DETECTION OF MYCOPLASMA BY DNA STAINING AT THE ULTRASTRUCTURAL LEVEL

The Feulgen-like reaction with the osmium ammine-B complex was employe d for the detection of mycoplasma infection in cell cultures used for research and biotechnological purposes. General morphology of mycoplas mas in ultrathin sections and after negative staining were also invest igated. The ultrastructure of the various mycoplasmas exhibited charac teristic features previously described by other authors. Sometimes it was difficult to distinguish mycoplasma organisms from cell surface pr ojections. In sections of culture cells infected by mycoplasmas, stain ed with osmium ammine-B, only cell nuclei DNA and mycoplasma DNA were intensely contrasted. DNA in mycoplasma could be distinguished from ce llular DNA because of its filamentous aspect; the latter appears in gr anular form. The difference of DNA aggregation in prokaryotic and euka ryotic chromatins could be due to the relative ratio of protein to DNA , which in prokaryotes is about 10 times less than in eukaryotes. The presence of mycoplasma DNA inside the cytoplasm of cultured cells has not been observed in samples studied during this work. Application of Feulgen-like osmium ammine-B reaction for specific DNA staining at the ultrastructural level is a sensitive and relatively rapid technique f or direct examination of mycoplasmas in cell cultures and tissues infe cted by these microorganisms.