Scientists at the Food and Drug Administration systematically monitor the meat and poultry sold in supermarkets around the country for the presence of disease-causing bacteria that are resistant to antibiotics. These food products are bellwethers that tell us how bad the crisis of antibiotic resistance is getting. And they’re telling us it’s getting worse. But this is only part of the story. While the F.D.A. can see what kinds of antibiotic-resistant bacteria are coming out of livestock facilities, the agency doesn’t know enough about the antibiotics that are being fed to these animals. This...