Eighteen months ago, a gene that confers resistance to colistin — known as an ‘antibiotic of last resort’ — emerged in bacteria from pigs in China. Since then, the resistance gene, called mcr-1, has been found around the world at an alarming rate, according to several presentations at the American Society for Microbiology (ASM) meeting in New Orleans, Louisiana, last week.
In some places, nearly 100% of farm animals carry mcr-1, and an increasing number of people do as well. The gene’s spread is one of the clearest examples of how antibiotic use on farms can lead to resistance in human infections, says Lance Price, an antibiotic researcher at George Washington University in Washington DC.
Colistin has been around since the 1950s, but was rarely used in people because it causes kidney problems. Instead, many countries use it to promote growth in livestock — a practice that seems to have selected for colistin-resistant bacteria. That’s a problem, because physicians have increasingly turned to colistin over the past decade to treat patients who don’t respond to other antibiotics.