This year, up to 2 million Americans will contract drug-resistant bacterial infections. Microbiologist and immunologist Silvia Caballero wants to do something about that. After graduating from Weill Cornell Medical College in 2009 and going to work at Memorial Sloan Kettering Cancer Center, she developed a type of lab mouse whose gut replicates the human systems infected by drug-resistant bugs. She then turned the bodies of the mice against the invaders, discovering natural bacteria within the gut that could beat back the infection. Now working for Vedanta Biosciences in Massachusetts, she heads the company’s multidrug-resistant organism decolonization program, whose goal is to do for people what Caballero did for the mice. Her treatment protocol could go into early trials in two years. —Jeffrey Kluger