Medical mycology terminology: Which group of fungi exhibits yeast-like growth at human body temperature (about 37°C) but mold-like filamentous growth at room temperature (about 25°C)?

Introduction / Context:
Several clinically important pathogenic fungi alter their growth form depending on temperature. Recognizing this temperature-dependent morphology helps in diagnosis and understanding pathogenesis.

Given Data / Assumptions:

• At approximately 37°C (host temperature) these organisms are yeast-like.
• At approximately 25°C (room temperature) they grow as molds with hyphae.
• This reversible switch is characteristic and diagnostic.

Concept / Approach:
Dimorphism describes fungi that can exist in two distinct morphologies. Classic examples include Histoplasma capsulatum, Blastomyces dermatitidis, and Coccidioides species (the latter forms spherules in tissue). The mnemonic “mold in the cold, yeast in the heat” summarizes the concept.

Step-by-Step Solution:
Match the temperature cue with morphology: hyphae at ~25°C, yeast at ~37°C. Associate this switch with the term “dimorphic.” Exclude groups that are obligately molds or yeasts. Select “Dimorphic fungi.”

Verification / Alternative check:
Laboratory culture at two temperatures demonstrates the switch; tissue histology shows yeast-like forms in infections.

Why Other Options Are Wrong:

• Black bread molds / Water molds: Environmental molds lacking temperature-driven yeast conversion.
• Sac fungi: Taxonomic term (Ascomycota), not all are dimorphic.
• Obligate yeasts: Do not form molds.

Common Pitfalls:
Confusing taxonomic labels with physiological traits or assuming all yeasts are dimorphic.

Final Answer:
Dimorphic fungi.