Pneumococcal Toxins Reversibly Affect Cochlear Electrophysiology

Abstract

Objectives: Streptococcus pneumoniae (pneumococcus) produces various toxic proteins such as pneumolysin, autolysin, neuraminidase, hyaluronidase and pneumococcal surface protein A. To evaluate effects on the sensorineural component of hearing of such an infection in the middle ear a sterile suspension of pneumococcus containing all these toxins was instilled into the round window niche. Material and Methods: Inner ear function was evaluated by a frequency-specific auditory brainstem response (ABR) technique using the rat as experimental animal. Both ABR threshold curves and intensity-latency (I-L) curves were investigated. Results: The electrophysiological effects of pneumococcal toxin on the middle and the inner ear were moderate. Sensorineural hearing loss appeared from 1 day after instillation especially at high frequencies (31.5-20 kHz) and gradually extended into the frequencies 16, 14 and 12 kHz. The threshold impairment was reversible and improved within 2 weeks after exposure. The mean threshold change ranged from 5 to 10 dB at high frequencies. Conclusions: Our experimental results are compatible with previously reported clinical findings. The I-L curve investigation was useful to distinguish the changes due to conductive or sensorineural or mixed type of hearing loss. The I-L curve is more accurate than ABR threshold diagrams to identify minor electrophysiological changes of the cochlea.

Interleukin-2 Affects Cochlear Function Gradually but Reversibly

“…In contrast, the effects of, for instance, pneumococcal toxin on the cochlea appeared quickly and tended to peak on early days (days 1-3) [18]. The secondary (toxin-) induced inflammation is likely to modify the immediate and direct effects of the toxins prolonging the entire challenge of the cochlea.…”