Treatment of Pseudomonas otitis in the dog (Sponsored by Pfizer)
Otitis externa is a common presenting problem in clinical practice. In chronic cases, the infection frequently extends to the middle ear. While multiple factors contribute to otitis development and subsequent secondary infections, the organisms found most often in affected ears include Staphylococcus species, Malassezia pachydermatis, and Pseudomonas aeruginosa.1
P. aeruginosa, a gram-negative bacillus, is ubiquitous in the environment but an uncommon inhabitant of the normal external ear canal and middle ear of dogs. As small animal veterinarians can attest, ears infected with P. aeruginosa can be some of their most challenging cases. Studies have reported moderate to high levels of resistance to some commonly used antimicrobials of P. aeruginosa isolates from cases of otitis externa.1-4
Clinical signsAnimals with P. aeruginosa ear infections typically exhibit one or more of the following clinical signs or conditions:
In some otitis cases, patients fail to respond to initial empirical therapy or the condition recurs rapidly after apparently successful therapy. If this occurs, perform culture and susceptibility testing of the otic exudate. Samples are easily obtained by inserting sterile swabs to the junction of the vertical and horizontal external ear canals.
If you suspect otitis media, obtain a sample from the middle ear (tympanic bulla cavity) using either a sterile calcium alginate (Calgi) swab or a syringe attached to a 3-F tomcat catheter to instill, and subsequently suction, 0.5 ml of sterile saline. If the tympanic membrane is intact—as is often the case—you must perform a myringotomy in the caudoventral quadrant of the pars flaccida tensa to gain entry into the middle ear.
In otitis media cases, it's important to obtain separate cultures from the external and middle ears because the organisms and their antibiotic susceptibility patterns often differ between these two locations.1