People with weakened immune systems are at constant risk of infection. Pseudomonas aeruginosa, a common environmental bacterium, can colonize different body parts, such as the lungs, leading to persistent, chronic infections that can last a lifetime — a common occurrence in people with cystic fibrosis. But the bacteria can sometimes change their behavior and enter the bloodstream, causing chronic localized infections to become acute and potentially fatal. How and why the switch happens in humans has remained unknown. However, researchers at the Georgia Institute of Technology have identified the major mechanism behind the transition between chronic and acute P. aeruginosa infections. Marvin Whiteley -- professor in the School of Biological Sciences and Bennie H. and Nelson D. Abell Chair in Molecular and Cellular Biology -- and Pengbo Cao, a postdoctoral researcher in Whiteley's lab, discovered a gene that drives the switch. By measuring bacterial gene expression in human tissue samples, the researchers identified a biomarker for the transition. (This story was also covered in Technology Networks and News Medical Life Sciences.)