Etiology of chronic pneumonia in rats and a study of the experimental disease in mice.

The lungs of conventional rats with chronic pneumonia contained Streptobacillus moniliformis and Mycoplasma pulmonis. These organisms singly and in combination failed to produce lung disease when inoculated into specific pathogen-free rats. On the other hand, diseased lung homogenate not containing cultivable organisms caused a chronic pneumonia when inoculated into specific pathogen-free rats. The organism involved was seen by electron microscopy and is morphologically indistinguishable from the grey lung agent of Andrewes and Glover and Nelson's enzootic bronchiectasis "virus." All of these agents have morphological and biological properties which indicate close relationship to the mycoplasmas. However, we failed to culture them either in tissue cultures or on inanimate media and conclude that a group of highly fastidious mycoplasma-like agents are a cause of chronic pneumonia in rodents.