickens treated with antibiotics.

As for the rest, they all received Fs from the group.

Most top U.S. chain restaurants, including Subway, Wendy’s, Burger King and Kentucky Fried Chicken (KFC), have so far failed to effectively respond to this growing public health threat by publicly adopting policies restricting routine antibiotic use by their meat suppliers.

The issue of antibiotic use in chain restaurants is critically important in a country where so many people eat out so often. A recent Gallup poll found that eight of 10 Americans eat at fast-food restaurants at least monthly and half at least weekly. Roughly half the money Americans spend on food is spent eating out.

The Centers for Disease Control and Prevention estimates that each year at least 2 million Americans contract antibiotic-resistant infections, and 23,000 die from them.

The researchers called on federal regulators to "move quickly" to adopt policies that prohibit the use of medically important antibiotics for growth promotion and disease prevention and to mandate collection of information on antibiotic use by livestock producers.

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