Dimorphic fungi are fungi that have a yeast (or yeast-like) phase and a mold (filamentous) phase. One of the characteristics common to most dimorphic fungi is the ability to convert the mold forms to the yeast forms by incubating subcultures in enriched media at 35°-37°C. In general, dimorphic fungi produce a mold form at 25-30°C and a yeast form at 35-37°C. An exception is Coccidioides immitis, which is not thermally dimorphic. Colonies of dimorphic molds are gray-white and have a delicate cobweb appearance on blood agar. This appearance and delayed growth are characteristics of dimorphic fungi.
Dimorphic fungi that are considered pathogens include:
- Blastomyces dermatitidis
- Histoplasma capsulatum
- Coccidioides immitis
- Paracoccidioides brasiliensis
- Sporothrix schenckii
Safety Note: All mold cultures (with the possible exception of cultures from clear-cut cases of dermatophytosis) should be handled in a class II biological safety cabinet. Any mounting reagents intended for microscopy use should contain a disinfectant.9
9. Leber AL, Burnham CD (Ed.) Clinical Microbiology Procedures Handbook, 5 Volume Set, 5th ed. Washington, D.C.: ASM Press; March 21, 2023.
