The evolution of bacteria resistant to a new antibiotic is not merely a threat, but an inevitability. In this ongoing battle, our only option is to find ways to slow the evolution of resistant strains and encourage the evolution of susceptible strains. And that’s where Carl’s research comes into the picture. His goal is to understand the process through which antibiotic resistant infections evolve and spread in hospitals so that we can better manage them.

Recently, Carl and his colleagues became interested in a strategy being considered for use in hospitals called cycling. The idea is simple: doctors in a hospital would cycle through antibiotics, prescribing a particular antibiotic for period of time and then switching to a new one. Researchers and clinicians thought that cycling would reduce levels of antibiotic resistance because the bacteria would not have time to evolve to keep up with the changing drugs — just as a resistant strain for Drug #1 evolves and spreads, along comes Drug #2, and strains resistant to Drug #1 no longer have any advantage.

Doctors have been successful using a similar idea to increase the effectiveness of HIV drugs in a single patient — the patient cycles through various drugs, switching to a new one as his or her virus population evolves to be resistant to the old one. Could the same method work on a larger scale in hospitals?