Acute otitis media was produced in 110 chinchillas by inoculation of type 23 Streptococcus pneumoniae directly into the middle ear cavity by tympanotomy. During the first three days after inoculation, inflammatory cells were seen in the mucoperiosteum of the middle ear. After four to seven days, there was purulent exudation in the middle ear cavity, and 40% of the animals had pneumococcal meningitis and/or bacteremia. The middle ears were sterile in five of 28 animals sacrificed during the second week and in six of seven animals sacrificed at six weeks, although subepithelial changes persisted in the mucoperiosteum. Levels of antibody to S. pneumoniae in serum were measured by radioimmunoassay; mean values were 6.1 ng of pneumococcal antibody nitrogerr/rnl in 28 uninfected control animals and 16.5 ng of antibody nitrogenjrnl in 29 animals sacrificed two weeks after inoculation (P < 0.025). Opsonic activity of serum against S. pneumoniae was evaluated in infected and uninfected chinchillas. The opsonic titer was significantly higher in infected animals sacrificed at six weeks than in uninfected controls. Although pneumococcal polysaccharide antigen was found by counterimmunoelectrophoresis in 25 of 30 middle ear effusions, it could not be detected in the serum from infected animals. Methods for infection and sacrifice of chinchillas yielded reproducible results. This model should permit evaluation of the pathologic response to other serotypes of S. pneumoniae and possibly to prophylactic and therapeutic regimes.
Bibliographical noteFunding Information:
Received for publication March 29, 1976, and in revised form June 2,1976. This paper was presented in part at the 15th Interscience Conference on Antimicrobial Agents and Chemotherapy, Washington, D.C., September 24-26,1975. These studies were supported in part by contract no. NOI-AI-52533 from the National Institutes of Health and in part by grant no. 1I\S 07623-08 from the U.S. Public Health Service. We gratefully acknowledge the donation of chinchillas by Mr. Charles E. Stites, Royal American Chinchilla Inc., Kansas City, Kansas. Dr. Gerald Schiffman performed the radioimmunoassay antibody studies. We are grateful to Sherry Lamey for processing of the pathologic specimens and for providing the photomicrographs. Assistance in preparation of the manuscript was provided by Chris Mattison and Patti Lorenz, and technical assistance was provided by Jeffrey Pearce and Karen Petty. Please address requests for reprints to Dr. G. Scott Giebink, Department of Pediatrics, University Hospitals, Box 483 Mayo, Minneapolis, Minnesota 55455.