Nature Reviews Microbiology 4, 934–952 (2006)

In the above article there was an error in the equation shown in Box 1. This error had no impact on the graph shown in the Box, but the authors wish to apologise to readers for any confusion caused. The correct equation is shown below; additionally, in the box table, the value for parameter b (the selection pressure exerted by antibiotic 2, which is expressed as the proportion of the selection pressure exerted by antibiotic 1) should have read 0–60%.