In cystic fibrosis, sputum cultures commonly grow which organism?

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

Answer: (A)

In cystic fibrosis, the thick, sticky mucus in the airways creates a prime habitat for bacteria, and one organism stands out as the typical culprit in long-standing lung infections: Pseudomonas aeruginosa. This organism is a versatile, gram-negative rod that thrives in moist environments and is especially adept at persisting in the CF airway due to its ability to form biofilms and produce protective alginate. These biofilms shield it from both immune defenses and many antibiotics, allowing chronic colonization and gradual lung damage over time. Although Staphylococcus aureus and Haemophilus influenzae can be found, particularly earlier in life, Pseudomonas aeruginosa is the most commonly cultured organism in CF sputum and is a hallmark of established CF lung disease. This understanding underpins management strategies that target chronic Pseudomonas infection, such as inhaled antibiotics and tailored anti-pseudomonal therapies.