Experimental otitis media due to Streptococcus pneumoniae: immunopathogenic response in the chinchilla

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 nitrogen/ml in 28 uninfected control animals and 16.5 ng of antibody nitrogen/ml in 29 animals sacrificed two weeks after inoculation (P less than 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.