Lung infections are very common in patients suffering from the inherited disease cystic fibrosis and other patients who are on intensive care units. The commonest cause of these infections is a bacterium called "Pseudomonas aeruginosa". Lung infections caused by these bacteria are especially difficult to treat and result in mortality of over 50% of affected patients on intensive care units. This research will study specific poisons or toxins produced by the bacterium that enable it to damage the lungs of these patients. The aim is to help develop new therapies for this condition and hopefully reduce the numbers of deaths resulting from the infection.