eLife Assessment
This important study, which will be of interest to those studying the evolution and maintenance of antibiotic resistance, addresses the hypothesis that antibiotic resistance arising de novo during treatment will carry a higher fitness cost and will revert to susceptibility more readily than resistance that has been transmitted between hosts. There are, however, concerns that the 'putatively transmitted isolates' in this study do not necessarily represent resistant isolates that have been transmitted between hosts. The support for the central claim of different patterns of reversion between isolates with de novo resistance and putatively transmitted resistant isolates is currently incomplete.