<prompt> The causative agent for virulent external ear infection in a diabetic elderly is mostly byStaphylococcusStreptococcusPseudomonasHemophilus influenzae  <response>: Pseudomonas aeruginosa is the agent which is responsible for virulent external ear infection in diabetics, mainly Necrotizing otitis externa. Ref: Textbook of diseases of ENT, PL Dhingra, 7th edition, pg no. 55 