Transmission Electron Microscopy and Immunogold Staining of Mollicute Surface Antigens

Mollicutes include the smallest, free-living microorganisms. They are cell-wall-less bacteria, many of which produce disease in humans, animals, plants, or insects. Morphologically, mollicutes are extremely variable and pleomorphic, even in pure culture. Some organisms assume a predominantly spherical (0.3–0.8 μm in diameter) or flask-shaped appearance, whereas others may form filaments or branched structures. Genetically, mollicutes are related to Gram-positive bacteria, but the lack of a cell wall prevents a typical staining reaction. Thin sections reveal a simple ultrastructure consisting of cell membrane and cytoplasm, including ribosomes and a characteristic prokaryotic nucleoid.