The antibiotics given to livestock are often the same ones given to humans, or very similar, thus if pathogens develop resistance in livestock they could pass to humans. A study published earlier this year showed that Staphylococcus aureus could jump from humans into pigs, where it became resistant to tetracycline and methicillin. And then it could jump back from pigs to humans.
Oftentimes antibiotics are given to healthy animals in sub-therapeutic doses. Partly this is to prevent disease outbreaks in the large-scale confined animal feeding operations (CAFOs) where most of our livestock are now housed. Another reason is that some of these drugs appear to increase animal growth rates, although why this is so is unclear.
In addition to microbial resistance, antibiotics released to the environment can be detrimental to aquatic organisms. Antibiotics enter rivers and streams through discharge from livestock facilities, aquaculture, and human sewage.
