<prompt> Which is the most frequent pulmonary pathogen causing recurrent pneumonia in cystic fibrosis?PseudomonasEnterococciStreptococciKlebsiella  <response>: Cystic fibrosis has a high prevalence of airway colonization with Staphylococcus aureus, Pseudomonas aeruginosa and Burkholderia cepacia. The CF airway epithelial cells or surface liquids provide a orable environment for harbouring these organisms. P. aeruginosa undergo a mucoid transformation in the CF airways-generates a biofilm that provides a hypoxic environment and thereby protects Pseudomonas against antimicrobial agents. 