Which of the following is the most common organism isolated from chronic suppurative otitis media with safe disease (tubotympanic type)?

Explanation

## Microbiology of CSOM — Safe vs Unsafe Disease **Key Point:** Chronic suppurative otitis media (CSOM) is classified into two types based on site of perforation and organisms involved. The most common organism in **both** safe (tubotympanic) and unsafe (atticoantral) disease is **Pseudomonas aeruginosa**. ### Safe Disease (Tubotympanic/Attic-Sparing) - Perforation in pars tensa (central) - **Most common organism: Pseudomonas aeruginosa** - Also: Staphylococcus aureus, Proteus mirabilis, E. coli, anaerobes - Lower risk of serious complications - Better prognosis with medical management ### Unsafe Disease (Atticoantral/Marginal) - Perforation at margins or attic region - **Most common organism: Pseudomonas aeruginosa** (also predominant) - Also: Proteus, E. coli, anaerobes, Staphylococcus aureus - Higher risk of bone erosion, intracranial complications - Often requires surgical intervention (mastoidectomy) **High-Yield (Scott-Brown's Otorhinolaryngology / Dhingra ENT):** Multiple large microbiological studies of CSOM discharge consistently identify *Pseudomonas aeruginosa* as the single most frequently isolated organism in tubotympanic (safe) CSOM, accounting for approximately 30–40% of isolates. *Staphylococcus aureus* is the second most common organism. **Clinical Pearl:** Pseudomonas aeruginosa produces biofilms and proteases that perpetuate chronic infection. Its presence in CSOM requires topical ciprofloxacin (fluoroquinolone ear drops) as first-line treatment. In immunocompromised or diabetic patients, Pseudomonas can cause malignant (necrotising) otitis externa — a life-threatening extension. | Feature | Safe Disease (Tubotympanic) | Unsafe Disease (Atticoantral) | |---------|------------------------------|-------------------------------| | **Perforation site** | Pars tensa (central) | Attic, marginal, or posterosuperior | | **Most common organism** | *Pseudomonas aeruginosa* | *Pseudomonas aeruginosa* | | **Other organisms** | S. aureus, Proteus, E. coli | Proteus, E. coli, anaerobes | | **Bone erosion** | Rare | Common (cholesteatoma) | | **Complications** | Minimal | Facial paralysis, meningitis, brain abscess | | **Treatment** | Medical (topical ciprofloxacin, aural toilet) | Often surgical (mastoidectomy) | > **Reference:** Dhingra PL, *Diseases of Ear, Nose and Throat*, 7th ed.; Scott-Brown's Otorhinolaryngology, 8th ed. — both cite Pseudomonas aeruginosa as the most common isolate in CSOM (tubotympanic type).