Respiratory infections are a public-health concern, as they are a major cause of mortality worldwide, due in part to difficulties in treating the persistent antibiotic-resistant bacteria that cause them. Biofilm formation in the lungs and in endotracheal tubes of patients with respiratory diseases who require mechanical ventilation worsens the problem even further. Antibiotic interventions often fail to eradicate the infection, and alternative approaches are therefore needed. Genetically modified bacteria offer a promising strategy to treat infections in different organs. As an example, the engineered Escherichia coli Nissle 1917 has been used to treat Pseudomonas aeruginosa infections in the gut. However, no such approach has been developed to combat respiratory infections. Now, Mazzolini et al. have engineered a Mycoplasma pneumoniae strain to treat and prevent P. aeruginosa infections in the lung.