NONTYPABLE AND ENCAPSULATED HAEMOPHILUS-INFLUENZAE YIELD DIFFERENT CLINICAL COURSES OF EXPERIMENTAL OTITIS-MEDIA

Middle ears of male Sprague-Dawley rats were injected with suspensions of thirteen Haemophilus influenzae strains of different sero- and bio types and at various concentrations. Systemic and local changes were m onitored by clinical observations, otomicroscopy, and analysis of bact erial samples from blood and middle ears. Two patterns of response wer e recognized, a nontypeable and an encapsulated pattern. The nontypeab le H. influenzae middle ear infection required a high bacterial dose a nd was well past its peak 8 days after challenge, when the encapsulate d H. influenzae otitis media was still purulent. The most severe infec tions were caused by H. influenzae type b strains. The overall mortali ty rate was zero and the animals recovered without permanent deteriora tion or otomicroscopically discernable changes. The results of this st udy show the rat to be a suitable animal model for the study of H. inf luenzae otitis media.