Longitudinal study of the efficacy of ampicillin in the treatment of pneumococcal otitis media in a chinchilla animal model.

A chinchilla animal model was used to determine the effects of early antibiotic treatment with ampicillin or the local and systemic protective mechanisms during pneumococcal acute otitis media with effusion (AOME). The right bullae of 74 chinchillas were inoculated with 170 colony-forming units (CFU) of Streptococcus pneumoniae type 7F, and animals were randomly assigned to 1 of 2 groups: early (24 hours postinoculation) and late (12 days postinoculation) initiation of ampicillin treatment. During the first challenge, 52 chinchillas died within a 1-month period, apparently from suppurative complications of AOME. Following the resolution of AOME in their right ears, all surviving animals were challenged for the second time by bilateral bullar inoculations using 130 CFU of the same organism. All 10 animals in the early ampicillin treatment group developed severe bilateral AOME, whereas only 3 of the 12 animals in the late ampicillin treatment group developed a recurrence of AOME in the right ear. Significantly, 8 of the 12 animals in this group developed severe left AOME. These findings suggest the presence of a local middle ear defense system and support the results of previous similar studies in which S pneumoniae types 3 and 6A were used. The results of the present study also suggest that in the chinchilla the early administration of a systemic antibiotic (ampicillin) interferes with this defense mechanism.