Morphology and Nature of Pleuropneumonia-Like Microörganisms. ∗

We have recently isolated from the lungs of rats and mice 5 strains of pleuropneumonia-like Microörganisms. The purpose of this note is to indicate that the morphology of these strains, like that of the L₁ strains of Klieneberger, 1 is essentially bacterial.

Most authors regard the organism of pleuropneumonia bovis and similar organisms as in a class distinct from bacteria or other well-known Microörganisms. They have a characteristic morphology and colonial appearance. Especially in pathological tissues or exudates they are filterable, and the diseases which they produce are often mistaken for virus diseases. The microbes included by Klieneberger 2 in this group produce tiny colonies consisting of fine pleomorphic, very fragile granules, which later swell up to form large round bodies. The vacuolization and coalescence of these round bodies produce eventually a foam-like appearance of the colonies. Saprophytic strains cultivated by Laidlaw and Elford, 3 and by Seiffert, 4 have been included in the pleuropneumonia group on the basis of filterability and special morphology. 5

One of us 6 , 7 has pointed out that Klieneberger's L₁ strain, isolated from the streptobacillus moniliformis, is but a variant of this bacillus. For it not only can be isolated regularly from this bacillus, but occasionally reverts to it, and it conforms essentially to bacterial morphology. In young colonies, fine bacterial filaments are present, containing deeply stained granules. Part of these forms degenerate, and part swell up to large round bodies. A similar process can be observed occasionally with various bacteria, i. e., colon or influenza bacilli. The L₁ strains differ from the other bacteria only by the regular occurrence of this phenomenon.

The morphology of the strains was studied by staining directly on the agar the developing colonies.