## Identification of Pseudomonas aeruginosa **Key Point:** Pseudomonas aeruginosa is identified by three hallmark features: 1. **Oxidase-positive** reaction (distinguishes from Enterobacteriaceae) 2. **Blue-green pigment** (pyoverdine and pyocyanin production) 3. **Gram-negative rod** morphology ### Virulence Factor in Chronic Lung Infection **High-Yield:** Alginate is a mucoid exopolysaccharide produced by P. aeruginosa in chronic respiratory infections, particularly in cystic fibrosis and COPD patients. This polysaccharide: - Forms a biofilm matrix that protects bacteria from antibiotics and immune clearance - Results in the characteristic **mucoid colony morphology** observed in culture - Is the hallmark of chronic, difficult-to-treat respiratory colonization - Leads to chronic suppurative airway inflammation ### Clinical Context **Clinical Pearl:** COPD patients with P. aeruginosa colonization have accelerated lung function decline and increased mortality. The mucoid phenotype indicates established chronic infection with biofilm formation, making eradication extremely difficult. ### Antibiotic Resistance Pattern Ceftazidime resistance in P. aeruginosa is commonly due to: - Extended-spectrum β-lactamase (ESBL) production - Altered penicillin-binding proteins - Efflux pump upregulation (MexAB-OprM system) | Feature | P. aeruginosa | B. cepacia | A. baumannii | |---------|---------------|-----------|---------------| | Oxidase | Positive | Positive | Negative | | Pigment | Blue-green | None | None | | Mucoid in chronic infection | Yes (alginate) | No | No | | Gram stain | Negative rod | Negative rod | Negative rod | [cite:Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases 9e Ch 230]
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