A new study shows that the most popular burger chains in the U.S. like McDonalds and Burger King don’t have a policy for sourcing antibiotic free beef. Overuse of antibiotics in livestock can cause resistant bacteria to spread, putting humans at risk of developing life threatening infections. Shake Shack and BurgerFi are the only two burger chains that use antibiotic free meat. The findings were released by advocacy groups including consumer reports and the Center for Food and Drug Safety. McDonald’s says it will roll out a global antibiotics policy for beef this year.