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 10⁴ to 10⁶ 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 10⁴ to 10⁶ 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 10⁷ killed animals within 12 hours after inoculation. Three of five animals that were inoculated with a 10⁶ dose died 3 days after inoculation; two of three animals that were inoculated with a 10⁵ dose lived to 15 days after inoculation. One of two animals that were inoculated with a 10⁴ 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 10⁵ dose, with morphologic features similar to those in human disease. This is an effective model for this study of meningogenic labyrinthitis.