Swimmer's ear, a form of external otitis, is most commonly caused by which organism?

• A. Acinetobacter baumannii-calcoaceticus complex
• B. Bordetella bronchiseptica
• C. Haemophilus influenzae
• D. Pseudomonas aeruginosa

Answer: (D)

External otitis tends to occur when moisture and friction irritate the ear canal, creating an environment where certain bacteria can thrive. The organism most commonly responsible is Pseudomonas aeruginosa, an opportunistic bacterium that loves warm, moist environments like a swimmer’s ear. Its ability to grow robustly in the ear canal and form protective biofilms makes it a frequent cause of otitis externa after water exposure. The other organisms listed are less typical culprits for this specific infection pattern—Acinetobacter and Bordetella are more often linked to hospital or respiratory infections, and Haemophilus influenzae is a common cause of otitis media rather than external otitis. So Pseudomonas aeruginosa best explains swimmer’s ear.