For a patient with a dimorphic fungal infection, which phrase best describes their growth pattern?

• A. Mold in sunlight, Yeast in darkness
• B. Mold in the cold, Yeast in the heat
• C. Mold in water, Yeast in air
• D. Yeast in cold, Mold in warm

Answer: (B)

In the context of dimorphic fungi, the phrase describing their growth pattern can be most accurately characterized by the transition from a mold form to a yeast form depending on temperature. Dimorphic fungi typically grow as molds (filamentous structure) at lower temperatures, generally around 25°C (77°F), which is often associated with their environmental conditions. When the temperature rises, such as in the human body at approximately 37°C (98.6°F), these fungi transition into their yeast form, which is more conducive for pathogenesis in warm-blooded hosts.

This temperature-dependent switch allows these fungi to adapt to different environments, effectively enhancing their survival and infectivity. Understanding this unique characteristic is crucial when considering the biology and pathogenicity of fungi like Histoplasma capsulatum or Coccidioides immitis, both of which exhibit this dimorphic growth pattern.