Malakoplakia of the skin. Ultrastructure and quantitative x-ray microanalysis of Michaelis-Gutmann bodies.

The etiologic agent in a case of malakoplakia of the skin was identified as Staphylococcus aureus from culture of the lesion and from ultrastructural observations. Ultrastructurally, electron-dense inclusions were observed in addition to membranous whorls and Michaelis-Gutmann (MG) bodies. These were labeled "precalcification formations" since they possessed an organic crystalline structure. These formations may act as nucleation centers for further incorporation of organic and inorganic material. Deposition of fine crystalline material in the outer region may occur as the structure becomes saturated with inorganic elements, thus completing formation of the MG body. Quantitative x-ray microanalysis of MG bodies demonstrated the presence of phosphorus, calcium, and iron, with average concentrations of 2.1%, 2.6%, and 0.7% by weight, respectively.