High-Voltage Electron microscopy of Histoplasma capsulatum

Abstract

Histoplasma capsulatum (Hc) is a pathogenic fungus frequently involved in lung infections, especially in immunocompromised individuals such as AIDS patients. It has been the subject of numerous investigations by light, transmission, and scanning electron microscopy. However, these studies did not afford a clear picture of the He cell architecture, for which three-dimensional views of the cellular organelles are deemed necessary. For this purpose, we have studied yeast cells of He by means of techniques used in high—voltage electron microscopy (HVEM).Yeast cells of He grown at 37°C in appropriate culture media were fixed with glutaraldehyde-osmium in cacodylate buffer, dehydrated through an ethanol series and embedded in Epon-Araldite, according to standard procedures. Thick sections (0.25-0.5 μm), picked up on Formvar-coated slot-grids, were stained for 4 h at 50°C with uranyl acetate and lead citrate, and examined under the AEI EM7 Mk 1.2 MV Albany HVEM at an accelerating voltage of 1.0 MV.