A new contrast agent that targets microbes can be used to illuminate bacterial infections in living animals. It could ultimately enable doctors to safely spare more of a limb during amputations. It's usually clear when a patient has a bacterial infection and needs to be treated with antibiotics, says Jason Bowling, director of epidemiology at the University of Texas Health Science Center at San Antonio, who was not involved with developing the imaging agent. But sometimes an infection is more difficult to diagnose. For example, it can be difficult to tell when a patient who has pain at the site of a hip or knee replacement has an infection. This sometimes leads doctors to prescribe antibiotics when they aren't necessary. An imaging scan capable of detecting bacteria would quickly answer the question, sparing uninfected patients from unnecessary antibiotics or even from surgery to remove the implant. Where there is an infection and the implant is removed, imaging could help ensure that no new hardware is implanted until the infection has been completely cleared.