A 32-year-old woman with cystic fibrosis develops chronic airway colonization with Pseudomonas aeruginosa. Her sputum shows mucoid colonies on culture. Which feature best distinguishes mucoid P. aeruginosa from non-mucoid P. aeruginosa in chronic respiratory infection?

Explanation

## Mucoid vs. Non-Mucoid Pseudomonas aeruginosa in Chronic Infection ### Phenotypic Conversion in CF Airway Disease **Key Point:** Mucoid P. aeruginosa represents a phenotypic switch characterized by **overproduction of alginate exopolysaccharide**, which forms a thick capsule, reduces motility, and is a hallmark of chronic CF lung colonization. ### Comparative Features: Mucoid vs. Non-Mucoid Phenotypes | Feature | Mucoid P. aeruginosa | Non-Mucoid P. aeruginosa | |---------|----------------------|-------------------------| | **Alginate production** | Abundant (thick capsule) | Minimal | | **Colony morphology** | Mucoid, slimy, viscous | Smooth, translucent | | **Motility** | Reduced/absent (non-motile) | Motile (flagellated) | | **Pyocyanin** | Often retained | Present | | **Biofilm formation** | Enhanced | Lower | | **Antibiotic penetration** | Reduced (protective) | Greater | | **Virulence (acute)** | Lower | Higher | | **Chronicity marker** | Yes (CF adaptation) | No | **High-Yield:** The mucoid phenotype emerges during chronic CF lung infection due to **upregulation of algU (sigma factor)** and represents an adaptive response to the CF airway microenvironment. This is a critical prognostic finding in CF patients. ### Pathophysiology of Mucoid Conversion 1. **Alginate synthesis** — increased expression of genes encoding alginate biosynthetic enzymes 2. **Loss of flagellar function** — mutations in flagellar genes reduce motility 3. **Biofilm architecture** — alginate-encased bacteria form protected microcolonies 4. **Immune evasion** — capsule shields bacteria from phagocytosis and antibiotics **Clinical Pearl:** Detection of mucoid P. aeruginosa in CF sputum is a **negative prognostic indicator** signifying transition to chronic infection and accelerated lung function decline. It typically appears after 2–3 years of colonization. **Mnemonic: MUCOID** — **M**ultiple **U**nregulated **C**apsule **O**verproduction **I**n **D**isease ### Why Alginate Overproduction is the Best Discriminator Alginate capsule production is the **defining structural difference** that: - Explains the mucoid colony morphology - Accounts for reduced motility - Correlates with biofilm formation - Predicts clinical chronicity [cite:Cystic Fibrosis Foundation Clinical Practice Guidelines; Prescott's Microbiology 12e Ch 21]