Aerobic and Anaerobic Microbiology of External Otitis Itzhak Brook, Edith H. Frazier, and David H. Thompson
From the Departments of Pediatrics. Pathology. and Otolaryngology. Naval Medical Center. Bethesda. Maryland
Staphylococcus aureus and Pseudomonas aeruginosa have been identified as the predominant isolates recovered in cases of external otitis [1, 2]. Studies that employed culture methodology adequate for the recovery ofanaerobic bacteria have implicated anaerobic organisms as important pathogens in upper respiratory infections , including chronic otitis media . However, no attempts have been made to investigate the role of anaerobes in external otitis, although several cases were reported to be possibly due to anaerobic bacteria , and one report described the presence of anaerobes in an abscess of the external ear . It seems, therefore, that a study of the anaerobic as well as the aerobic and facultative flora of the infected external ear is of importance. This is of particular importance since many of the anaerobes recovered from patients with upper respiratory infections are resistant to commonly used antimicrobial drugs . This. report describes the experience over a period of 6 years at a military hospital in regard to the etiologic diagnosis of aerobic and anaerobic bacteria in external otitis.
Materials and Methods Clinical and microbiological data from patients whose external otitis had been diagnosed between June 1979 and June 1985 were retrospectively reviewed. Only patients
Received 4 February 1992; revised 9 June 1992. The opinions and assertions contained herein are the private ones of the authors and are not to be construed as official or as reflecting the views ofthe U.S. Department of the Navy or the Department of Defense at large. Reprints or correspondence: Dr. Itzhak Brook. Armed Forces Radiobiology Research Institute. Bethesda. Maryland 20889-5603.
Clinical Infectious Diseases
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whose external ear fluid specimens were processed for aerobic as well as anaerobic bacteria were included in the study. Only individuals who had acute external otitis for < 14 days were included. Microorganisms were isolated from 56 (84%) of the 67 patients whose specimens were sent to the laboratory. However, medical records were available only in 46 instances, and only those were included in the final analysis. The patients were 7-69 years old (average, 29 years), and 34 were males. Antimicrobial therapy was given to 8 patients within 2 weeks before sample collection: ampicillin in 4 cases, dicloxacillin in 2, erythromycin in I, and trimethoprim-sulfamethoxazole in 1. Specimens were obtained with use of two sterile cotton swabs. One swab was sent for isolation of aerobic bacteria in a Vacutainer transport system (Culturette, Becton-Dickinson, Rutherford, NJ), and the other swab was placed in an anaerobic transport system (Port-a-Cul, Becton-Dickinson, Cockeysville, MD). When an abscess was present, direct needle aspiration was performed after the area was cleansed with povidone-iodine, and the specimen was transported to the laboratory in a syringe sealed with a rubber stopper. The time between collection of materials and the inoculation of the specimen was generally