Bacteriological characterization of the effusion material in an animal model for serous and purulent otitis media.

By means of cleaving the soft palate and blocking the Eustachian tube, two otomicroscopically well defined types of otitis media, serous and purulent, were created in an animal model (rat). The microbiological pattern of these conditions were characterized at 1, 2, 3, 4 and 6 weeks after the onset. Samples were collected from the middle ear cavity via the bulla tympanica and cultured for aerobic as well as anaerobic bacteria. The serous effusion was culture-negative. The purulent effusion material was culture positive, and mixed with Gram-positive (S. aureus, S. epidermidis, Strept. faecalis) and Gram-negative (E. coli, Proteus mirabilis) bacteria of which the latter dominated. No anaerobic species were detected. The study shows that the two otomicroscopically different types of otitis media also differ with regard to the microbiological pattern. The rat thus provides the opportunity to study these two different inflammatory middle ear responses--infectious and noninfectious--during standardized conditions.