Experimentally induced otitis media with effusion following inoculation with the outer cell wall of nontypable Haemophilus influenzae

Summary Previously, we extracted lipopolysaccaride endotoxin (LPS) from an axenic culture of Haemophilus influenzae and inoculated it into the middle ears of guinea pigs, inducing temporary serous effusions. In the present study, we tried to clarify whether the immunological mechanism responsible for producing the otitis media following outer cell wall inoculation was persistent. We extracted the outer cell wall from nontypable H. influenzae, using Zollinger's method, and inoculated extracts into the middle ears of guinea pigs that had previously received three injections of nonviable H. influenzae in Freund's complete adjuvant. Histological evaluations were performed from day 2 to day 24. Effusions and mucosal changes persisted for a longer time than in the LPS-inoculated model. Hypertrophied mucosae and increased numbers of goblet cells with hypersecretion were visible in the specimens on days 23–24. The condition seemed to show a greater similarity to chronic otitis media with effusion in children than did the LPS-inoculated model. We concluded that both the biological activity of the outer cell wall and immunological mechanisms might induce prolonged otitis media. We speculate that not only single middle ear infection but also general infections and repetitive middle ear infections may contribute to prolonged otitis media.