Morphology of fungi
- Monomorphic fungi: fungi that exist exclusively as either yeast or mold
- Yeasts: unicellular fungi, occasionally organize into hyphae and pseudohyphae
- Pseudohyphae have:
- Variable width
- Clear constrictions at cell junctions
- Irregular septation
- Irregular branching
- Pseudohyphae have:
- Molds: multicellular fungi, organized into hyphae
- True hyphae have:
- Parallel-sided walls (uniform diameter)
- No constrictions at septa (cross walls)
- Regular, evenly spaced septation
- Regular branching
- True hyphae have:
- Yeasts: unicellular fungi, occasionally organize into hyphae and pseudohyphae
- Dimorphic fungi: fungi that can exist as both mold or yeast, depending on temperature
- Molds typically grow at approx. 20°C and yeasts grow at 37 °C.
- Examples: Histoplasma capsulatum, Blastomyces dermatitidis, Coccidioides immitis, Paracoccidioides brasiliensis, and Sporothrix schenckii
- Most commonly cause subacute pulmonary infections
Mnemonic
Mold in the cold, yeast in the heat!
Tip
- Canonical dimorphic fungi: yeasts (25 ℃) → mold (37 °C, = true hyphae)
- Candidiasis: pseudohaphae (25 ℃, formed by yeasts) → germ tubes (37 °C, = true hyphae)