A New Rat Model of Otitis Media Caused by Streptococcus pneumoniae : Conditions and Application in Immunization Protocols

Abstract

Streptococcus pneumoniae (pneumococcus [Pn]) can be cultured from up to 50% of acute otitis media (AOM) effusions, and these bacteria are the most common cause of AOM-related complications. With the recent advent of antibiotic-resistant Pn strains, treatment of Pn infections may meet with serious difficulties. Prevention through vaccination, notably for the four most common 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 appropriate animal AOM model, which is presented here. The four involved Pn serotypes are not pathogenic to the rat, which was chosen as the experimental animal for practical reasons. To induce a natural infection (i.e., ascending through the eustachian tube), the mucociliary clearance of the eustachian tube was impaired by infusing histamine into the tympanic cavity on 2 consecutive days before intranasal inoculation of the bacteria. With this simple protocol, high and reproducible infection rates, as determined with bacterial 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 infection 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 effect against the induction of otitis media with these bacteria. This shows that immunity to Pn 14 AOM can be induced by both mucosal and systemic presentations of antigen. In conclusion, we have developed an animal model for Pn-induced AOM, which is suitable for the evaluation of the protecting effect of immunization.

Chronic tympanic membrane perforation: a better animal model is needed

“…In all of the above models, animals that demonstrated signs of otitis media and otitis externa were excluded. As there are a number of documented animal models for acute [62][63][64][65][66][67][68][69][70][71][72][73][74][75][76][77][78] and chronic 44,56,62,[79][80][81][82][83][84][85][86][87][88][89][90][91][92][93] otitis media, the key to developing an animal model for chronic perforation may involve perforation in the setting of an existing otitis media model. Myringotomy during acute otitis media prolongs the effects of infection on the tympanic membrane.…”

Mucosal Vaccination Against Encapsulated Respiratory Bacteria – New Potentials for Conjugate Vaccines?

“…Despite the outstanding efficacy of conjugate vaccines against invasive disease in infants and children [47, 48, 55, 56], they have been less efficacious against mucosal infections such as pneumococcal otitis media, both in humans [57] and experimental animal models [100–102]. It has been demonstrated that circulating PS‐specific antibodies may reduce nasopharyngeal colonization [53, 54, 103], and repeated colonization is associated with a poor systemic PS‐specific antibody response [104].…”

Acute otitis media develops in the rat after intranasal challenge of Streptococcus pneumoniae

“…The tip of the catheter was placed at the level of the nasopharyngeal orifice of the ET, which was approximately 33 mm from the nostril. Through this intranasal catheter rats were inoculated with 100 mL PnC, type 3 (approximately 10 7 colony‐forming units [CFU]/mL) suspended in Todd‐Hewitt broth (Difco). The bacteria were obtained from the Department of Clinical Bacteriology, Umeå University, and had been stored frozen at −70°C.…”

“…In these animals, the ET function becomes impaired and an otitis media develops that is caused by the indigenous nasopharyngeal bacterial flora 4 . However, in a recent study, nasal challenge with Streptococcus pneumoniae (PnC) was shown to cause AOM in rats 7 . Its development was facilitated by administration of histamine through the tympanic membrane (TM) into the MEC.…”