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
Malignant otitis externa is most commonly caused by - 
Select and explain. 
A. P. aeruginosa, B. S. aureus, C. St. penumoniae, D. S. epidermidis
A: P. aeruginosa
Answer: A: P. aeruginosa 
Explanation: Ans. is 'a' i.e., P. aeruginosa Although otitis externa is also known as swimmer's ear, malignant otitis externa isn't due to water remaining in the ear canal. Bacteria such as Pseudomonas aeruginosa and Staphylococcus aureus often cause malignant otitis externa. The most frequent pathogen is Pseudomonas aeruginosa.