A recent decision by McDonald’s could save America from a health apocalypse. The restaurant chain has announced that within two years it “will only source chicken raised without antibiotics important to human medicine.” Raising animals on antibiotics has become standard practice on many farms, because it allows farmers to pack animals closer together without fear of disease spreading.But many believe that the liberal use of antibiotics on animals raised for human consumption has made human beings much more vulnerable to bacteria. Bacteria have evolved defenses to widely used antibiotics —a phenomenon called “antibiotic resistance”—leaving us with fewer options for fighting off various illnesses. Scientists have recently had some success in developing new antibiotics, which would help stave off some of the more nightmarish scenarios that could happen in a world without effective antibiotics.But reducing our excessive use of existing drugs is still an important goal, and that’s where McDonald’s comes in. The move is potentially game-changing because fast-food chain is one of the biggest buyers of chicken, so the way it chooses to buy its chicken will have very large ripple effects throughout the market. It could push farms that want to supply the chain to change their practices (possibly making chicken more expensive) and it may inspire other chains to follow suit, or speed up current efforts.Public health enthusiasts, particularly those focused on the antibiotic threat, are rightly cheered by the company’s decision for exactly these reasons (the upshot for those specifically concerned about animal treatment is less clear, since McDonald’s will still buy chickens raised on antibiotics that have no human medical uses). But why did McDonald’s do it, especially if it could increase the cost of one of their inputs? A long story in the New York Times this Sunday situated the decision within the overall business troubles facing the company. The company’s performance has recently been lackluster for a variety of complex reasons. One appears to be that so-called “fast casual” chains like Chipotle, which advertise their products as healthier and more upscale than those of your typical burger joint, have been eating McDonald’s lunch lately among middle-tier consumers. McDonald’s could be attempting to win some of those customers back with this health-conscious choice.Whatever the reason for the change, it is likely to have large effects on the way chicken is raised in this country—and perhaps help cut down on the threat generated by antibiotic resistance. In a truly delightful bit of irony, perhaps 20 or 30 years from now we will see McDonald’s as the chain that averted a health catastrophe.