The farming of animals for human consumption uses considerably more antibiotics than are used in human health.
The widespread use of antibiotics encourages antibiotic strains of bacteria to evolve. This evolution and spread of resistance can be truly rapid.
Research shows that segments of DNA conferring drug resistance can jump between different species and strains of bacteria with disturbing ease.
There are now some bacterial infections in humans, such as MRSA (methicillin-resistant Staphylococcus aureus), for which there is almost no antibiotic treatment avialble. MRSA has become a global and serious problem in hospitals.
- A summary of the problem, from the Scientific American: https://www.scientificamerican.com/article/how-drug-resistant-bacteria-travel-from-the-farm-to-your-table/
- How some farmers in Holland are tackling the problem, which has led to a reduction in the use of antibiotics in pig farming in that country: http://www.bbc.com/news/av/magazine-41132589/how-one-girl-s-illness-changed-what-a-nation-eats