This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: ENT
The most common causative organism for external otitis in adults is: 
Select and explain. 
A. Streptococcus viridans, B. Staphylococcus epidermidis, C. Pseudomonas aeruginosa, D. E. coli
C: Pseudomonas aeruginosa
Answer: C: Pseudomonas aeruginosa 
Explanation: Otitis externa is an inflammatory and infectious process of the external auditory canal. Pseudomonas aeruginosa and Staphylococcus aureus are the most commonly isolated organisms. Less commonly isolated organisms include Proteus species, Staphylococcus epidermidis, diphtheroids, and Escherichia coli.