Pathogenicity and its mechanism of Mycoplasma hyorhinis

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(l)Induction of otitis media by intratympanic inoculation of Mycoplasma hyorhinisFifteen SPF piglets, known to be free of Mycoplasma, were allocated in three groups : non-treatment control, intratympanic inoculation of Mycoplasma hyorhinis (Mhr) , and sham operated. Mild to moderate inflammation of the auditory tube and tympanic cavity first appeared at 7 days post inoculation (DPI) in Mhr-inoculated piglets. The degree of the inflammation was aggravated in the piglets sacrificed at 14 DPI.Immunohistochemistry and electron microscopical examinations revealed Mhr on the luminal surface of the auditory tube and tympanic cavity. The ear lesions weakened at 25 DPI.Mhr was isolated from the tympanic cavity from 0 to 14 DPI,but the amounts decreased at 25 DPI.The present experiment indicated that Mhr inoculated into the tympanic cavity could cause a self-limited otitis media in SPF piglets.(2) Induction of otitis media by intranasal inoculation of MhrEleven SPF piglets were allocated in the following 4 groups : negative control, intranasal inoculation of Mhr, intranasal inoculation of Pasteurella multocida (Pm) , and intranasal inoculation of Mhr and Pm. Subacute eustachitis was found in 10 of 12 middle ear of 6 piglets inoculated with Mhr. Immunohistochemistry and ultrastructure confirmed the infection of Mhr in the les ion. None of the piglets inoculated only with Pm showed otitis and synergistic action of Mhr and Pm was not found.The present experiment indicated that intranasally infected Mhr, but not Pm alone could cause eustachitis.These two experiments substantiated our previous hypothesis that Mhr is the primary cause of otitis media of piglets