Otitis externa is an uncommon disorder. It may result from infection with bacteria (Escherichia coli, Staphylococcus aureus, Pasteurella multocida, Proteus mirabilis, Pseudomonas aeruginosa, Klebsiella oxytoca, Enterococcus spp.), fungi (Candida spp., Microsporum gallinae) or mycobacteria, or infestation with arthropod parasites (Cnemidocoptes). It may occur as an extension of generalised skin disease or may be due to neoplasia or trauma.