Rosh Pediatrics Practice Exam

In a pediatric cystic fibrosis patient with worsening respiratory symptoms, which pathogen is most likely to be cultured from sputum?

1. Mycobacterium avium

2. Peptostreptococcus anaerobius

3. Pseudomonas aeruginosa

4. Streptococcus pneumoniae

The correct answer is: Pseudomonas aeruginosa

Cystic fibrosis is characterized by the accumulation of thick, viscous mucus in the airways, which creates an environment that is highly conducive to bacterial infections. In this population, Pseudomonas aeruginosa is the most common pathogen associated with respiratory infections. The reason this organism is frequently isolated in patients with cystic fibrosis is due to its ability to adapt and survive in the hostile environment of the lungs. Pseudomonas aeruginosa has various virulence factors, such as biofilm formation, which enable it to persist in the airways and resist clearance mechanisms. In addition, the chronic inflammation resulting from repeated infections can lead to progressive lung damage and further exacerbation of respiratory symptoms. While the other pathogens listed can cause respiratory illness in other contexts, they are not typically the primary pathogens of concern in cystic fibrosis patients. Mycobacterium avium, for example, does not commonly affect this patient population, while Peptostreptococcus anaerobius is an anaerobic bacterium that usually doesn't play a significant role in pulmonary infections. Streptococcus pneumoniae can cause pneumonia but is generally not associated with the chronic pulmonary disease seen in cystic fibrosis patients. Thus, the significant risk of airway infection and the