Canine otitis externa is a common problem, with a reported prevalence of 10% to 20%.1 The most challenging of these cases often involve the gram-negative bacterium Pseudomonas aeruginosa because of its unpredictable antimicrobial sensitivity profile.2 In dogs, P. aeruginosa can be cultured from about 0.4% of normal ears and 20% of otitic ears and is frequently found in chronic, recurrent cases
of otitis.3,4 Ears infected with Pseudomonas species are generally painful and often have extensive ulceration of the epithelial lining of the ear canal.4 Treatment typically involves general ear cleansing and may require antimicrobial sensitivity testing to identify the specific
topical antibiotic that may be effective. Treating these ears can be frustrating because of changing susceptibility profiles.
The organism can become resistant to all available antibiotics or may become susceptible only to expensive or difficult-to-obtain
antibiotics. A product that can inactivate isolates with multiple antibiotic resistances would be useful for treating this
condition.
We designed a study to evaluate Sanova cleanser (Alcide Corporation) for in vivo efficacy against naturally occurring P. aeruginosa otitis in dogs. Sanova is a USDA-approved antimicrobial solution for use in food processing. The two-part solution consists
of a base solution of 2,400 ppm sodium chlorite and an activator solution of 1.2% citric acid. When the liquids are mixed,
bioactive chlorine compounds, including chlorine gas and chlorine dioxide, are formed in the solution. These compounds are
bactericidal. In unpublished in vitro studies, this cleanser has been shown to effectively destroy isolates of P. aeruginosa and Pseudomonas vulgaris within 15 seconds of contact.5 For this prospective study, we evaluated the effect of this cleanser on objective quantitative culture results and subjective
clinical scores.
Materials and methods
Study subjects were client-owned pet dogs with naturally occurring ear disease of at least six weeks' duration that was diagnosed
as P. aeruginosa otitis externa upon referral to a specialty veterinary dermatology clinic. The clients signed a consent form, and the patients
were enrolled in this study if they met each of the following criteria: a complete otoscopic visualization of the external
ear canal and the tympanum revealed abnormalities consistent with an uncomplicated otitis externa; results of cytologic examination
of the exudates were consistent with the exclusive presence of Pseudomonas species infection; and culture results were positive for only P. aeruginosa. Visualization with a handheld diagnostic head otoscope and otoscope cone confirmed that the tympanum was intact and that
no foreign objects or tumors complicated the infection. If necessary, patients were lightly sedated to allow complete visualization
of the external ear canal and tympanum.
We took ear swab samples from the juncture of the horizontal and vertical canals and prepared heat-fixed impression smears
on glass slides. We stained the slides with Gram's stain and examined them microscopically for the exclusive presence of large,
gram-negative rods consistent with Pseudomonas species.6 We then used sterile swabs to collect samples of the ear exudates from the juncture of the horizontal and vertical canals
for bacterial culture and antimicrobial sensitivity testing. The swabs were sent in transport media to a commercial laboratory
for bacterial culture and sensitivity testing by using standard disk diffusion techniques and a standard battery of antibiotics.
The presence of other organisms identified on cytology or culture resulted in the patient's being excluded from the study.
All patients had been treated unsuccessfully with oral antibiotics, ear cleansers, or topical antibiotic and corticosteroid
preparations before referral to the specialty dermatology clinic. These treatments were stopped at least 48 hours before enrollment
in the study.
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