This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Cystic fibrosis & Sleep apnea, Subject name: Medicine
[{'content': 'Which is the most frequent pulmonary pathogen causing recurrent pneumonia in cystic fibrosis? \nSelect and explain. \nA. Pseudomonas, B. Enterococci, C. Streptococci, D. Klebsiella', 'role': 'user'}, {'content': 'Answer: A \nExplanation: 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.', 'role': 'assistant'}]