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Role of the bacterial cell wall in middle ear inflammation caused by Streptococcus pneumoniae
B D Carlsen1, M Kawana, C Kawana
1Otitis Media Research Center, University of Minnesota School of Medicine, Minneapolis 55455.
Abstract:
The pathogenesis of middle ear inflammation caused by Streptococcus pneumoniae was explored in the chinchilla model with different pneumococcal cell wall (CW) preparations, including isolated native CW, M1 muramidase CW (M1-CW) digest, amidase CW digest, and M1 peptidoglycan (M1-PG) digest. Inflammatory cell and lysozyme concentrations in middle ear fluid (MEF) were measured between 6 and 72 h after the middle ears were inoculated with one of the preparations or sterile saline. Middle ear histopathology was measured quantitatively at 72 h. Native CW, M1-CW digest, and amidase-CW digest caused significantly more inflammatory cell influx and lysozyme accumulation in MEF than saline did. M1-PG digest also caused more inflammatory cell influx and lysozyme accumulation in MEF than saline did but caused less inflammation than native CW or either CW digest. Epithelial metaplasia was significantly greater in ears inoculated with native CW than in ears inoculated with the CW or PG digest or with saline. Pneumococcal CW is, therefore, the principal factor that initiates middle ear inflammation in acute pneumococcal otitis media, and CW teichoication seems to be important in initiating this response.
Insights
Streptococcus pneumoniae cell wall components trigger middle ear inflammation. Native cell wall and its digests cause significant inflammation, with peptidoglycan showing a lesser effect.
Area of Science:
- Microbiology
- Immunology
- Otolaryngology
Background:
- Acute otitis media is a common infection, often caused by Streptococcus pneumoniae.
- The role of specific pneumococcal components in initiating middle ear inflammation requires further elucidation.
Purpose of the Study:
- To investigate the role of Streptococcus pneumoniae cell wall (CW) components in the pathogenesis of middle ear inflammation.
- To compare the inflammatory potential of different pneumococcal CW preparations in a chinchilla model.
Main Methods:
- Chinchilla middle ears were inoculated with native CW, M1-CW digest, amidase CW digest, M1-PG digest, or saline.
- Middle ear fluid (MEF) was analyzed for inflammatory cells and lysozyme concentrations from 6 to 72 hours post-inoculation.
- Middle ear histopathology was quantitatively assessed at 72 hours.
Main Results:
- Native CW, M1-CW digest, and amidase-CW digest induced significantly higher inflammatory cell influx and lysozyme accumulation in MEF compared to saline.
- M1-PG digest also increased inflammatory markers but to a lesser extent than native CW or CW digests.
- Epithelial metaplasia was most pronounced in ears treated with native CW.
Conclusions:
- Pneumococcal CW is the primary factor initiating middle ear inflammation in acute otitis media.
- Teichoic acid modification of the CW appears crucial for initiating this inflammatory response.