Antibiotics are medicines derived by extracting chemical substances produced by molds or bacteria which inhibit the growth of, or kill, microorganisms. These substances are used as cures for bacterial infections in animals. On some farms, antibiotics are administered regularly to prevent disease, especially in operations that confine animals in densely populated pens. Preventative use of antibiotics leads to higher rates of antibiotic resistant bacteria, which pose health threats to humans and animals alike.