The role of anaerobic bacteria in otitis media: microbiology, pathogenesis, and implications on therapy

The current knowledge of the recovery of anaerobic bacteria from cases of acute and chronic otitis media is reviewed. Although techniques for cultivation of anaerobes were used in the studies presented, the methodologies of collection, transportation, and cultivation of the specimens varied. Consequently, there were differences in the rates of recovery of these organisms and the species isolated. Anaerobes, mainly gram-positive cocci, were recovered from a quarter of ear aspirates in acute otitis media in about one third mixed with aerobic and facultative bacteria. In a study of otitis media with effusion, anaerobic bacteria were recovered in 12% of the culture-positive aspirates. The predominant anaerobes were gram-positive cocci and Bacteroides melaninogenicus. Several studies reported the recovery of anaerobes in about half of the patients with chronic otitis media and in those with cholesteatoma. The predominant anaerobes were gram-positive cocci, Bacteroides sp, and Fusobacteria sp. Many of these organisms produced beta-lactamase and might have contributed to the failure of these patients to respond to penicillins. The potential synergistic relationships between the various aerobic and anaerobic bacteria and the role of the capsule of anaerobic bacteria as a virulence factor are discussed.