A preliminary study on the ultrastructure of Actinomadura pelletieri and its host tissue reaction.

This is the first report on the fine structure of Actinomadura pelletieri. The in vitro ultrastructure of the organism and that of the grain in vivo were similar. The grain consisted of packed filaments with a faintly electron-dense matrix in between. The individual filament was septate, the cytoplasm was either vacuolated or contained intracellular organelles and the cytoplasmic membrane was adherent to the filamentous wall, which has three electron-dense and two electron-lucent layers. The absence of cement substance around the grain may partially explain the aggressive and destructive behaviour of this organism and may probably also explain its good response to medical treatment. The inflammatory host reaction was similar to that seen with all mycetoma organisms except that there was a massive neutrophil reaction. This was confirmed by electron microscopy.