DEEP in your lungs, there's a battle raging. It's a warm, moist environment where the ever-opportunistic bacterium Pseudomonas aeruginosa has taken up residence. If your lungs are healthy, chances are the invader will be quickly dispatched. But in the mucus-clogged lungs of people with cystic fibrosis, the bacterium finds an ideal habitat. First, the microbes quietly multiply and then they suddenly switch their behaviour. A host of biochemical changes sticks the population of cells together, forming a gluey biofilm that even a potent cocktail of antibiotics struggles to shift. Microbes like P. aeruginosa were once thought of as disorganised renegades,...