Patients with cystic fibrosis are often infected by pseudomonas aeruginosa, a bacterium that infects the lungs and prevents breathing, often causing death. P. aeruginosa itself can also be infected by viruses, which can affect the clinical outcomes of cystic fibrosis patients. Researchers have now used P. aeruginosa as a kind of 'model system' for understanding how bacteria's interactions with viruses may affect human health.