In cystic fibrosis, sputum cultures commonly yield which organism?

• A. Haemophilus influenzae
• B. Staphylococcus aureus
• C. Pseudomonas aeruginosa
• D. Streptococcus pneumoniae

Answer: (C)

In cystic fibrosis, thick, poorly cleared airway secretions create an environment where certain bacteria can establish long-term infection. Pseudomonas aeruginosa is particularly well suited to persist in CF airways; it often colonizes chronically and develops a mucoid, biofilm-forming phenotype that protects it from immune defenses and antibiotics. Because of these adaptations, it is the organism most commonly recovered from sputum cultures in CF patients, especially as they age. Other bacteria like Haemophilus influenzae and Staphylococcus aureus can be seen, particularly earlier in life, but they are less typical of the persistent infections seen in CF airways, and Streptococcus pneumoniae is not the usual dominant pathogen.