Understanding how pneumococcal proteins affect the pathology of the middle ear and inner ear is important for the development of new approaches to prevent otitis media and its complications.
To determine the viability and virulence of Streptococcus pneumoniae mutants deficient in pneumolysin (Ply−) and pneumococcal surface protein A (PspA−) in the chinchilla middle ear.
Bullae of chinchillas were inoculated bilaterally with wild-type (Wt), Ply−, PspA−, and Ply−/PspA− strains. Bacterial colony-forming units (CFUs) in middle ear effusions were counted at 48 hours. The CFUs of the PspA− group were also counted at 6 to 36 hours after inoculation. Temporal bone histopathological results were compared.
Setting and Participants
Twenty-seven chinchillas in an academic research laboratory.
Chinchilla middle ears were inoculated with S pneumoniae to produce sufficient volumes of effusions and noticeable histopathological changes in the ears.
Main Outcomes and Measures
The CFU counts in the middle ear effusions and histopathological changes were compared to determine the effect of pneumococcal protein mutations on chinchilla ears.
At 48 hours, CFUs in middle ears were increased for the Wt and Ply−/PspA− strains, but Ply− remained near inoculum level. No bacteria were detected in the PspA− group. The CFUs of PspA− decreased over time to a low level at 30 to 36 hours. In vitro, PspA− in Todd-Hewitt broth showed an increase in bacterial growth of 2 logs at 43 hours, indicating PspA− susceptibility to host defenses in vivo. The PspA− and Ply− groups had fewer pathologic findings than the Wt or Ply−/PspA− groups. Histopathological analysis showed significant differences in the number of bacteria in the scala tympani in the Wt group compared with the Ply−, PspA−, and Ply−/PspA− groups. The PspA− strain was the least virulent.
Conclusions and Relevance
The PspA− mutant was much less viable and less virulent in the ear than the Wt, Ply−, and Ply−/PspA− strains. There was no significant attenuation in the viability and virulence of the Ply−/PspA− mutant compared with the Wt or single mutants. The viability and virulence of pneumococcal mutants seemed to be protein and organ specific.