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Early inflammatory changes of the Haemophilus influenzae-induced experimental otitis media
1Department of Otolaryngology, Niigata University School of Medicine, Japan.
Abstract:
Haemophilus influenzae is one of the most frequent pathogens of acute otitis media. To determine the middle ear response during the early stage of acute inflammation, a small amount of H. influenzae was inoculated into the bullae of guinea pigs through the tympanic membrane. The bullae were harvested at 6, 12, 24, 36, and 48 hours after H. influenzae inoculation and washed with phosphate-buffered saline (PBS). The number of viable H. influenzae and inflammatory cells, the concentrations of myeloperoxidase (MPO) and lysozyme in the washing suspensions were measured, and compared with those in PBS-inoculated control ears. The number of viable H. influenzae increased very rapidly from 6 to 12 hours after inoculation and remained stationary up to 48 hours. The number of inflammatory cells and the MPO concentration were significantly higher in the H. influenzae-inoculated ears than in the control ears from 12 to 48 hours after inoculation. The lysozyme concentration was already significantly higher at 6 hours in the H. influenzae-inoculated ears; the lysozyme was released in the middle ear before the accumulation of inflammatory cells and degranulation of MPO from inflammatory cells. The results indicated that inflammatory reactions were present already at 6 hours after bacterial inoculation, and were rapidly accelerated during the subsequent hours. Consequently, acute middle ear inflammatory responses were seen immediately following inoculation of viable bacteria, and these responses originated in direct responses of middle ear mucosa, and oxidative and non-oxidative neutrophil metabolic products, which may cause tissue injury.
Insights
Early middle ear inflammation from Haemophilus influenzae involves rapid bacterial growth and inflammatory cell accumulation. Lysozyme release precedes neutrophil response, indicating immediate mucosal reactions and potential tissue injury.
Area of Science:
- Otolaryngology
- Microbiology
- Immunology
Background:
- Haemophilus influenzae is a primary cause of acute otitis media.
- Understanding early middle ear inflammation is crucial for effective treatment.
Purpose of the Study:
- To investigate the initial inflammatory responses in the middle ear following Haemophilus influenzae inoculation.
- To characterize the temporal dynamics of bacterial load, inflammatory cells, and key mediators.
Main Methods:
- Guinea pigs were inoculated with Haemophilus influenzae into the middle ear.
- Bacterial counts, inflammatory cells, myeloperoxidase (MPO), and lysozyme were measured at various time points (6-48 hours).
- Results were compared to control groups receiving phosphate-buffered saline (PBS).
Main Results:
- Haemophilus influenzae rapidly increased in viable numbers within 6-12 hours.
- Inflammatory cells and MPO concentrations elevated significantly from 12 hours onwards.
- Lysozyme levels increased significantly as early as 6 hours, preceding inflammatory cell accumulation.
Conclusions:
- Acute middle ear inflammation begins rapidly after bacterial inoculation.
- Early responses involve direct mucosal reactions and neutrophil-derived products.
- Lysozyme release indicates an immediate non-cellular inflammatory mechanism.