Several dimorphic fungi have saprophytic counterparts with similar, look-alike microscopic features. These are shown in the table below:
|Dimorphic Fungus||Saprophytic Mold Counterpart||Common Microscopic Morphologic Features|
|Blastomyces dermatitidis||Chrysosporium species |
Scedosporium species also produces single, oval microconidia similar in appearance to those of B. dermatitidis. However, the conidia of Scedosporium species are slightly larger and have a dark pigmentation.
|Production of small, smooth, oval microconidia, each supported by a delicate conidiophore ("lollipop").|
|Histoplasma capsulatium||Sepedonium species||Production of large, spherical macroconidia, which, when mature may have prickly surfaces.|
|Coccidioides immitis||Malbranchia species||Production of alternate staining arthroconidia.|
These methods can be used to differentiate the dimorphic fungi from their saprophytic counterparts:
- The dimorphic fungus can be converted to a yeast form by incubation at body temperature and the saprophytic mold cannot.
- Dimorphic fungi will grow in culture media containing cycloheximide and the saprophytic molds will not.
- Dimorphic fungi will show positive reactions in antigen-specific nucleic acid probe assays.