Which microorganism is the most common cause of otitis externa?

Pseudomonas aeruginosa is recognized as the most common pathogen responsible for otitis externa, often referred to as swimmer's ear. This condition typically arises when water becomes trapped in the ear canal, creating a moist environment conducive to bacterial growth. Pseudomonas aeruginosa thrives in such environments; it's a gram-negative bacterium commonly found in water and soil, which explains its prevalence in cases of otitis externa, especially in individuals who swim frequently or have increased exposure to water.

The virulence of Pseudomonas aeruginosa is attributed to its ability to form biofilms, resist antibiotics, and cause inflammatory responses within the ear canal. This makes it particularly effective at establishing infections in the moist environment of the ear, where it can flourish and lead to the classic symptoms of otitis externa, such as pain, itching, and discharge.

Other organisms like Streptococcus pyogenes, Haemophilus influenza, and Moraxella catarrhalis are associated with various ear infections, but they more commonly cause otitis media rather than otitis externa. Therefore, recognizing Pseudomonas aeruginosa's role in otitis externa is crucial for appropriate evaluation and management in patients presenting with symptoms indicative of this condition.