Chain restaurants are more willing than ever to bend to the will of customers, and when it comes to the latest outcry against antibiotics in meat and poultry, Chipotle and Panera are at the top of the food chain.

The aptly titled "Chain Reaction II," scores the top 25 chains in the United States, based on their antibiotic-free zones. The report grades restaurants on policy in purchases, stringency, and transparency.

From positive to poor, here are the report's findings:

• Chipotle and Panera both earned a solid A for their use of antibiotic-free meat and poultry.
• Chick-fil-A and Subway both earned a B.
• McDonald's, Wendy's, and Taco Bell were all within the C range, earning a C+, C, and C-, respectively.
• Pizza Hut was graded a D+, and Papa Johns a D.
• Applebee’s, Arby’s, Buffalo Wild Wings, Burger King, Chili’s, Dairy Queen, Denny’s, Domino’s, Dunkin’ Donuts, IHOP, Jack in the Box, KFC, Little Caesars, Olive Garden, Sonic and Starbucks, all were graded an F, meaning they did not disclose usage or did not use antibiotic-free sources.

Research for the report was compiled by the Natural Resources Defense Council, the Food Animal Concerns Trust, Friends of the Earth, Consumers Union, and Center for Food Safety.

Steven Roach, food safety program director of Food Animal Concerns Trust, told Friends of the Earth the trend was being fueled by antibiotic overuse and more consumer demand for healthier choices: “Antibiotic resistant infections already cause more than 23,000 deaths and up to $55 billion in costs each year and antibiotic misuse in animal agriculture threatens to drive these numbers even higher.”

The Food and Drug Administration reports that about 95 percent of all medically important antibiotics are added to the food and water of animals, and such usage has grown faster than in any other industry.