Most large U.S. fast-food chains still serve meat from farm animals that have been routinely fed antibiotics, consumer groups said in a new report, which concluded that many companies have not yet laid out plans to curb the practice.

Subway, Starbucks, KFC and Domino's Pizza were among the industry leaders graded "F" for their antibiotic policies in the report from consumer and health groups, titled "Chain Reaction," released on Tuesday.

The groups, which did not release results to companies prior to publication, based their grades on public statements, survey responses and correspondence with individual chains.

As a result, companies given failing grades were not immediately able to comment.
An estimated 70 percent of antibiotics important to human health are sold for use in meat and dairy production.

Concern is growing among public health experts that the overuse of such drugs, particularly those important to human medicine, are contributing to rising numbers of life-threatening human infections from antibiotic-resistant bacteria dubbed "superbugs."

The U.S. Centers for Disease Control and Prevention (CDC) estimates that 2 million people are infected with drug resistant bacteria each year and 23,000 die.

"From bacon cheeseburgers to chicken nuggets, most meat served by America's chain restaurants comes from animals raised in industrial-scale facilities, where they are routinely fed antibiotics to prevent disease that is easily spread in crowded, unsanitary, stressful conditions," said Kari Hamerschlag, a lead author of the report who is senior program manager at Friends of the Earth.

Subway was cited, in particular, for failing to publicly state a policy or plan to cut antibiotic use in the meats it buys, despite repeated requests by the report's authors for clarification.

Chipotle Mexican Grill and Panera Bread, were top finishers with "A" grades. These popular chains have won loyal followings for policies that include strict limits on antibiotic use.

Chick-fil-A, which is making meaningful progress toward its goal of only buying chicken raised without antibiotics by 2019, got a "B" in the report.

McDonald's Corp and Dunkin' Donuts got "C" grades. McDonald's plans to only source chicken raised without antibiotics important to human medicine by 2017. Dunkin' Donuts aims to prohibit suppliers from using medically important antibiotics or antimicrobials in healthy animals, but it has not set a timeline.