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The contribution of pneumococcal cell wall to the pathogenesis of experimental otitis media
M L Ripley-Petzoldt1, G S Giebink, S K Juhn
1Department of Pediatrics, School of Medicine, University of Minnesota, Minneapolis.
Abstract:
We studied the contribution of pneumococcal cell wall to the pathogenesis of otitis media in chinchillas after middle ear inoculation of killed, encapsulated type 7F Streptococcus pneumoniae; killed, unencapsulated R6 S. pneumoniae; and isolated R6 pneumococcal cell wall. Ears inoculated with encapsulated and unencapsulated pneumococci had significantly higher concentrations of polymorphonuclear and mononuclear leukocytes and lysozyme in middle ear fluid and developed more epithelial metaplasia and granulation tissue than did saline-inoculated ears. The mean concentration of lysozyme in middle ear fluid was higher in ears inoculated with killed, unencapsulated than encapsulated pneumococci. The middle ear mucoperiosteum of ears inoculated with pneumococcal cell wall showed significantly more polymorphonuclear leukocytes, epithelial metaplasia, subepithelial congestion, and granulation tissue than did control ears. Because nonviable, unencapsulated pneumococci and pneumococcal cell wall caused middle ear inflammation in the chinchilla model of otitis media, it is possible that cell envelope and cell wall components released during bacterial lysis may contribute to chronic otitis media with effusion in humans.
Insights
Pneumococcal cell wall components contribute to otitis media pathogenesis. Even dead bacteria and cell walls caused inflammation, suggesting a role in chronic middle ear infections.
Area of Science:
- Microbiology
- Pathogenesis
- Otolaryngology
Background:
- Otitis media is a common middle ear infection.
- The role of specific bacterial components in otitis media pathogenesis requires further investigation.
Purpose of the Study:
- To investigate the contribution of pneumococcal cell wall to otitis media pathogenesis.
- To evaluate the inflammatory response in a chinchilla model after inoculation with Streptococcus pneumoniae components.
Main Methods:
- Chinchillas were inoculated in the middle ear with killed encapsulated Streptococcus pneumoniae, killed unencapsulated R6 S. pneumoniae, or isolated R6 pneumococcal cell wall.
- Inflammatory markers, including leukocyte and lysozyme concentrations, and tissue changes were assessed in middle ear fluid and mucoperiosteum.
Main Results:
- Inoculation with both encapsulated and unencapsulated pneumococci led to increased leukocytes and lysozyme in middle ear fluid, and greater epithelial metaplasia and granulation tissue.
- Killed, unencapsulated pneumococci induced higher lysozyme concentrations than encapsulated pneumococci.
- Pneumococcal cell wall inoculation significantly increased polymorphonuclear leukocytes, epithelial metaplasia, congestion, and granulation tissue compared to controls.
Conclusions:
- Nonviable, unencapsulated pneumococci and pneumococcal cell wall components can induce middle ear inflammation.
- These findings suggest that bacterial cell envelope and cell wall components may contribute to the pathogenesis of chronic otitis media with effusion in humans.