Strains of bacteria able to resist multiple antibiotics pose a growing threat to public health, yet the means by which resistance quickly emerges aren’t well understood. Scientists led by physics professor Terence Hwa at the University of California, San Diego, thought that the variety of environments in which bacteria encounter antibiotic drugs could play an important role. They have developed a mathematical model, published in the June 18 early online edition of the Proceedings of the National Academy of Sciences, that demonstrates how that would work.