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 dermatitidis
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 that help differentiate them from the saprophytic hyaline molds (which they could resemble microscopically) are growth in culture media containing cycloheximide; and. they show positive reactions in antigen-specific nucleic acid probe assays.
Another dimorphic fungus, Sporothrix schenckii is the agent of subcutaneous sporotrichosis, an infection that may result in granulomatous inflammation with the presence of multi-nucleated giant cells; however, grains or granules are not formed.
Of interest: The genus Ajellomyces is the telomorphic (or "perfect form") of Blastomyces dermatitidis. These molds produce ascocarps that contain ascospores.
These true pathogens will not be covered in this course, except as a comparison to the hyaline molds which can sometimes mimic their microscopic appearance.
