Microbiology of normal external auditory canal

Objectives: To isolate and characterize bacteria and fungi from the healthy ear and to obtain susceptibility profiles on each bacterial isolate. Study Design: Prospective. Methods: Specimens were collected from the external c anals and cerumen of healthy subjects. Species-level identification was obt ained by combining phenotypic and genotypic data. End-point minimal inhibit ory concentration testing was performed using National Committee for Clinic al Laboratory Standards recommended methods. Results: One hundred sixty-fou r subjects were cultured. Seventeen canal and 16 cerumen specimens showed n o growth. One hundred forty-eight cerumen specimens yielded 314 organisms, including 23 fungi. One hundred forty-seven canal specimens yielded 310 org anisms, including 7 fungi. Of 291 bacteria isolated from cerumen, 99% were Gram-positive. Of 302 bacteria isolated from the canal, 96% were Gram-posit ive. Staphylococci were 63% of both the cerumen bacteria and the canal bact eria. Coryneforms represented 22% of the bacteria in cerumen and 19% in the canal. Turicella otitidis was the primary coryneform isolated from both th e canal and the cerumen. Streptococci-like bacteria were 10% from the cerum en, 7% from the canal. In both cerumen and canal, Alloiococcus otitis was m ore than 95% of the streptococci-like bacteria. Fifteen gram-negative organ isms were isolated from the canal and cerumen, including four Pseudomonas a eruginosa strains. The percentages of Staphylococcus epidermidis isolates t hat had high-level resistance (greater than or equal to8 mug/mL) were as fo llows: to neomycin, 28% from cerumen and 11% from the canal; to oxacillin, 28% from cerumen and 25% from the canal; and to ofloxacin, 15% from cerumen and 19% from the canal. Conclusions: Turcella otitidis and A. otitidis wer e present with a much higher frequency than previously described, lending e vidence that they be considered normal otic flora. Corynebacterium auris, p reviously reported only in children, was isolated from normal adults.