A new rat model of otitis media caused by Streptococcus pneumoniae: Conditions and application in immunization protocols

Streptococcus pneumoniae (pneumococcus [Pn]) can be cultured from up to 50% of acute otitis media (AOM) effusions, and these bacteria are the most com mon cause of AOM-related complications. With the recent advent of antibioti c-resistant Pn strains, treatment of Pn infections may meet with serious di fficulties. Prevention through vaccination, notably for the four most commo n occurring Pn serotypes in humans (i.e., Pn 6B, Pn 14 Pn 19F, and Pn 23F), is a helpful alternative. Testing of vaccine efficacy should occur in an a ppropriate animal AOM model, which is presented here. The four involved Pn serotypes are not pathogenic to the rat, which was chosen as the experiment al animal for practical reasons. To induce a natural infection (i.e., ascen ding through the eustachian tube), the mucociliary clearance of the eustach ian tube was impaired by infusing histamine into the tympanic cavity on 2 c onsecutive days before intranasal inoculation of the bacteria. With this si mple protocol, high and reproducible infection rates, as determined with ba cterial cultures, of Pn-induced AOM (approximately 70%) with the two major Pn serotypes 14 and 19F (Pn 14 and Pn 19F) were obtained, whereas lower inf ection rates (25 to 50%) with Pn 6B and Pn 23F were obtained. In this model , intranasal priming with pneumococci, as well as subcutaneous vaccination with Pn 14 tetanus toxoid-conjugated polysaccharide, induced a protective e ffect. against the induction of otitis media with these bacteria. This show s that immunity to Pn 14 AOM can be induced by both mucosal and systemic pr esentations of antigen. In conclusion, we have developed an animal model fo r Pn-induced AOM, which is suitable for the evaluation of the protecting ef fect of immunization.