Pathogens vs. Opportunists

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The page below is a sample from the LabCE course Mycology: Hyaline and Dematiaceous Fungi (retired 8/31/2022). Access the complete course and earn ASCLS P.A.C.E.-approved continuing education credits by subscribing online.

Learn more about Mycology: Hyaline and Dematiaceous Fungi (retired 8/31/2022) (online CE course)
Pathogens vs. Opportunists

Fungi can also be grouped as either true pathogens, organisms that typically can cause human disease in healthy humans, or as opportunists. Examples of true, obligate pathogenic fungi include:
  • Coccidioides immitis
  • Histoplasma capsulatum
  • Blastomyces dermatiditis
  • Sporothrix spp.
  • Emmonsia spp.
These obligate pathogens are known as dimorphic fungi because they have both a yeast phase and a filamentous mold phase. They usually form the yeast phase at body temperature (35-37° C), and the mold form at 25-30° C). Procedures which help differentiate them from the saprophytic hyaline molds (which they could resemble microscopically) are growth in culture media containing cycloheximide, and they show positive reaction in antigen specific nucleic acid probe assays.
These true pathogens will not be covered in this course, except as comparison to the hyaline molds which can sometimes mimic their microscopic appearance.