Microbiology of otitis externa

Microbiologic and clinical data from 26 patients with otitis externa were prospectively evaluated. Specimens were processed for aerobic and anaerobic bacteria. Bacterial growth was noted in 23 specimens. A total of 33 aerobic and 2 anaerobic bacteria were recovered. Aerobic bacteria only were isolated in 21 (91%) patients, anaerobic bacteria only in 1 (4%), and mixed aerobic and anaerobic bacteria in 1 (4%). The most common isolates were Pseudomonas aeruginosa(14 instances), Staphylococcus aureus(7), Acinetobacter calcoaceticus (2), Proteus mirabilis (2), Enterococcus faecalis (2), Bacteroides fragilis(1), and Peptostreptococcus magnus(1). One isolate was recovered in 13 (57%) patients, 2 isolates in 8 (35%), and 3 isolates in 2 (9%). These data illustrate the polymicrobial nature of otitis externa in about half of the patients and the role of anaerobic bacteria in 8% of them. Further studies are warranted to evaluate the therapeutic implications of these findings.