Exactly five years have passed since the moment the world of medicine most feared became reality. In the spring of 2016, in Pennsylvania, a 49-year-old woman suffering from an infection was attacked by a bacterium bearing the gene scientists had feared: MCR-1. It was the first time a bacterium with this gene had been discovered in a human being. The bad news: The bacterium was resistant to the strongest antibiotic that existed, colistin. The worse news was that it could easily transmit that resistance to other bacteria.