Morphologic and Microbiologic Features of Nasal Cavity and Middle Ear in Germfree, Defined-Flora, Conventional, and Chronic Respiratory Disease-Affected Rats

SUMMARY Gross and microscopic morphologic and microbiologic features of the nasal cavity and middle ear were investigated in 146 weanling, adult, and aged rats from germfree, defined-flora, conventional, and 3 chronic respiratory disease ( crd )-affected colonies. In germfree and defined-flora rats, mucosa of the nasal cavity and the middle ear had few lymphocytes and no inflammation. Four endoturbinates and 2 ectoturbinates were in each choana. The eustachian tube connected the nasopharynx with the tympanic cavity which was lined by low cuboidal and simple squamous epithelium. Rhinitis and otitis media were associated with crd in rats of all ages and were characterized by necrosis of the epithelium, submucosal lymphocytic infiltration, and aggregation of neutrophils in the nasal and tympanic cavities. In chronic otitis media, there were cystic metaplasia of the tympanic mucosa and many cholesterol clefts. Organisms most frequently isolated from crd -affected rats were Mycoplasma sp . and Diplococcus pneumoniae ; these organisms were never isolated from rats which did not have lesions of crd .