Colistin, an antibiotic discovered in the late 1940s, is not a great drug. Its use comes with a startling list of potential side effects. These include dizziness, severe itching, numbness, and formication—the horrific feeling that insects are crawling on your skin. Oh, and the drug might also make your kidneys fail.
Because colistin’s side effects are so severe, it’s considered a drug of last resort. In recent years, bacteria have developed a growing resistance to antibiotics. When bacteria become antibiotic resistant, the drugs no longer kill the bacteria—so patients stay sick. The more we use an antibiotic, the more likely bacteria are to become resistant to it. But we don’t use colistin very often. Clinicians dole it out only to treat infections that are resistant to safer pharmaceuticals. If it’s a choice between colistin and death, well, the feeling of creepy crawlers on your skin doesn’t sound so bad.
But in 2015, researchers discovered a strain of E. coli bacteria resistant to potent drug. When exposed to colistin, E. coli—a bacteria that can cause potentially deadly infections—didn’t die. Since one of colistin’s main uses is to treat antibiotic resistantE. coli infections, it was a particularly scary plot twist.
The culprit? Bacon. You see, while colistin is rarely used in humans, Chinese pig farmers took to using the drug in animal feed. Antibiotics help the porkers stave off infections in crowded conditions. They also help farm animals gain weight faster, thus making them ready for slaughter sooner. But the practice also put enough colistin into the environment to allow resistant E. coli to evolve. Frequently exposed to the drug, strains of the pathogen with the mutations required to survive it became more likely to breed and spread than non-resistant strains.
“If we keep going on like that, wasting our antibiotics on nonessential purposes, eventually nothing is going to work,” says Thomas Van Boeckel, an epidemiologist at the Institute of Integrative Biology in Zurich, Switzerland.
Van Boeckel co-authored a study released today in the journal Science that tries to figure out the best way to get farm animals off antibiotics. The issue, you see, goes further than colistin in Chinese pigs.