Electron Microscopic Studies of Mycoplasma (PPLO strain 880) in Artificial Medium and in Tissue Culture

Abstract

Mycoplasma [pleuropneumonia-like organisms (PPLO)] strain 880 was studied in broth cultures and in several cell culture lines. This strain exhibited considerable pleomorphism in size, internal structure, and shape, including forms with filamentous projections. The most common form observed was 0.5 to 1 µ in diameter and had a nuclear area of fibrillar strands, probably DNA. The cytoplasm of the organisms contained ribosome-like granules and a RaHened vacuole which indented the nuclear area. There were various other forms, including “elementary bodies” 100 mµ. in diameter that were very electron-dense. In the tissue culture lines in which the cells grew as a monolayer, the Mycoplasma were closely associated with the cell surface and were occasionally seen in membrane-lined cytoplasmic vacuoles. In cell lines that did not aHach to the glass, the Mycoplasma were fewer and not attached to the cell surface. Although the ultrastructure of this strain is similar to that of previously described strains, there are differences in details of structure which may be related either to the growth conditions used or to characteristics of the strain. The various forms of the organism are consistent with the suggestion that Mycoplasma may have several mechanisms of reproduction (growth). The intracellular Mycoplasma may be protected from antibiotics. This would partly explain the difficulty of eradicating Mycoplasma from infected cell cultures.