Middle ear susceptibility to Pseudomonas infection during acute otitis media.

Pneumococcal otitis media was induced bilaterally, and Pseudomonas was inoculated unilaterally into the middle ears of 36 chinchillas to study the pathogenesis of chronic suppurative otitis media. Half of the animals were treated with penicillin prior to Pseudomonas inoculation (day 7, late Pseudomonas), and half were inoculated with Pseudomonas before penicillin treatment (day 3, early Pseudomonas). A third group of 18 chinchillas received unilateral Pseudomonas inoculation without pneumococcus or penicillin (control). Animals with early Pseudomonas were significantly less susceptible to Pseudomonas infection in the Pseudomonas-inoculated ear than animals with late Pseudomonas and controls. Susceptibility to Pseudomonas infection in the contralateral ears, which were not inoculated with Pseudomonas, was significantly lower in early Pseudomonas and control animals than in late Pseudomonas animals. Increased susceptibility in the late Pseudomonas group might have been due to altered nasopharyngeal microflora or persisting eustachian tube dysfunction--factors that may be important in the pathogenesis of chronic suppurative otitis media in humans.