Demonstration of Nasopharyngeal and Middle Ear Mucosal Biofilms in an Animal Model of Acute Otitis Media

Objectives: We performed this study to determine the role of nasopharyngeal and middle ear (ME) biofilms in acute otitis media (AOM). Methods: Sixty female 6-month-old chinchillas, free of ME disease, were utilized. Experimental animals were inoculated with influenza A followed by Streptococcus pneumoniae 7 days later. Control animals were inoculated with Sorensen's phosphate buffer. Daily otoscopy and tympanometry was performed, and the animals were painlessly sacrificed on days 1, 2, 5, 8, and 14. All mucosae were harvested and prepared for scanning electron microscopy. Results: The ME inflammation, initially detected on day 2 after bacterial inoculation, peaked on day 8. Eight percent of the dually inoculated chinchillas displayed type B tympanograms, and 40% displayed type C. Otoscopic evaluation of tympanic membrane inflammation was rated from 0 to 4 (0 = normal and 4 = severe drainage and/or inflammation) according to an otoscopic grading system. Ten percent of the experimental chinchillas had a grade 2 score, 20% had grade 3, and 6.7% had grade 4. The controls demonstrated no abnormal tympanometric or otoscopic findings. Scanning electron microscopic imaging showed dense biofilms on 83% of the nasopharynges and 67% of the MEs on day 8 in the experimental animals. All animals with ME biofilms had biofilms in the nasopharynx. The controls did not demonstrate biofilm formation. Conclusions: The study parallels the natural pathogenesis of AOM in humans. The demonstration of mucosal biofilms in both the nasopharynx (58%) and the ME (47%) of animals with ME inflammation and/or infection lends further support to the importance of mucosal biofilms in the pathogenesis of AOM.