Induction of temporary otitis media in specific-pathogen-free pigs by intratympanic inoculation of Mycoplasma hyorhinis

Abstract

Objective - To examine whether Mycoplasma hyorhinis inoculated into the tympanic cavity can cause otitis media in pigs. Animals - 17- or 22-day-old specific-pathogen-free pigs. Procedure - Histologic and bacteriologic examinations were performed on specimens from the tympanic cavity and auditory tube at 0, 7, 14, and 25 days after intratympanic inoculation of M hyorhinis (auditory tube cloning strain 14). Results - In M hyorhinis-inoculated pigs, mild to moderate inflammation of the auditory tube and tympanic cavity first appeared at postinoculation day (PID) 7. In pigs euthanatized at PID 14, the degree of inflammation was aggravated. Immunohistochemical analysis revealed M hyorhinis antigens on the luminal surface of the auditory tube and tympanic cavity. By PID 25 lesions had lessened. By use of transmission and scanning electron microscopic examinations, mycoplasmal organisms were identified among the cilia in the auditory tubes at PID 14 but not at PID 25 Results of bacteriologic examination indicated that 104 to 106 color-changing units of M hyorhinis were isolated from the tympanic cavity at PID 0. Variable numbers of M hyorhinis were isolated at PID 7 and 14, and numbers were decreased at PID 25. Conclusions - M hyorhinis inoculated into the tympanic cavity can cause a self-limiting otitis media in SPF pigs.