Acute Streptococcus pneumoniae meningogenic labyrinthitis. An experimental guinea pig model and literature review.

OBJECTIVE

To create an experimental model of Streptococcus pneumoniae type 3 meningogenic labyrinthitis (a leading cause of deafness) similar to that in human disease.

DESIGN

Cohort analytic study of guinea pigs that were inoculated intrathecally with varying dilutions of S pneumoniae type 3; the progress of the disease was compared with that in saline solution-inoculated control animals.

SUBJECTS

Healthy adult Hartley guinea pigs without clinical evidence of middle ear disease that were conveniently sampled.

INTERVENTIONS

Intrathecal inoculation of 10(4) to 10(6) colony-forming units of S pneumoniae type 3 into 13 guinea pigs; signs and symptoms of meningitis/labyrinthitis were observed for 15 days and compared with those in two saline solution-inoculated control animals.

MAIN OUTCOME MEASURES

Morbidity--labyrinthitis, meningitis; end point--death.

RESULTS

The 10(4) to 10(6) colony-forming units of S pneumoniae type 3 caused inflammation that extended from the meninges to the inner ear via the cochlear aqueduct within 3 days after inoculation; a dose of 10(7) killed animals within 12 hours after inoculation. Three of five animals that were inoculated with a 10(6) dose died 3 days after inoculation; two of three animals that were inoculated with a 10(5) dose lived to 15 days after inoculation. One of two animals that were inoculated with a 10(4) dose did not become infected. Inflammation extended to the middle ear by round-window destruction. Reactive bone formation simulated labyrinthine osteosclerosis. Observers assessed histologic slides "blindly."

CONCLUSION

Guinea pigs can survive 15 days after intrathecal inoculation of a 10(5) dose, with morphologic features similar to those in human disease. This is an effective model for this study of meningogenic labyrinthitis.