For many patients, infection begins with colonization. A resistant organism first establishes itself quietly in the gut, often without causing symptoms, before it goes on to cause invasive disease or spread to other patients. Stopping that first step — colonization — offers one of the most direct ways to prevent infections and interrupt transmission.

While the gut microbiome is recovering, the door is open for drug-resistant bacteria to move in. The beneficial bacteria are too depleted to crowd out invaders and that gives drug-resistant bacteria room to grow, even strains that would normally struggle to compete. We study how that gap opens, and how a healthy gut community closes it back up by crowding resistant bacteria out.