Otitis externa in dogs: microbiology and antimicrobial susceptibility

The aims of the study were to determine the prevalence of bacterial/yeast otitis externa in dogs and to analyse antimicrobial susceptibility. Among 257 swab ear samples from Bulgarian dogs with otitis externa, bacteria and yeast species were isolated in 93.77% of cases as mono-infections (109 cases) involving mainly coagulase positive staphylococci (60 strains), Malassezia pachidermatis (97 strains) and Pseudomonas aeruginosa (42 strains) and more often as poly-infections (132 cases). The other agents scarcely identified were β-haemolytic Streptococcus spp., Proteus mirabilis and Escherichia coli, the 2 last species being almost exclusively found in poly-infections. The sensitivity of isolated bacteria to antimicrobial drugs, most commonly used treatment of otitis externa has been tested. The high sensitivity to beta-lactams and aminoglycoside-aminocyclitols was established in Gram positive bacteria, while Gram negative bacteria were sensitive to aminoglycoside-aminocyclitols, polymyxin B and enrofloxacin. These results highlight the relative high frequency of yeasts and the necessity of coupling antimicrobial susceptibility tests to bacterial isolation.