Ultrastructure of mycoplasmal capsules as revealed by stabilization with antiserum and staining with ruthenium red.

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Abstract
The collapse of the capsular glycocalyx was effectively prevented when tissue blocks from the pneumonic lungs of pigs infected with Mycoplasma hyopneumoniae or the tracheas of chickens infected with M. gallisepticum were treated with respective specific antisera before fixation and staining with ruthenium red. The antisera prepared against different mycoplasma species and preimmune sera had no stabilizing effects on the capsular glycocalyces. The stabilized capsules of M. hyopneumoniae extended for .apprx. 125 nm outside the limiting membrane and were 3 times thicker and less dense than those of cells not treated with specific antiserum of cells exposed to heterologous antiserum or preimmune serum. The thickness of the stabilized capsules of M. gallisepticum measured about 40 nm; that of untreated capsules was about 20 nm. In both mycoplasma species, the capsules appeared to consist of fibrillar elements, seemingly being radially oriented, and fine granular material. The capsular material extended to spaces separating mycoplasmal cells from each other and from the epithelial surface, and seemed to play an important role in the colonization of the respiratory tract of pigs or chickens. In the case of M. gallisepticum, the terminal bleb was considered to be the primary attachment factor.