A 62-year-old male with chronic obstructive pulmonary disease (COPD) and recent hospitalization develops a productive cough with green sputum, fever (38.5°C), and dyspnea. Sputum culture grows Pseudomonas aeruginosa. Regarding the epidemiology and risk factors for P. aeruginosa infection, all of the following are correct EXCEPT:

Question

Accepted Answer

A. P. aeruginosa is highly susceptible to penicillin G and ampicillin, making these agents the first-line treatment for respiratory infections. ## Pseudomonas aeruginosa: Epidemiology, Risk Factors, and Antibiotic Resistance

**Key Point:** P. aeruginosa is a leading nosocomial pathogen with intrinsic resistance to many beta-lactams. Recognizing its resistance profile is essential for appropriate empiric therapy.

### Epidemiology and Risk Factors

| Factor | Significance |
|---|---|
| **Habitat** | Ubiquitous in moist environments; water systems, soil, hospital equipment |
| **Obligate aerobe** | Requires oxygen; thrives in ventilator circuits and water supplies |
| **CF patients** | CFTR mutation → abnormal mucus → impaired clearance → chronic colonization |
| **Nosocomial risk** | Immunosuppression, prolonged antibiotics, catheters, mechanical ventilation |

### Antibiotic Resistance Profile

**High-Yield:** P. aeruginosa is **intrinsically resistant** to:
- Penicillin G (~~NOT susceptible~~)
- Ampicillin (~~NOT susceptible~~)
- First-generation cephalosporins
- Macrolides (erythromycin, azithromycin)

**Agents WITH activity against P. aeruginosa:**
1. **Antipseudomonal beta-lactams:** Piperacillin-tazobactam, ceftazidime, cefepime, meropenem
2. **Fluoroquinolones:** Ciprofloxacin, levofloxacin
3. **Aminoglycosides:** Tobramycin, amikacin (often combined with beta-lactams)
4. **Aztreonam:** Monobactam antibiotic

**Clinical Pearl:** In this patient with hospital-acquired pneumonia (HAP) due to P. aeruginosa, empiric therapy should include an antipseudomonal beta-lactam (e.g., piperacillin-tazobactam or cefepime) ± an aminoglycoside or fluoroquinolone, NOT penicillin G or ampicillin.

**Warning:** Penicillin G susceptibility testing against P. aeruginosa is rarely performed because resistance is so predictable; using penicillin G would result in clinical failure.

**Mnemonic: CAFE** — Ceftazidime, Aminoglycosides, Fluoroquinolones, Extended-spectrum beta-lactams (for P. aeruginosa coverage).

Answer

B. Patients with cystic fibrosis have a genetic defect in the CFTR gene, leading to impaired mucociliary clearance and chronic P. aeruginosa colonization

Answer

C. P. aeruginosa is an obligate aerobe and thrives in oxygen-rich hospital water systems and ventilator circuits

Answer

D. Immunosuppression, prolonged antibiotic use, and indwelling catheters are major risk factors for P. aeruginosa nosocomial infection

Explanation

Practice similar questions