Microbiology of Normal External Auditory Canal

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Abstract
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 canals and cerumen of healthy subjects. Species‐level identification was obtained by combining phenotypic and genotypic data. End‐point minimal inhibitory concentration testing was performed using National Committee for Clinical Laboratory Standards recommended methods.Results One hundred sixty‐four subjects were cultured. Seventeen canal and 16 cerumen specimens showed no growth. One hundred forty‐eight cerumen specimens yielded 314 organisms, including 23 fungi. One hundred forty‐seven canal specimens yielded 310 organisms, including 7 fungi. Of 291 bacteria isolated from cerumen, 99% were Gram‐positive. Of 302 bacteria isolated from the canal, 96% were Gram‐positive. Staphylococci were 63% of both the cerumen bacteria and the canal bacteria. Coryneforms represented 22% of the bacteria in cerumen and 19% in the canal. Turicella otitidis was the primary coryneform isolated from both the canal and the cerumen. Streptococci‐like bacteria were 10% from the cerumen, 7% from the canal. In both cerumen and canal, Alloiococcus otitis was more than 95% of the streptococci‐like bacteria. Fifteen gram‐negative organisms were isolated from the canal and cerumen, including four Pseudomonas aeruginosa strains. The percentages of Staphylococcus epidermidis isolates that had high‐level resistance (≥8 μg/mL) were as follows: 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 were present with a much higher frequency than previously described, lending evidence that they be considered normal otic flora. Corynebacterium auris, previously reported only in children, was isolated from normal adults.

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