Pseudomonas spp., most commonly P. aeruginosa, are common opportunistic pathogens of the external ear canals of dogs, where they contribute to otitis externa. In chronic cases, this infection often leads to otitis media.

A critical and often frequently overlooked aspect of managing Pseudomonas otitis cases is to identify and treat the underlying disease that predisposes the ear canals to secondary infection. If this is not done, the Pseudomonas infection will likely recur, thereby promoting development of strains of organisms with multiple drug resistance.

Common underlying causes of Pseudomonas otitis include: food allergy or hypersensitivity, atopy, keratinization disorders (primary seborrhea), hypothyroidism, Cushing's syndrome, and aural foreign bodies.

While topical local treatment is advocated by all, currently there is a controversy regarding use of systemic antibiotics in the treatment of Pseudomonas otitis externa. One group believes that systemic antibiotics for long periods of time (4-16 weeks) are needed to eliminate the infection, especially if there is middle ear involvement. The other group no longer uses systemic antibiotics (except where there is radiographic evidence of fluid in middle ear or bony lysis of the tympanic bulla), believing that high enough tissue levels are not reached in the ear to kill Pseudomonas. These colleagues utilize topical treatments that clean the canals and provide high concentrations of topical antibiotics (usually enrofloxacin) within the ear canal and middle ear. Systemic antibiotics also contribute more to antibiotic resistance seen in cases of recurrent otitis externa/media.

Typical clinical findings at presentation include: anorexia; evidence of ear debris, discharge, excoriation, self-mutilation, foul odor, painfulness, excessive scratching, collapse of erect ear; and lowering and shaking of head. On otoscopy, there is hyperplasia and inflammation of the ear canal.

In chronic or unresponsive cases of otitis, suspected or coinfirmed otitis media, or when numerous rod-shaped bacteria are seen on cytology, diagnosis depends upon culture of ear swabs or needle aspirate with isolation and identification of microorganisms, followed by determination of bacterial sensitivity. Differential diagnosis of Pseudomonas otitis includes: Malassezia spp, other secondary bacterial causes of otitis externa (Staphylococcus intermedius, Enterococcus spp, Proteus spp, Streptococcus spp, and Escherichia coli), and otic neoplasia or foreign body reaction (e.g fox tail).