Microbial flora and antimicrobial susceptibility patterns of isolated pathogens from the horizontal ear canal and middle ear in dogs with otitis media.

OBJECTIVE: To compare microbial flora and antimicrobial susceptibility patterns of isolated pathogens from the horizontal ear canal and middle ear in dogs with otitis media.
DESIGN: Prospective study. ANIMALS: 23 dogs with chronic bilateral otitis externa. PROCEDURES: Swab specimens of the horizontal ear canal and middle ear were obtained for cytologic analysis, bacterial culture, and antimicrobial susceptibility testing. Integrity of the tympanic membrane was observed. If the tympanic membrane was intact, myringotomy was performed to collect specimens.
RESULTS: Otitis media was diagnosed in 38 of 46 (82.6%) ears evaluated. The tympanic membrane was intact in 71.1% of the ears with otitis media. The 3 most common organisms isolated from the horizontal ear canal and middle ear were Staphylococcus intermedius, yeast, and Pseudomonas spp. A difference in total isolates or susceptibility patterns between the horizontal ear canal and middle ear was found in 34 (89.5%) ears. Compared with results of bacterial culture, cytologic examination of swab specimens was not as effective for detection of rods and cocci from the middle ear. CLINICAL IMPLICATIONS: In dogs with chronic otitis externa, otitis media often exists even when there is an intact tympanic membrane. In our study, the same isolates were rarely found in the horizontal ear canal and middle ear. Therefore, to choose appropriate antimicrobial agents, in addition to cytologic examination, bacterial culture and susceptibility testing of swab specimens from the horizontal ear canal and middle ear should be performed.