Pseudomonas aeruginosa was injected intranasally into four groups of chinchillas to determine if these bacteria can invade the middle ear by way of the eustachian tube. One group completed penicillin treatment of bilateral penumococcal otitis media (POM), and the second group started penicillin treatment of bilateral POM at the time of P. aeruginosa injection. A third group had no POM, but completed a course of penicillin treatment before P. aeruginosa injection, and a fourth group had no POM and received no penicillin. Middle ear susceptibility to nasally injected P. aeruginosa was significantly higher in animals with POM (61%) than in animals without POM (32%, p = 0.001). Forced eustachian tube opening pressures did not correlate with P. aeruginosa susceptibility. Thus, P. aeruginosa, the principle pathogen of chronic suppurative otitis media, can invade the middle ear by way of the eustachian tube, and acute otitis media predisposes to middle ear infection by P. aeurginosa.
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