Histoplasma capsulatum var duboisii, some cells multiply just by budding

Histoplasma capsulatum is a dimorphic fungus that can occur in a yeast and mycelial or mold form. He has medical importance as a causative agent of histoplasmosis, a systemic fungus disease ( mycosis ) of man.


The morphology of Histoplasma capsulatum is dependent on temperature, at 25 ° C, the mold form, accepted the yeast form at 37 ° C. As a yeast, which is also the infectious form, the individual cells rather small (2-3 microns ), but significantly greater in the variety duboisii (up to 15 microns ). In the Giemsa and Gram staining the cell wall takes no color, so that the yeasts appear surrounded by an empty envelope structure, which was previously misinterpreted as a capsule (hence capsulatum ). The yeast form reproduces by budding.

At lower temperatures, the mycelial forms, the spores ( conidia ) formed. It can be cultivated on nutrient media as a culture, where several weeks of incubation is necessary.


Histoplasma capsulatum is common in the warm regions of the world (tropical and subtropical America, Africa and Indonesia). Its natural habitat is the soil.


  • Kayer, Bienz, Eckert, Zinkernagel: Medical Microbiology. 9th edition. Thieme, Stuttgart 1998, ISBN 3-13-444806-8.