EFFECT OF PSEUDOMONAS-AERUGINOSA EXOTOXIN-A ON INNER-EAR FUNCTION

Electrophysiological changes were studied in the albino rat following instillation of Pseudomonas aeruginosa exotoxin A into the middle ear cavity through the tympanic membrane. Hearing threshold was measured b y a burst-elicited, frequency-specific auditory brainstem response (AB R) technique prior to exposure, then 24 and 48 h, 5 days, 2 and 4 week s after the toxin instillation. A single dose (I mu g/20 mu l) of Pseu domonas aeruginosa exotoxin A raised the ABR threshold over the whole frequency range, by 5-25 dB, particularly in the high tones. All thres hold shifts were of combined conductive and cochlear type, reversible, with deterioration starting at 24-48 h and recovery at 2-4 weeks. Eff usion of serous fluid occurred at 24 or 48 h, resulting in conductive hearing loss. Latency/intensity curves revealed a cochlear component i n addition to conductive hearing loss. Morphological examination by SE M showed slight and inconsistent derangement of OHCs. It is concluded that Pseudomonas aeruginosa exotoxin A causes middle ear inflammation, facilitating penetration to the inner ear and that this toxin also re versibly affects cochlear function.