Antibiotics have made a massive contribution to human health by reducing the mortality and economic costs associated with bacterial disease. Unfortunately, antibiotic resistance in pathogenic bacteria threatens to undermine the clinical utility of antibiotics and we are currently faced with ominous possibility of a post-antibiotic era. Research in the MacLean lab is focused on understanding the fundamental evolutionary processes that drive the spread and maintenance of resistance, primarily using controlled in vitro experimental evolution in the opportunistic pathogenic bacterium Pseudomonas aeruginosa. The main themes that we work on are outlined below.