Novel rat model of tympanostomy tube otorrhea

Tympanostomy tube otorrhea (TTO), caused by the presence of pathogenic bacteria in the middle ear, is the most common complication of TT insertion. No studies have described a reproducible animal model of TTO. We aimed to develop a rat model of TTO which, in turn, could be used to assay the levels of TNF-α and IL-1β through the course of the infection.

The left Eustachian tubes of 55 male Sprague-Dawley albino rats were occluded with gutta-percha (ETO=Eustachian Tube Occlusion). Middle ear (ME) effusion was ascertained by weekly otomicroscopy. At 3 weeks tympanostomy tubes were placed bilaterally and the MEs were inoculated bilaterally with Streptococcus pneumoniae through the tubes. The rats were randomly assigned to one of two daily ototopical treatments: ciprofloxacin/dexamethasone (CDX) or placebo. The animals in each of the two treatment groups were further divided to receive 1, 2, 5 or 7 days of treatment. The rats were sacrificed after treatment was finished. The rates of otorrhea, positive middle ear (ME) cultures, and levels of TNF-α and IL-1β in the ME fluid were measured.

Left ETO followed by ME inoculation with S. pneumoniae and treatment with placebo resulted in persistent infection (100% culture-positive ME fluid at 10 days) and otorrhea (85.7%). Persistent infection of the left ear was accompanied by significantly elevated the levels of IL-1β and TNF-α. Ears treated with CDX had lower rates of otorrhea at all time points and lower levels of IL-1β and TNF-α.

This study is the first to describe a reproducible animal model of acute TTO. Surgical obstruction of the ET, followed by TT placement and ME inoculation with S. pneumoniae induced persistent otorrhea and infection. Both IL-1β and TNF-α appear to be potential markers of persistent middle ear infection. This novel model may be used in future studies of the pathogenesis and therapy of TTO.