Otoprotectant Minimizes Hearing Defects Caused by Pseudomonas aeruginosa Exotoxin A

Abstract

Exotoxin A, produced by Pseudomonas aeruginosa (PaExoA), penetrates from the middle ear in to the cochlea and causes sensorineural hearing loss (SNHL). In this investigation we studied electrophysiological changes in the albino rat following instillation of PaExoA and N^G-nitro-L-arginine methyl ester (L-NAME), a known inhibitor of nitric oxide synthesis, into the middle ear. Hearing thresholds were measured by auditory brainstem response (ABR) technique. Latency/intensity curves were constructed to distinguish between cochlear and conductive components of hearing loss. PaExoA caused damage to cochleae and SNHL, mainly at high frequencies. This impairment was blocked by L-NAME. It would appear that nitric oxide may be a significant link in the mechanism of SNHL caused by bacterial toxin. L-NAME acts as an otoprotectant against the deleterious action of PaExoA.