Pneumonia due to Mycoplasma in gnotobiotic mice. 3. Lesions in the lungs of gnotobiotic mice after multiple intranasal inoculations of broth cultures of Mycoplasma pneumoniae.

Lung lesions characterized by extensive peribronchial and perivascular round cell infiltration and intrabronchial plugging with polymorphonuclear leukocytes were produced in 5 of 44 Ha/ICR gnotobiotic mice sacrificed 3 to 10 days after three intranasal inoculations of broth cultures of Mycoplasma pneumoniae. After 10 days, no significant lesions were seen, and the proportion of lungs positive for M. pneumoniae dropped off sharply. M. pneumoniae persisted for longer periods (up to 24 days) in the trachea, nasopharynx, and anterior nares. These findings would seem to represent a self-limited respiratory infection due to M. pneumoniae in gnotobiotic mice. Ring forms within granular alveolar pneumocytes were seen by electron microscopy in the lungs of triply inoculated gnotobiotic controls receiving sterile horse-serum broth as well as in the lungs of mice receiving broth cultures of M. pneumoniae. Ring forms must now be considered to be part of the nonspecific cellular reactions of pneumocytes to foreign substances in the lungs of mice rather than intracytoplasmic developmental forms of mycoplasma as previously proposed.