In vivo resistance to bacterial biofilm formation on tympanostomy tubes as a function of tube material.

Adherent bacterial biofilms have been implicated in the irreversible contamination of implanted medical devices. We evaluated the resistance of various tympanostomy (pressure equalization [PE]) tube materials to biofilm formation using an in vivo model. PE tubes of silicone, silver oxide-impregnated silicone, fluoroplastic, silver oxide-impregnated fluoroplastic, and ion-bombarded silicone were inserted into the tympanic membranes of 18 Hartley guinea pigs. Staphylococcus aureus was then inoculated into the middle ears. An additional 8 guinea pigs were used as controls; the PE tubes were inserted without middle ear inoculation. All PE tubes were removed on day 10 and analyzed for bacterial contamination using culture, immunofluorescence, and scanning electron microscopy (SEM). All infected ears developed otitis media with otorrhea, but none of the animal control ears drained. Fluorescence imaging of the animal control tubes showed large cellular components consistent with inflammation. The infected tubes showed heavy DNA fluorescence consistent with bacteria and inflammatory cells. All animal control tubes except the ion-bombarded silicone tubes showed adherent inflammatory film on SEM. Also, all tubes placed in infected ears except the ion-bombarded silicone tubes showed adherent bacterial and inflammatory films on SEM. Nonadherent surface properties such as the ion-bombarded silicone may be helpful in preventing chronic PE tube contamination.