<prompt> Malignant otitis externa is caused byHemophilus influenzaePseudomonas aeroginosaStreptococcus pyogenesE. coli  <response>: Malignant otitis externa is often caused by difficult to treat bacteria such as Pseudomonas aeruginosa. Only are cases of malignant otitis externa due to S.aureus, Proteus mirabilis and Aspergillus fumigates have been repoed.Ref: PL Dhingra, Diseases of Ear, Nose Throat, 7th edition, pg no. 55 