The most commonly encountered bacterial pathogens in the lungs of patients with cystic fibrosis are:
**Core Concept**
Cystic fibrosis (CF) is a genetic disorder characterized by thick, sticky mucus production in the lungs, leading to recurrent respiratory infections and inflammation. The disease creates an environment conducive to the growth of certain bacterial pathogens.
**Why the Correct Answer is Right**
The most commonly encountered bacterial pathogens in the lungs of CF patients are Pseudomonas aeruginosa and Staphylococcus aureus. Pseudomonas aeruginosa is a gram-negative rod that adheres to the respiratory epithelium, producing biofilms that are resistant to antibiotics and host immune defenses. Staphylococcus aureus is a gram-positive cocci that can cause acute infections and is often colonized in the CF airway. The chronic infection and inflammation caused by these pathogens lead to progressive lung damage and decline in lung function.
**Why Each Wrong Option is Incorrect**
**Option A:** Escherichia coli is a common gut commensal but is not typically associated with CF lung infections.
**Option B:** Haemophilus influenzae is a gram-negative rod that can cause respiratory infections, but it is not as common in CF patients as Pseudomonas aeruginosa and Staphylococcus aureus.
**Option C:** Klebsiella pneumoniae is a gram-negative rod that can cause respiratory infections, but it is not a primary pathogen in CF patients.
**Clinical Pearl / High-Yield Fact**
CF patients are at increased risk of developing antibiotic-resistant bacterial infections, emphasizing the need for careful antibiotic stewardship and regular pulmonary function monitoring.
**Correct Answer:** C. Staphylococcus aureus