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1. To compare the photyic characteristics of persistent vs. eradicated Pseudomonas aeruginosa in cystic fibrosis 2. To compare the pulmonary microbiome in CF patients in whom Pseudomonas aeruginosa is eradicated vs. in CF patients in whom Pseudomonas aeruginosa persists following tobramycin inhalation therapy Background: The most common cause of death in cystic fibrosis (CF) patients is respiratory failure due to chronic bacterial pulmonary infection(1). The majority of CF patients are ultimately chronically infected with P. aeruginosa (PA) in their lungs, which is associated with more rapid lung function decline and increased mortality (2-4). As children with CF age, an increasing number will acquire PA infection. The current standard of care is to try to eradicate new PA acquisition, usually with inhaled tobramycin treatment, in order to prevent its long-terms deleterious effects(5-6). However, typically, in 10-40 % of patients, eradication treatment fails(7-8). There is little known about whether there are specific bacterial characteristics of the original infecting PA organism or properties of the co-infecting microbial community (microbiome), that contribute to the persistence of PA in the lung and eradicatio